Adenosine transport was characterized in human umbilical artery smooth muscle cells isolated from non-diabetic and diabetic pregnant subjects. Transport of adenosine was mediated by a Na+-independent transport system inhibited by nanomolar concentrations of nitrobenzylthioinosine (NBMPR) in both cell types. Diabetes increased adenosine transport, an effect that was associated with a higher maximal velocity (Vmax) for NBMPR-sensitive (es) saturable nucleoside transport (18 ± 2 vs. 61 ± 3 pmol (µg protein)-1 min-1, P < 0.05) and the maximal number of binding sites (Bmax) for specific [3H]NBMPR binding (74 ± 4 vs. 156 ± 10 pmol (µg protein)-1, P < 0.05), with no significant changes in the Michaelis-Menten (Km) and dissociation (Kd) constants, respectively. Adenosine transport was unaltered by inhibition of nitric oxide (NO) synthase (with 100 µM NG-nitro-L-arginine methyl ester, L-NAME) or protein synthesis (with 1 µM cycloheximide), but was increased by inhibition of adenylyl cyclase activity (with 100 µM, SQ-22536) in non-diabetic cells. Diabetes-induced adenosine transport was blocked by L-NAME and associated with an increase in L-[3H]citrulline formation from L-[3H]arginine and intracellular cGMP, but with a decrease in intracellular cAMP compared with non-diabetic cells. Expression of inducible NO synthase (iNOS) was unaltered by diabetes. Dibutyryl cGMP (dbcGMP) increased, but dibutyryl cAMP (dbcAMP) decreased, adenosine transport in non-diabetic cells. dbcGMP or the NO donor S-nitrosoacetylpenicillamine (SNAP, 100 µM) did not alter the diabetes-elevated adenosine transport. However, activation of adenylyl cyclase with forskolin (1 µM), directly or after incubation of cells with dbcAMP, inhibited adenosine transport in both cell types. Our findings provide the first evidence that adenosine transport in human umbilical artery smooth muscle cells is mediated by the NBMPR-sensitive transport system es, and that its activity is upregulated by gestational diabetes.

The aim of our study was to develop and validate a simple surgical model in the sheep which allows control of the gas composition of the blood supplying the carotid and central chemosensitive area independently of the rest of the body. This approach was made possible due to the specific features of the cranial circulation in the sheep. An extracorporeal circuit, consisting of a pump and a gas exchanger, was placed at the level of the two common carotid arteries to create a pressure gradient between the carotid and the systemic systems and to reverse blood flow in the vertebral vessels via the occipital arteries. When a pressure gradient of about 40 Torr was created between the systemic and carotid circulation, we found that no blood could reach the carotid bodies and the medulla without passing though the extracorporeal circulation. This was established (1) by measuring vertebral blood flow; and (2) by injecting either a coloured suspension or particles labelled with 99m*Tc into the systemic or the carotid circulation. The slope of the relationship between minute ventilation (V˙E) and systemic arterial PCO2 (Pa,CO2) during high CO2 inhalation in seven hyperoxic vagotomised and anaesthetised sheep was dramatically reduced, but remained above zero, when Pa,CO2 was maintained constant in the cephalic circuit (0.11 ± 0.15 vs. 0.70 ± 0.35 l min-1 Torr-1 for the control tests). This residual V˙E response to CO2 inhalation remains to be explained since it could not be accounted for by any of the chemical or circulatory changes occurring in the cephalic circulation. Nevertheless, this preparation provides an easy method of maintaining chemical and circulatory homeostasis at the chemoreceptor level. Experimental Physiology (2003) 88.5, 581-594.

