Different Doses Of Streptozotocin Research Articles

Streptozotocin-Induced Type 1 and 2 Diabetes Mellitus Mouse Models Show Different Functional, Cellular and Molecular Patterns of Diabetic Cardiomyopathy.

The main cause of morbidity and mortality in diabetes mellitus (DM) is cardiovascular complications. Diabetic cardiomyopathy (DCM) remains incompletely understood. Animal models have been crucial in exploring DCM pathophysiology while identifying potential therapeutic targets. Streptozotocin (STZ) has been widely used to produce experimental models of both type 1 and type 2 DM (T1DM and T2DM). Here, we compared these two models for their effects on cardiac structure, function and transcriptome. Different doses of STZ and diet chows were used to generate T1DM and T2DM in C57BL/6J mice. Normal euglycemic and nonobese sex- and age-matched mice served as controls (CTRL). Immunohistochemistry, RT-PCR and RNA-seq were employed to compare hearts from the three animal groups. STZ-induced T1DM and T2DM affected left ventricular function and myocardial performance differently. T1DM displayed exaggerated apoptotic cardiomyocyte (CM) death and reactive hypertrophy and fibrosis, along with increased cardiac oxidative stress, CM DNA damage and senescence, when compared to T2DM in mice. T1DM and T2DM affected the whole cardiac transcriptome differently. In conclusion, the STZ-induced T1DM and T2DM mouse models showed significant differences in cardiac remodeling, function and the whole transcriptome. These differences could be of key relevance when choosing an animal model to study specific features of DCM.

Relationship Between Insulin-Receptor Substrate 1 and Langerhans' Islet in a Rat Model of Type 2 Diabetes Mellitus.

In vivo studies on pathogenesis of type 2 diabetes mellitus (T2DM) have been reported, however, the relationship between insulin-receptor substrate 1 (IRS1) and the area of Langerhans' islets was unknown. Therefore, a correlation between both parameters was assessed. Diabetic groups were fed with a high-fat diet (HFD) and injected with three different doses of streptozotocin, namely 25, 35 and 45 mg/kg, and compared to a control group after 9 weeks. Administration of HFD/streptozotocin increased the level of fasting blood glucose but reduced the level of IRS1 and the area of Langerhans' islets in diabetic groups. The coefficient of correlation between IRS1 and area of Langerhans' islets was 0.259 (p=0.232). In addition, the coefficient of correlation for fasting blood glucose with the area of Langerhans' islets and IRS1 was -0.520 (p=0.011) and -0.603 (p=0.002), respectively. The reduction of IRS1 was weakly correlated with the destruction of Langerhans' islets, suggesting there is an intermediate step between both parameters.

Cardiac metabolic changes and atherosclerotic risk during prediabetic and diabetic experimental conditions in rats

Background and Aims: The aim of this study was to examine the induction of prediabetes and diabetes mellitus (DM) type I and their influence on the metabolic changes and atherosclerotic risk in Wistar male rats using different doses of streptozotocin (STZ).

EFFECTIVE DOSE OF STREPTOZOTOCIN FOR INDUCTION OF DIABETES MELLITUS AND ASSOCIATED MORTALITY RATE IN WISTAR ALBINO RATS

Background: To understand severity and complications of diabetes mellitus and to analyze effects of drugs, it is necessary to create diabetic animal model. There are different doses of streptozotocin to induce diabetes mellitus in rats that may be associated with mortality or may be insufficient for induction of DM. The objective of our study was to optimize the dose of streptozotocin to create a diabetic animal model with sustained hyperglycemia and to document the toxic dose at which there may be high mortality rate. Methods: This experimental animal study was conducted at animal house, faculty of pharmacy Ziauddin University Karachi in April 2019. The sample size included 30 albino wistar rats divided into five Groups A, B, C, D and E “with 6 rats each group”. Group A was the control, while streptozotocin at different concentrations was administered intraperitoneally in Group B, C, D and E respectively. Blood sample was drawn from lateral tail vein of animals and hyperglycemic profile was checked on 2nd, 4th, 6th, 8th and 10th day. Results: When compared to control Group A, hyperglycemic profile (blood glucose level >180) was achieved in Group B, C, D and E after 48 hours. High mortality rate was observed in Group E followed by Group D. Group C had persistent hyperglycemia while Group B had reversible hyperglycemic profile. Conclusion: Intraperitoneal dose of streptozotocin 60 mg/kg created diabetic animal model with persistent hyperglycemia. However, dose above increased the mortality rate and below failed to create diabetic animal model.

