Studies on streptozotocin diabetes

Hypoglycaemic and hypolipidaemic effects of fractions from kolaviron, a biflavonoid complex from Garcinia Kola in streptozotocin-induced diabetes mellitus rats

In the search for natural hypoglycaemic agents as alternatives to synthetic ones that are expensive and not easily accessible, and to justify the use of Garcinia kola seeds in traditional African medicine to treat diabetes, the hypoglycaemic and hypolipidaemic effects of fractions from kolaviron (KV) (a Garcinia kola seed extract) were investigated in normal and streptozotocin (STZ)-diabetic rats. KV, a biflavonoid complex from Garcinia kola seed, was separated by thin-layer chromatography into three fractions; Fraction I (FI), Fraction II (FII) and Fraction III (FIII) with RF values of 0.48, 0.71 and 0.76, respectively. In normoglycaemic rats, KV, FI and FII administered at a dose of 100 mg kg−1 body weight elicited significant (P < 0.05) hypoglycaemic activity within 4 h of oral administration. Precisely, KV, FI and FII decreased blood glucose levels of normoglycaemic rats by 66%, 50% and 61%, respectively, when compared with controls 30 min after oral administration of the extracts. In hyperglycaemic rats, KV, FI and FII significantly (P < 0.05) reduced blood sugar levels in STZ-diabetic rats within 4 h of oral administration. Furthermore, KV alone produced a significant (P < 0.05) anti-diabetic effect from day 3 to day 7 of oral intubation of STZ-diabetic rats. In addition, the extracts showed favourable effect on the plasma lipid profile of STZ-diabetic rats, and also decreased significantly (P < 0.05) the STZ-induced increase in the activity of microsomal glucose-6-phosphatase and lipid peroxidation (LPO) products. This study confirms the anti-diabetic and hypo-lipidaemic effects of KV in STZ-diabetic rats. These observed effects of KV are attributed to two of its fractions, FI and FII, with RF values of 0.48 and 0.71, respectively.

Brain glucose transporter protein 2 and sporadic Alzheimer’s disease

Sporadic Alzheimer’s disease (sAD) is associated with decreased glucose/energy metabolism in the brain. The majority of glucose utilization in the brain appears to be mediated through glucose transporter protein 1 and 3 (GLUT1 and GLUT3). Deficiency of GLUT1 and GLUT3 in the brain has been found in sAD patients post mortem; however this is not unique to the disease as it is associated with different clinical syndromes as well. In line with recent findings that insulin resistant brain state precedes and may possibly cause sAD, an experimental sAD model based on the central application of the streptozotocin (STZ-icv rat model), which is a selective GLUT2 substrate, has drawn attention to the possible significance of the brain GLUT2 in sAD etiopathogenesis. Important steps in the GLUT2 and sAD interplay are reviewed and discussed. It is concluded that increased vulnerability of GLUT2 expressing neurons may be involved in development of sAD.

Circadian Variations in the Activities of 6‐Phosphogluconate Dehydrogenase and Glucose‐6‐Phosphate Dehydrogenase in the Liver of Conrol and Streptozotocin‐Induced Diabetic Rats

The aim of this study was to examine: the 24 h variation of 6-phosphogluconate dehydrogenase and glucose-6-phosphate dehydrogenase activities, key enzymes for the maintenance of intracellular NADPH concentration, in rat liver in control and streptozotocin-induced diabetic animals. Adult male rats were fed ad libitum and synchronized on a 12:12 h light-dark cycle (lights on 08:00 h). One group of animals was treated with streptozotocin (STZ, 55 mg/kg, intraperitoneal) to induce experimental diabetes. Eight weeks after STZ injection, the animals were sacrificed at six different times of day--1, 5, 9, 13, 17 and 21 Hours After Lights On (HALO)--and livers were obtained. Enzyme activities were determined spectrophotometrically in triplicate in liver homogenates and expressed as units per mg protein. 6-phosphogluconate dehydrogenase activity was measured by substituting 6-phosphogluconate as substrate. Glucose-6-phosphate dehydrogenase activity was determined by monitoring NADPH production. Treatment, circadian time, and interaction between treatment and circadian time factors were tested by either one or two way analysis of variance (ANOVA). Two-way ANOVA revealed that 6-phosphogluconate dehydrogenase activity significantly depended on both the treatment and time of sacrifice. 6-phosphogluconate dehydrogenase activity was higher in control than diabetic animals; whereas, glucose-6-phosphate dehydrogenase activity did not vary over the 24 h in animals made diabetic by STZ treatment. Circadian variation in the activity of 6-phosphogluconate dehydrogenase was also detected in both the control and STZ treatment groups (one-way ANOVA). Time-dependent variation in glucose-6-phosphate dehydrogenase activity during the 24 h was detected in control but not in diabetic rats. No significant interaction was detected between STZ-treatment and time of sacrifice for both hepatic enzyme activities. These results suggest that the activities of NADPH-generating enzymes exhibit 24 h variation, which is not influenced by diabetes.

Evolution of oxidative stress parameters and response to oral vitamins E and C in streptozotocin-induced diabetic rats

Type I diabetes in humans and streptozotocin (STZ)-induced diabetes in rats has been associated with oxidative stress, but antioxidant therapy has given contradictory results, in part related to the absence of common conditions used to evaluate in-vivo antioxidant properties. This prompted the study of an experimental model of antioxidant therapy in STZ-treated rats. Adult female rats received STZ (50 mgkg(-1)) and were studied 7 or 14 days later. Adipose tissue weight progressively decreased with the time of treatment, whereas plasma triglycerides increased at 7 days, before returning to control values at 14 days after STZ treatment. STZ diabetic rats had increased plasma thiobarbituric acid reacting substances and alpha-tocopherol levels, but the latter variable was decreased when corrected for total lipids. STZ diabetic rats showed a higher GSSG/GSH ratio at Day 14 and lower GSH + GSSG at Day 7 in liver. To evaluate the effect of short-term antioxidant therapy, rats received 5 doses of vitamins C and E over 3 days before being killed on Day 14. Treatment with antioxidants decreased plasma lactic acid and thiobarbituric acid reacting substances, as well as urine 8-isoprostane, and decreased plasma uric acid in controls. Vitamins increased the plasma alpha-tocopherol/lipids ratio only in control rats, although the plasma and liver alpha-tocopherol concentration increased in both groups. STZ diabetic rats showed moderate oxidative stress and treatment with antioxidant vitamins caused a significant change in a selected group of oxidative stress markers, which reflected an improvement in some of the complications associated with this disease. The present experimental conditions can be used as a sensitive experimental model to study the responsiveness of diabetes to other antioxidant interventions.