The effect of chronic inflammation induced by Freund's Complete Adjuvant (FCA) on rat articular blood vessels and knee joint diameter was investigated. Blood flow changes in response to phenylephrine (an α1-adrenoceptor agonist) in FCA-treated and contralateral knee joints were studied over a 40 day period, using the laser Doppler flowmetery (LDF) technique. Unilateral injection of FCA (0.2 ml) increased the injected knee diameter on all days examined post-injection (P < 0.001) and its maximum increase (53 ± 2 %) was reached on day 3. After this, the diameter decreased gradually but did not return to its initial value. In control animals, topical application of 10-13-10- 7 mol phenylephrine onto the exposed joint capsule decreased blood flow dose dependently (11.1 ± 4.4 to 58.2 ± 4.5 %, respectively, P < 0.001). Unilateral injection with FCA attenuated the phenylephrine response in both ipsilateral and contralateral knees compared with the response of control animals (5.2 ± 1.6 to 48.3 ± 6.1 % and 1.9 ± 2.2 to 45.3 ± 5.6 %, respectively, P < 0.05). The reduction persisted for 3 weeks after FCA injection (ipsilateral for 21 days; contralateral for 30 days, P < 0.001). Subsequently the response returned towards normal. To avoid the influence of α2-adrenoceptors, yohimbine (an α2-adrenoceptor antagonist) was injected (0.5 mg kg-1, I.P.) 30 min before phenylephrine application. Yohimbine blocked the vasoconstrictor effect of 10-10-10-7 mol clonidine (an α2-adrenoceptor agonist, topical application) by 44-67.7 % inhibition, respectively (P < 0.001). Prazosin (an α1-adrenoceptor antagonist, 0.1 mg kg-1, I.P.) blocked the vasoconstrictor effect of phenylephrine (10-10-10-7 mol, topical application) effectively (42 to 69.8 % inhibition, respectively, P < 0.001). To assess the role of nitric oxide (NO) on the observed responses, N G-nitro-L-arginine methyl ester (L-NAME, NO synthase inhibitor) was applied topically (0.2 µmol) 5 min before phenylephrine application. L-NAME application at 7 and 14 days after FCA injection potentiated the vasoconstrictor response in the FCA-treated knee (P < 0.001) but had no significant effect on the contralateral knee. Blood pressure monitoring during phenylephrine, clonidine and L-NAME administration indicated that topical application of the drugs had no significant effect on the systemic blood pressure. These findings indicate that the vasoconstrictor response to phenylephrine was decreased in chronic inflammation and increased NO production could be involved.

It is well established that painful distension of hollow viscera such as the oesophagus can evoke a reflex tachycardia and pressor response; however, the nature of the oesophageal afferent pathway(s) remains controversial. This study investigated the afferent arc which mediates these reflex cardiovascular changes in the decerebrate rat. In addition, the effect of oesophageal distension on the respiratory activity of the costal diaphragm was studied. Focal distension of the oesophagus (volume of 0.3 ml applied for 10 s) just above the diaphragmatic hiatus evoked a reproducible presssor response and tachycardia in the decerebrate rat. Respiration was transiently inhibited at the beginning of oesophageal distension and prior to the rise in blood pressure. Neuromuscular blockade with the nicotinic acetylcholine receptor blocker α-bungarotoxin (140 µg bolus) had no effect on the magnitude of the cardiovascular response. Therefore the efferent supply to the striated muscle of the rat oesophagus was not essential in mediating this reflex. Signal averaging of the mean blood pressure response showed that neither selective ablation of oesophageal spinal afferents nor bilateral vagotomy altered the early trajectory of the pressure response. Bilateral vagotomy reduced the peak magnitude of the response to sustained oesophageal distension. In contrast, selective removal of spinal afferents had no effect on the response. Ablation of both neural pathways was essential to abolish the reflex cardiovascular and respiratory responses. It can be concluded that both vagal and spinal afferent pathways are utilised in the reflex cardiorespiratory response to painful oesophageal distension. Although ablation of one neural pathway had no effect on the response it was still implicated in the reflex, since ablation of both pathways was necessary to prevent the cardiorespiratory changes. This study emphasises the need for caution when inferences are made concerning single selective ablations of multiply innervated organs. Experimental Physiology (2002) 87.1, 41-48.

The regulation of placental anion transport influences fetal accretion and placental homeostasis. We investigated whether efflux of 125I- or 36Cl- from multinucleated cytotrophoblast cells derived from human term placenta is regulated by one of three stimuli: (a) the calcium ionophore A23187, (b) a 'cocktail' of agents designed to raise intracellular levels of cAMP, (c) a hyposmotic solution. After loading with the appropriate isotope for 2 h and thorough washing, cells were exposed to sequential aliquots of buffer applied and removed each minute. Following an equilibration period of 5 min one of the stimuli was applied at room temperature At the end of the experiment the cells were lysed to give a lysate count which was used to express the count obtained from each aliquot as percentage efflux of that possible for that minute. The cAMP 'cocktail' and A23187 were applied for 5 min; the hyposmotic solution was applied for 10 min. The results for 125I- at 7 min showed that the mean efflux in the presence of hyposmotic shock was greater than control (5Σ7 ± 1Σ0 % min-1versus 2Σ2 ± 0Σ1 % min-1, respectively; mean ± S.E.M., n = 4 placentas). Similarly mean efflux at 6 min in the presence of A23187 was also significantly greater than control (6Σ5 ± 1Σ9 % min-1versus 2Σ6 ± 1Σ0 % min-1, respectively, n = 3 placentas). The mean efflux in the presence of the cAMP cocktail was not different from control at any time point. The results were qualitatively the same if 36Cl- was used in the place of 125I- and when the experiment was performed with 36Cl- in a HCO3- buffer gassed with CO2. Mean 125I- efflux at 6 min in response to hyposmotic challenge was 33 % less (P < 0Σ01) in the presence of 1 mM 4,4′-diisothiocyanatostilbene-2,2′-disulphonic acid (DIDS) and 37 % less (P < 0Σ005) in the presence of 10 µM tamoxifen but no different if the hyposmotic solution was nominally calcium free. We conclude that there are differential effects of second messengers on anion efflux from the differentiated cytotrophoblast cells.

