Hyperglycemia In Diabetic Rats Research Articles

Neuropathy in diabetic BB/Wor rats treated with insulin implants.

To elucidate the pathophysiology of diabetic neuropathy many workers have examined nerve specimens from diabetic rats. While most workers found that animals with high blood glucose levels develop neuropathy, some researchers report that the peripheral nerves are normal in hyperglycaemic rats. Hypoglycaemia may also cause neuropathy. Some workers suggest that neuropathy is linked to fluctuations of the blood glucose level. In the present study we examine plantar nerves of diabetic BB/Wor rats maintained on an eu-/hyperglycaemic or an eu-/hypoglycaemic regime with insulin implants. Treatment with implants worked well. Light microscopic examination of nerve fibres in non-diabetic control rats and in eu-/hyperglycaemic diabetic rats showed a normal picture. Preparations from eu-/hypoglycemic rats showed irregular myelin sheaths and signs of Wallerian degeneration. The lengths and diameters of the largest internodes were significantly subnormal. We conclude, that periodic moderate hypoglycaemia, but not periodic moderate hyperglycaemia, elicits neuropathy in diabetic BB/Wor rats treated with insulin implants.

Constitutive nitric oxide synthase (cNOS) activity in Langerhans islets from streptozotocin diabetic rats.

Nitric oxide synthase activity was measured in Langerhans islets isolated from control and streptozotocin diabetic rats. The activity of the enzyme was linear up to 150 micrograms of protein from control rats and was optimal at 0.1 microM calcium, when it was measured after 45 min of incubation at 37 degrees C in the presence of 200 microM arginine. Specific activity of the enzyme was 25 x 10(-4) nmol [3H]citrulline 45 min-1 mg protein-1. Streptozotocin diabetic rats exhibited less enzyme activity both in total pancreas homogenate and in isolated Langerhans islets when compared to control animals. Nitric oxide synthase activity measured in control and diabetic rats 15 days after the last streptozotocin injection in the second group of animals corresponded only to a constitutive enzyme since it was not inhibited by aminoguanidine in any of the mentioned groups. Hyperglycemia in diabetic rats may be the consequence of impaired insulin release caused at least in part by reduced positive modulation mediated by constitutive nitric oxide synthase activity, which was dramatically reduced in islets severely damaged after streptozotocin treatment.

Reduced glucose clearance as the major determinant of postabsorptive hyperglycemia in diabetic rats

The relationships between postabsorptive glucose concentration and hepatic glucose output (HGO) and glucose clearance were studied in rats one day after treatment with various doses of streptozotocin (STZ; 0, 15, 30, 40, 50, or 75 mg/kg; n = 6 per dose; study 1). Glucose fluxes were estimated using a prolonged (6-h) infusion of [3-3H]glucose to ensure complete tracer equilibration at hyperglycemia. Postabsorptive glucose was significantly increased at the high doses of STZ (50 and 75 mg/kg; P < 0.01) and was strongly correlated with glucose clearance across all doses (r = -0.85, P < 0.001) but less strongly with HGO (r = 0.46, P < 0.01). In the group treated with 50 mg/kg STZ, postabsorptive glucose was increased twofold compared with the control (i.e., zero dose) group, with no change in HGO and a 45% decrease in glucose clearance, indicating that the hyperglycemia was due to a decrease in glucose clearance. To understand the cellular mechanisms of decreased glucose clearance in STZ diabetic rats, skeletal muscle glucose clearance and intracellular glucose and glucose 6-phosphate (G-6-P) concentrations were determined in normal and STZ (50 mg/kg) diabetic rats at their postabsorptive glucose levels as well as at matched hyperglycemia (12 mM; study 2). Glucose clearance was significantly decreased in soleus (P < 0.05) muscles of the diabetic rats, and this was associated with significantly decreased intracellular glucose and G-6-P levels at matched hyperglycemia (P < 0.05), suggestive of decreased glucose transport. In conclusion, postabsorptive hyperglycemia in STZ diabetic rats was largely due to decreased glucose clearance, although increased HGO may also have been a contributing factor at the highest STZ dose. The decrease in postabsorptive glucose clearance in STZ diabetic rats appeared to be associated with an impairment of glucose transport in soleus (type I) muscles.