Streptozocin-induced diabetic mouse model of urinary tract infection

Diabetics have a higher incidence of urinary tract infection (UTI), are infected with a broader range of uropathogens, and more commonly develop serious UTI sequelae than nondiabetics. To better study UTI in the diabetic host, we created and characterized a murine model of diabetic UTI using the pancreatic islet beta-cell toxin streptozocin in C3H/HeN, C3H/HeJ, and C57BL/6 mouse backgrounds. Intraperitoneal injections of streptozocin were used to initiate diabetes in healthy mouse backgrounds, as defined by consecutive blood glucose levels of >250 mg/dl. UTIs caused by uropathogenic Escherichia coli (UTI89), Klebsiella pneumoniae (TOP52 1721), and Enterococcus faecalis (0852) were studied, and diabetic mice were found to be considerably more susceptible to infection. All three uropathogens produced significantly higher bladder and kidney titers than buffer-treated controls. Uropathogens did not have as large an advantage in the Toll-like receptor 4-defective C3H/HeJ diabetic mouse, arguing that the dramatic increase in colonization seen in C3H/HeN diabetic mice may partially be due to diabetic-induced defects in innate immunity. Competition experiments demonstrated that E. coli had a significant advantage over K. pneumoniae in the bladders of healthy mice and less of an advantage in diabetic bladders. In the kidneys, K. pneumoniae outcompeted E. coli in healthy mice but in diabetic mice E. coli outcompeted K. pneumoniae and caused severe pyelonephritis. Diabetic kidneys contained renal tubules laden with communities of E. coli UTI89 bacteria within an extracellular-matrix material. Diabetic mice also had glucosuria, which may enhance bacterial replication in the urinary tract. These data support that this murine diabetic UTI model is consistent with known characteristics of human diabetic UTI and can provide a powerful tool for dissecting this infection in the multifactorial setting of diabetes.

The effect of experimental diabetes on the twenty-four-hour pattern of the vasodilator responses to acetylcholine and isoprenaline in the rat aorta

The aim of this study was to investigate whether time-dependent variations in the relaxant effect of acetylcholine, an endothelium-dependent vasorelaxant via muscarinic receptors, and isoprenaline, a nonselective beta-adrenoceptor agonist in rat aorta, are influenced by streptozotocin (STZ)-induced experimental diabetes. Adult male rats were divided randomly into two groups: control and STZ-induced (STZ, 55 mg/kg, intraperitoneal) diabetes. The animals were synchronized to a 12:12 h light-dark cycle (lights on 08:00 h) and sacrificed at six different times of day (1, 5, 9, 13, 17, and 21 hours after lights on; HALO) eight weeks after STZ injection. The in vitro responsiveness of thoracic aorta rings obtained from control and diabetic rats to acetylcholine (10(-9)-10(-5) M) and isoprenaline (10(-10)-10(-3) M) was determined in six different times. EC(50) (the concentration inducing half of the maximum response) values and maximum responses were calculated from cumulative concentration-response curves of the agonists and were analyzed with respect to time and STZ treatment. Treatment, time, and interactions between treatment and time were tested by two-way analysis of variance (ANOVA). To analyze differences due to biological time, one-way ANOVA was used. STZ treatment did not significantly change EC(50) values or maximum responses for both agonists. There were statistically significant time-dependent variations in the EC(50) values for isoprenaline and maximum responses for both acetylcholine and isoprenaline in control groups by one-way ANOVA, but significant time-dependent variations disappeared in the aortas isolated from STZ-induced diabetic rats. The vasodilator responses to acetylcholine and isoprenaline failed to show any significant interaction (treatmentxtime of study) between STZ treatment and time of sacrifice in both EC(50) values and maximum responses by two-way ANOVA. These results indicate there is a basic temporal pattern in the responses to acetylcholine and isoprenaline in rat aorta which continues in diabetes. It is shown for the first time that experimental diabetes does not change the 24 h pattern of responses to acetylcholine and isoprenaline, and that time-dependent variations in the responses to these agonists disappear in diabetic animals. Although further studies are required to define the underlying mechanism(s) of these findings, results suggest that experimental diabetes can modify the time-dependent vasorelaxant responses of rat aorta. This may help to understand the circadian rhythms in cardiovascular physiology and pathology or in drug effects in diabetes.

Brain insulin system dysfunction in streptozotocin intracerebroventricularly treated rats generates hyperphosphorylated tau protein

The intracerebroventricular (icv) application of streptozotocin (STZ) in low dosage was used in 3-month-old rats to explore brain insulin system dysfunction. Three months following STZ icv treatment, the expression of insulin-1 and -2 mRNA was significantly reduced to 11% in hippocampus and to 28% in frontoparietal cerebral cortex, respectively. Insulin receptor (IR) mRNA expression decreased significantly in frontoparietal cerebral cortex and hippocampus (16% and 33% of control). At the protein/activity level, different abnormalities of protein tyrosine kinase activity (increase in hippocampus), total IR beta-subunit (decrease in hypothalamus) and phosphorylated IR tyrosine residues (increase) became apparent. The STZ-induced disturbance in learning and memory capacities was not abolished by icv application of glucose transport inhibitors known to prevent STZ-induced diabetes mellitus. The discrepancy between reduced IR gene expression and increase in both phosphorylated IR tyrosine residues/protein tyrosine kinase activity may indicate imbalance between phosphorylation/dephosphorylation of the IR beta-subunit causing its dysfunction. These abnormalities may point to a complex brain insulin system dysfunction after STZ icv application, which may lead to an increase in hyperphosphorylated tau-protein concentration. Brain insulin system dysfunction is discussed as possible pathological core in the generation of hyperphosphorylated tau protein as a morphological marker of sporadic Alzheimer's disease.