The role of endothelins in the renal damage associated with ischaemic-reperfusion (I-R) injury during organ transplantation was determined by selective blockade of the ETA receptors with the receptor antagonist ABT-627. The integrity of kidney function was determined 2 and 8 weeks after transplantation by investigation of the renal response to angiotensin II. Under pentobarbitone anaesthesia (70 mg kg-1, I.P.), rats underwent a right nephrectomy. Transplantation of the left kidney was performed after 2 h cold ischaemia without or with ABT-627 treatment. Control animals underwent left renal denervation. The renal response to angiotensin II was measured 2 weeks later following blockade of endogenous production of angiotensin II with captopril. A further transplant group was allowed to recover for 8 weeks before the terminal study. In the control group, angiotensin II reduced renal blood flow (RBF), glomerular filtration rate (GFR), urine flow rate (UV), and fractional sodium excretion (FENa) by 29 ± 5 %, 19 ± 4 %, 25 ± 4 % and 32 ± 7 %, respectively. Conversely, in the transplant group, angiotensin II left RBF unchanged and increased GFR (59 ± 12 %) and UV (93 ± 8 %). FENa decreased by 24 ± 9 %. In both the transplant group treated with ABT-627 and the long-term recovery group, the renal response to angiotensin II was normalised. In conclusion, renal transplantation following 2 h cold I-R injury resulted in a temporary abnormal renal response to angiotensin II, which was reversed by ETA receptor antagonism at the time of transplantation. Experimental Physiology (2001) 86.3, 365-372.

The effects of longitudinal stretch on vasoreactivity were assessed in isolated, pressurised arteries from the rat mesentery, rat mid-cerebral and human subcutaneous vascular beds. A stretch-dependent increase in reactivity was observed only in rat third order mesenteric arteries. Longitudinal stretch >> 20 % (force equal to 0·23 ± 0·04 mN) optimises vasoconstrictor responses to noradrenaline and phenylephrine in rat third order mesenteric arteries. Stretch did not affect the vasoconstriction response to depolarisation by 30 mM K+ PSS in any of the arteries studied. Similarly, stretch had no affect on pressure-dependent myogenic responses in rat mid-cerebral arteries. Endothelium-independent and endothelium-dependent mechanisms of vasorelaxation were unaffected by stretch in rat third order mesenteric arteries. Likewise, stretch did not affect vasoreactivity in rat mid-cerebral and human subcutaneous resistance arteries. Our results show that longitudinal stretch in isobaric-mounted rat third order mesenteric arteries is an important methodological consideration. Considering our results, we recommend that isobaric-mounted rat third order mesenteric arteries are stretched >> 20 % to provide optimal experimental conditions for pharmacological studies.

Increased fetal lung expansion, induced by tracheal obstruction (TO), is a potent stimulus for fetal lung growth, but rapidly reduces surfactant protein (SP) mRNA levels. Our aim was to determine the time course for the re-expression of the surfactant proteins in fetal lung tissue following the release of a TO and to relate these to the changes in lung liquid volume. Fetal sheep were exposed to either: (1) no treatment (controls); (2) 4 days of TO; (3) 4 days of TO, followed by release of the obstruction for 24 h; (4) 4 days of TO followed by release of the obstruction for 3 days. Four days of TO increased lung liquid volumes from 26.8 ± 1.9 to 72.0 ± 5.6 ml kg-1 and reduced SP-A, SP-B and SP-C mRNA levels to 38.5 ± 10.7, 56.8 ± 10.3 and 18.3 ± 5.3 % of control values, respectively. One day after TO release, lung liquid volumes were reduced to 17.4 ± 5.3 ml kg-1 (control 128 days, 31.0 ± 3.8 ml kg-1) and SP-A and SP-B mRNA levels were not different from control levels. In contrast, SP-C mRNA levels only increased to 45.4 ± 17.3 % of control. Three days after TO release, lung liquid volumes increased to 48.0 ± 8.5 ml kg-1 and SP-A and SP-B mRNA levels were reduced to 48.8 ± 10.2 % and 71.5 ± 19.8 % of control, respectively; SP-C mRNA levels remained at 35.3 ± 12.3 % of control. Following the release of a TO, SP-A, SP-B and SP-C mRNA levels were closely and inversely related to the volume of lung liquid. Based on these relationships, the lung liquid volumes that equate to 100 % expression were considerably less than control lung volumes (< 10 vs. 30-40 ml kg-1) in fetuses of this age. Thus, the changes in fetal lung SP-A, SP-B and SP-C mRNA levels following the release of a TO are variable, differ between the proteins and are closely related to the changes in lung liquid volumes. We conclude that the re-expression of surfactant proteins following TO is variable and that the change in lung liquid volume is potentially a good indicator for surfactant protein re-expression. Experimental Physiology (2001) 86.1, 55-63.

