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Diabetogenic Effect of Streptozotocin in the Rat During the Perinatal Period

The diabetogenic effect of streptozotocin was investigated in the rat during the fetal and neonatal life. Streptozotocin was directly injected in the vitellin vein of the fetus or in the saphenous vein of the neonate. In the 21.5 day old fetus, diabetogenic activity was demonstrated with a single dose of 100 μg/gm. administered the day before, and this was indicated by a fall in the pancreatic insulin content to 20 per cent and a lowering of the plasma insulin to 60 per cent of the controls. A single dose (100 μg/gm.) of streptozotocin administered on the day of birth produced an overt diabetes in the neonate: the maximal fall in the pancreatic insulin content (7 per cent of the controls) was observed four days after the streptozotocin injection, during the highest blood glucose level (300 per cent of the controls). A significant increase in the pancreatic glucagon content was observed twenty-four hours after the maximal insulin depletion. Liver glycogen content was occasionally decreased. More severe diabetes was obtained by two streptozotocin injections (50μg/gm.), with lowest pancreatic and highest blood glucose levels at 1 per cent and 60 per cent, respectively. A clearcut drop of the plasma insulin/glucose ratio was observed in the drug-treated animals. Three weeks after injection(s), basal blood glucose and plasma insulin levels were normal, although impairment of insulin secretion still appeared after glucose load and insulin pancreatic content was still slightly lower. A rapid and spontaneous, if not quite complete recovery, is a characteristic pattern of the streptozotocin diabetes in the neonate as compared to that in the adult.

Chemical diabetes in the adult rat as the spontaneous evolution of neonatal diabetes

SummaryInjection of streptozotocin in newborn rats induced a severe diabetic syndrome on day 4 after birth, with acute hyperglycaemia and glycosuria. Over the next 3 weeks spontaneous recovery occurred as attested by normal basal blood glucose and plasma insulin levels. Recovery was, however, incomplete in the adult since a definite impairment in insulin release and glucose disposal was observed. This state was characterized by the following features: 1) a 72% decrease in pancreatic insulin stores without change in pancreatic glucagon stores; 2) a slight but consistent elevation of blood glucose in the fasted and fed basal states and especially of blood glucose 90 min after an IV glucose load (2 g/kg) performed under pentobarbitone anaesthesia; 3) a considerable decline in the glucose-induced insulin release with a decrease in the maximal response. Both early and late phases of insulin release were impaired, as indicated by in vivo glucose infusion experiments. Basal plasma glucagon levels were normal. Over a period of 12 months with a normal laboratory diet no aggravation of the chemical diabetic state was observed. This new experimental syndrome is a potentially interesting model for the study of the influence of environmental factors on the development of overt diabetes.

Glucose Insensitivity and Amino-acid Hypersensitivity of Insulin Release in Rats with Non-insulin-dependent Diabetes: A Study with the Perfused Pancreas

Non-insulin-dependent diabetes (NIDDM) was obtained in adult rats following a neonatal streptozotocin injection. Rats with NIDDM exhibited slightly lowered plasma insulin, slightly elevated basal plasma glucose values (<200 mg/dl), anancreatic insulin stores (50% of the controls). Insulin secretion was studied in this model using the isolated perfused pancreas technique. Insulin response to glucose stimulation over the range 5.5–22 mM was lacking, thus indicating complete loss of B-cell sensitivity to glucose. Even in presence of theophylline, the B-cells remained insensitive to glucose. In contrast, glyceraldehyde elicited an insulin release as important as that obtained in the control pancreata. This could possibly suggest that the Bcell dysfunction in rats with NIDDM involves a block in glucose metabolism in the early steps of glycolysis prior to the triose-phosphate. Mannose stimulated insulin secretion less in the diabetics than in the controls. The insulin secretion obtained in response to isoproterenol indicated that the ability of the adenylcyclase to generate cAMP in the B-cells of the diabetics was not decreased. The insulinotropic actions of acetylcholine and tolbutamide were normal and increased, respectively, as compared with the controls. In the absence of glucose, the B-cells of the diabetics were unexpectedly hypersensitive to arginine and leucine. The α-ketoisocaproate effect in the diabetics was not significantly different from that obtained in the controls. The possibility that enhancement of insulin response to leucine in the diabetics might be related to a more active conversion of leucine to ketoisocaproate along the first steps of intraislet leucine metabolism is proposed.

