Kenneth C. Gorray

RESPONSES OF PANCREATIC B CELLS TO ALLOXAN AND STREPTOZOTOCIN IN THE GUINEA PIG

Guinea pigs injected with streptozotocin were significantly hyper-glycemic on day 1 after injection but only mildly so on day 14. However, serum insulin levels were significantly depressed on day 14; at this time the animals had lost 25% of their initial body weights and were severely glycos-uric. The volume fraction of inimunostainable B cells in the pancreas was reduced to one third of control values by day 1 after injection and remained at this level by day 14. Animals thai received alloxan were slightly hyperglycemic on day 1 but not on day 14. Both serum insulin and volume fraction of B cells in the pancreas were reduced by 70% on day 1 but had returned to control levels by day 14. Body weights for this group were equivalent to controls at both time points. These data indicate that (1) streptozotocin treatment of guinea pigs causes a diabetes-like condition characterized by insulin deficiency, pancreatic B cell loss, glycosuria, and weight loss, which are not reversed in the first 2 weeks after injection, whereas hyperglycemia is only transitory; (2) alloxan also produces a diabetes-like condition early after injection, but all signs of diabetes disappear within 2 weeks, by which time serum insulin levels and the volume fraction of B cells in the pancreas have returned to normal. The experimental results suggest that regeneration of islet B cells following destruction by alloxan may be the primary cause of the recovery of alloxan-injected guinea pigs from the effects of the drug, whereas the persistence of insulin deficiency is consistent with an absence of islet B cell regeneration in the streptozotocin-treated animals.

Immunocytochemical detection of B cells in the guinea pig pancreas using guinea pig antiserum to porcine insulin.

The purpose of this study was to determine if antisera to an heterologous insulin could replace specific anti-guinea pig insulin serum for immunoperoxidase localization of guinea pig B cells. We found that antisera to porcine insulin was effective for this purpose even though it was produced by guinea pigs. The immunostaining results obtained with anti-porcine insulin sera and anti-guinea pig insulin serum were identical, by both light and electron microscopic immunoperoxidase staining. Control experiments supported the conclusion that the guinea pig antisera to porcine insulin contained antibodies that reacted with guinea pig insulin.

Micro-insulin radioimmunoassay: measurement of the insulin response during glucose tolerance tests in guinea pigs.

Summary A method is presented for the radioimmunoassay of insulin levels in small volumes of serum collected by multiple bleedings of guinea pigs. The validity of this technique was evaluated by both parallelism and recovery studies. The assay was utilized to measure the insulin response to a glucose tolerance test in fed, fasted, and fasted + refed groups of animals. Insulin levels in guinea pigs under basal conditions were 10-fold higher than those reported for other species. A significant decline in both basal blood glucose and insulin levels occurred following a 24-hr fast. Fasted guinea pigs also demonstrated an impairment of glucose tolerance and a delayed insulin peak; both of these abnormalities were reversed by refeeding. These results suggest that although the guinea pig possesses an unusually high blood level of immunoreactive insulin, its insulin and glucose responses to fasting and glucose tolerance tests are similar to those reported for other species.

Synthetic guinea pig insulin B-chain C-terminal decapeptide: a novel immunogen for generating immunocytochemical-grade antisera.:

Antisera to guinea pig insulin are not commonly available, largely because of the short supply and limited immunogenicity of the intact hormone. To overcome these problems we have employed a novel reagent, synthetic guinea pig insulin B-chain C-terminal decapeptide, as a hapten for raising antibodies that react with intact guinea pig insulin. The decapeptide, coupled to bovine serum albumin, was successfully used as an immunogen in rabbits. The resulting anti-serum was employed for immunocytochemical staining of guinea pig insulin in pancreatic sections. The specificity of the staining was verified by both pre-absorption and pre-immune serum controls. The utility of this new antiserum for investigations of guinea pig insulin physiology is discussed.

In Vitro Toxicity of Alloxan for Guinea Pig B Cells: Comparison with Rat B Cells

Abstract Previous studies have shown that guinea pigs are resistant to the in vivo diabetogenic action of alloxan and that this resistance may be accompanied by a regeneration of B cells in the initial days following administration of the drug. In the studies reported here, we used the measurement of insulin and glucagon released over a 7-day culture period as indices of islet cell viability and examined effects of in vitro exposure to alloxan upon subsequent release of insulin and glucagon from guinea pig (alloxan-resistant) and rat (alloxan-sensitive) islet cell cultures. An alloxan dose-dependent decrease in subsequent insulin release was found. However, whereas the lowest concentration of the drug (1 mM) produced a significant depression in insulin release in rat islet cultures, with maximal depression occurring after exposure to 5 mM alloxan, insulin release from guinea pig cultures was not significantly depressed by 1 or 2 mM alloxan, and S mM alloxan treatment produced a submaximal depression. Furthermore, insulin release from guinea pig but not rat cultures increased transiently at between 6 and 18 hr during the first day following exposure to all doses of alloxan. Treatment with high doses of the drug (40 mM or greater) caused the same maximal chronic depression of insulin release for both species. In contrast, glucagon release from cultures of both species was not affected significantly following alloxan treatment. Thus, guinea pig B cells are more resistant than those of the rat to the action of alloxan, but this resistance can be overcome by employing high doses of the drug. Other factions unidentified by the present studies may also be involved in the failure of guinea pigs to develop diabetes following in vivo treatment with alloxan.