Genes mediating environment interactions in type 1 diabetes

The relative risk of type 1 (autoimmune) diabetes mellitus for a sibling of an affected patient is fifteen times that of the general population, indicating a strong genetic contribution to the disease. Yet, the incidence of diabetes in most Western communities has doubled every fifteen years since the Second World War - a rate of increase that can only possibly be explained by a major etiological effect of environment. Here, the authors provide a selective review of risk factors identified to date. Recent reports of linkage of type 1 diabetes to genes encoding pathogen pattern recognition molecules, such as toll-like receptors, are discussed, providing a testable hypothesis regarding a mechanism by which genetic and environmental influences on disease progress are integrated.

Development of a porcine model of type 1 diabetes by total pancreatectomy and establishment of a glucose tolerance evaluation method

PURPOSE

To develop and evaluate the efficacy of diabetes-targeted cell therapies in humans, a reliable model in larger animals is highly desirable. This article reports the surgical technique of total pancreatectomy in pigs and the biochemical analysis of the characteristics of totally pancreatectomized pigs.

METHODS

Surgical total pancreatectomy was conducted in 23 pigs. Blood glucose, insulin, biochemistries, activity index, and intravenous glucose tolerance test (IVGTT) were examined to assess the pathophysiological profiles of diabetic pigs.

RESULTS

A total of 14 pigs successfully underwent total pancreatectomy without requiring biliary reconstruction and were analyzed in the present study. Activity index was decreased from day 5 on and the mean survival of totally pancreatectomized pigs was 7.6 +/- 2.7 days. No endogenous insulin secretion was confirmed in these pigs. Pigs which received total pancreatectomy demonstrated significantly higher levels of ketone bodies. IVGTT performed within 4 days after total pancreatectomy showed a spontaneous decrease in blood glucose levels despite an absence of endogenous insulin secretion. IVGTT on day 5 or later showed continued hyperglycemia in pigs with total pancreatectomy. Histological examination showed atrophy of hepatocytes and decreased glycogen storage in the liver and decreased mucus production of the small intestine.

CONCLUSION

This article describes a porcine model of diabetes created by total pancreatectomy and it analyzes the pathophysiological profiles in the animals. The present study has suggested that IVGTT on day 5 or later after total pancreatectomy is a reliable method to evaluate the efficacy of cell therapies.

Effects of atorvastatin and pravastatin on glucose tolerance in diabetic rats mildly induced by streptozotocin

Effects of atorvastatin and pravastatin on glucose tolerance in mildly induced diabetic rats by streptozotocin at 24 mg/kg, i.v. were studied. Non-diabetic and diabetic rats were given orally 0.5% carboxymethylcellulose (control), 8 mg/kg atorvastatin or 8 mg/kg pravastatin once a day for 6 weeks. An oral glucose tolerance test (OGTT) was carried out 1, 2, 3, and 6 weeks after the administration. The blood glucose and plasma insulin levels measured before OGTT in the diabetic rats were not different from those in the non-diabetic rats. However, the hyperglycemic response to OGTT in the diabetic rats significantly exceeded that in the non-diabetic rats. The plasma insulin increased by OGTT in the diabetic rats appeared to be lower than that in the non-diabetic rats. Statin treatments for 1 week did not modify the OGTT-induced hyperglycemia appreciably, although there were some significant differences. More than 2 weeks after administration, the blood glucose levels at several time points after a glucose intake in the atorvastatin-treated diabetic rats were significantly higher than the respective levels in the control diabetic rats. Neither atorvastatin nor pravastatin modified the OGTT-induced insulin secretion. Statins, especially atorvastatin, may influence the glucose tolerance in mildly induced diabetic rats without alterations of insulin secretion.

Diabetic cardiomyopathy: recent evidence from mouse models of type 1 and type 2 diabetes

Diabetic cardiomyopathy is defined as ventricular dysfunction of the diabetic heart in the absence of coronary artery disease. With the use of both in vivo and ex vivo techniques to assess cardiac phenotype, reduced contractile performance can be observed in experiments with mouse models of both type 1 (insulin-deficient) and type 2 (insulin-resistant) diabetes. Both systolic dysfunction (reduced left ventricular pressures and decreased cardiac output) and diastolic dysfunction (impaired relaxation) is observed in diabetic hearts, along with enhanced susceptibility to ischemic injury. Metabolism is also altered in diabetic mouse hearts: glucose utilization is reduced and fatty acid utilization is increased. The use of geneticallyengineered mice has provided a powerful experimental approach to test mechanisms that may be responsible for the deleterious effects of diabetes on cardiac function.Key words: cardiac function, cardiac metabolism, cardiac phenotype.

Effects of Petroselinum crispum extract on pancreatic B cells and blood glucose of streptozotocin-induced diabetic rats

This study investigated both morphologically and biochemically whether parsley (Petroselinum crispum), which is used as a folk remedy to decrease blood glucose, has any antidiabetic effect on pancreatic B cells of rats. Parsley extract was given to male diabetic rats. In the diabetic group given parsley extract, it was detected that the number of secretory granules and cells in islets and other morphologic changes were not different from the control diabetic group, while the blood glucose levels in the diabetic group given the plant extract were reduced in comparison to the diabetic group. In addition, a decrease was observed in the weight of the control diabetic group and the diabetic group given the plant extract. It is suggested that the plant therapy can provide blood glucose homeostasis and cannot regenerate B cells of the endocrine pancreas.

The potential mechanism of the diabetogenic action of streptozotocin: inhibition of pancreatic beta-cell O-GlcNAc-selective N-acetyl-beta-D-glucosaminidase

Streptozotocin (STZ), an analogue of GlcNAc, inhibits purified rat spleen O-GlcNAc-selective N-acetyl-beta-D-glucosaminidase (O-GlcNAcase), the enzyme that removes O-GlcNAc from protein. We have shown previously that STZ increases pancreatic islet O-linked protein glycosylation. In light of these data, we investigated the possibility further that STZ causes beta-cell death by inhibiting O-GlcNAcase. In isolated islets, the time course and dose curve of STZ-induced O-glycosylation correlated with beta-cell toxicity. STZ inhibition of rat islet O-GlcNAcase activity also paralleled that of its beta-cell toxicity, with significant inhibition occurring at a concentration of 1 mM. In contrast, STZ inhibition of rat brain O-GlcNAcase and beta-TC3 insulinoma cell O-GlcNAcase was significantly right-shifted compared with islets, with STZ only significantly inhibiting activity at a concentration of 5 mM, the same concentration required for beta-TC3 cell toxicity. In comparison, N-methyl-N-nitrosourea, the nitric oxide-donating portion of STZ, did not cause increased islet O-glycosylation, beta-cell toxicity or inhibition of beta-cell O-GlcNAcase. Enhanced STZ sensitivity of islet O-GlcNAcase compared with O-GlcNAcase from other tissues or an insulinoma cell line suggests why actual islet beta-cells are particularly sensitive to STZ. Confirming this idea, STZ-induced islet beta-cell toxicity was completely blocked by GlcNAc, which also prevented STZ-induced O-GlcNAcase inhibition, but was not even partially blocked by glucose, glucosamine or GalNAc. Together, these data demonstrate that STZ's inhibition of beta-cell O-GlcNAcase is the mechanism that accounts for its diabetogenic toxicity.