Effects of feeding acarbose on muscle glucose transport and GLUT4 protein in lean and obese diabetic ( [formula omitted]) rats

The Zucker diabetic fatty rat ( ZDF Gmi -fa ), a model for noninsulin-dependent diabetes mellitus (NIDDM), was used to evaluate the action of dietary acarbose (20 week, 40 mg/100 g diet) in improving hyperglycemia. Muscle glucose uptake and glucose transport were measured during hindlimb perfusion. GLUT4 protein was also measured in the perfused muscle. Insulin resistance was not observed in skeletal muscle from diabetic animals compared with lean controls as concluded from equivalent hemicorpus glucose uptake and muscle glucose transport rates. Three fold increases in both GLUT4 protein and glucose transport were observed in acarbose-fed lean rats compared with lean controls. Acarbose feeding significantly decreased hyperglycemia in diabetic rats. This improvement seems not to be the result of an increase in insulin-stimulated glucose transport in muscle as insulin sensitivity and responsiveness were unchanged.

Magnetic resonance imaging as a monitor of kidney enlargement and regression in experimental diabetes in rats.

The aim of the present study was to use magnetic resonance imaging as a non-invasive measure of renal enlargement and regression in experimental diabetes in rats. Rats were randomized into three groups: (1) non-diabetic control animals, (2) diabetic animals, untreated for 30 days after streptozotocin treatment and (3) diabetic animals treated with insulin from day 21 to day 30 after streptozotocin administration. Magnetic resonance images were obtained from anaesthetized rats and kidney, cortex, medulla and pelvis volumes were calculated throughout the experiment until day 30. In untreated diabetic animals, a marked increase in kidney volume was seen 4 days after the induction of diabetes (P < 0.05) and after 30 days this increase amounted to 73%, with similar increases in the cortex (63%) and medulla (69%). No change was seen in the pelvis volume. Insulin administration on day 21 to untreated diabetic rats abruptly reduced kidney volume by 21%, cortex volume by 27% and medulla volume by 18%, and after 4 days all three parameters were similar to those seen in non-diabetic controls. In conclusion, the present study has demonstrated the applicability of magnetic resonance imaging as a non-invasive measure of renal enlargement and regression in experimental diabetes in rats. In untreated hyperglycaemic diabetic rats, with manifest diabetic renal enlargement, acute regression in renal volume was observed concomitant with insulin-induced normoglycaemia.

Accelerated gastric emptying of glucose in Zucker type 2 diabetic rats: role in postprandial hyperglycaemia.

Patients with early non-insulin-dependent diabetes mellitus (NIDDM) empty glucose solutions from their stomachs more rapidly than non-diabetic control subjects, and this exacerbates postprandial hyperglycaemia. To determine if accelerated gastric emptying occurred in a rat model of NIDDM and influenced postprandial hyperglycaemia, gastric emptying of glucose was measured, and the effect of slowing the gastric emptying rate on postprandial hyperglycaemia was observed. We tested eight male obese Zucker diabetic rats and eight age-matched lean Zucker controls at 10-13 weeks of age to measure gastric emptying of glucose (by gamma scintigraphy). Rats fasted overnight were gavaged with 30% glucose at 1 ml/100 g body weight. Separately, six Zucker diabetic rats and six lean controls were tested for sensitivity to the inhibitory effects of cholecystokinin and secretin on gastric emptying. The diabetic rats emptied glucose significantly faster than controls (t1/2 = 37.3 +/- 1.5 vs 58.8 +/- 2.3 min in controls), and aging exaggerated this differential. Camostat, a stimulant of cholecystokinin and secretin release, added to the glucose meal significantly slowed gastric emptying (t1/2 = 123 +/- 23 and 166 +/- 19 min, diabetic vs lean, respectively), and significantly reduced postprandial hyperglycaemia in diabetic rats. Compared to Zucker lean controls, Zucker diabetic rats were as sensitive (cholecystokinin) or more sensitive (secretin) to gastrointestinal hormones that inhibit gastric emptying. The results demonstrate accelerated gastric emptying in a rat model of NIDDM, consistant with similar observations in humans with early NIDDM. These results also support the proposal that interventions to slow gastric emptying improve glucose control in this disease.