Cardiac Oxidative Stress And Matrix Metalloproteinases Activities In Streptozotocin-Induced Metabolic Syndrome And Diabetes Mellitus In Wistar Male Rats

Background and Aims: The aim of this study was to examine the induction of metabolic syndrome and diabetes mellitus (DM) type I in Wistar male rats using different doses of streptozotocin (STZ), and their influence on the cardiac tissue oxidative stress parameters.

Insulin deprivation induces PP2A inhibition and tau hyperphosphorylation in hTau mice, a model of Alzheimer\u2019s disease-like tau pathology

Abnormally hyperphosphorylated tau aggregated as intraneuronal neurofibrillary tangles is one of the two neuropathological hallmarks of Alzheimer’s disease (AD). The majority of AD cases are sporadic with numerous environmental, biological and genetic risks factors. Interestingly, insulin dysfunction and hyperglycaemia are both risk factors for sporadic AD. However, how hyperglycaemia and insulin dysfunction affect tau pathology, is not well understood. In this study, we examined the effects of insulin deficiency on tau pathology in transgenic hTau mice by injecting different doses of streptozotocin (STZ), a toxin that destroys insulin-producing cells in the pancreas. One high dose of STZ resulted in marked diabetes, and five low doses led to a milder diabetes. Both groups exhibited brain tau hyperphosphorylation but no increased aggregation. Tau hyperphosphorylation correlated with inhibition of Protein Phosphatase 2A (PP2A), the main tau phosphatase. Interestingly, insulin injection 30 minutes before sacrifice partially restored tau phosphorylation to control levels in both STZ-injected groups. Our results confirm a link between insulin homeostasis and tau phosphorylation, which could explain, at least in part, a higher incidence of AD in diabetic patients.

Determination of the Best Concentration of Streptozotocin to Create a Diabetic Brain Using Histological Techniques

Alzheimer's disease (AD) is one of the most important disorders among neurodegenerative diseases which is characterized by neurofibrillary tangles and senile plagues. Intercerebroventricular (ICV) streptozotocin administration is a form of sAD which was applied to examine different factors following AD. Previous reports used different doses of streptozotocin (STZ) to create Alzheimer's model, but no standard dose has been introduced. Therefore, we decided to investigate the best concentration of STZ to induce a diabetic brain with lowest mortality rate and high severity of destruction. We treated rats with three different doses of STZ (STZ 1.5, 2.25, and 3mg/kg, ICV). Spatial memory for treated rats was evaluated by Morris water maze (MWM). Locomotor activities of rats were assessed by open field test. Histological observation such as immunohistochemistry, immunofluorescence, and Nissl staining were performed on the brain especially in CA1, CA3, and DG regions of hippocampal neurons at residues P-ser396 and P-ser404. Our data suggest that although the percentage hyperphosphorylation of tau protein by injection of STZ 3mg/kg was about 10% more than STZ 2.25mg/kg compared to the control group, we considered the latter doses due to no effect on motor activities and enhance the number of glial cells.