We studied the effects of an external acute 10 min application of cytoskeletal interfering agents on cardiac L-type calcium current (ICa,L). We found that colchicine, taxol and cytochalasin D had no direct effect on the L-type calcium channel as indicated by the absence of effect on voltage-dependent parameters. Phalloidin induced a shift in the I-V curve which renders it difficult to use in excitation-contraction coupling studies. Microfilaments of actin did not seem to regulate cardiac ICa,L as indicated by the lack of effect of cytochalasin D on ICa,L amplitude and inactivation kinetics. On the contrary, microtubules seem to be involved in the calcium-dependent inactivation of ICa,L. This involvement might be direct, i.e. a physical link between the microtubules and some part of the channel protein, or it could be indirect, i.e. the calcium chelating properties and physical obstacle of microtubules in the space between the sarcolemma and the SR.

The intracellular mechanisms responsible for inhibition of osteoclast activity are of significant interest in the search for more effective ways of managing bone diseases associated with enhanced bone resorption. Previous studies have suggested that the protein kinase C (PKC) pathway is an important inhibitory second messenger in osteoclasts. We, therefore, investigated the effects of the synthetic peptide fragments, PKC(530-558) and (19-36), which correspond to parts of the catalytic and regulatory domains of PKC, on the activity of isolated osteoclasts. These fragments have been shown to activate and inhibit PKC, respectively, in biochemical studies employing isolated rat brain PKC, but have rarely been employed in studies of cellular activity. PKC(19-36), an enzyme inhibitor (PKC-I), had no effect by itself on osteoclastic bone resorption. However, PKC(530-558), a PKC activator (PKC-A), caused a dose-responsive inhibition of bone resorption, which was accompanied by a rapid and distinctive change in osteoclast morphology. This effect was reversible: (a) upon removal of PKC-A, (b) upon continuous exposure to this fragment for more than 36 h, or (c) in the presence of PKC-I. In conclusion, a short synthetic peptide fragment of PKC (PKC-A) significantly inhibits osteoclastic bone resorption; this, together with the fact that the inhibitory effect is abolished in the presence of PKC-I, provides further evidence for an important physiological role for the PKC pathway in the regulation of osteoclast activity. Selective activation of this pathway may have important therapeutic implications for the management of bone diseases associated with enhanced resorption.

It has been reported that long-term selective inhibition of neuronal nitric oxide synthase (nNOS) produces elevated blood pressure (BP) in normal rats. The present study was designed to analyse the possible influences of the sodium-retaining hormone deoxycorticosterone acetate (DOCA) and of an increased sodium intake on BP effects induced by the chronic blockade of nNOS with 7-nitroindazole (7NI). Two experiments were performed using 7NI at a dose of either 10 mg kg-1 day-1 (experiment 1) or 30 mg kg-1 day-1 (experiment 2). The following groups were used in both experiments: control rats, and rats that received either 1 % saline drinking water (Salt), deoxycorticosterone acetate (DOCA), 7NI, 7NI plus 1 % saline (7NI + Salt) or 7NI plus DOCA (7NI + DOCA). The tail systolic BP (SBP) was measured in all rats once a week. At the end of the experimental period, the mean arterial pressure (MAP) and metabolic, morphological and renal variables were measured. There were no significant differences in the tail SBP, final MAP or glomerular filtration rate between the experimental groups and the control group. In both experiments, the plasma renin activity (PRA) was significantly inhibited in the Salt groups and suppressed in the DOCA groups. The PRA significantly increased in the 7NI groups, whereas the 7NI + Salt and 7NI + DOCA groups showed a significant inhibition in PRA, especially compared to the 7NI groups in the two experiments. We conclude that chronic nNOS blockade is unable to increase BP in normal, saline-drinking or DOCA-treated rats. Furthermore, the nNOS blockade does not interfere with the counterbalance between renin and an increased sodium intake or retention. Experimental Physiology (2003) 88.2, 243-250.