Interactions of the kallikrein-kinin and renin-angiotensin systems in experimental diabetes.

The kallikrein-kinin system (KKS) has been postulated to play a role in modulation of hemodynamic function in diabetes and to contribute to the hemodynamic effects of angiotensin-converting enzyme inhibition (CEI). To further explore the KKS and its interactions with the renin-angiotensin system (RAS), studies were conducted in nondiabetic control rats and in moderately hyperglycemic diabetic rats. In protocol 1, control and diabetic rats were studied before and after administration of one of two dissimilar B2 kinin receptor antagonists (BK2As), or vehicle. At a low dose (0.5 microg x kg-1 x min-1), the first generation antagonist D-Arg,[Hyp3,Thi5,8,D-Phe7]-bradykinin significantly reduced the glomerular filtration rate (GFR) and renal plasma flow rate in diabetic rats, despite variable effectiveness in blocking the hypotensive response to injected bradykinin. However, a similar hemodynamic effect occurred in nondiabetic rats, suggesting that the observed effect was not specific to diabetes. Higher doses (20 microg bolus, then 1 microg x kg-1 x min-1 infusion) did not affect hemodynamics in either group, perhaps because of partial agonist effect. The second BK2A tested was the newer compound, icatibant (Hoe 140; D-Arg,[Hyp3,Thi5,D-Tic7,Oic8]-bradykinin). Hoe 140 consistently blocked the vasodepressor action of injected bradykinin, but had no effect on systemic or renal hemodynamics in either control or diabetic rats. In protocol 2, control and diabetic rats were pretreated with the CEI ramipril for 1-2 weeks, after which renal function was studied before and after Hoe 140 (0.1 mg s.c. and i.v.) or vehicle. CEI lowered blood pressure in both groups. Hoe 140 did not affect renal function in control rats, but in diabetic rats pretreated with ramipril, it induced a modest but significant decline in GFR. Ramipril induced the predicted changes in the systemic and intrarenal RAS, while acute BK2A had no consistent effect on RAS parameters. These studies suggest that the endogenous KKS has only a minor role in modulation of renal hemodynamics in the euvolemic diabetic rat, in the absence of KKS stimulation by CEI. However, angiotensin-converting enzyme is also kininase II, which serves to increase endogenous kinin activity. The increased kinin activity resulting from CEI treatment may participate, to a modest degree, in hemodynamic regulation of the diabetic kidney.

Cardioprotective effects of troglitazone in streptozotocin-induced diabetic rats

Troglitazone, a new oral antidiabetic agent, shows hypoglycemic effects in insulin-resistant animal models and humans. This study was conducted to evaluate the effects of troglitazone on the heart of diabetic animals. Streptozotocin (STZ)-induced diabetic rats and age-matched controls were treated with troglitazone as a 0.2% food admixture for 6 weeks. Basal and postischemic cardiac functions at 14 weeks of age were then examined in isolated working heart. Troglitazone treatment did not attenuate the insulinopenia and hyperglycemia of diabetic rats, but it partially improved the hypertriglyceridemia. Troglitazone treatment partially restored the basal heart rate and cardiac work of diabetic rats to nearly control values. Troglitazone also improved the postischemic functional deficits of diabetic rats: heart rate (untreated 61% of baseline at 30-minute reperfusion v treated 92%, P < .001), left ventricular (LV) developed pressure (54% v 94%, P < .001), peak positive ([ LV + dP dt ] 54% v 93%, P < .001) and negative ([ LV - dP dt ] 53% v 94%, P < .001) first derivative of LV, and cardiac work (44% v 98%, P < .001). Diabetic animals showed ultrastructural damage including disarray of sarcomere, disorganization of mitochondrial matrix, cytoplasmic vacuolization, and invagination of nuclear membrane; these were partially normalized by troglitazone treatment. Our results suggest that troglitazone treatment has a cardioprotective effect on the basal and postischemic cardiac function of STZ-induced diabetic rats.

Metabolism of glucose, glycogen, and high-energy phosphates during transient forebrain ischemia in diabetic rats: effect of insulin treatment.