Establishment of a Rat Model of Type II Diabetic Neuropathic Pain

To establish a rat model of type II diabetic neuropathic pain. Sixty Sprague Dawley rats were randomly divided into two groups: group A (N = 10) was fed a normal diet, and group B (N = 50) was fed a high-fat and high-sugar diet. After 8 weeks, the body weight of all rats was recorded, and rats in both groups had their fasting plasma glucose, insulin concentration, and insulin sensitivity index measured and calculated. Subsequently, the rats in group B were randomly divided into three subgroups that were each given different doses of streptozotocin (STZ) by a single intraperitoneal injection (subgroup B1 received 30 mg/kg, subgroup B2 received 35 mg/kg, and subgroup B3 40 mg/kg). Two weeks after the STZ injection, the four groups of rats had their insulin sensitivity index, mechanical withdrawal threshold, and thermal withdrawal latency assessed, allowing us to establish a rat model of type II diabetic neuropathic pain and to determine the optimum dose of STZ. Four weeks after STZ injection (2 weeks after the model was established), the pain threshold was measured in the rats in group A and the group treated with the most effective STZ dose. We also measured the expression of phosphorylated extracellular signal-regulated kinase (p-ERK), phosphorylated cyclic AMP response element-binding protein (p-CREB), and phosphorylated N-methyl d-aspartate receptor subtype B (p-NR2B) in the dorsal root ganglion (DRG) and spinal cord dorsal horn regions, which are closely related to neuropathic pain, and also recorded the TTX-R sodium currents in the acutely isolated DRG neurons. After 8 weeks of a high-fat, high-sugar diet, the body weight of the rats in group B was significantly increased. Although the fasting blood glucose levels did not change significantly, the fasting insulin levels were slightly elevated, and the insulin sensitivity index was significantly reduced. Two weeks after STZ injection, the blood glucose levels of the rats in subgroup B1 were elevated but did not remain so for a prolonged period. In contrast, the rats in subgroup B3 had elevated blood glucose that was accompanied by a high mortality rate, while the blood glucose levels of the rats in subgroup B2 were moderately elevated and relatively stable. In addition, the pain threshold was significantly decreased (P < 0.05), and the mortality was low in this group. Because of this, the dose of STZ that was used in group B2 was considered the most effective dose of STZ for induction of diabetes. Four weeks after STZ injection, the pain threshold in the rats of group B2 was still significantly decreased, and the expression of p-ERK, p-CREB, and p-NR2B in the dorsal root ganglion (DRG) and spinal cord dorsal horn was significantly increased. The tetrodotoxin-resistant sodium current density in DRG neurons was also significantly elevated (P < 0.05). A rat model of type II diabetic neuropathic pain can be established by feeding rats a high-fat, high-sugar diet for 8 weeks, in combination with intraperitoneal injection of 35 mg/kg STZ. This model can be stably maintained for at least 2 weeks.

Protective effects of a nicotinamide derivative, isonicotinamide, against streptozotocin-induced β-cell damage and diabetes in mice

ObjectiveNicotinamide rescues β-cell damage and diabetes in rodents, but a large-scale clinical trial failed to show the benefit of nicotinamide in the prevention of type 1 diabetes. Recent studies have shown that Sirt1 deacetylase, a putative protector of β-cells, is inhibited by nicotinamide. We investigated the effects of isonicotinamide, which is a derivative of nicotinamide and does not inhibit Sirt1, on streptozotocin (STZ)-induced diabetes in mice. Research design and methodsMale C57BL/6 mice were administered with three different doses of STZ (65, 75, and 100mg/kg BW) alone or in combination with subsequent high-fat feeding. The mice were treated with isonicotinamide (250mg/kg BW/day) or phosphate-buffered saline for 10days. The effects of isonicotinamide on STZ-induced diabetes were assessed by blood glucose levels, glucose tolerance test, and immunohistochemistry. ResultsIsonicotinamide effectively prevented hyperglycemia induced by higher doses of STZ (75 and 100mg/kg BW) alone and low-dose STZ (65mg/kg BW) followed by 6-week high-fat diet in mice. The protective effects of isonicotinamide were associated with decreased apoptosis of β-cells and reductions in both insulin content and insulin-positive area in the pancreas of STZ-administered mice. In addition, isonicotinamide inhibited STZ-induced apoptosis in cultured isolated islets. ConclusionsThese data clearly demonstrate that isonicotinamide exerts anti-diabetogenic effects by preventing β-cell damage after STZ administration. These findings warrant further investigations on the protective effects of isonicotinamide and related compounds against β-cell damage in diabetes.

