The diabetogenic impact of ethanol remains as a focal point of basic and clinical investigations. In this study, Wistar rats were subjected to daily intragastric ethanol administration (10 ml/kg body weight injection with 0 (control), 10, 20 and 33 % (v/v) ethanol in the injections, respectively) for 19 weeks. At the end of the administration, we found that the fasting plasma glucose level of the 33 % (v/v) ethanol-loaded group was 18 % higher than the control. Insulin sensitivity was decreased in a dose-dependent manner in all the ethanol-loaded groups (r − 0·842, P < 0·001) during intraperitoneal insulin tolerance test. Necrotic/haemorrhagic injury was detected in the pancreas and islet β-cell mass was significantly reduced in the 33 % (v/v) ethanol-loaded rats by immunohistochemical and morphometric analysis. At the molecular level, we detected a dose-dependent attenuation of phosphatidylinositol 3-kinase activity (r − 0·956, P < 0·001) and GLUT-4 expression (GLUT-4 mRNA, r − 0·899, P < 0·001; GLUT-4 protein, r − 0·964, P < 0·001) in skeletal muscle. These results demonstrated that drinking is a conditional aetiological factor for diabetes and excessive ethanol intake is negatively associated with both insulin sensitivity and β-cell mass. The whole-body insulin resistance might result from the ethanol-induced insulin signalling defects in muscle.

The insulin-independent and combined effects of fatty acids (FA; linoleic and oleic acids) and insulin in modulating lipid accumulation and adipogenesis in 3T3-L1 cells was investigated using a novel protocol avoiding the effects of a complex hormone ‘induction’ mixture. 3T3-L1 cells were cultured in Dulbecco’s modified Eagle’s medium (DMEM) plus serum (control) or in DMEM plus either 0.3 mmol/l linoleic or oleic acids with 0.3 mmol/l FA-free bovine serum albumin in the presence or absence of insulin. Cells were cultured for 4 to 8 days and cell number, lipid accumulation, peroxisome proliferator-activated receptor-gamma (PPAR-γ) and glucose transporter 4 (GLUT-4) protein expression were determined. Cell number appeared to be decreased in comparison with control cultures. In both oleic acid and linoleic acid-treated cells, notably in the absence (and presence) of insulin, oil-red O stain-positive cells showed abundant lipid. The percentage of cells showing lipid accumulation was greater in FA-treated cultures compared with control cells grown in DMEM plus serum (P < 0.001). Treatment with both linoleic and oleic acid-containing media evoked higher levels of PPAR-γ than observed in control cultures (P < 0.05). GLUT-4 protein also increased in response to treatment with both linoleic and oleic acid-containing media (P < 0.001). Lipid accumulation in 3T3-L1 cells occurs in response to either oleic or linoleic acids independently of the presence of insulin. Both PPAR-γ and GLUT-4 protein expression were stimulated. Both proteins are considered markers of adipogenesis, and these observations suggest that these cells had entered the physiological state broadly accepted as differentiated. Furthermore, 3T3-L1 cells can be induced to accumulate lipid in a serum-free medium supplemented with FA, without the use of induction protocols using complex hormone mixtures. We have demonstrated a novel model for the study of lipid accumulation that will improve the understanding of adipogenesis in adipocyte lineage cells.