Hyperglycemia associated with diabetes mellitus will exacerbate neurologic injury after global brain ischemia. Studies in a rat model of forebrain ischemia (bilateral carotid occlusion plus hypotension for 10 min) discovered that acute restoration of normoglycemia in diabetics, using an insulin infusion, resulted in a neurologic outcome that was similar to normoglycemic rats without diabetes. The current study evaluated cerebral glucose, glycogen, lactate, and high-energy phosphate concentrations to identify metabolic correlates that might account for an alteration in postischemic outcome. Fifty-four pentobarbital-anesthetized Sprague-Dawley rats were assigned to three groups: chronically hyperglycemic diabetic rats (D; N = 18); insulin-treated, acutely normoglycemic diabetic rats (ID; N = 18); and nondiabetic rats (ND; N = 18). These groups were further divided into groups of six rats each that received either no ischemia, forebrain ischemia of 10 min duration without reperfusion, or ischemia plus 15 min of reperfusion. Brains were excised after in situ freezing, and metabolites were measured using enzymatic fluorometric techniques. Before ischemia, D rats had greater concentrations of brain glucose (12.18 +/- 2.67 micromol/g) than did either ID (5.10 +/- 1.33) or ND (3.20 +/- 0.27) rats (P < 0.05). Preischemic brain glycogen was similar in all groups. At the completion of ischemia, brain lactate concentrations in D were 86% greater than in ID and 61% greater than in ND (P < 0.05), reflecting a higher intraischemic consumption of glucose plus glycogen in D (P < 0.05). High-energy phosphate concentrations, as assessed by the energy charge of the adenylate pool, were better preserved in D (energy charge = 0.60 +/- 0.28) than in either ID (0.29 +/- 0.09) or ND (0.36 +/- 0.07; P < 0.05) rats. After 15 min of reperfusion, the energy charge returned to preischemic values (i.e., 0.91-0.92) in all groups. These studies demonstrated greater intraischemic carbohydrate consumption and lactate production in D than in ID or ND rats. Under these conditions, intraischemic-but not postischemic-energy status was better in D rats. Acute insulin therapy in ID rats resulted in a metabolic profile that was similar to that of ND rats. These results suggest that, in this model, primary energy failure during ischemia is not the origin of greater injury in hyperglycemic diabetics, nor is energy enhancement the origin of improved outcome after acute insulin treatment.

Niceritrol prevents the decrease in red blood cell 2,3-diphosphoglycerate and neuropathy in streptozotocin-induced diabetic rats

Nerve ischemia/hypoxia has been linked to the pathogenesis of diabetic complications. Red blood cell 2,3-diphosphoglycerate is an important regulator of peripheral tissue oxygenation; however, the relationship between 2,3-diphosphoglycerate concentration and diabetic complications has not been studied in detail. This investigation focused on the relationship between red blood cell 2,3-diphosphoglycerate and diabetic neuropathy, by measuring motor nerve conduction velocity and sciatic nerve blood flow in streptozotocin-induced diabetic rats. The effect of treatment with niceritrol, a nicotinic acid derivative that acts as a vasodilator and reduces serum lipid concentrations, on 2,3-diphosphoglycerate concentration and diabetic neuropathy was also examined. Untreated diabetic rats had significantly lower concentrations of red blood cell 2,3-diphosphoglycerate, higher concentrations of serum total cholesterol and triglyceride, as well as reduced motor nerve conduction velocity and sciatic nerve blood flow, compared to untreated normal rats. Niceritrol prevented these abnormalities without correcting hyperglycemia in diabetic rats, but had no effect on these parameters in normal rats. Red blood cell 2,3-diphosphoglycerate concentration and motor nerve conduction velocity showed a positive correlation with sciatic nerve blood flow and 2,3-diphosphoglycerate, respectively. These observations suggest that ischemia/hypoxia plays an important role in the development of diabetic neuropathy, and that niceritrol has a therapeutic effect on this condition by improving endoneurial ischemia/hypoxia.

Receptors for atrial natriuretic peptide are decreased in the kidney of rats with streptozotocin-induced diabetes mellitus.