Streptozotocin-Induced Cytotoxicity, Oxidative Stress and Mitochondrial Dysfunction in Human Hepatoma HepG2 Cells

Streptozotocin (STZ) is an antibiotic often used in the treatment of different types of cancers. It is also highly cytotoxic to the pancreatic beta-cells and therefore is commonly used to induce experimental type 1 diabetes in rodents. Resistance towards STZ-induced cytotoxicity in cancer cells has also been reported. Our previous studies have reported organ-specific toxicity and metabolic alterations in STZ-induced diabetic rats. STZ induces oxidative stress and metabolic complications. The precise molecular mechanism of STZ-induced toxicity in different tissues and carcinomas is, however, unclear. We have, therefore, investigated the mechanism of cytotoxicity of STZ in HepG2 hepatoma cells in culture. Cells were treated with different doses of STZ for various time intervals and the cytotoxicity was studied by observing the alterations in oxidative stress, mitochondrial redox and metabolic functions. STZ induced ROS and RNS formation and oxidative stress as measured by an increase in the lipid peroxidation as well as alterations in the GSH-dependent antioxidant metabolism. The mitochondria appear to be a highly sensitive target for STZ toxicity. The mitochondrial membrane potential and enzyme activities were altered in STZ treated cells resulting in the inhibition of ATP synthesis. ROS-sensitive mitochondrial aconitase activity was markedly inhibited suggesting increased oxidative stress in STZ-induced mitochondrial toxicity. These results suggest that STZ-induced cytotoxicity in HepG2 cells is mediated, at least in part, by the increase in ROS/RNS production, oxidative stress and mitochondrial dysfunction. Our study may be significant for better understanding the mechanisms of STZ action in chemotherapy and drug induced toxicity.

Characterizing the induction of diabetes in juvenile cynomolgus monkeys with different doses of streptozotocin

Juvenile (2-23 years old) cynomolgus monkeys are frequently used as recipients in non-human primate islet transplantation studies. The aim of this study was to examine the effects of different doses of streptozotocin (STZ), and find the optimal dose for inducing diabetes in these monkeys. Fifteen juvenile (2-3 years old) cynomolgus monkeys were separated into three groups and administered with different doses of STZ (100, 68 or 60 mg kg(-1)). Basal and glucose-stimulated blood glucose, insulin, and C-peptide levels, as well as body weights were monitored. Hepatic and renal function tests and pancreatic immunohistochemistry were performed before and after STZ treatment. Monkeys treated with both 100 and 68 mg kg(-1) of STZ exhibited continuous hyperglycemia, which coincided with a nearly complete loss of islet β-cells. Two monkeys received 60 mg kg(-1) of STZ, but only one became completely diabetic. During the first week following STZ treatment, hepatic and renal function slightly increased in these three groups. However, 24 hours post-STZ, serum total bile acid levels were significantly increased in monkeys treated with 100 mg kg(-1) than those treated with 68 mg kg(-1) of STZ (P<0.05). These data suggest that 100 mg kg(-1) and 68 mg kg(-1) of STZ can safely induce diabetes in cynomolgus monkeys aged 2-3 years, but 68 mg kg(-1) of STZ, rather than 100 mg kg(-1) of STZ, may be more appropriate for inducing diabetes in these monkeys. Furthermore, body surface area, rather than body weight, was a more reliable determinant of dosage, where 700 mg m(-2) of STZ should be the lower limit for inducing diabetes in juvenile monkeys.