Lipid peroxidation in the pancreas and other organs in streptozotocin diabetic rats

We studied the relationship between changes in lipid peroxides and those in catalase activity in pancreases, livers and hearts of streptozotocin-induced diabetic rats. Animals were killed 2 or 7 weeks after saline or streptozotocin (32 mg/kg, i.v.) injection. The levels of blood glucose and plasma insulin in the 2-week streptozotocin-treated rats were 176.8+/-20.5 mg/dl and 29.9+/-3.2 microU/ml, respectively. In the pancreas, the lipid peroxide level significantly decreased and the catalase activity significantly increased 2 weeks after streptozotocin injection. These changes recovered after 7 weeks. In the heart, the lipid peroxide level significantly increased without any change of catalase activity 2 weeks after the initiation of diabetes. After 7 weeks, the catalase activity significantly increased and the lipid peroxide level returned to the control level. In the liver, there was no change in the lipid peroxides and catalase in the 2-week streptozotocin-treated rats, whereas the catalase activity significantly increased 7 weeks after the injection. It was suggested that the defense system in the pancreas to oxidative stress may be evoked in an early stage of streptozotocin-induced diabetes.

Superoxide dismutase reduces islet microvascular injury induced by streptozotocin in the rat

Intravenous administration of streptozotocin (STZ) leads to permanent diabetes mellitus in rats. We investigated the possible role of islet microcirculatory changes and free radical formation in this animal model. In vivo fluorescence microscopy was performed for 4 h after administration of STZ. Vascular permeability, capillary blood flow, and endothelial leukocyte adhesion were measured in endocrine and exocrine pancreatic tissue. The earliest microcirculatory event was an increase in vascular permeability in pancreatic islets, with a peak 1 h after STZ administration. The difference between islet and exocrine tissue light intensity was +15.8 +/- 5.6% at t = 60 min. Islet blood flow velocity significantly decreased after 3 h, whereas blood flow in the exocrine pancreas was not affected. Complete stasis of islet blood flow was observed only in rats receiving STZ. Neither increased leukocyte adhesion to islet vascular endothelium nor ischemia-reperfusion phenomena were observed. Prophylactic administration of the radical scavenger superoxide dismutase prevented STZ-induced damage to the islet microcirculation in the initial phase of this model. We conclude that STZ leads to severe microcirculatory disturbances within pancreatic islets in rats. Apparently, these changes are mediated at least in part by free oxygen radicals.

Antihyperglycemic activity of phenolics from Pterocarpus marsupium

Glucose levels in rats with hyperglycemia induced by streptozotocin were determined after i.p. administration of marsupsin (1), pterosupin (2), and pterostilbene (3), three important phenolic constituents of the heartwood of Pterocarpus marsupium. Marsupsin and pterostilbene significantly lowered the blood glucose level of hyperglycemic rats, and the effect was comparable to that of 1,1-dimethylbiguanide (metformin).

Lens glutathione, lens protein glycation and electrophoretic patterns of lens proteins in STZ induced diabetic rats

As diabetes is a very complex disease, with the pathological symptoms varying with age, diabetic type and means of control, it still warrants many in vivo and in vitro studies. During hyperglycaemia, increases in the sorbitol pathway, nonenzymatic glycosylation of lens proteins and damage to antioxidant systems have been reported to cause opacification of the lens leading to cataract formation. In this study, intracapsular extracts of lenses from STZ induced diabetic female rats were examined. Total protein, glutathione and nonenzymatic glycosylation were determined by the Lowry, Ellman reagent and thiobarbituric acid methods respectively. Laemmli protein electrophoresis was also carried out on the lens homogenates. After a period of as short as 5 weeks, a decrease in lens glutathione, and an increase in nonenzymatic glycosylation of lens proteins were found. The electrophoresis showed an increase in proteins of high molecular weight.

Development of secondary hyperparathyroidism and bone disease in diabetic rats with renal failure

Renal osteodystrophy in diabetic patients on maintenance hemodialysis is characterized by a higher prevalence of low bone turnover and is associated with a relative deficiency of parathyroid hormone (PTH) as compared with non-diabetic hemodialysis patients. The goal of the study was to evaluate how diabetes affected the development of secondary hyperparathyroidism (2 degrees HPT) and bone disease in azotemic rats. Three groups of 5/6 nephrectomized, pair-fed male Wistar rats maintained on a high phosphorus (1.2%) diet were studied: (1) the control group, non-diabetic azotemic rats (NDR); and two streptozotocin-induced diabetic azotemic groups, (2) poorly-controlled diabetic rats (PCDR) which received only enough NPH insulin to maintain the blood glucose between 300 and 400 mg/dl, and (3) well-controlled insulin-treated diabetic rats (IDR) which received a continuous insulin infusion for 14 days via a subcutaneously implanted miniosmotic pump. Serum calcium, phosphorus and creatinine levels were similar among the three groups. Blood glucose levels were greater in the PCDR group than the IDR and NDR groups (358 +/- 11 vs. 83 +/- 9 and 87 +/- 8 mg/dl, respectively; P < 0.001). Rats in the PCDR group weighed less at sacrifice as compared with the IDR and NDR groups (P < 0.05). Serum PTH levels (normal 47 +/- 2 pg/ml) were elevated, but not different among the three groups (136 +/- 34, 147 +/- 21 and 98 +/- 8 pg/ml in the PDCR, IDR and NDR groups, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Short-term diabetes alters K+ currents in rat ventricular myocytes