To determine whether decreased renal responsiveness to atrial natriuretic peptide (ANP) in diabetes is mediated by alterations in the renal ANP receptor, ANP receptor density and affinity were measured 17-20 d after streptozotocin injection and compared with values in vehicle-treated controls and streptozotocin-treated rats made euglycemic with insulin. Plasma ANP concentration was significantly greater in hyperglycemic diabetic rats than in control or euglycemic diabetic rats. Both in glomeruli and inner medulla, ANP receptor dissociation constant did not differ among the three study groups, whereas the maximum binding capacity was decreased significantly in hyperglycemic diabetics in comparison with controls and euglycemic diabetics. Glomerular clearance receptors were also decreased significantly in hyperglycemic diabetic rats in comparison with control and euglycemic diabetic rats. To determine whether the decreased number of renal ANP receptors in diabetic rats was associated with a decreased biological response, we measured ANP-dependent cyclic GMP (cGMP) accumulation by isolated glomeruli and inner medullary collecting duct cells in vitro. cGMP accumulation was significantly less in hyperglycemic diabetic rats than in controls or euglycemic diabetic rats both in the presence or absence of the phosphodiesterase inhibitor zaprinast. cGMP phosphodiesterase activity in inner medullary collecting duct cells obtained from control and hyperglycemic diabetic rats did not differ. Thus, the decreased number of biologically active ANP receptors in the kidneys of diabetic rats is accompanied by decreased biological responsiveness in vitro and provides a potential explanation for the reduction in renal sensitivity to ANP in this condition.

Expression of growth-related protooncogenes during diabetic renal hypertrophy

Experimental type 1 diabetes mellitus is characterized by an early increase in kidney weight and glomerular volume, but changes in gene expression accompanying diabetic renal growth have not been elucidated. The early response genes, c-fos, c-jun, and c-myc encode proteins that regulate gene transcription, thus influencing the cellular responses to a stimulus. Accordingly, we studied c-fos, c-jun, and c-myc expression in glomeruli during the rapid phase of glomerular hypertrophy that follows the onset of hyperglycemia in diabetic rats. Total RNA was extracted by the method of Chomczynski from isolated glomeruli of streptozotocin (60 mg/kg i.v.) induced diabetic rats 24, 48, and 96 hours, and 1 week after the onset of hyperglycemia (blood glucose > 15 mmol/liter). A second group of rats, studied after streptozotocin administration, received twice daily insulin to maintain normoglycemia. A group of age-matched normal rats served as the control group. Northern blot analysis was performed with cDNA probes for c-fos, c-jun, and c-myc, and GAPDH. mRNA levels for c-fos increased fourfold 24 hours after the onset of hyperglycemia, but returned to baseline by 48 hours. mRNA levels for c-jun increased threefold 24 hours after the onset of hyperglycemia, in diabetic glomeruli, and the increase was sustained for one week. Intensive insulin treatment normalized blood glucose levels and abrogated the increases in c-fos and c-jun expression. There was no discernable increase in c-myc mRNA levels in the diabetic glomeruli.(ABSTRACT TRUNCATED AT 250 WORDS)

The Cardiac Renin-Angiotensin System in STZ-Induced Diabetes

To determine the effect of diabetes on the cardiac renin-angiotensin system, we compared angiotensin II binding density and renin, angiotensinogen, and type 1 angiotensin II (AT1) receptor mRNA levels in hearts of Sprague-Dawley rats 14 days after the administration of streptozotocin (STZ), in vehicle-treated control rats, and in STZ-administered rats made euglycemic with insulin. Myocardial angiotensin II receptor density, determined using an in situ autoradiographic technique, was increased significantly in hyperglycemic diabetic rats in comparison with control rats and euglycemic diabetic rats (P < 0.01) as a result of an increase in both AT1 and AT2 (type 2 angiotensin II) subtypes. The myocardial AT1 receptor mRNA level, determined by slot blot hybridization, was also significantly greater in the hyperglycemic diabetic rats (P < 0.005). Neither plasma renin concentration nor cardiac renin or angiotensinogen mRNA levels differed among the three study groups. In an additional experiment, control and diabetic rats were infused with angiotensin II (200 ng.kg-1.min-1 i.p. for 7 days) or vehicle. Plasma renin concentration decreased significantly, whereas no significant changes occurred in cardiac renin or angiotensinogen steady-state mRNA levels. As in the first experiment, levels of AT1 receptor mRNA were significantly greater in the diabetic rats. Thus, myocardial angiotensin II receptor density is increased in diabetic rats in association with an increase in steady-state AT1 receptor mRNA levels, an abnormality that appears to be independent of changes in the circulating renin-angiotensin system.