Characterization of STZ-Induced Type 2 Diabetes in Zucker Fatty Rats

The Zucker fatty (ZF) rat is a disease model of obesity and metabolic syndrome, such as hyperlipidemia and insulin resistance, resulting from hyperphagia owing to the loss of function of the leptin receptor, but it rarely develops hyperglycemia. We examined the effects of different doses of streptozotocin (STZ). A low dosage of STZ (30 mg/kg body weight, i.p.) elevated blood glucose levels in ZF rats up to 300 mg/dl within a week, and to nearly 500 mg/dl by 5 weeks after injection of STZ. Besides hyperglycemia, STZ-treated ZF (STZ-ZF) rats retained metabolic syndrome features such as hyperlipidemia and hyperinsulinemia. The stimulated insulin secretion in response to orally-loaded glucose disappeared completely in STZ-ZF rats. Although there were no significant differences in the morphology of pancreatic islets between vehicle-treated ZF (Cont-ZF) and STZ-ZF rats, the insulin content was markedly decreased in STZ-ZF rats. The hepatic gene expression for gluconeogenic enzymes was upregulated in STZ-ZF rats compared with Cont-ZF rats. Metformin lowered the blood glucose levels of STZ-ZF rats in a dose-dependent manner. These results suggest that STZ-ZF rats are useful for studies of T2DM and for the evaluation of the efficacy of anti-diabetic drugs.

Different diabetogenic response to moderate doses of streptozotocin in pregnant rats, and its long-term consequences in the offspring.

Diabetes during pregnancy results in congenital malformations and long-term postnatal diseases. Experimental models are still needed to investigate the mechanism responsible for these alterations. Thus, by the administration of different doses of streptozotocin (STZ) (0, 25, 30, or 35 mg/kg body weight, intravenous) at the onset of pregnancy in rats, the present study sought an appropriate animal model for this pathology. At day 6 of pregnancy, plasma glucose was progressively higher with an increasing STZ dose, and in rats receiving the 35-mg dose, 2 subgroups were detected: some animals had plasma glucose levels above controls but below 200 mg/dL (mildly diabetic, MD), whereas others had levels above 400 mg/dL (severely diabetic, SD). At day 20 of pregnancy, the MD rats had normal glycemia, but after an oral glucose load (2 g/kg body weight), plasma glucose increased more and insulin increased less than in controls. The SD rats maintained their hyperglycemia and had a greatly impaired oral glucose tolerance. At day 20, fetuses of SD dams were fewer, weighed less, and had enhanced plasma glucose and triglycerides and decreased insulin, whereas those from MD dams did not differ from controls. At birth, newborns from MD dams had higher body weight, plasma insulin, and liver triglycerides as well as total body lipid concentrations than controls, and on day 21, remained macrosomic and showed higher plasma glucose and liver triglyceride concentrations. At 70 days of age, offspring of MD dams had impaired oral glucose tolerance but normal plasma insulin change in the case of females, whereas plasma insulin increased less in males. These alterations were manifest more in those offspring from dams that had > 50% macrosomic newborns than in those from dams that had < 50% macrosomic newborns. In conclusion, whereas our MD rats mimic the changes taking place in gestational diabetic women and show the long-term risk of macrosomia, the SD rats are more similar to uncontrolled diabetics. Thus these two rat models, obtained with moderate amounts of STZ, could be used to study the pathophysiological consequences of these different diabetic conditions.

Evidence of a glycemic threshold for the development of cataracts in diabetic rats