The electrophysiological properties of single ventricular myocytes from control rats and from rats made diabetic by streptozotocin (STZ) injection (100 mg/kg body weight) have been investigated using whole-cell voltage-clamp measurements. Our major goal was to define the effects of diabetes on rate-dependent changes in action potential duration and the underlying outward K+ currents. As early as 4 to 6 days after STZ treatment, significant elevation of plasma glucose levels occurs, and the action potential duration increases. In both control and diabetic rats, when the stimulation rate is increased, the action potential is prolonged, but this lengthening is considerably more pronounced in myocytes from diabetic rats. In ventricular myocytes from diabetic rats, the Ca(2+)-independent transient outward K+ current (I(t)) is reduced in amplitude, and its reactivation kinetics are slowed. These changes result in a smaller I(t) at physiological heart rates. The steady-state outward K+ current (IK) also exhibits rate-dependent attenuation, and this phenomenon is more pronounced in cells from diabetic rats. These STZ-induced changes in I(t) and IK also develop when a lower dose (55 mg/kg) of STZ is used and measurements are made after 7 weeks of treatment. These electrophysiological effects are not related to the hypothyroid conditions that accompany the diabetic state, since they cannot be reversed by replacement of the hormone L-triiodothyronine to physiological levels. Direct effects of STZ could be ruled out, since preceding the STZ injection with a bolus injection of 3-O-methylglucose, which prevents development of hyperglycemia, prevents the electrophysiological changes.(ABSTRACT TRUNCATED AT 250 WORDS)

Circadian rhythms of plasma corticosterone at different times after induction of diabetes. Responses to corticoadrenal stimulation in light and dark phases

In this study we have tried to determine the effects of streptozotocin-induced (50 mg/kg) diabetes (15 and 30 day duration) on circadian rhythms of plasma corticosterone concentrations and on the responsiveness of the adrenal glands to exogenously administered ACTH at the time of maximum and minimum levels of plasma corticosterone. Rats were kept under controlled lighting 12h light/12h dark (12L/12D) and fed ad libitum. The corticosteroid circadian pattern in control (C) rats is characterized as one in which peak corticosterone concentrations occur at the beginning of the dark phase (activity period), with a decrease over the remainder of the 24h period. Circadian rhythmicity of plasma corticosterone concentration was absent in the diabetic rats 15 days after induction (D15 rats), with higher mean levels than the C. However, in the diabetic rats 30 days after induction (D30 rats) there is a recovery of this rhythm with similar acrophase and amplitude to the C rats. One hour after stimulation by ACTH (5 IU/kg) at the time of maximum and minimum levels of plasma corticosterone, the C rats showed similar plasma corticosterone levels. In the D15 rats, levels of corticosterone in the light phase one hour after ACTH administration were higher than in the dark phase; being lower than C in this phase. The loss of capacity to respond during the dark phase may be due to adrenal blunting in this phase with high levels of plasma corticosterone. In D30 rats, there is a more noticeable loss of capacity for adrenal response in the light than in the dark phase, with values lower than C and D15 rats in both phases. These findings suggest that the duration of diabetes has a significant role in both plasma corticosterone rhythms and adrenal sensitivity to ACTH administration.

Morphological characteristics of the depository surface of alveolar bone of diabetic mice

Sharpey's fibers support teeth by attachment of periodontal ligament fibers to alveolar bone. The effects of diabetes mellitus on this support mechanism have not been described and were the subject of this study. Male Swiss mice were rendered diabetic by streptozotocin. Mandibles were removed 9 weeks after injections, the mineralizing front of the depository surface of the interdental septum was exposed by fracture through the periodontal ligament, rendered anorganic, and examined by scanning electron microscopy. No significant reduction in alveolar crest height was evident in diabetic as compared to control animals; however, significant changes in the a) mineralization patterns of bone depository surfaces and Sharpey's fibers, and b) number of Sharpey's fibers inserting into alveolar bone were evident in diabetics. Unmineralized fissures, characteristic of Sharpey's fibers of control, were nearly obliterated by mineralized tissue in diabetic animals. The mineralizing front of the middle and apical thirds of the diabetic alveolar wall was covered by numerous large calcified globules resembling enlarged calcospherites, which were not evident over the cervical third or control tissues. The mean Sharpey fiber density was greater in controls than in diabetics (p less than 0.001); however, there was no significant difference between their mean diameters. These observations suggest that, in early diabetes, Sharpey's fibers and depository surfaces of the middle and apical thirds of the interdental septum have morphologic evidence of aging, which precedes significant reduction in alveolar crest height. These changes may weaken the attachment of periodontal ligament fibers to bone and reduce resistance of the periodontium to intrusive forces.

Morphometric investigations on intrarenal vessels of streptozotocin-diabetic rats

We have investigated 975 different grazing sections of vessels in kidney preparations of 20 rats of the Wistar strain. Half of these genetically identical animals had an insulin-deficiency diabetes induced by injection of streptozocin. The kidneys were removed for investigation after 2 and 12 weeks duration of diabetes. The vessel cross-section, wall, lumen and endothelial surface area were determined in renal arteries, arterioles and preglomerular afferent arterioles in a blind experiment. Statistically detecteable changes were found in the diabetic vessels in the early stage of the diabetes. Preglomerular afferent arterioles showed a highly significant and increasing lumen dilatation commencing after 2 weeks. Diabetic arteries and arterioles developed narrower lumina. A significant thickening of the endothelium took place at the same time in both vessel types. All three vessel regions became smaller and had thinner walls than healthy vessels as the diabetes progressed. The findings on the afferent vessels indicate that haemodynamic effects on the glomerulus are to be expected. Familial diabetic gloermulopathy begins with a reversible hyperfiltration. However, the mechanism has not been clarified in the context of the diabetic metabolic disorder, and this change is probably the haemodynamic consequence of the substantial dilatation of the preglomerular afferent arterioles. With their renin-positive segment, these arterioles are the centre of intrarenal regulation. The increase of the capillary glomerular pressure associated with the dilatation of the preglomerular afferent arterioles is a crucial factor in the development of diabetic glomerulopathy.