34 Rats with streptozotocin diabetes mellitus are resistant to the action of atrial natriuretic peptide to increase vascular permeability

Introduction: Atrial natriuretic peptide (ANP) infusion increases hematocrit and decreases plasma volume by inducing a shift of plasma fluid from the vascular towards the interstitial compartment. Rats with experimental diabetes mellitus resulting from streptozotocin treatment exhibit renal resistance to infused ANP. Methods: To determine whether resistance to the extrarenal actions of ANP also occurs under these conditions, changes in arterial pressure and hematocrit were measured during infusion of ANP (1 μg/kg per min for 45 min) in anesthetized binephrectomized rats 2–3 weeks after induction of diabetes. Results: Blood glucose was significantly elevated in diabetic compared with control and insulin-treated diabetic rats. Arterial pressure decreased similarly in control, diabetic and insulin-treated diabetic rats (by 7.611.6, 9.611.9 and 8.212%, respectively; all P<0.002). In control rats, hematocrit increased progressively to a maximal value of 9.510.9% corresponding to a decrease in plasma volume of 1611%. In contrast, the ANP-induced increase in hematocrit was markedly blunted in diabetic rats (1.610.8%, P<0.0001 versus ANP infusion in control rats), corresponding to a decrease in plasma volume of only 2.211%. In addition, reducing the hyperglycemia in diabetic rats by insulin therapy restored the increase in hematocrit to ANP (8.511.1%, P<0.0001 and P=NS versus ANP infusion in diabetic and control rats respectively). Plasma volume measured at the end of the infusion period was similar in control and insulin-treated diabetic rats infused with ANP (21.311.4 and 22.511.4 ml/kg). In contrast, plasma volume was significantly higher in diabetes (3211.1 ml/kg) compared with both ANP and vehicle (25.211.1 ml/kg) infused control rats. Conclusions: This study demonstrates that (1) the effect of ANP on hematocrit and volemia is blunted in streptozotocin-induced diabetes while its hypotensive action is preserved, and (2) restoring the glucose levels to normal in diabetic rats by insulin treatment normalizes the hemoconcentrating effect to exogenous administered ANP. Such an effect may account for the plasma volume expansion observed in untreated diabetic rats.

Glucose Tolerance and Blood Pressure Are Improved in the Spontaneously Hypertensive Rat by Ethyl-2- (6-(4-chlorophenoxy)-hexyl)oxirane- 2-carboxylate (Etomoxir), an Inhibitor of Fatty Acid Oxidation

We have demonstrated that glucose tolerance and insulin action are impaired in the spontaneously hypertensive rat (SHR), and that free fatty acids are elevated. Etomoxir, an inhibitor of fatty acid oxidation, has been shown to improve hyperglycemia in diabetic rats. We therefore performed oral glucose tolerance tests in SHR to assess glucose tolerance and insulin action in response to etomoxir. Because of the proposed relation between insulin action and hypertension, we examined the effect of etomoxir on blood pressure. Thirteen-week-old male SHR were randomized into two groups. Food was withdrawn at 8 AM and at 11 AM, animals received etomoxir (50 mg/kg) or control vehicle by gavage. Oral glucose tolerance tests were started at 1 PM. In other studies, 21-week-old male SHR were randomized into two groups. Animals were treated by gavage with etomoxir (50 mg/kg) or control vehicle, and blood pressure was measured noninvasively before and after treatment. Two weeks later, these experiments were repeated, but the treatments were reversed. In etomoxir-treated rats, the glucose response was significantly lower, whereas the insulin response was not significantly different. The combination of lowered glucose response, in the face of an unchanged insulin response, suggests an improvement in insulin action. However, fasting free fatty acids were higher, as was the free fatty acid response following etomoxir treatment. There was a dramatic decrease in blood pressure following etomoxir, with significant differences at 1.25, 3, 4.5, and 21 h after dosing. In summary, etomoxir treatment improved glucose tolerance and insulin action in SHR, whereas free fatty acid values were higher.(ABSTRACT TRUNCATED AT 250 WORDS)