Development of Obesity in Zucker Rats: Early Insulin Resistance in Muscles But Normal Sensitivity in White Adipose Tissue

Euglycemic-hyperinsulinemic clamps were performed on 4- and 12-wk-old anesthetized lean and obese Zucker rats. During the clamp studies, total glucose production and utilization were assessed with a 3-[3H]glucose perfusion, whereas local glucose utilization was determined by measuring 2-deoxy-1-[3H]glucose 6-phosphate accumulation in various tissues. In the basal state, 4 wk-old obese rats were hyperinsulinemic (159 ± 8 vs. 82 ± 9 μU/ml), whereas glucose turnover rate was similar to that observed in lean rats (14.9 ± 1.9 vs. 12.5 ± 1.9 mg · min−1 · kg−1). Glucose utilization was identical in skeletal muscles, whereas it was increased in white adipose tissue of obese rats (22 ± 4 vs. 8 ± 2 ng · min−1 · mg−1). At plasma insulin level of 500 μU/ml, glucose production was totally suppressed in both groups, whereas overall glucose utilization was slightly less in 4-wk-old obese than in lean rats. This was due to a reduced stimulation of glucose utilization in skeletal muscles and brown adipose tissue. In contrast, glucose utilization in periovarian white adipose tissue was similarly increased in lean and obese rats. For a maximal insulin concentration (1500 μU/ml), all the differences were abolished between lean and obese young Zucker rats. In older (12-wk-old) obese rats, glucose utilization in various tissues was markedly reduced at maximal insulin level compared with that observed in age-matched lean animals. Thus, a decreased insulin sensitivity in skeletal muscles and brown adipose tissue with a normal insulin sensitivity in white adipose tissue could contribute to the development of obesity in young Zucker rats by preferentially channeling glucose toward this tissue.

Inheritance of Diabetes Mellitus as Consequence of Gestational Hyperglycemia in Rats

Our study investigated whether a deterioration of glucose homeostasis and insulin secretion in adult female rats from hyperglycemic dams could be transmitted to the next generation independent of genetic interferences. Dams (F0) were rendered hyperglycemic by continuous glucose infusion during the last week of pregnancy. Females born of these rats (F1) exhibited glucose intolerance and impaired insulin secretion in vivo at adulthood. When they were 3 mo old, they were mated with males born of control dams. During pregnancy, their glucose tolerance remained impaired compared with that of controls. Consequently, F2 newborns of F1 hyperglycemic dams showed the main features of newborns from diabetic mothers: they were hyperglycemie, hyperinsulinemic, and macrosomic. As adults, they displayed basal hyperglycemia and defective glucose tolerance and insulin secretion. This indicates that the long-range deteriorating effects on glucose homeostasis of gestationai hyperglycemia in the F1generation are transmitted to the F2 generation and suggests that a perturbed fetal metabolic environment contributes to the inheritance of diabetes mellitus.

Impaired Glucose Homeostasis in Adult Rats From Hyperglycemic Mothers

The purpose of our study was to investigate whether nondiabetic gestationai hyperglycemia during fetal life could have additional effects on glucose homeostasis and insulin secretion in the adult rat. Hyperglycemia without the main other metabolic disorders and vascular injuries associated with diabetes was produced in unrestrained pregnant rats by continuous glucose infusion during the last week of pregnancy. Control rats were infused with distilled water. Compared with controls, the newborns from hyperglycemic rats were hyperglycemic and hyperinsulinemic. When studied longitudinally up to 3 mo, they showed slightly but significantly increased basal plasma glucose levels and normal basal insulin concentrations compared with controls. Glucose tolerance and insulin secretion in response to a glucose load (0.5 mg/kg, i.v.) were altered: Plasma glucose values were more increased at 5 min and remained higher 90 min after glucose injection; incremental plasma insulin values and the insulinogenic indexes (ΔIRI/ΔG) were always lower in rats from hyperglycemic mothers than in controls. These alterations were more and more marked with advancing age (1–3 mo). These data show that gestationai hyperglycemia may lead to persistent impairment of glucose homeostasis and insulin secretion in the adult rat.

Insulin and Glucagon during the Perinatal Period: Secretion and Metabolic Effects on the Liver

Insulin and glucagon are detected in the plasma of most species early in gestation. In the fetus at term, insulin and glucagon secretion can be modified by long-term changes in glucose concentration but the responsiveness of A and B cells to glucose is lower than in the adult. The plasma insulin/glucagon molar ratio is high in the fetus at term, then decreases dramatically immediately after birth and remains low during the first hours of extrauterine life. This situation results in favored hepatic glycogen storage and prevented gluconeogenesis in utero, and sharp glycogen breakdown and active gluconeogenesis during the early postnatal period.

