n0-STZ Rats Research Articles

Ghrelin prevents development of diabetes at adult age in streptozotocin-treated newborn rats

Ghrelin, a stomach-derived hormone, functions in multiple biological processes, including glucose metabolism and cellular differentiation and proliferation. In this study, we examined whether early treatment with ghrelin can regenerate beta cells of the pancreas in an animal model of diabetes mellitus, the n0-STZ model, in which neonatal rats are injected with streptozotocin (STZ) at birth. Following administration of ghrelin to n0-STZ rats from postnatal days 2 to 8, we examined beta cell mass, mRNA expression levels of insulin and of pancreatic and duodenal homeobox 1 (Pdx1) gene, and pancreatic morphology on days 21 and 70. In addition, we investigated the effects of ghrelin on beta cell replication. By day 21, ghrelin treatment increased pancreatic expression of insulin and Pdx1 mRNA in n0-STZ rats. The number of replicating cells was also significantly increased in the ghrelin-treated n0-STZ model. At day 70, n0-STZ rats exhibited hyperglycaemia, despite slight increases in plasma insulin levels. Ghrelin treatment resulted in the improvement of plasma glucose levels, which were associated with normal plasma insulin levels. Pancreatic insulin mRNA and protein levels were significantly increased in ghrelin-treated n0-STZ model animals. These findings suggest that ghrelin promotes regeneration of beta cells in STZ-treated newborn rats. Thus, early administration of ghrelin may help prevent the development of diabetes in disease-prone subjects after beta cell destruction.

Glucagon-like peptide-1 and exendin-4 stimulate beta-cell neogenesis in streptozotocin-treated newborn rats resulting in persistently improved glucose homeostasis at adult age.

In neonatal Wistar rats injected with streptozotocin (STZ) at birth (n0-STZ model), a recognized model of beta-cell regeneration, we investigated the capacity of early treatment with glucagon-like peptide 1 (GLP-1) or exendin-4 to promote beta-cell regeneration and thereby improve islet function in the long term, when animals become adults. To this end, n0-STZ rats were submitted to GLP-1 or exendin-4 from postnatal day 2 to day 6 only, and their beta-cell mass and pancreatic functions were tested on day 7 and at 2 months. On day 7, both treatments increased body weight, decreased basal plasma glucose, decreased insulinemia, and increased pancreatic insulin content in n0-STZ rats. At the same age, the beta-cell mass, measured by immunocytochemistry and morphometry methods, was strongly increased in n0-STZ/GLP-1 and n0-STZ/Ex rats compared with n0-STZ rats, representing 51 and 71%, respectively, of the beta-cell mass in Wistar rats, whereas n0-STZ beta-cell mass represented only 21% of the Wistar control value. Despite such early improved beta-cell mass, which is maintained at adult age, the basal and glucose-stimulated insulin secretion (in vivo after intravenous glucose load or in vitro using perfused pancreas) were not improved in the 2-month-old n0-STZ rats previously treated with GLP-1 or exendin-4 compared with untreated n0-STZ rats. However, both treated groups significantly exhibited a decreased basal plasma glucose level and an increased plasma glucose clearance rate compared with the 2-month-old untreated n0-STZ group at adult age. These findings in the n0-STZ model indicate for the first time that GLP-1 or exendin-4 applied during the neonatal diabetic period exert both short- and long-term beneficial effects on beta-cell mass recovery and glucose homeostasis. However, the increase in beta-cell mass, which is still present in the adult n0-STZ rats previously treated, contrasts with the poor beta-cell responsiveness to glucose. Further studies are needed to understand the dissociation between beta-cell regeneration and the lack of improvement in beta-cell function.

Glucagon like-peptide 1 or exendin-4 administration limited to the transient neonatal hyperglycemic period in the n0-STZ rat model of NIDDM exerts a long-term favorable influence on glycemic control in the adult

Glucagon like-peptide 1 or exendin-4 administration limited to the transient neonatal hyperglycemic period in the n0-STZ rat model of NIDDM exerts a long-term favorable influence on glycemic control in the adult

Glucose-induced insulin mRNA accumulation is impaired in islets from neonatal streptozotocin-treated rats.