Effects of insulin on blood, plasma, and brain glucose in hyperglycemic diabetic rats

This study, in biologically bred hyperglycemic diabetic rats, examined the effect of a intravenous insulin infusion (1.5 units.hr-1) on blood, plasma, and brain glucose concentrations to determine their relationship during decreasing blood and plasma glucose levels. The data were compared to saline-treated diabetic rats and saline-treated nondiabetic littermates. The volume and duration of the treatment infusion were similar in all groups. Insulin infusion in diabetic rats produced the expected reduction in blood and plasma glucose, and normoglycemia was produced within 78 +/- 37 minutes (mean +/- SD). However, once normoglycemia was achieved, brain glucose was still significantly greater by 44% than in nondiabetic rats (p = 0.015). Moreover, the ratio of brain to plasma glucose was more than 50% greater in diabetic than nondiabetic rats, irrespective of whether or not they received insulin (p less than 0.01). We conclude that measurement of blood or plasma glucose in diabetic subjects will tend to underestimate the amount of glucose in the brain and that this relationship is not influenced by acute insulin therapy.

Spatially resolved changes in diabetic rat skeletal muscle metabolism in vivo studied by 31P-n.m.r. spectroscopy

Phase-modulated rotating-frame imaging (p.m.r.f.i.), a localization technique for 31P-n.m.r. spectroscopy, has been applied to obtain information on the heterogeneity of phosphorus-containing metabolites and pH in the skeletal muscle of control and streptozotocin-diabetic rats. Using this method, the metabolic changes in four spatially resolved longitudinal slices (where slice I is superficial and slice IV is deep muscle) through the ankle flexor muscles have been investigated at rest and during steady-state isometric twitch-contraction at 2 Hz. At rest, intracellular pH was lower, and phosphocreatine (PCr)/ATP was higher, throughout the muscle mass in diabetic compared with control animals. The change in PCr/ATP in diabetic muscle correlated with a decrease in the chemically determined ATP concentration. During the muscle stimulation period, the decrease in pH observed in diabetic muscle at rest was maintained, but not exacerbated, by the contractile stimulus. Stimulation of muscle contraction caused more marked changes in PCr/(PCr + Pi), PCr/ATP and Pi/ATP in the diabetic group. These changes were most evident in slice III, which contains the greatest proportion of fast glycolytic-oxidative (type IIa) fibres, in which statistically significant differences were observed for all metabolite ratios. The results presented suggest that some degree of heterogeneity occurs in diabetic skeletal muscle in vivo with respect to the extent of metabolic dysfunction caused by the diabetic insult and that regions of the muscle containing high proportions of type IIa fibres appear to be most severely affected.

Pentamidine-induced beta cell toxicity is not preventable by high glucose

The incidence of beta cell damage attributable to pentamidine treatment of pneumocystis pneumonia is increasing in frequency because of the AIDS epidemic. We carried out in vitro studies in perfused rat islets using insulin secretion as an index of beta cell damage to study the effects of pentamidine and to test whether glucose can prevent toxicity in this physiologic model. Isolated islets were cultured for 16-18 hours of static incubation, in a culture medium containing 100 mg/dl glucose, with or without pentamidine (10(-6) M, a therapeutic concentration). Islets were then perfused with media containing 60 mg/dl followed by 300 mg/dl glucose concentrations to study the insulin secretory response. Incubation of islets with pentamidine was associated with subsequent basal hypersecretion of insulin (0.40 +/- 0.05 microU/islet .5 minute vs. 0.18 +/- 0.04 microU/islet .5 minute, p less than .005), and an insulin secretory response to glucose which was completely abolished (0.05 +/- 0.04 microU/islet .5 minute versus 1.12 +/- 0.02 microU/islet .5 minute, p less than .005). To determine whether glucose may protect against the effects of pentamidine, islets were then exposed to high glucose concentrations during simultaneous incubation with pentamidine. Coincubation with high glucose did not prevent these insulin secretory defects. A more extended culture of pentamidine-treated islets in the absence of pentamidine and at a glucose concentration of 100 mg/dl did not result in any recovery of insulin secretion. We conclude that pentamidine-induced beta cell damage is irreversible, not preventable by incubation with high glucose concentrations, and may therefore result from a mechanism different to that of alloxan.

[Periodontal reactions to orthodontic forces in the diabetic metabolic state]

The reaction of the periodontium to orthodontic tooth movement was studied in rats with streptozotocin diabetes. Forces employed to initiate mesial movement of first molar were 10 N 20 N 30 N and the duration of application was three, six, ten and 14 days. The 14-day rats were treated with fluorochrome sequential labelling according to Rahn. Diabetes mellitus in rats is accompanied by characteristic changes: The most important findings were: 1. a slow osseous regeneration, as could be shown by fluorescence microscopy, 2. the new bone ist unable to pick up the labellings in a sequential manner, 3. a weakening of the periodontal ligamentum, 4. microangiopathies in the gingiva area. the specific diabetic changes are more pronounced following orthodontic tooth movement.

A sigmoidal relationship between liver stearoyl CoA desaturase activity and serum hormone concentrations caused by streptozocin and its antagonists

Stearoyl CoA desaturase activity in liver microsomes, and insulin, thyroxine, and triiodothyronine levels in serum were measured after administration of streptozocin (STZ) and its antagonists to rats. The effect of STZ, which caused hyperglycemia and inhibited the desaturase activity, was antagonized by 2-desoxyglucose and 3-O-methyl-glucose; 1-O-methyl-3-desoxyglucose and 1-O-methyl-3-O-methylglucose were without any effect. The enzyme activity plotted against insulin levels showed a broad sigmoidal curve, whereas the activities versus thyroid hormone levels showed steeper sigmoidal curves.

Serotonergic function in diabetic rats: psychotherapeutic implications

Extracellular serotonin in striatum was studied in untreated streptozotocin-induced diabetic rats and in untreated nondiabetic rats that served as age-, food-, and sex-matched controls. Extracellular serotonin was studied under anesthesia in vivo and dynamically with voltammetry. The results showed that an early and significant increase in extracellular serotonin occurred in striatum in the untreated acutely (3 days) diabetic rat. In untreated long-term (3-7 weeks) diabetic rats, however, the increase in serotonin in extracellular fluid in striatum decreased and returned to normal. The findings show a change in serotonergic function in acutely diabetic rats. The serotonergic alteration may have psychotherapeutic implications.

