The sensitivity and response to insulin in vitro of (a) the incorporation of U-C-14-glucose into glycogen in the isolated diaphragm muscle, and (b) the oxidation of l-C-14 glucose in the epididymal fat pad and in adipocytes, has been studied in obese hyperglycemic mice fed ad libitum, in obese mice fasted for twenty-four hours and in obese mice maintained on a restricted diet from weaning and in lean mice, at two to four months of age and at six to eight months of age. In both age groups, there was a significant, although reduced, insulin effect in the muscle from obese mice but this was normal in the six to eight-month-old group of obese mice on a restricted diet. The glucose oxidation in the epididymal fat pad of the obese mice fed ad libitum was very reduced in both age groups. Fasting the obese mice for twenty-four hours did not restore glucose oxidation to normal, but it was normal in fat pads from obese mice kept on a restricted diet. There was no insulin effect on the fat pad of obese mice in either age group even after a twenty-four-hour fast. The response and sensitivity of the tissue to insulin was partially restored in the obese mice on a restricted diet. There were only small differences in sensitivity between adipocytes prepared from obese and lean epididymal fat pads. The maximum response to insulin in adipocytes from obese mice was usually lower than that in adipocytes from lean mice at glucose concentrations of 0.03 per cent but equal or higher at glucose concentrations of 0.2 per cent. The clear responses to low concentrations of insulin of the isolated diaphragm muscle and adipocyte suspension from obese mice on a restricted diet and of the adipocytes from obese mice fed ad libitum, suggest that a decreased sensitivity to insulin at the cellular level is not the primary defect in the obese hyperglycemic syndrome.

The pituitary neurointermediate lobe of genetically obese (ob/ob) mice contains a hormone which stimulates insulin release and which cross-reacts with a -COOH-terminal ACTH antiserum, suggesting that it is related to corticotropin-like intermediate lobe peptide (CLIP), the 18-39 fragment of ACTH. The hormone, which we have called beta-cell-tropin, has been shown to be present in the plasma of the ob/ob mouse and to potentiate glucose induced insulin secretion. We have now shown that ACTH22-39 prepared by tryptic digestion of human synthetic CLIP behaves similarly on Biogel chromatography and on reverse-phase HPLC to the naturally occurring beta-cell-tropin. Furthermore, beta-cell-tropin and ACTH22-39 have indistinguishable antigenic and insulin releasing properties.

1. A technique for perfusion of the mouse liver has been developed, and aspects of carbohydrate metabolism have been investigated in the perfused liver of normal and genetically obese mice, homozygous for the recessive gene ob. 2. Rates of gluconeogenesis in perfused mouse liver were faster than those reported for slices of mouse liver, particularly from lactate and pyruvate. 3. The rate of glycogen breakdown to glucose, but not to lactate, was faster in liver from fed obese mice. 4. The capacity for glycogen synthesis from glucose was enhanced in liver from 20h-starved obese mice. 5. The capacity for gluconeogenesis from a number of substrates was not significantly altered in livers from fed or starved obese mice when compared with that of lean mice. 6. These results suggest that the liver contributes to the hyperglycaemia of the obese mice by increased glycogenolysis, and that liver glycogen in obese mice is maintained by synthesis from dietary glucose.

SUMMARY The biochemical parameters of blood glucose, serum insulin and pancreatic insulin and glucagon were determined after single injections of the diabetogenic agent streptozotocin and in untreated animals from a strain of genetically obese mice and their lean litter-mates. Histological observations on α and β islet cells were also made in these animals by employing the phosphotungstic acid—haematoxylin and aldehyde—fuchsin staining techniques. In untreated obese mice, endocrine hyperactivity was indicated by the presence of exceptionally large, highly vascular islets and by duct cell-islet metaplasia. After streptozotocin injection, approximately half of the lean mice showed extensive β-cell necrosis and these animals became hyperglycaemic and hypoinsulinaemic with a much reduced pancreatic insulin over a long term. The remaining treated lean mice, whose biochemical parameters did not differ significantly from normal, showed little or no evidence of islet damage. The response of obese mice to streptozotocin treatment was less clear-cut than that of lean animals. Essentially similar histological changes were observed, though these were not consistently correlated with biochemical data. There was histological and biochemical evidence of islet cell recovery from the effects of the drug both in lean and in obese mice, and in all hyperglycaemic animals with initial severe islet damage a marked α-cell response was observed, namely an increased proportion of α cells and their random deployment throughout the islets.

1. The metabolism of [U-(14)C]glucose by the isolated diaphragm muscle of normal rats, rats rendered diabetic with streptozotocin and rats with transitory insulin deficiency after an injection of anti-insulin serum was studied. 2. The incorporation of [(14)C]glucose into glycogen and oligosaccharides was significantly decreased in the diabetic diaphragm muscle and in the muscle from rats treated with anti-insulin serum. 3. Neither diabetes nor transitory insulin deficiency influenced the oxidation of glucose, or the formation of lactate and hexose phosphate esters from glucose. 4. Insulin fully restored the incorporation of glucose into glycogen and maltotetraose in the diabetic muscle, but the incorporation into oligosaccharides, although increased in the presence of insulin, was significantly lower than the values obtained with normal diaphragm in the presence of insulin.