According to the glucose toxicity hypothesis, hyperglycemia contributes to defective beta-cell function in type 2, non-insulin-dependent diabetes mellitus. This concept is supported by substantial data in rodent models of diabetes. However, the ability of glucose to stimulate the accumulation of insulin mRNA, a critical feature of normal beta-cell physiology, has not been investigated in in vivo models of chronic hyperglycemia. The aim of this study was to determine whether glucose-induced insulin mRNA accumulation is impaired in the neonatal streptozotocin-treated rat (n0-STZ rat), a model of non-obese, non-insulin-dependent diabetes mellitus. Islets of Langerhans isolated from n0-STZ and control rats were cultured for 24 h in the presence of 2.8 or 16.7 mmol/L glucose, and insulin mRNA levels were measured by Northern analysis. Insulin mRNA levels were increased more than twofold by glucose in control islets. In contrast, no significant effect of glucose was found on insulin mRNA levels in n0-STZ islets. We conclude that insulin gene regulation by glucose is impaired in n0-STZ rat islets.

Glucose-induced insulin mRNA accumulation is impaired in islets from neonatal streptozotocin-treated rats.

According to the "glucose toxicity" hypothesis, hyperglycemia contributes to defective beta-cell function in type 2, non-insulin-dependent diabetes mellitus. This concept is supported by substantial data in rodent models of diabetes. However, the ability of glucose to stimulate the accumulation of insulin mRNA, a critical feature of normal beta-cell physiology, has not been investigated in in vivo models with chronic hyperglycemia. The aim of this study was to determine whether glucose-induced insulin mRNA accumulation is impaired in the neonatal streptozotocin-treated rat (n0-STZ rat), a model of non-obese, non-insulin-dependent diabetes mellitus. Islets of Langerhans isolated from n0-STZ and control rats were cultured for 24 h in the presence of 2.8 or 16.7 mmol/l glucose, and insulin mRNA levels were measured by Northern analysis. Insulin mRNA levels were increased more than twofold by glucose in control islets. In contrast, no significant effect of glucose was found on insulin mRNA levels in n0-STZ islets. We conclude that insulin gene regulation by glucose is impaired in n0-STZ rat islets.

Glucagon-like peptide-1(7-36)-amide confers glucose sensitivity to previously glucose-incompetent beta-cells in diabetic rats: in vivo and in vitro studies.

The effects of glucagon-like peptide-1(7-36)-amide (GLP-1) on cAMP content and insulin release were studied in islets isolated from diabetic rats (n0-STZ model) which exhibited impaired glucose-induced insulin release. We first examined the possibility of re-activating the insulin response to glucose in the beta-cells of the diabetic rats using GLP-1 in vitro. In static incubation experiments, GLP-1 amplified cAMP accumulation (by 170%) and glucose-induced insulin release (by 140%) in the diabetic islets to the same extent as in control islets. Using a perifusion procedure, GLP-1 amplified the insulin response to 16.7 mM glucose by diabetic islets and generated a clear biphasic pattern of insulin release. The incremental insulin response to glucose in the presence of GLP-1, although lower than corresponding control values (1.56 +/- 0.37 and 4.53 +/- 0.60 pg/min per ng islet DNA in diabetic and control islets respectively), became similar to that of control islets exposed to 16.7 mM glucose alone (1.09 +/- 0.15 pg/min per ng islet DNA). Since in vitro GLP-1 was found to exert positive effects on the glucose competence of the residual beta-cells in the n0-STZ model. we investigated the therapeutic effect of in vivo GLP-1 administration on glucose tolerance and glucose-induced insulin release by n0-STZ rats. An infusion of GLP-1 (10 ng/min per kg; i.v.) in n0-STZ rats enhanced significantly (P < 0.01) basal plasma insulin levels, and, when combined with an i.v. glucose tolerance and insulin secretion test, it was found to improve (P < 0.05) glucose tolerance and the insulinogenic index, as compared with the respective values of these parameters before GLP-1 treatment.

Insulin secretion and glucose tolerance after islet transplantation in rats with noninsulin-dependent diabetes induced by neonatal streptozotocin