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)

Plasma corticosterone, motor activity and metabolic circadian patterns in streptozotocin-induced diabetic rats

Experiments were conducted in male rats to study the effects of streptozotocin-induced diabetes on circadian rhythms of (a) plasma corticosterone concentrations; (b) motor activity; and (c) metabolic patterns. Animals were entrained to LD cycles of 12:12 hr and fed ad libitum. A daily rhythm of plasma corticosterone concentrations was found in controls animals with peak levels at 2400 hr and low values during the remaining hours. This rhythm was statistically confirmed by the cosinor method and had an amplitude of 3.37 micrograms/100 ml and the acrophase at 100 hr. A loss of the normal circadian variation was observed in diabetic animals, with a nadir at the onset of light period and high values throughout the remaining hours; cosinor analysis of these data showed no circadian rhythm, delete and a higher mean level than controls. As expected, normal rats presented most of their motor activity during the dark period with 80% of total daily activity; the cosinor method demonstrated a circadian rhythm with an amplitude of 60% of the mean level and the acrophase at 0852 hr. Both diabetic and control rats showed a similar activity during the light phase, but diabetic animals had less activity than controls during the night and their percentage of total daily activity was similar in both phases of the LD cycle (50% for each one). With the cosinor method we were able to show the persistence of a circadian rhythm in the motor activity of diabetic rats, but with a mesor and amplitude lower than in controls (amplitude rested at 60% of the mean level) and its acrophase advanced to 0148 hr.(ABSTRACT TRUNCATED AT 250 WORDS)

Ultrastructural aspects of streptozotocin cytotoxicity on rat pancreatic islets in vitro. Test of a protective effect of zinc

Pancreatic islets, newly formed in vitro were incubated in the presence of streptozotocin (STZ; 0.4 mM) for up to 6 h. Ultrastructural changes first appeared between 2 and 4 h; heterochromatization, was followed by swelling of nuclear and reticular membranes, vesiculation of the Golgi apparatus, fragmentation of cell membranes and finally mitochondrial destruction. At the end of the experiment all the B cells were destroyed, whereas the other cell types remained intact. Exogenous ZnSO4 was added during preincubation periods to increase the intrainsular zinc content and to determine any protective effect against STZ-cytotoxicity. Since the addition of zinc had no obvious effect, it is suggested that STZ cytotoxicity on B cells cannot be attributed to competition for zinc between copper-zinc superoxide dismutase (Cu-Zn-SOD) and the crystallization of insulin.

Comparative interactions of streptozotocin and chlorozotocin with DNA of an insulin-secreting cell line (RINr)

Both streptozotocin and chlorozotocin, the 2-chloroethyl analogue of streptozotocin, are diabetogenic chemicals in rodents. Although these chemicals are similar structurally, they appear to act on pancreatic B cells via different mechanisms. In studies here, damage and repair of DNA after exposure of an insulin-secreting cell line to streptozotocin and chlorozotocin were assessed by nucleoid sedimentation and alkaline elution. Equitoxic concentrations of streptozotocin and chlorozotocin caused significant single-strand breakage of DNA (p less than 0.005). These lesions were repaired in a time-dependent manner, with most repair completed by 24-h post-exposure to chemicals. Additionally, chlorozotocin caused DNA-DNA and DNA-protein crosslinks in insulinoma cells. When proteinase K was included in the crosslinking assay, a substantial proportion of the chlorozotocin-associated crosslinks proved to be DNA interstrand in nature. Analysis of the amount of interstrand crosslinking in insulinoma cells after exposure to chlorozotocin for 1 h showed that formation of interstrand crosslinks was slow. Increasing amounts appeared over a 24-h period. These results suggest that the formation of irreversible DNA interstrand crosslinks may be a critical factor in cytotoxicity and diabetogenicity caused by chlorozotocin.

Effects of prostaglandin E2 and indomethacin on 25-hydroxyvitamin D3-1 alpha-hydroxylase activity in isolated kidney cells of normal and streptozotocin-induced diabetic rats

The effects of prostaglandin E2 (PGE2) (1 microM) and indomethacin (IN) (20 microM) on 1,25 dihydroxyvitamin D3 production were studied in renal cell suspensions isolated from control, streptozotocin-induced diabetic, and insulin-treated diabetic rats. Renal cortex cells were isolated by enzymatic digestion, and preincubated for 30 min at 37 degrees C with the appropriate additive(s) followed by a 1 h incubation with 8 nM 25-hydroxyvitamin D3 in serum-free medium. Radioactivity incorporated into that fraction of the cell suspension extract co-eluting with synthetic 1,25-dihydroxyvitamin D3 on high pressure liquid chromatography was determined. All animals were raised for 5 weeks on a vitamin D-deficient diet. Isolated kidney cells from vitamin D-deficient rats showed dose-dependent response of 1,25 dihydroxyvitamin D3 production to PGE2. Cells from control animals demonstrated a stimulatory effect of PGE2 (P less than 0.05) and a suppressive effect of IN (P less than 0.01) on 1,25 dihydroxyvitamin D3 production. In contrast, cells from diabetic rat kidneys failed to respond to these agents, alterations which were reversed by insulin treatment. The accumulated data suggest that depressed synthesis of 1,25 dihydroxyvitamin D3 previously observed in the experimental diabetic rat is due, at least in part, to an impaired production and response to PGE2-like prostaglandins.

The partial protective effect of the hydroxyl radical scavenger dimethyl urea on streptozotocin-induced diabetes in the mouse in vivo and in vitro

The protective effect on streptozotocin-induced diabetes of dimethyl urea, a hydroxyl radical scavenger, has been evaluated in vivo and in vitro. Pretreatment with dimethyl urea before a single diabetogenic dose of streptozotocin partially protected NMRI mice from hyperglycaemia, whereas the serum glucose of C57BL/KsJ mice increased during week 2 of observation. When the pancreases of these latter mice were examined histologically, insulitis was found in 15 out of 22 animals. The protective effect of dimethyl urea in the NMRI mice was not due to short-term hyperglycaemia induced by the drug, since pretreatment with glucose did not protect from streptozotocin but potentiated its diabetogenic effect. Dimethyl urea reduced the inhibition caused by streptozotocin on proinsulin biosynthesis of NMRI islets in vitro. It is suggested that streptozotocin-induced diabetes in mice may involve generation of hydroxyl radicals which are toxic to islet B cells. If this immediate cytoxicity is reduced by a scavenger, a more slowly developing hyperglycaemia and an accompanying insulitis may occur in particularly susceptible animals.