Most cancer deaths result from the cancer either being intrinsically resistant to chemotherapeutic drugs, or becoming resistant after being initially sensitive (Leyland-Jones, Dalton, Fisher & Sikic, 1993). Often, in cells grown in cell culture, drug resistance correlates with the presence of one or more of the so-called P-glycoproteins or multidrug resistance (MDR) proteins, products of the mdr family of genes (Endicott & Ling, 1989). The mdr genes (with two forms in humans (MDR1 and MDR2), and three (mdr1, mdr2 and mdr3) in mice and hamsters) have been cloned, sequenced (Gros, Croop & Housman, 1986) and shown to be members of the 'ABC' (ATP binding cassette) or 'traffic ATPase' superfamily (Doige & Ames, 1993). All members of this superfamily (which includes the CFTR chloride ion channel, the product of the STE6 gene in yeast that transports the [alpha]-mating factor polypeptide, bacterial protein translocator HlyB that exports haemolysin, and many bacterial permeases) have a membrane transport function and share homologous sequences that often bind ATP (Kane, Pastan, Gottesman, 1990; Gros & Buschman, 1993) and can hydrolyse it. Human MDR1 and mouse mdr1 and mdr3 (Tang-Wai, Kajiji, Dicapua, de Graaf, Roninson & Gros, 1995) confer multidrug resistance, while human MDR2 and mouse mdr2 transport phosphatidylcholine and function as lipid translocases (Smit et al. 1993). The genes have tandem repeated structures, each coding for polypeptide sequences which putatively straddle the membrane six times, and each containing an ATP-binding region. The MDR genes code for glycoproteins of molecular weight 150000-180000. In drug-resistant cells, the genes are generally present as multiple repeats on episomes. Some clinical studies show that expression of the MDR1 gene is enhanced in drug-resistant tumours in patients and that this expression is a good predictor of resistance (Chan et al. 1991).Expression of the mdr genes is associated with a greatly increased resistance to the killing action of many cytotoxic drugs (Biedler & Riehm, 1970; Johnson, Chitnis, Embrey & Gregory, 1978). It brings about a marked (up to fiftyfold) reduction in the cellular steady-state level of its numerous 'substrates' (Dano, 1973; Inaba, Kobayashi, Sakurai & Johnson, 1979; Fojo, Akiyama, Gottesman & Pastan, 1985) which are fairly hydrophobic compounds but possess also some hydrophilicity. Many of these substrates are weak bases. Some bear permanent positive charges (Lampidis et al. 1989), but zwitterions seem not to be substrates. The MDR protein transports such drugs actively out of the cells in which the mdr gene is expressed (Lankelma, Spoelstra, Dekker & Broxterman, 1990; Dordal, Winter & Atkinson, 1992), that is, it is a drug pump. The protein can be present in as many as 8 × 105 (Sehested, Simpson, Skovsgaard & Jesnsen, 1989; Demant, Sehested & Jensen, 1990) or even 3 × 106 (Shapiro & Ling, 1994) copies per cell. Resistance is reversed by numerous compounds, termed 'reversers', 'modulators', or 'chemo-sensitizers' (e.g. verapamil; Tsuruo, Iida, Yamashiro, Tsukagoshi & Sakurai, 1982) and also by other MDR substrates (Horio, Lovelace, Pastan & Gottesman, 1991). P-glycoprotein has been isolated from cell membranes and demonstrated to be an ATPase, with a turnover number of some 25 s-1 at 37¡C (Ambudkar, Lelong, Zhang, Cardarelli, Gottesman & Pastan, 1992; Urbatsch, Al-Shawi & Senior, 1994; Sharom, Yu, Chu & Doige, 1995). P-glycoprotein is often present in tissues and at tissue surfaces that transport water and nutrients (kidney, gut, the blood-brain barrier; Thiebaut, Tsuruo, Hamada, Gottesman, Pastan & Willingham, 1987; Lum & Gosland, 1995), but is also present in the pancreas.What might be the physiological role of the P-glycoproteins? It was early suggested that they may be concerned in the protection of the organism from toxic, perhaps mutagenic, xenobiotic substances (Gottesman & Pastan, 1988). Their appearance in cytotoxin-resistant tumours would be an example of the ectopic expression of genes that is so often encountered in tumours. P-glycoprotein thus acts as a double-edged sword, protecting its wielder in most situations, at the expense of aiding in his or her destruction when tumours have already developed (Gottesman & Pastan, 1988). Studies using animals in which one or other mdr gene has been knocked out have thrown light on the matter. Thus, Schinkel et al. (1994), in an elegant study using mice with a knock-out mutation in the mdr1A gene, have shown that the P-glycoprotein is a major component of the blood-brain barrier, ensuring that lipid-soluble toxins (ivermectin, for example) are pumped out of the brain tissues across that barrier, protecting the organism against brain damage. P-glycoprotein acts also to keep intracellular drug concentrations low in a number of other body tissues. Blocking P-glycoprotein using knock-out mice (Schinkel et al. 1994) or by the addition of reversers of P-glycoprotein (Lyubimov, Lan, Pashinsky, Ayesh & Stein, 1995) leads to a significant rise in the tissue content of vinblastine. The tissues in which P-glycoprotein brings about a reduced concentration of cytotoxin are, in many cases, just those that are intrinsically resistant to chemotherapy by cytotoxins (Lum & Gosland, 1995).There is no fully accepted model for the mechanism of action of this important molecule. There is much evidence that P-glycoprotein behaves quite differently from conventional membrane pumps. The 'vacuum cleaner' model (Raviv, Pollard, Bruggemann, Pastan & Gottesman, 1990), in which P-glycoprotein is a machine that cleans its substrates out of the plasma membrane, and delivers them to the exterior aqueous phase, provides an intriguing general framework for discussion of the pump's action and is the basic standpoint of this paper.