The present study was designed to identify in a model of noninsulin-dependent diabetes induced by neonatal streptozotocin (n0-STZ), the long-term consequences of an islet graft upon 1) glucose handling of the recipient and, 2) glucose response of the residual β cells in the recipient pancreas. We have examined, 4 and 8 wk after islet implantation under the kidney capsule of syngeneic diabetic n0-STZ rats, their tolerance to glucose administered in vivo, together with their insulin release in response to glucose in vivo (oral glucose tolerance test) as well as in vitro (perfused pancreas). The results in the islet-grafted n0-STZ rats, were compared to those obtained in nongrafted nondiabetic rats and nongrafted n0-STZ rats. Our study shows that transplanting a limited number (900) of adult islets under the kidney capsule reverses to normal, many parameters of the noninsulin-dependent diabetic state in the n0-STZ rat model: these include body weight, basal plasma glucose in both the nonfasted and postabsorptive states, and basal plasma insulin in the postabsorptive state. Furthermore, tolerance to oral glucose administration was greatly improved in the transplanted rats and it was correlated with restoration of a manifest glucose-induced insulin secretion in vivo as evaluated (ΔI) during an oral glucose tolerance test. Our data clearly show that the insulin response to glucose from the endogenous pancreas of n0-STZ diabetic rat was not really improved by long-term (8 wk) basal normoglycemia. More precisely, we were able to detect a slight but significant improvement of the early phase of insulin release in vitro in response to glucose; however, the overall insulin response remained 15 times lower than the normal one with no reapparance of the late phase of insulin release. After cessation of glucose stimulation in vivo, off-response of insulin, which is also a landmark of the impaired insulin release by the β cells of n0-STZ rats, was still detectable in the perfused pancreas of the transplanted n0-STZ rats. Finally, because the reactivity to glucose of the endogenous residual β cells was not regained, the insulin released in vivo during the oral glucose test in the graft-bearing n0-STZ rats can be attributed mainly to functioning of the grafted islets population.

Insulin secretion and glucose tolerance after islet transplantation in rats with noninsulin-dependent diabetes induced by neonatal streptozotocin.

The present study was designed to identify in a model of noninsulin-dependent diabetes induced by neonatal streptozotocin (n0-STZ), the long-term consequences of an islet graft upon 1) glucose handling of the recipient and, 2) glucose response of the residual beta cells in the recipient pancreas. We have examined, 4 and 8 wk after islet implantation under the kidney capsule of syngeneic diabetic n0-STZ rats, their tolerance to glucose administered in vivo, together with their insulin release in response to glucose in vivo (oral glucose tolerance test) as well as in vitro (perfused pancreas). The results in the islet-grafted n0-STZ rats, were compared to those obtained in nongrafted nondiabetic rats and nongrafted n0-STZ rats. Our study shows that transplanting a limited number (900) of adult islets under the kidney capsule reverses to normal, many parameters of the noninsulin-dependent diabetic state in the n0-STZ rat model: these include body weight, basal plasma glucose in both the nonfasted and postabsorptive states, and basal plasma insulin in the postabsorptive state. Furthermore, tolerance to oral glucose administration was greatly improved in the transplanted rats and it was correlated with restoration of a manifest glucose-induced insulin secretion in vivo as evaluated (delta 1) during an oral glucose tolerance test. Our data clearly show that the insulin response to glucose from the endogenous pancreas of n0-STZ diabetic rat was not really improved by long-term (8 wk) basal normoglycemia. More precisely, we were able to detect a slight but significant improvement of the early phase of insulin release in vitro in response to glucose; however, the overall insulin response remained 15 times lower than the normal one with no reappearance of the late phase of insulin release. After cessation of glucose stimulation in vivo, off-response of insulin, which is also a landmark of the impaired insulin release by the beta cells of n0-STZ rats, was still detectable in the perfused pancreas of the transplanted n0-STZ rats. Finally, because the reactivity to glucose of the endogenous residual beta cells was not regained, the insulin released in vivo during the oral glucose test in the graft-bearing n0-STZ rats can be attributed mainly to functioning of the grafted islets population.

Changes in islet blood flow in rats with NIDDM.

Islet blood flow was quantified in NIDDM rats either of the GK strain on after neonatal injection of STZ (n0-STZ), using the non-radioactive microsphere technique. In the basal state, there was a good correlation between plasma insulin level and islet blood flow, i.e. both were increased or decreased in comparison to those of control rats in GK and n0-STZ rats, respectively. The increased islet blood flow and plasma insulin levels observed in the GK rats were abolished by bilateral subdiaphragmatic vagotomy. During a glucose challenge, whereas plasma insulin and islet blood flow were doubled in control rats, these parameters were not modified in the diabetic rats. These data demonstrate an alteration in the islet blood flow of diabetic rats during a glucose challenge which could participate in the abnormal glucose-induced insulin secretion previously described in these two models.

