Potentiation of the diabetogenic effect of streptozocin by phentolamine in the rat

Beta cell rest and recovery--does it bring patients with latent autoimmune diabetes in adults to euglycemia?

Diabetes mellitus in humans is a heterogeneous disorder classified clinically into two main types. The diagnosis of type 1 versus type 2 diabetes is made phenotypically using criteria such as age at onset, abruptness of hyperglycemic symptoms, presence of ketosis, degree of obesity and the perceived need for insulin replacement. The pathogeneses of type 1 and type 2 diabetes are believed to be different. Type 1 diabetes is an autoimmune disease mediated by cellular effector mechanisms; whereas classic type 2 diabetes is not autoimmune but results from insulin resistance and a nonautoimmune insulin secretory defect. Most type 1 diabetes patients are diagnosed in childhood or young adulthood before the age of 35 years. However, there is clearly a subgroup of patients clinically diagnosed with type 2 diabetes who are greater than 35 years of age and have evidence of autoimmunity. The disease of these autoantibody-positive type 2 diabetics is often termed latent autoimmune diabetes in adults (LADA), slowly progressive type 1 diabetes, latent type 1 diabetes, and type 1.5 diabetes. This group of patients comprises approximately 10-15% of Caucasian type 2 diabetes patients. Type 1.5 diabetes patients tend to present with islet cell autoantibodies, islet-reactive T cells, higher HbA(1c) levels, lower C peptide, and a propensity toward insulin dependency compared to autoantibody-negative classic type 2 diabetes subjects.

Sympathetic nervous system and experimental diabetes: role of adrenal medullary hormones

The sympathetic nervous system is of major importance in the regulation of various physiological functions. The present review discusses the mechanisms which control glucose homeostasis and the role of the sympathetic nervous system in experimental diabetes with special emphasis on the role of adrenal medullary hormones, over-activity of the sympathetic nervous system and its relationship to hypertension in the diabetic state and the effect of stress. The chapter also reviews the ability of various drugs and pharmacological agents to produce hyperglycemia in experimental animals and how this information can be used in screening new chemical entities and in differentiating the mode of action of these agents.

Metabolic state of the pancreas affects end-point titre in the islet cell antibody assay

Quantification of islet cell antibodies is used increasingly to evaluate pre-clinical Type 1 (insulin-dependent) diabetes mellitus. If expression of the antigen(s) reacting with islet cell antibodies varies depending upon the functional state of the pancreatic islets, this may partly explain differences in assay sensitivity between laboratories. To address this question we altered Beta-cell function in Osborn-Mendel rats, by dietary manipulation prior to killing. Rats were fed chow (n = 7) or a high sucrose/high fat "cafeteria" diet (n = 8) or were fasted for 18 h (n = 6) until immediately prior to killing. Using frozen sections of these rat pancreata in the indirect immunofluorescent test for islet cell antibodies, we determined the end-point titre for 18 sera in which islet cell antibodies had been previously quantified in our standard human pancreas assay. These sera included ten positive sera and eight normal negative control sera. The four most strongly positive sera gave significantly higher end-point titres on "cafeteria" diet-fed pancreata and lower titres on fasted pancreata (p less than 0.04 to 0.002). None of non-diabetic control sera were positive on any substrate. These data suggest that islet antigen expression is increased when Beta-cell function is increased by dietary manipulation. Improved sensitivity in the islet cell antibody assay might be possible by altering Beta-cell function before or immediately after pancreas collection.

Culture of mouse pancreatic islets in different glucose concentrations modifies B cell sensitivity to streptozotocin

There have previously been divergent data published regarding the effects of glucose on the diabetogenic effects of streptozotocin. In order to further explore this issue, two separate sets of experiments were performed. In the first, mouse pancreatic islets were maintained in culture for 3 days at different glucose concentrations (5.6, 11.1 and 28 mmol/l) and then exposed to streptozotocin. After another 3 days in culture at 11.1 mmol/l glucose, the B cell function was evaluated by measurement of glucose-stimulated insulin release, the number of islets recovered after culture, and the islet DNA and insulin contents. In the second group of experiments islets were first maintained in culture at 11.1 mmol/l glucose, then treated with streptozotocin and subsequently cultured for 6 days at the different glucose concentrations given above. It was found that islets maintained in a medium containing 28 mmol/l glucose before or after streptozotocin exposure showed less signs of damage than islets cultured in 11.1 mmol/l glucose. A similar, but less pronounced, decreased sensitivity to streptozotocin was found in islets precultured in 5.6 mmol/l glucose, in comparison with those islets cultured in 11.1 mmol/l glucose. Culture at 5.6 mmol/l glucose just after streptozotocin treatment did not induce any improvement in islet survival or function. It is suggested that the increased damage induced by streptozotocin to islets precultured at 11.1 mmol/l glucose, in comparison with 5.6 mmol/l glucose, can be related to the fact that an increased metabolic activity of B cells render them more susceptible to the toxin.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic receptors and the onset of streptozotocin-induced diabetes in mice

Treatment with yohimbine, an alpha 2-adrenergic blocker, prior to the injection of a subdiabetogenic dose of streptozotocin (STZ) produced hyperglycemia and hypoinsulinemia in mice 7 days later. Prazosin, an alpha 1-adrenergic blocker, was ineffective. The capacity of phentolamine and phenoxybenzamine to potentiate the diabetogenic effect of STZ was intermediate between that of yohimbine and prazosin. Propranolol and hexamethonium inhibited the potentiating action of yohimbine. Yohimbine enhanced the potentiating effect of isoproterenol on the STZ-induced diabetes. Acute changes in phase glucose and insulin levels induced by STZ were potentiated by yohimbine but not by prazosin. The insulin releasing ability of the pancreatic islets 7 days after STZ was all but lost in mice pretreated with yohimbine but not with prazosin. These results suggest that the beta- and alpha 2-, not alpha 1-adrenergic system which modulates insulin release from pancreatic islets influences the response to the diabetogenic action of STZ in mice.

Participation of adrenal medulla in 6-amino-nicotinamide-induced hyperglycaemia in the rat

In fasted rats 6-aminonicotinamide (6-AN) produced delayed hyperglycaemia, the peak effect being seen by 7 h. Fasting plasma insulin concentrations were not significantly altered but liver glycogen concentrations were decreased following treatment with 6-AN. Adrenalectomy, demedullation and pretreatment with reserpine, phentolamine, nicotinamide and nicotinic acid completely blocked the hyperglycaemic response whereas guanethidine and propranolol or oxprenolol were ineffective. Catecholamine concentrations in the adrenal venous plasma were markedly increased by treatment with 6-AN, the peak effect being seen by 5 h. It is concluded that adrenal medullary release, which is slow in onset, is mainly responsible for the development of sustained hyperglycaemia in the rat.