Isolated normal rat islets were pre-incubated with Streptozotocin (STZ), N-methylnitrosourea (MNU) or alloxan for 5, 10, 30 or 60 minutes at 0 degree C or 37 degrees C, and then were washed and incubated at 37 degrees C for 60 minutes with glucose (16.7 mM). Suppression of the insulinotropic response to glucose during incubation required 10 minutes of pre-incubation with the nitrosoureas whose effects were directly related to concentration and were temperature dependent. The suppressive effects of both nitrosoureas could be reduced or abolished by simultaneous addition to the pre-incubation media of nicotinamide, 2-deoxyglucose or 3-0-methyl-glucose, but were unaffected by reduced glutathione, glucosamine, N-acetylglucosamine or mannoheptulose. Unlike the nitrosoureas, alloxan was B-cytotoxic at 0 degree C. The effect of alloxan at 0 degree C was blocked by glutathione but not by glucose. The evidence in this study is inconsistent with the concept that the glucose moiety of STZ promotes entry and action of this nitrosourea in pancreatic islet cells. Secondly, it shows that the immediate B-cytotoxic action of alloxan differ from that of STZ or MNU and is not abolished by decrease in temperature.

Addition of glucose (16.7 mM) to isolated pieces of rat pancreas increased insulin secretion 5.4-fold over basal secretion rates. Ether at 1, 1.5 and 2 MAC inhibited this insulinogenic effect of glucose in a dose-related manner by 5, 18 (P less than 0.01) and 29 (P less than 0.01) per cent, respectively.

Somatostatin at a final concentration of 1 μg or 10 μg/ml did not affect glucose stimulated oxidation of either D-[14C]1 or D-[14C]6 glucose, but inhibited both insulin release and cyclic AMP accumulation by isolated rat islets of Langerhans.

Glucagon secretion and its control have been studied in perifused isolated islets of Langerhans of the rat. It was shown that a low concentration of glucose per se does not cause increased glucagon secretion, but that at low glucose concentrations the amino acid arginine stimulates a biphasic secretory response. Such amino acid stimulated glucagon secretion can be suppressed by increasing the glucose content of the perifused media from 1.67 to 5.5 or 16.7 mM; insulin secretion is also then increased. Since high concentrations of added porcine insulin (10 mU/ml) did not affect amino acid stimulated glucagon secretion at low glucose concentration, it was concluded that high concentrations of glucose and not insulin secreted in response to that glucose are probably responsible for suppression of glucagon secretion. At low concentrations of glucose, epinephrine (2.5 × 10−7 M) also stimulated glucagon secretion. It is concluded that isolated rat islets of Langerhans can be used for the study of glucagon secretion in vitro, and that substances appearing in the blood in vivo at low glucose concentrations are probably responsible for increased glucagon secretion under conditions associated with hypoglycemia.

Rabbits and guinea-pigs were immunized with various pancreatic antigens in Freund's adjuvant. Rabbits received unfractionated bovine insulin and the "A" component and "single peak" insulin separated from it by gel-filtration. All produced antibodies capable of reacting with porcine insulin but none were found to have pancreatic lesions when killed up to 6 weeks after initial injection. Guinea-pigs immunized with bovine "A" component developed pancreatic peri-ductulitis which appeared most frequently (10/20) in animals killed 30 days after a single injection and less frequently in animals killed after 60 (4/10) and 90(1/10) days. Similar lesions were found in only a small proportion of control animals (2/23) or of guinea-pigs immunized with single peak bovine insulin (3/22). Guinea-pigs immunized with homogenates of homologous and heterologous islets of Langerhans developed signs of peri-ductulitis in a high proportion of animals killed up to about 60 days after first injection (18/26). None of these animals exhibited clearly defined signs of diabetes mellitus and the incidence of induced lesions could not be correlated with levels of circulating insulin-binding antibodies.

Relative to body weight, the plasma volumes of 60 normal guinea pigs fell from 5.2 to 3.7 ml/100 g body wt as body weight increased from about 600 to 1200 g. Lower values reported by others are attributed to differences in methodology. Slightly higher plasma volumes were found in 37 insulin-immunized guinea pigs. After exsanguination at the time of death, trapped plasma accounted for 10 to 20% of the weights of the livers, kidneys, and spleens, more being trapped when death occurred before exsanguination could be effected.

Groups of normal rats and of normal and insulin-immunized guinea pigs were injected intravasculary with mixtures of radio-iodinated and unlabelled porcine insulins. No differences could be discerned between the fates of radio-iodinated and unlabelled insulins in normal or immune guinea pigs except with respect to the kidneys of normal animals, which seemed to accumlate TCA-precipitable radioactive substances devoid of immunoreactivity. The abnormally slow disappearance of insulin from the plasma and its persistent accumulation in the livers and spleens of immune guinea pigs were not affected by prior treatment for three days with large daily doses (ca 20 mg/kg body wt.) of hydrocortisone acetate.

The distribution of insulin injected into normal rats and guinea pigs as the free hormone or as insulin-antibody complexes was studied by extraction of immunoreactive insulin and by following the fate of125I- or131I-labeled insulin in the plasma, liver, kidneys and spleens of the injected animals. Injected free hormone rapidly disappears from the plasma to accumulate transiently in the liver, and, to a greater extent, in the proximal convoluted tubules of the kidneys. When insulin-antibody complexes formedin vitro are injected, the hormone disappears more slowly from the plasma and concentrates in the liver and spleen where it can be demonstrated by autoradiography in reticulo-endothelial cells; little or none is found in the kidneys. After injection into insulin-immunized guinea pigs, the hormone disappears very slowly from the plasma and accumulates almost exclusively in the liver with no evidence of concentration by any particular cell type; little or none is found in the kidneys or spleen.

Journal Article Effect of Hormones on Accumulation of Cyclic AMP-14C in Isolated Pancreatic Islets of Rats Get access E. A. MILLER, E. A. MILLER *Department of Pharmacology, Indiana University School of Medicine Indianapolis, Indiana 46202 Search for other works by this author on: Oxford Academic Google Scholar P. H. WRIGHT, P. H. WRIGHT *Department of Pharmacology, Indiana University School of Medicine Indianapolis, Indiana 46202 Search for other works by this author on: Oxford Academic Google Scholar D. O. ALLEN D. O. ALLEN *Department of Pharmacology, Indiana University School of Medicine Indianapolis, Indiana 46202 Search for other works by this author on: Oxford Academic Google Scholar Endocrinology, Volume 91, Issue 4, 1 October 1972, Pages 1117–1119, https://doi.org/10.1210/endo-91-4-1117 Published: 01 October 1972 Article history Received: 27 December 1971 Published: 01 October 1972

The sulfonylureas, tolbutamide, tolazamide and acetohexamide significantly diminish uptake of insulin by the isolated perfused rat liver, whereas the nonhypoglycemic metabolite of tolbutamide, carboxytolbutamide, has no such effect. These results suggest that the sustained action of the sulfonylureas may in part be due to reduced hepatic uptake of endogenously secreted insulin.