Splenic participation in glycemic homeostasis in obese and non-obese male rats.

We evaluated the effects of splenectomy on glucose homeostasis in obese and non-obese rats. Obesity was induced by subcutaneous injections of monosodium glutamate (MSG; 4g/kg) in neonatal rats. Control (non-obese) animals received equimolar saline. Splenectomy (SPL) was performed at 21 or 60 days of life (SPL21 and SPL60) in MSG obese and non-obese groups. Glucose tolerance, insulin resistance (IR), adiposity, histology of white adipose tissue (WAT) depots and glucose-induced insulin secretion (GIIS) in isolated pancreatic islets were evaluated at 90 days of life. In non-obese, despite of hyperphagia, the spleen ablation reduced body weight gain and energy efficiency, without changes in GIIS or IR. Slight reduction in glucose tolerance and augmented adipocyte size in subcutaneous WAT was noted in non-obese SPL21 group. In MSG-SPL21 rats was observed augmented body weight gain and energy efficiency, without alter adipocyte size. In contrast, MSG-SPL60 rats had lower body weight gain, reduced energy efficiency and smaller adipocyte size in WAT visceral depot in relation to MSG non-operated. Spleen ablation reduced insulin plasma levels in the MSG-SPL21 and MSG-SPL60 groups. Moreover, splenectomy reduced GIIS and improved glucose tolerance in MSG-SPL21 group. In MSG-SPL60 rats were observed reduction in IR, without changes in GIIS, despite of elevated glucokinase expression in pancreatic islets. In conclusion, spleen ablation reduces body weight in non-obese rats and slightly modifies glucose homeostasis. In contrast, in MSG-induced obesity, absence of the spleen can ameliorate glucose tolerance and reduce insulin secretion, improving insulin sensitivity.

The effect of chronic oral vitamin D supplementation on adiposity and insulin secretion in hypothalamic obese rats.

Reduced plasma vitamin D (VD) levels may contribute to excessive white adipose tissue, insulin resistance (IR) and dyslipidaemia. We evaluated the effect of chronic oral VD supplementation on adiposity and insulin secretion in monosodium glutamate (MSG)-treated rats. During their first 5 d of life, male neonate rats received subcutaneous injections of MSG (4 g/kg), while the control (CON) group received saline solution. After weaning, groups were randomly distributed into VD supplemented (12 µg/kg; three times/week) and non-supplemented (NS) rats, forming four experimental groups (n 15 rats/group): CON-NS, CON-VD, MSG-NS and MSG-VD. At 76 d of life, rats were submitted to an oral glucose tolerance test (OGTT; 2 g/kg), and at 86 d, obesity, IR and plasma metabolic parameters were evaluated. Pancreatic islets were isolated for glucose-induced insulin secretion (GIIS), cholinergic insulinotropic response and muscarinic 3 receptor (M3R), protein kinase C (PKC) and protein kinase A (PKA) expressions. Pancreas was submitted to histological analyses. VD supplementation decreased hyperinsulinaemia (86 %), hypertriacylglycerolaemia (50 %) and restored insulin sensibility (89 %) in MSG-VD rats, without modifying adiposity, OGTT or GIIS, compared with the MSG-NS group. The cholinergic action was reduced (57 %) in islets from MSG-VD rats, without any change in M3R, PKA or PKC expression. In conclusion, chronic oral VD supplementation of MSG-obese rats was able to prevent hyperinsulinaemia and IR, improving triacylglycerolaemia without modifying adiposity. A reduced cholinergic pancreatic effect, in response to VD, could be involved in the normalisation of plasma insulin levels, an event that appears to be independent of M3R and its downstream pathways.