Insulin secretion in experimental obesity

Rates of lipogenesis and plasma insulin concentrations in inbred lines of mice differing in fatness

Rates of lipogenesis de novo and plasma concentrations of insulin were compared during post-natal growth in two inbred lines of mice (VL/fDk (VL) and SWR/fNIMR (SWR] in which differences in growth and fatness are probably due to multiple not single gene effects. Irrespective of sex, the lipogenic rate/g was higher in the fatter VL mice in the liver and all other tissues except the head, where it was lower, and the gonadal fat pad, where it was not different. Adult mice in general had lower lipogenic rates than those measured soon after weaning. In both lines the lipogenic rate/g of tissue was higher in males in the liver and in females in the gonadal fat pad. Plasma insulin concentrations were higher in VL mice and tended to rise with age. These results demonstrate that metabolic differences associated with differences in fatness in inbred lines of mice in which fatness is controlled by more than one gene, are qualitatively but not quantitatively similar to those observed by other workers in lines of mice differing in fatness due to a single gene mutation.

Pancreatic polypeptide and other hormones in pancreas of obese (ob/ob) mice

The insulin, glucagon, somatostatin and pancreatic polypeptide content of acid-ethanol extracts of pancreas from lean and obese (ob/ob) mice of various ages was determined by radioimmunoassay. Rat and mouse pancreatic polypeptide react weakly with antibodies to avian, bovine and canine pancreatic polypeptide, but immunoassay for this peptide was possible using an antibody to the carboxyl-terminal hexapeptide of bovine pancreatic polypeptide and amino-terminal labelled bovine pancreatic polypeptide as tracer. The insulin, glucagon and pancreatic polypeptide content of pancreas from obese mice was greater than that of lean controls. The increase in insulin content uniformly involved ventral, dorsal and splenic lobes. Glucagon content was elevated primarily in the splenic lobe. Pancreatic polypeptide content was most significantly elevated in the splenic lobe where pancreatic polypeptide cells are infrequent in normal lean mice and this was accompanied by increased numbers of pancreatic polypeptide cells per islet in this lobe.

Islet cell function in gold thioglucose-induced obesity in mice

Blood insulin, blood glucose and the biosynthesis and release of insulin have been studied in mice made obese with a single injection of gold thioglucose. In such mice, blood glucose levels were normal, though serum insulin rose in parallel with the development of obesity. When compared with controls, insulin secretion and synthesis were increased in isolated islets of Langerhans from obese mice, over a wide range of glucose concentrations. However, in obese animals, insulin biosynthesis was augmented above control levels at 2 mmol/l glucose, whilst the increase in insulin secretion accompanying obesity only became evident at glucose concentrations greater than 5 mmol/l. After 2 min incubation, cyclic AMP rose more in islets from obese mice than in controls, though cyclic AMP levels did not significantly differ in either group after 10 min incubation with glucose. Glucose oxidation was also increased in islets of Langerhans from obese mice. It seems possible that changes in glucose oxidation, as well as in cyclic AMP levels, contribute to the alteration in the B cell response in this type of obesity.

Laboratory animals exhibiting obesity and diabetes syndromes

Spontaneous hyperglycemia, hyperinsulinemia and obesity are common features for at least one period of the lifetime in some strains of mice. Both genetic and environmental factors are involved in the pathogenesis of the diabetes-like syndrome, making these strains excellent models for studies in both obesity and diabetes-like states. The metabolic peculiarities can be due to a dominant gene, as for the yellow obese, or a single recessive gene, as in the obese and the diabetes mouse; or they can be of polygenic origin, as for the KK and the NZO mouse. However, the severity of the metabolic disorder is due to the interaction of the mutant genes iwth modifiers in the bat genes themselves. Studies on the pathophysiology and biochemistry of these animals have revealed interstrain differences, different patterns of development of the metabolic disorder, and different degrees of severity of the diabetes-like syndrome. Although the primary causes of the syndrome remain unclear in some strains, an involvement of hypothalamic feeding centers has been implicated.