Blunted effect of ANP on hematocrit and plasma volume in streptozotocin-induced diabetes mellitus in rats

Atrial natriuretic peptide (ANP) infusion increases hematocrit and decreases plasma volume by inducing a transfer of plasma fluid from the vascular to the interstitial compartment. Diabetes mellitus is associated with resistance to the renal actions of ANP. We explored the possibility that the extrarenal responses to ANP may also be altered in the diabetic state by measuring changes in arterial pressure and hematocrit during infusion of ANP (1 microgram.kg-1 x min-1 for 45 min) into anesthetized, acutely nephrectomized rats 2-3 wk after induction of diabetes from intravenous streptozotocin (STZ) injection (60 mg/kg). Blood glucose was significantly elevated in diabetic rats when compared with control and insulin-treated diabetic rats. Arterial pressure during ANP infusion decreased similarly in control; diabetic, and insulin-treated diabetic rats (by 7.6 +/- 1.6, 9.6 +/- 1.9, and 8.2 +/- 2% respectively; all P < 0.002). In control rats, hematocrit increased progressively to a maximum value of 9.5 +/- 0.9% as a result of the infusion, corresponding to a decrease in plasma volume of 16.3 +/- 1.3%. In contrast, the ANP-induced increase in hematocrit was markedly blunted in diabetic rats (1.6 +/- 0.8%; P < 0.0001 vs. ANP infusion in control rats). Reducing the hyperglycemia in diabetic rats by insulin therapy restored the increase in hematocrit in response to ANP (8.5 +/- 1.1%; P < 0.0001 vs. ANP infusion in diabetic rats and P = NS vs. control rats). ANP infusion increased plasma ANP levels to the same extent in the three groups, whereas plasma guanosine 3',5'-cyclic monophosphate (cGMP) was significantly less in diabetic as compared with control and insulin-treated diabetic rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of an atrial natriuretic peptide receptor antagonist on glomerular hyperfiltration in diabetic rats.

Previous studies from this laboratory implicated atrial natriuretic peptide (ANP) as a possible mediator of glomerular hyperfiltration in diabetic rats. In this study, the potential of HS-142-1 (HS), a novel polysaccharide compound with ANP receptor antagonist properties, to ameliorate glomerular hyperfiltration in diabetic rats was assessed. Initially, it was confirmed that a bolus iv injection of HS blocked both diuretic and natriuretic responses to exogenous ANP in normal Munich-Wistar rats. The acute effects of HS in moderately hyperglycemic diabetic rats with glomerular hyperfiltration and hyperperfusion were then determined. In diabetic rats, HS (20 mg/kg bolus iv) lowered GFR by approximately 46% from hyperfiltering (1.86 +/- 0.06 mL/min) to normal (1.13 +/- 0.13 mL/min) levels, whereas GFR in vehicle-treated diabetic rats remained unchanged (1.92 +/- 0.08 mL/min to 1.77 +/- 0.09 mL/min). In nondiabetic euvolemic rats, GFR was reduced by 20% after HS, whereas GFR in vehicle-treated controls was unchanged. In contrast, HS had no effect on GFR in hydropenic rats. Effective RPF was not significantly reduced in either diabetic or normal euvolemic rats in response to HS; consequently, significant reductions in filtration fraction were observed in both groups. Urine flow and sodium excretion rates were significantly reduced after HS in both diabetic and nondiabetic groups but not in hydropenic or vehicle-treated groups. These data show that HS ameliorates glomerular hyperfiltration in diabetic rats, further supporting the hypothesis that intrarenal actions of natriuretic peptides contribute significantly to glomerular hyperfiltration in experimental diabetes mellitus.