We examined the effect of time after birth and β3-adrenergic agonist (Zeneca D7114) administration on uncoupling protein-1 (UCP1) abundance and thermoregulation in the lamb. Forty twin lambs, all born normally at term, were maintained at a cold ambient temperature of between 3 and 8 °C. At 0.5, 1.75, 5.25, 11.25 and 23.25 h after birth eight sets of twins were fed 20 ml of formula milk ± 10 mg kg-1 of β3-adrenergic agonist, and 45 min after feeding brown adipose tissue (BAT) was sampled. Colonic temperature was measured and BAT analysed for UCP1 abundance, GDP-binding to mitochondrial protein (i.e. thermogenic activity) and catecholamine content. Colonic temperature declined between 1.25 and 6 h from 40.2 °C to 39.2 °C and then increased to 39.8 °C at 12 h, but increased after feeding at all ages. UCP1 abundance increased from 1.25 h after birth, to peak at 2 h after birth in controls, compared with 6 h after birth in β3-adrenergic agonist-treated lambs. The level of GDP-binding to mitochondrial protein did not change significantly with age but was increased by β3-adrenergic agonist treatment. The noradrenaline (norepinephrine) content of BAT increased between 1.25 and 12 h after birth, irrespective of β3-adrenergic agonist administration. The total weight of perirenal BAT plus its lipid, protein and mitochondrial protein content declined over the first 6 h of life. UCP1 development continues over the first 24 h of neonatal life, and can be manipulated by β3-adrenergic agonist administration. This may represent one method of improving thermoregulation in newborn lambs. Experimental Physiology (2001) 86.1, 65-70.

We examined mean (± S.E.M.) changes in wall tension in isolated rat intrapulmonary arteries on switching from control conditions (pH 7.38 ± 0.01; PCO2, 34.4 ± 0.5 mmHg) to hypercapnic acidosis (pH change, -0.24 ± 0.01; PCO2 change, +27.5 ± 0.9 mmHg), isohydric hypercapnia (pH change, -0.02 ± 0.01; PCO2 change, +28.5 ± 0.8 mmHg) and normocapnic acidosis (pH change, -0.24 ± 0.01; PCO2 change, -0.5 ± 0.3). Arteries were submaximally preconstricted with prostaglandin F2alpha; and changes in tension are expressed as a percentage of the 80 mM KCl-induced contraction (%Po). Mean changes in wall tension on switching to hypercapnic acidosis (+4.4 ± 3.7 %Po), isohydric hypercapnia (+1.9 ± 2.2 %Po) and normocapnic acidosis (-1.5 ± 1.9 %Po) were not significantly different from the change observed on switching to control conditions (+3.5 ± 1.1 %Po), and were unaltered by endothelial removal. In isolated carotid preparations, the change in tension in isohydric hypercapnia (-6.8 ± 7.1 %Po) was not significantly different from that observed in control switches (+8.6 ± 3.2 %Po). Significant reductions in tension (P < 0.001) were observed in hypercapnic (-42.9 ± 7.8 %Po) and normocapnic acidosis (-36.4 ± 9.0 %Po). These data suggest that intrapulmonary arteries are resistant to the vasodilator effects of extracellular acidosis observed in systemic (carotid) vessels.