Calcium homeostasis in chronic streptozotocin-induced diabetes mellitus in the rat

Calcium homeostasis was studied in freely fed control, streptozotocin diabetic, long-term and short-term insulin-treated diabetic rats 7 wk after the induction of diabetes. In contrast to the short-term (5-12 day) diabetic rat model, intestinal absorption of calcium was markedly enhanced in chronically insulin-deficient animals. Moreover, conventional balance studies showed that these animals were in positive calcium balance despite severe hypercalciuria. Intestinal hyperabsorption of calcium in long-standing diabetic rats occurred despite low levels of circulating 1,25-dihydroxyvitamin D and hypercorticosteronism and was attended by hypercalcemia and suppression of both plasma parathyroid hormone (PTH) and urinary cyclic 3',5'-AMP (cAMP). Long-term insulin replacement completely normalized the intestinal hyperabsorption of calcium, corrected the plasma calcium, and significantly increased circulating PTH and urinary cAMP excretion. Insulin therapy also corrected the decreased plasma 1,25-dihydroxyvitamin D observed in untreated diabetic animals. Intestinal hyperabsorption of calcium appeared to be only partially corrected by short-term insulin therapy. The accumulated results reveal decided differences in calcium homeostasis and hormonal response between the rats with long-standing diabetes and those with diabetes of short duration.

The effect of streptozotocin-induced diabetes in rats on cardiac contractile proteins

In order to determine whether diabetic cardiomyopathy in rats is associated with altered contractile proteins, male and female rats were made diabetic with intravenous streptozotocin (STZ). Calcium ATPase activity of cardiac actomyosin was significantly decreased after 1 week of diabetes and was depressed by 60% by 2 weeks. Rats pretreated with 3-O-methyl glucose to prevent the hyperglycemia caused by STZ had normal Ca2+-actomyosin ATPase activities, and non-diabetic rats whose food was restricted to keep their body and heart weights similar to those found in diabetic animals had only a slight fall in actomyosin ATPase activity. Ca2+-ATPase and actin-activated ATPase activities of pure myosin were similarly depressed in preparations from hearts of diabetic animals. Sodium dodecylsulfate gel electrophoresis and isoelectric focusing failed to reveal differences in the patterns of contractile proteins or light subunits between diabetics and controls, but pyrophosphate gels showed a shift in the myosin pattern. Because of depressed circulating thyroid hormone levels in diabetic animals, cardiac contractile proteins were also studied in preparations from thyroidectomized rats. Calcium activities of actomyosin and myosin ATPase were lower than values found in hearts of diabetic rats. When diabetic animals were kept euthyroid with thyroid replacement, actomyosin ATPase activity was still depressed. Thus STZ diabetes causes a significant decrease in cardiac contractile protein ATPase activity. This may be related to altered proportions of myosin isoenzymes.

Altered myocardial mechanics in diabetic rats

Diabetes mellitus is associated frequently with congestive heart failure in humans, even in the absence of associated coronary disease or hypertension. Nevertheless, the effects of the diabetic state on myocardial mechanics have not been studied. Accordingly, diabetes was induced in female Wistar rats by injection of streptozotocin (60 mg/kg). Left ventricular papillary muscles were studied 5, 10, and 30 weeks later and compared with controls. Relaxation was delayed significantly and velocity of shortening was depressed at all loads. However, the passive and active force-length curves, as well as the series elastic properties, were not altered. The changes in cardiac performance were found over a range of muscle lengths, stimulus frequencies, and bath concentrations of calcium, glucose, and norepinephrine. The duration of diabetes had no major effect on the mechanical changes observed. The possible influences of drug-induced cardiac toxicity, malnutrition, and altered thyroid hormone levels have been considered; the latter two factors could not be excluded completely from having some influence on the mechanical properties of diabetic cardiac muscle. Evidence is cited showing abnormalities in calcium uptake by sarcoplasmic reticulum and depressed actomyosin ATPase activity. Thus a cardiomyopathic state has been produced in the rat consequent to the induction of experimental diabetes mellitus. Various mechanisms for this entity have been suggested.

Ultrastructural changes in Leydig cells of streptozotocin-induced diabetic rats

Hyperglycemia (experimental diabetes) was induced in adult male rats by destruction of the pancreatic beta cells with a single intravenous injection of streptozotocin (STZ). Testes from diabetic, from insulin-treated diabetic, and from sham-injected normal rats were fxed by vascular perfusion. The fine structure of Leydig cells was examined at two, three, and four weeks after the STZ injection in the untreated diabetic animals, and at four weeks in the controls and insulin-treated diabetic rats. A number of morphological changes was observed in Leydig cells of untreated diabetic animals. Most obvious of these was an accumulation of lipid droplets, not normally present in Leydig cells in adults of this species. Smooth endoplasmic reticulum (SER) was markedly reduced in Leydig cells of the hyperglycemic rats. Several types of intracellular bodies were seen exclusively in Leydig cells of the untreated diabetic animals. Many resembled secondary lysosomes or dense bodies, while others appeared to be autophagic vacuoles. In addition, a small, granule-containing lamellar structure was seen either within a typical dense body or free in the cytoplasm. Myelin-like structures were commonly observed within the cytoplasm of the Leydig cell or within mitochondria. The appearance of the mitochondria in diabetic rats was otherwise normal. The extracellular spaces surrounding Leydig cells from untreated hyperglycemic rats also contained large accumulations of myelin-like material. These structural changes appear to be direct consequences of the diabetic state of the animals, since the ultrastructure of insulin-treated diabetic rats did not differ from that of the controls. These findings may reflect an alteration or breakdown of Leydig cell components normally involved in the synthesis of androgen, and correlate with previous reports of lowered circulating levels of testosterone in diabetic rats.

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

The effect of alpha- and beta-adrenoceptor blocking agents and a beta2-agonist, salbutamol, on the diabetogenic effects of streptozocin (threshold doses) was investigated in the rat. Phentolamine and salbutamol potentiated the diabetogenic effect of streptozocin but phenoxybenzamine, tolazoline, oxprenolol and propranolol were without effect. The potentiating effect of phentolamine was blocked by oxprenolol. Potentiation of the diabetogenic effect by phentolamine is not related to alpha-adrenoceptor block, vasodilatation or insulin release. But it may be related to its ability to stimulate beta-adrenoceptors.