Insulin Secretion in Adult Rats After Intrauterine Exposure to Mild Hyperglycemia During Late Gestation

We investigated the effects of intrauterine mild hyperglycemia during late fetal life on glucose regulation and insulin secretion in adult rats. Unrestrained pregnant rats were continuously infused with glucose during the last week of pregnancy to induce mild hyperglycemia (6.5–8 mM). Control rats were infused with a glucose-free solution. The offspring were studied, as adults, from 1 to 20 mo by performing glucose tolerance and insulin secretion tests. Young-adult rats from hyperglycemie dams showed mild glucose intolerance and impairment of glucose-induced insulin secretion. This situation gradually evolved to basal hyperglycemia and severe impairment of glucose tolerance and insulin secretion. Insulin secretion was also studied in vitro in 20-mo-old rats with the isolated perfused-pancreas technique. Insulin release in response to glucose stimulation from pancreases of hyperglycemic dams was similar to that of controls, and the response to arginine was increased but not significantly. The possible involvement of enhanced sympathetic nervous system activity in the impairment of insulin secretion in adult rats from hyperglycemic mothers was then investigated by performing glucose tolerance and insulin secretion tests in the presence of the α2-blocker idazoxan in 8-mo-old rats. Under these conditions, rats from hyperglycemic dams recovered almost normal glucose tolerance, and glucose-induced insulin secretion was greatly improved. These data show that mild hyperglycemia induced in the fetus during late pregnancy leads to persistent impairment of glucose regulation and insulin secretion. They suggest that the impairment of insulin secretion in vivo results from a perturbation of the neuroregulation of insulin secretion rather than an intrinsic pancreatic β-cell defect.

Experimental Chemical Diabetes and Pregnancy in the Rat: Evolution of Glucose Tolerance and Insulin Response

The effect of pregnancy on the course of experimental chemical diabetes (CD) has been studied in the rat. Glucose tolerance tests (0.5 g/kg i.v.) have been performed serially in the virgin state (2 mo), late pregnancy (20.5 day of gestation), and 1 and 2 mo after delivery, in control and in CD female rats. During gestation in the controls basal plasma glucose is decreased, and plasma glucose levels after glucose load, and also lower than levels found in the virgin state. Glucose tolerance is not significantly affected. Nevertheless, glucose-induced insulin secretion in pregnant animals is increased compared with the virgin state. Glucose tolerance remains unchanged 1 and 2 mo postpartum, but insulin response to glucose becomes significantly lower than in the virgin state. In the pregnant CD rats basal plasma glucose is decreased, but plasma glucose levels after glucose load are similar to values found in the virgin state, thus suggesting decreased glucose tolerance. Glucose-induced insulin secretion is increased compared with the virgin state. Glucose tolerance remains deteriorated 1 and 2 mo postpartum, but insulin secretion is no longer significantly different.

Insulin Treatment Improves the Spontaneous Remission of Neonatal Streptozotocin Diabetes in the Rat

Neonatal rats injected with streptozotocin (STZ, 100 mg/kg) at birth exhibit an acute diabetes that is characterized by a spontaneous and incomplete remission. The short- and long-term effect of exogenous insulin on the course of this neonatal diabetes has been studied. Insulin treatment (20 mU/g body wt./day, for 4 days) diminished the percentage of glycosuric animals on day 5 after birth (10%) as compared with the percentage in the non-insulin-treated diabetics (STZ) (67%). On the 14th day, the body weight and the pancreatic insulin content of insulin-treated animals (STZ + I) were significantly higher than the corresponding values in the STZ animals. Glucose tolerance tests performed sequentially indicated that from 21 days to 7 mo, the plasma insulin response in the (STZ + I) females was clearly increased as compared with that observed in the STZ group. However, it did not reach the insulin response of the controls except in the 21-day-old females and, as a function of age, it declined progressively at variance with the normal age-related pattern. These findings indicate that insulin treatment (sufficient to reduce daily glycosuria) applied during the overtly diabetic period markedly improved the recovery of the insulin stores in the pancreas. Moreover, the long-term effect of the treatment was a long lasting if not permanent improvement of the in vivo insulin response to glucose.