Purpose. This study was aimed to establish a possible correlation between the levels of plasma glucose and degree of lens opacification. Levels of glycation- and glycoxidation-products in different lens protein fractions were also estimated with an aim to determine the involvement of these products in lens opacification. Methods. A wide range of hyperglycemia was induced by injecting different doses of streptozotocin to 1 month old rats and lenses were examined on the 75 th, 90 th and 150 th day post-injection. Lens opacification was measured by Scheimpflug imaging and densitometry. Levels of plasma glucose and glycated hemoglobin were measured after overnight fasting. On 90 th day, levels of Amadori products in lens water soluble (WS) fraction were measured by affinity chromatography. Similarly, advanced glycation end products (AGEs) in lens WS, urea soluble (US) and alkali soluble (AS) fractions were measured immunochemically using a monoclonal antibody against the major glycoxidation product, carboxymethyl lysine (CML). Results. Different dosages of streptozotocin injection resulted in a broad range of plasma glucose levels in the rats which were grouped into three groups on the basis of their plasma glucose levels: mildly diabetic (< 170 mg/dl plasma glucose), moderately diabetic (190–350 mg/dl) and severely diabetic (> 400 mg/dl). On the 75 th, 90 th and 150 th day post-injection, only the moderately and severely diabetic rats developed cataracts whereas lenses of the mildly diabetic rats remained clear. As seen on 90 th day, levels of glycated hemoglobin and Amadori products in lens WS fraction increased significantly in the moderately and severely diabetic groups whereas in the mildly diabetic rats these levels remained more or less same as in the control group. Levels of CML in WS fractions remained unchanged between control rats and different diabetic groups, while US fractions showed a decrease in CML in both the moderately and severely diabetic groups compared to the controls and the mildly diabetic group. Interestingly, AS fractions contained the highest level of CML; the moderately and severely diabetic groups showed about 2-fold higher levels than the controls and the mildly diabetic group. Conclusions. This study strongly supports the existence of plasma glycemic threshold above which incidence of diabetic cataract formation increases exponentially. This threshold level seems to be at ~180 mg/dl or 10 mM plasma glucose. Significant increase in the levels of glycation and glycoxidation products mainly in cataract lenses suggests that glycation and glycation-mediated oxidation play an important role in the development of diabetic cataracts.

Blood luteinizing hormone and prolactin concentrations in response to naltrexone challenge: Studies on rats with diabetes induced by different doses of streptozotocin

Opiate system involvement in diabetes induced by three different doses of streptozotocin (STZ; 40, 50, and 60 mg/kg body weight [BW]) was studied by monitoring luteinizing hormone (LH) and prolactin (PRL) levels as a response to naltrexone (Nalt) administration. After four weeks of diabetes a marked decrease in BW, as well as severe hyperglycemia and increased blood urea nitrogen (BUN) levels were found. The rats, whose diabetes was induced by 50 mg/kg of STZ, exhibited the highest amount of blood glucose ( P < 0.05, compared with the 40 mg/kg induced group) and BUN levels ( P < 0.004 compared with the order two groups) and BW loss. The normal response to Nalt, which is expressed by elevation of plasma LH and decreased plasma PRL levels was observed only in the low-dose STZ (40 mg/kg BW) diabetes-induced group, while in the other two diabetic groups (50 and 60 mg/kg BW) there was no significant change in plasma LH and PRL as a result of the Nalt challenge. Presensitization of the endogenous opioid receptors by morphine in normoglycemic (control) and “low-dose diabetic” rats (40 mg/kg BW of STZ), presented a clear difference between the two. Morphine pretreatment inhibited LH response to Nalt in the low-dose, STZ-induced diabetic rats, while no effect of morphine pretreatment on LH response to Nalt could be recorded in the normoglycemic group. Thus it can be concluded that in STZ-induced diabetes, plasma glucose and BUN levels do not reflect the neuroendocrine injury observed when monitored by LH and PRL secretion in response to Nalt challenge. Supersensitization of the opioid receptors before the Nalt challenge may increase the ability to reveal neuroendocrine system impairment.