Adrenic acid Δ4 desaturation and fatty acid composition in liver microsomes of spontaneously diabetic Wistar BB rats

We examined the Δ4 (n-6) desaturation and the fatty acid composition of liver microsomes in the insulin-dependent spontaneously diabetic Wistar Bio-Breeding (BB) rat. The desaturation of adrenic acid to n-6 docosapentaenoic acid was decreased in the normo- and hyperglycemic diabetic rats. Insulin treatment with 1.0 IU. 100 g body weight −1 twice a day for 2 days restored the reduced activity during the hypoglycemic period. The pattern of responses was similar to that of linoleic acid Δ6 and dihomo-γ-linolenic acid Δ5 desaturases, with a non-parallel relationship between the desaturation system and the glycemia. The microsomal fatty acid composition of BB rat liver reflected only partially to the Δ4 desaturation at different states of glycemia. Factors other than impaired desaturation system are involved in the fatty acid metabolism of spontaneously diabetic rats.

Angiotensin responsiveness in hyperfiltering and nonhyperfiltering diabetic rats.

Renal and systemic responses to angiotensin II were studied in hyperglycemic diabetic rats (streptozotocin, 60 mg/kg, i.v.) and vehicle-injected controls at 24 h, 1 wk, 2 mo, or at 6 to 12 mo. In normal rats, the GFR was less than 0.80 mL/min per 100 g body wt (0.57 +/- 0.02 mL/min per 100 g body wt; range: 0.40 to 0.79 mL/min per 100 g body wt; N = 45). Hyperfiltration (GFR > or = 0.80 mL/min per 100 g body wt) was observed in all diabetic rats studied at 1 wk (GFR, 1.03 +/- 0.07 mL/min per 100 g body wt; N = 5; P < 0.001 versus control). However, at earlier and later times, GFR was elevated in only 8 of 18 of the diabetic rats (44%), with an overall prevalence of 56% (13 of 23). Mean arterial pressure, plasma glucose, urine volume, and filtration fraction were not different in hyperfiltering diabetic rats compared with nonhyperfiltering diabetic rats or normal controls. Angiotensin II (12.5 ng/kg per minute i.v.) had no effect on GFR in normal rats or nonhyperfiltering diabetic rats, but it normalized GFR in hyperfiltering diabetic rats (0.74 +/- 0.05 mL/min per 100 g body wt). In contrast with the renal effects of angiotensin II, blood pressure responses were similar in hyperfiltering and nonhyperfiltering diabetic rats. The findings that angiotensin II infusion caused a greater fall in GFR in hyperfiltering diabetic rats than in nonhyperfiltering diabetic rats, but that blood pressure responses were similar, suggests a localized abnormality in angiotensin responsiveness in the kidneys.(ABSTRACT TRUNCATED AT 250 WORDS)

Renal renin-angiotensin system in diabetes: functional, immunohistochemical, and molecular biological correlations

Recent evidence indicates a role for the renin-angiotensin system (RAS) in the pathogenesis of glomerular injury in diabetes. To further explore the RAS in diabetes, studies were conducted in nondiabetic control rats and in moderately hyperglycemic diabetic (DM) rats. In DM rats, both acute and chronic therapy with the specific angiotensin II (ANG II) receptor antagonist losartan did not affect glomerular hyperfiltration or hyperperfusion but selectively normalized the glomerular capillary hydraulic pressure and ultrafiltration coefficient. To determine the basis of intrarenal hemodynamic responsiveness to RAS inhibition, we conducted biochemical, molecular biological, and immunohistochemical studies to assess endogenous RAS activity. Values for plasma renin concentration and serum angiotensin-converting enzyme (ACE) activity in DM rats were normal. In contrast, intrarenal renin protein content, and renin and angiotensinogen mRNAs, were increased in DM rats, suggesting disproportionate activation of the intrarenal RAS. Total renal ACE activity was significantly reduced in DM rats, but immunohistochemical studies indicated redistribution of ACE in the diabetic kidney. Proximal tubule ACE activity was reduced, but ACE immunostaining intensity was enhanced in glomeruli and renal vasculature. Together, these observations indicate increased RAS activity in those sites (glomeruli and vasculature) most likely to regulate hemodynamic function, potentially explaining the prominent responses to pharmacological blockade of ANG II formation and/or action.