Previous studies have shown that prolactin administration to pregnant rats results in offspring with enhanced abundance of the brown adipose tissue-specific uncoupling protein (UCP) 1. The present study therefore aimed to determine whether a similar effect was observed after birth and if the sex of the animal further influenced the responsiveness of brown adipose tissue mitochondria to prolactin administration. Daily prolactin injections were therefore commenced at 15, 35 or 60 days of age and continued for 4 days. The abundance of UCP1 was unchanged with age in females but decreased between 15 and 35 days in males and was lower in males than females by 60 days of age. Cytochrome c abundance remained unchanged with postnatal age in both males and females and was consistently higher in males at each sampling age. Prolactin decreased the abundance of UCP1 and cytochrome c when administered to female rats at 35 and 60 days of age, but had no effect at 15 days. In contrast, prolactin had no effect on UCP1 in male rats at any age, but did stimulate the abundance of cytochrome c at 15 days of age. In conclusion, the administration of prolactin to postnatal rats over the period in which maturation of the hypothalamic-pituitary axis and brown adipose tissue function is occurring did not enhance UCP1 abundance. In females, prolactin actually caused a reduction in UCP1 suggesting that in rats it is only prior to birth that prolactin has a stimulatory role on brown adipose tissue development. Experimental Physiology (2003) 88.4, 527-531.

The newborn pig is currently the most used species in animal neonatal research. Valid non-invasive monitoring is important in particular for long-term survival of unsedated animals. In the unsedated newborn pig (n = 35, median age 24 h, range 7-48 h) we standardized two-dimensional Doppler echocardiography and determined the normal ranges for cardiac function. Probe positioning had to be adjusted to the V-shaped thorax and the mid-line position of the heart. Six out of the sixteen animals < 20 h had a patent ductus arteriosus compared with one of the twenty animals > 20 h old. One atrial septal defect (5 mm) and one small ventricular septal defect were diagnosed. The average heart size was 0Σ7-0Σ9 % of body weight which is similar to human infants of the same size. The mean aortic diameter was 6Σ0 ± 0Σ5 mm (mean ± S.D.) and cardiac output was 0Σ38 ± 0Σ08 l min-1; both correlate with body weight (r = 0Σ80 and 0Σ73, respectively). Tricuspid regurgitation velocity was 3Σ0 ± 0Σ4 m s-1 (mean ± S.D.), giving an estimated pressure gradient across the tricuspid valve of 37 ± 9Σ7 mmHg. The aortic diameter and the heart weight per kg body weight are comparable to those reported for preterm neonates. The cardiac output and velocities across the four valves are more comparable with term neonates.

The effects of 7 days of 'dry' water immersion were investigated in six subjects. Changes in the contraction properties were studied in the triceps surae muscle. After immersion, the maximal voluntary contraction (MVC) was reduced by 18.9 % (P < 0.01), and the electrically evoked (150 impulses s-1) maximal tension during tetanic contraction (Po) was reduced by 8.2 % (P > 0.05). The difference between Po and MVC expressed as a percentage of Po and referred to as force deficiency was also calculated. The force deficiency increased by 44.1 % (P < 0.001) after immersion. The decrease in Po was associated with increased maximal rates of tension development (7.2 %) and relaxation. The twitch time-to-peak was not significantly changed, and half-relaxation and total contraction time were decreased by 5.3 % and 2.8 %, respectively, but the twitch tension (Pt) was not significantly changed and the Pt/Po ratio was decreased by 8.7 %. The 60 s intermittent contractions (50 impulses s-1) decreased tetanic force to 57 % (P < 0.05) of initial values, but force reduction was not significantly different in the two fatigue-inducing tests: fatigue index (the mean loss of force of the last five contractions, expressed as a percentage of the mean value of the first five contractions) was 36.2 ± 5.4 % vs. 38.6 ± 2.8 %, respectively (P > 0.05). While identical force reduction was present in the two fatigue-inducing tests, it would appear that concomitant electrical failure was considerably different. Comparison of the electrical and mechanical alterations recorded during voluntary contractions, and in contractions evoked by electrical stimulation of the motor nerve, suggests that immersion not only modifies the peripheral processes associated with contraction, but also changes central and/or neural command of the contraction. At peripheral sites, it is proposed that the intracellular processes of contraction play a role in the contractile impairment recorded during immersion. Experimental Physiology (2002) 87.1, 101-111.