Gastric mucosal secretions and lesions by different doses of streptozotocin in rats

The effects of various doses of streptozotocin (STZ) on gastric mucosal secretions and lesions were investigated in rats. STZ at a dose as low as 30 mg/kg significantly increased plasma glucose ( P < 0.05). The elevation of plasma glucose was dependent on the dose on STZ (30–65 mg/kg) administered. The levels of SGOT, SGPT, bilirubin and BUN also increased with the dose of STZ. The secretory rate of gastric H + decreased whereas the degree of mucosal hyperemia increased with increasing levels of plasma glucose. Treatment with insulin improved all abnormal conditions except the gastric mucosal lesions. The lesions occurred with low H +-secretory rate and low gastric emptying rate. It is suggested that STZ might act directly on the gastric mucosa. Its action depended on the dose administered and was not primarily related to the insulin deficit.

The development of the fetal rat intestine and its reaction to maternal diabetes: II. Effect of mild and severe maternal diabetes

Diabetes during pregnancy induces specifically structural and functional changes in the fetal endocrine pancreas. Other organs are affected as well. In this study, the fetal intestinal tract which is in close connection with the endocrine pancreas was analysed during diabetic gestation. The disease was induced by two different doses of streptozotocin which led to a mild or severe diabetic state in the mother. In fetuses from mildly diabetic as well as from severely diabetic rats, the time sequence in the appearance of the differentiated cells was identical and similar to that of controls. However, morphometric analysis of the intestine of fetuses from severely diabetic rats revealed a decrease in each of the parameters measured which led to a general hypotrophy of the intestine. In the fetuses from mildly diabetic rats, the values of the morphometric parameters of the duodenal mucosa remained unchanged and comparable to those of the control group. The vascularisation of the duodenum is modified in these fetuses because the volume density of the blood vessels is significantly increased. In conclusion, both diabetic states of the mother induce various alterations in the fetal intestine, including the blood vessels. The nature of the structural changes observed in the intestine could lead to modifications in the function of the entero-pancreatic system in these fetuses.

Influence of Age on the Sensitivity of the Rat to Streptozotocin

The relationship between age and sensitivity to the diabetogenic effect of streptozotocin was investigated. Changes in the serum levels of several parameters (glucose, immunoreactive insulin, lipids), as well as changes of the pancreatic insulin content were monitored at 2, 4, 8, 24 and 48 h after the intravenous administration of different doses of streptozotocin in rats of various weights. Different concentrations of blood glucose and lipid and different amounts of pancreatic immunoreactive insulin could be found in rats of different ages 24 and 48 h after injection of the same dose of the drug (in mg/kg body weight). Also, age-dependent changes of serum immunoreactive insulin could be observed as early as 4 h after streptozotocin administration. All these changes indicate that the sensitivity of the rat to the diabetogenic effect of streptozotocin is inversely related to the age of the animals. Most likely, age-dependent pancreatic factors have an important role. In fact, the changes of the minimum dose of streptozotocin required to cause diabetes in rats of different weights closely parallel the age-related changes of the total immunoreactive insulin content of the pancreas of the intact rats. The role of other age-related factors which may influence the effectiveness of streptozotocin action is briefly discussed.

Ability of circulating insulin to chronically regulate the cellular glucose transport system