Improvement in glucose-induced insulin secretion in diabetic rats after long-term gliclazide treatment: A comparative study using different models of non-insulin-dependent diabetes mellitus induced by neonatal streptozotocin

Understanding of the long-term action of sulfonylureas in humans with non-insulin-dependent diabetes mellitus (NIDDM) may be facilitated by studying the effect of long-term sulfonylurea administration to animal models of the disease. In this study two different versions of the neonatal streptozotocin-induced diabetes (STZ) rat model of NIDDM were used. The n5-STZ model (STZ on day 5 after birth), which is characterized by basal hyperglycemia, a marked reduction of pancreatic insulin stores, and insulin resistance, and the n0-STZ model (STZ on day of birth), which develops mild hyperglycemia, have an approximately 50% reduction in pancreatic insulin content, and no insulin resistance. The diabetic rats were given oral gliclazide (10 mg/kg/day) and compared with untreated diabetic rats and nondiabetic rats. Insulin secretion was studied the day after the last gliclazide dose using the isolated perfused pancreas preparation. In severely hyperglycemic n5-STZ rats (plasma glucose levels >16 mmol/L) the long-term gliclazide treatment did not lower the plasma glucose values, did not affect pancreatic insulin stores, and did not significantly modify in vitro insulin release in response to glucose or arginine. In moderately hyperglycemic n5-STZ rats (plasma glucose levels <16 mmol/L) the plasma glucose levels declined progressively and reached a mean of 8 mmol/L at the end of gliclazide therapy. The increase in pancreatic insulin stores in n5-STZ rats remained marginal. In the n0-STZ rats gliclazide treatment did not significantly modify the plasma glucose levels or the pancreatic insulin stores. After gliclazide therapy in both the n5-STZ gliclazide responder group and the n0-STZ group: (a) in vitro glucose-induced insulin secretion was increased three- to fivefold; (b) the response to arginine, which is increased in diabetic rats, was amplified by two- to threefold; (c) insulin release in response to gliclazide was unchanged. In conclusion, long-term gliclazide therapy augments stimulated insulin secretion in these two rat models of NIDDM and does not induce any refractoriness to short-term sulfonylurea administration. The improvement of β-cell function observed here was not related to the concomitant variations of hyperglycemia and/ or pancreatic insulin content.

Increased insulin action in rats with mild insulin deficiency induced by neonatal streptozotocin

The effect of chronic moderate insulin deficiency on in vivo insulin action was studied in young rats after neonatal (day of birth) streptozotocin (n0-STZ model) at a time (4 wk) when basal hyperglycemia is not yet established. The insulin action was quantified in vivo during insulin-glucose clamps performed on anesthetized rats while in the postabsorptive state; under basal or hyperinsulinemic conditions, total glucose production and utilization were assessed with a [3- 3H]-glucose perfusion, and local glucose utilization was estimated by measuring 2-deoxy-D-[1-3H]glucose 6-phosphate accumulation in various tissues. Compared with controls, the 4-wk-old n0-STZ rats were normoglycemic and hypoinsulinemic (P less than 0.05). The basal glucose production rate in the diabetics was significantly greater (P less than 0.05). During the clamp studies, suppression of endogenous glucose production by submaximal (1 nmol/l) or maximal (30 nmol/l) hyperinsulinemia was similar in both groups. Overall glucose utilization in the diabetics was significantly higher in the basal state and, after submaximal or maximal hyperinsulinemia, it remained significantly greater (P less than 0.001) than the corresponding utilization in the controls. This was correlated with an increased stimulation of glucose utilization in soleus muscle, diaphragm, white adipose tissue, and brown adipose tissue. In vitro studies using inguinal adipocytes showed that the glucose oxidative pathway retained normal sensitivity to insulin in the n0-STZ rats while the glucose conversion into lipids was significantly higher at sub-maximal insulin concentration compared with the control group.(ABSTRACT TRUNCATED AT 250 WORDS)

Increased Insulin Action in Cultured Hepatocytes from Rats with Diabetes Induced by Neonatal Streptozotocin*