A disturbed calcium homeostasis characterizes diabetic pregnancy. This study documents changes in bone mineral composition in diabetic pregnant rats and examines the effect of insulin replacement. Control pregnant (CP), diabetic pregnant (DP) and insulin-treated DP (DPi) rats were assessed for femoral calcium and magnesium content, bone mineral density (BMD) and the ratio of hypertrophic to maturing and proliferative cells in the femoral growth plate. DP rats showed a significantly (P < 0·01) lower body weight, femoral weight and length than CP rats. Femoral calcium and magnesium content was also significantly (P < 0·05) lower in DP rats, as was ash weight. When calcium and magnesium were normalized for ash weight no signficant differences were apparent. A significantly (P < 0·05) lower total BMD at the distal femur was seen in DP rats. This comprised a significantly (P < 0·01) lower trabecular BMD with no significant change in cortical BMD. A significantly (P < 0·05) higher ratio of hypertrophic to maturing and proliferative cells of the femoral growth plate was evident in DP animals. DPi rats showed normal blood glucose concentrations and femoral growth plate histology. DPi rats also showed normal femoral weight and length but only partially restored femoral ash weight and mineral content. Insulin failed to normalize total or trabecular BMD. Diabetes mellitus clearly has a marked effect on bone growth and mineral content in pregnancy which may be relevant to overall calcium homeostasis. The lower bone growth, bone calcium content and trabecular BMD may be unfortunate consequences of the marked hypercalciuria reported elsewhere in diabetes and may serve to maintain normocalcaemia in the disease.

It is generally accepted that pheromones act by stimulating of the dendritic receptors of the olfactory neurones massed in the olfactory epithelium. This study was designed to ascertain whether it is possible for the boar pheromone androstenol (5alpha-androst-16-en-3-ol) to be transported from the nasal cavity of anaesthetized gilts to the brain and hypophysis via local transfer from the blood in the perihypophyseal vascular complex. The experiment was performed on days 18-21 of the porcine oestrous cycle (crossbred gilts, n = 6). Tritiated androstenol (3H-A; total amount 108 d.p.m. (758 ng)) was applied for 1 min onto the respiratory part of the nasal mucosa, 4-6 cm from the opening of the nares. Arterial blood samples from the aorta and from the carotid rete were collected every 2 min during the 60 min period following administration of the steroid. Total radioactive venous effluent from the head was removed and an adequate volume of homologous blood was transfused into the heart through the carotid external vein. At the end of the experiment gilts were killed and tissue samples of the hypophysis and some brain structures were collected to measure radioactivity. In addition, corresponding control tissues were collected from three untreated gilts and from three heads of gilts 60 min after 3H-A was applied post mortem into the nasal cavity. The concentration of 3H-A was significantly higher (P < 0.0001) in the arterial blood of the carotid rete than that of aorta. The mean rate of 3H-A counter current transfer from venous to arterial blood in the perihypophyseal vascular complex, expressed as the ratio of the 3H-A concentration in arterial blood of the carotid rete to the 3H-A concentration in blood sampled simultaneously from the aorta, was 1.96 ± 0.1. The concentration of 3H-A in plasma from the venous effluent from the head ranged from 1.3 to 1.8 pg ml-1. During the 60 min period of the experiment, 0.68 % of the total applied dose of 3H-A was resorbed from the nasal cavity into the venous blood. Moreover, we found that 3H-A was present in the olfactory bulb (P < 0.01), amygdala, septum, hypothalamus, adenohypophysis, neurohypophysis (P > 0.05) and perihypophyseal vascular complex (P < 0.01). These results demonstrate that, in anaesthetized gilts, the boar pheromone androstenol may be resorbed from the nasal mucosa, transferred in the perihypophyseal vascular complex into arterial blood supplying the brain and hypophysis, and then arrested in the hypophysis and certain brain structures. We suggest that in addition to the standard neural pathway for signalling pheromones, another pathway exists whereby androstenol, as a priming pheromone, may be resorbed from the nasal cavity into the bloodstream and then pass locally from the perihypophyseal vascular complex into the arterial blood supplying the brain and hypophysis, thus avoiding the first passage metabolism in the liver.

Electromanometric recordings of caecal pressures were made in chronically cannulated ponies. Endoscopy allowed direct observation of the caecal base and cupola while recording intracaecal pressures and enabled a functional interpretation of caecal pressure profiles. Using gas-tight seals, the caecal gas cap baseline pressure (tone) was usually below atmosphere, becoming less negative postprandially. Diurnal variations were observed in the amplitude and frequency of caecal pressure profiles and the direction of caecal movements, during which intra-caecal gas cap pressures briefly became positive. A paraprandial (psychic) phase of enhanced caecal motility was observed. Manipulation of the caecal gas cap volume, by insufflation of nitrogen gas, demonstrated the capacity of the caecal base to regulate gas pressures and to eliminate fermenting gases.