We have tested the idea that the circulating plasma insulin level plays an important role in the long-term regulation, or maintenance, of the cellular glucose transport system, distinct from insulin's ability to acutely accelerate glucose transport. To study this hypothesis, groups of rats were made either hyperinsulinemic or hypoinsulinemic by daily insulin injections or Streptozotocin treatment, respectively. Different levels of hypoinsulinemia were produced by using different doses of Streptozotocin (40 and 55 mg/kg). Isolated adipocytes were prepared from each animal and glucose transport was assessed by measuring the initial rates of uptake of the nonmetabolyzable hexose 2-deoxy glucose. In cells from control animals, the Vmax of in vitro adipocyte glucose transport was 7.1 +/- 0.7 nmole/min/10(6) cells in the basal state and 22.9 +/- 0.9 nmole/min/10(6) cells in the presence of a maximally effective insulin concentration (25 ng/ml) in the buffer. In cells from the experimentally hyperinsulinemic animals, these Vmax values were increased to 11.7 +/- 0.8 and 44.2 +/- 1.1 nmole/min/10(6) cells. Using adipocytes from both groups of Streptozotocin treated (high dose, 55 mg/kg, low dose, 40 mg/kg) insulin deficient diabetic animals, Vmax values were found to be progressively decreased. Thus, in the low dose group, basal and insulin stimulated Vmax values were 1.6 +/- 0.5 and 5.7 +/- 0.7 nmole/min/10(6) cells, as compared to values of 0.9 +/- 0.2 and 1.7 +/- 0.6 in the high dose group. Furthermore, when hyperinsulinemia was induced by feeding rats high carbohydrate diets for 10 days, adipocyte glucose transport Vmax increased 50%. In contrast, when hypoinsulinemia was achieved by fasting rats for 72 hr, transport Vmax decreased by 50%. The apparent Km for 2-deoxy glucose uptake was the same under all conditions. In conclusion, assuming that the Vmax of transport is some function of the number of glucose transport carriers per cell, then these results support the hypothesis that in addition to acute acceleration of glucose transport, insulin is also an important long-term regulator of the number of available adipocyte glucose transport carriers.

Long-term regulation of adipocyte glucose transport capacity by circulating insulin in rats.

We have tested the idea that the circulating plasma insulin level plays an important role in the long-term regulation, or maintenance, of the cellular glucose transport system, distinct from insulin's ability to acutely accelerate glucose transport. To study this hypothesis, groups of rats were made either hyperinsulinemic or hypoinsulinemic by daily insulin injections, or streptozotocin treatment, respectively. Different levels of hypoinsulinemia were produced by using different doses of streptozotocin (40 and 55 mg/kg). The mean (+/-SE) 9 a.m. plasma insulin level for each experimental group was: hyperinsulinemic animals, 65+/-5 muU/ml; controls, 32+/-3 muU/ml; low dose streptozotocin group, 18+/-3 muU/ml; and high dose streptozotocin group 5+/-2 muU/ml. Isolated adipocytes were prepared from each animal and glucose transport was assessed by measuring the initial rates of uptake of the nonmetabolyzable hexose 2-deoxy glucose. The V(max) and K(m) values for adipocyte glucose transport were calculated from the 2-deoxy glucose uptake data. The results demonstrated that in cells from control animals the V(max) of in vitro adipocyte glucose transport was 7.1+/-0.7 nmol/min per 10(6) cells in the basal state and 22.9+/-0.9 nmol/min per 10(6) cells in the presence of a maximally effective insulin concentration (25 ng/ml) in the buffer. In cells from the experimentally hyperinsulinemic animals these V(max) values were increased to 11.7+/-0.8 and 44.2+/-1.1 nmol/min per 10(6) cells. Using adipocytes from both groups of streptozotocin-treated (high dose, 55 mg/kg; low dose, 40 mg/kg) insulin-deficient diabetic animals, V(max) values were found to be progressively decreased. Thus, in the low dose group, basal-and insulin-stimulated V(max) values were 1.6+/-0.5 and 5.7+/-0.7 nmol/min per 10(6) cells, as compared to values of 0.9+/-0.2 and 1.7+/-0.6 in the high dose group. Thus, when considered as group data a positive relationship was found between circulating plasma insulin levels and adipocyte glucose transport V(max), with increased V(max) values in hyperinsulinemic rats and decreased V(max) values in hypoinsulinemic rats. Furthermore, when the individual data were analyzed, highly significant correlation coefficients were found between the height of the plasma insulin level and both the basal (r = 0.82, P < 0.001) and insulin-stimulated (r = 0.93, P < 0.001) V(max) values. The apparent K(m) for 2-deoxy glucose uptake was the same under all conditions. In conclusion, assuming that the V(max) of transport is some function of the number of glucose transport carriers per cell, then these results support the hypothesis that in addition to acute acceleration of glucose transport, insulin is also an important long-term regulator of the number of available adipocyte glucose transport carriers.