Previous studies have shown that Wistar rats injected at birth (n0) with STZ (n0-STZ) develop as adults a noninsulin-dependent diabetic state characterized by a lack of insulin response to glucose in vivo, a mild basal hyperglycemia, and an impaired glucose tolerance. Our former in vivo studies using the insulin-glucose clamp technique revealed an increased insulin action upon hepatic glucose production in these animals. We have now cultured hepatocytes from these mildly diabetic rats in parallel with hepatocytes from control rats, to examine more closely basal and insulin-regulated glucose production and glucose incorporation into glycogen. In addition, we extended our investigation to other hepatic functions such as lipid synthesis and amino acid transport, which could not be studied in vivo. Although glucose production from glycogenolysis or gluconeogenesis in absence or presence of glucagon was identical in the two cell populations, glucagon-stimulated glycogenolysis was more sensitive to insulin action in diabetic hepatocytes. Similarly, insulin action on glucose incorporation into glycogen, lipogenesis, and amino acid transport were enhanced in diabetic hepatocytes. The hormone effect was manifested by an increase in the sensitivity and/or in the responsiveness, reflecting the multiplicity of the pathways whereby the insulin signal is transduced through the insulin receptor to multiple postreceptor sites. To gain insight into the possible mechanism of these disturbances, we evaluated the initial insulin receptor interaction and the kinase activity of the receptor beta-subunit. In accordance with our previous study on intact livers, we found no alteration in either of these parameters in n0-STZ rat hepatocytes. Thus, the present study clearly demonstrates that these diabetic rats exhibit a postreceptor hyperresponsiveness to insulin at the cellular level. It strengthens the notion that a beta-cell deficiency with glucose intolerance does not necessarily lead to a hepatic insulin resistance.

Long-term gliclazide treatment improves the in vitro glucose-induced insulin release in rats with Type 2 (non-insulin-dependent) diabetes induced by neonatal streptozotocin

Neonatal rats treated with streptozotocin on the day of birth (n0-STZ) or on day 5 (n5-STZ) exhibited when fully grown a very mild or frank basal hyperglycaemia respectively and a specific failure of insulin release in response to glucose. To determine whether short (1 day) or long-term (30 days) gliclazide treatment modifies the pancreatic insulin content and the B-cell response to secretagogues, diabetic rats were given oral gliclazide (10 mg/kg per day) and compared to control diabetic and non-diabetic rats. Insulin secretion in the isolated perfused pancreas was studied the day after the last gliclazide administration. In severely hyperglycaemic n5-STZ rats (plasma glucose levels greater than 16 mmol/l) long-term gliclazide treatment did not lower the plasma glucose values, did not affect the pancreatic insulin stores, nor did it significantly modify the insulin release in vitro in response to glucose or arginine. In moderately hyperglycaemic n5-STZ rats (plasma glucose levels less than 16 mmol/l) the plasma glucose levels declined progressively reaching 8 mmol/l as a mean at the end of the gliclazide therapy. In the n5-STZ rats responsive to gliclazide the pancreatic insulin stores were increased twofold as compared to values in untreated n5-STZ rats, however, this difference did not reached significance and the pancreatic insulin stores in the responsive gliclazide treated rats remained depleted by 76% compared to normal insulin stores. In the n0-STZ rats (very mild hyperglycaemia) the long-term gliclazide treatment did not significantly modify the plasma glucose levels or the pancreatic insulin stores.(ABSTRACT TRUNCATED AT 250 WORDS)

Relation of Insulin Deficiency to Impaired Insulin Action in NIDDM Adult Rats Given Streptozocin as Neonates

We assessed the impact of chronic insulin deficiency on basal and insulin-stimulated glucose utilization by the whole-body mass in vivo in female albino Wistar rats. This assessment was based on a comparison of results in rats given streptozocin (STZ) on day of birth (n0-STZ), when 2 days old (n2-STZ), or when 5 days old (n5-STZ). At 10 wk of age, the n2-STZ rats exhibited characteristics similar to those obtained in the n0-STZ rats: normal growth, modest elevation of basal plasma glucose (8.23 +/- 0.24 mM), glucose intolerance, depleted pancreatic insulin stores (approximately 50% of normal value), and lack of insulin release in response to glucose in vivo. In contrast, the n5-STZ rats exhibited frank basal hyperglycemia (glucose 11.9 +/- 1.1 mM) and glucose intolerance, increased glycosylated hemoglobins, strong reduction of the pancreatic insulin stores (10% of normal value), decreased basal plasma insulin levels (50% of normal value), and lack of insulin release in response to glucose in vivo. Changes in the sensitivity of the neonatal beta-cell to STZ and the regeneration capacity of the beta-cells during the 1st postnatal wk were liable factors for the contrast. In vivo insulin action was assessed with the euglycemic-hyperinsulinemic clamp technique in 10-wk-old anesthetized animals. In the n2-STZ rats compared with controls 1) endogenous glucose production was significantly higher despite a normal plasma insulin level in the basal state, 2) endogenous glucose production rate was similarly suppressed by hyperinsulinemia, and 3) glucose utilization by the whole-body mass was similarly increased by hyperglycemia.(ABSTRACT TRUNCATED AT 250 WORDS)