Quantitative morphology of the rat kidney during diabetes mellitus and insulin treatment

A morphometric study was performed on moderately hyperglycaemic streptozotocin diabetic rats after 10 and 50 days of diabetes, and on groups of rats that, after initial hyperglycaemia for 50 days, were insulin treated for 2 h or for 5, 15 or 38 days. A group of hyperglycaemic diabetic animals were fasted for 18 h. Another group of rats had acute hyperglycaemia induced by intravenous glucose injection. After 10 and 50 days of diabetes, kidney weight was increased by 55 and 93%. Glomerular volume, tubule length, and tubular and interstitial volume increased in diabetic animals compared with controls. After 4 h insulin treatment, the kidney weight was 20% decreased; after 5 days it was 31% decreased. After 38 days the kidney weight was still 26% greater than in controls. In diabetic animals, 18 h fasting induced a 30% decrease in kidney weight. In normal animals, acute hyperglycaemia induced a 22% increase in kidney weight. Volume fractions of most kidney structures remained similar in all groups. However, the glomerular volume fraction was smaller during kidney enlargement, and the tubular volume fraction was larger after induced hyperglycaemia compared with controls. In conclusion, high blood glucose levels in diabetic and normal animals are associated with increased kidney weight. In hyperglycaemic diabetic animals, normalization of blood glucose after insulin treatment or fasting was followed by a decrease in kidney weight.     

Progressive glomerular injury in the MWF rat is predicted by inborn nephron deficit

It has been suggested that a reduced number of nephrons may predispose to systemic hypertension and glomerular injury. Compensatory hemodynamic changes, due to a low number of glomeruli, might be responsible for glomerular functional and structural changes. It is difficult to evaluate this hypothesis in humans because of limitations in estimating the number of nephrons in the living kidney. The aim of the present study was to estimate nephron number, single glomerular hemodynamics, and glomerular volume in male and female MWF rats, a strain that spontaneously develops systemic hypertension, proteinuria, and glomerulosclerosis. Male and female Wistar rats were used as controls. At 12 to 14 wk of age, male MWF rats developed proteinuria, whereas female MWF and Wistar rats showed normal urinary protein excretion rate. Glomerular number was significantly reduced in male and female MWF rats (13,690+/-1,489 and 12,855+/-1,781 gl/ kidney, respectively) compared with Wistar rats (26,955+/-2,171 and 27,166+/-1,754 gl/kidney, respectively). The mean number of nephrons per unit of body weight was also lower in MWF males (88+/-10) compared with MWF females (139+/-20) and compared with male and female Wistar animals (142+/-14 and 221+/-22 gl/g body wt). Whole-kidney hemodynamic parameters and the number of nephrons were used to calculate single-nephron filtration rate and plasma flow. Both measures were markedly elevated in male MWF rats relative to values obtained in the other three groups. Similarly, glomerular volume was significantly greater in MWF males than in other animals. These results suggest that an inborn deficit of nephrons may be responsible for spontaneous development of later-in-life hypertension and renal dysfunction. The data also indicate the need to investigate the role of this potential pathogenetic factor for human hypertension and kidney disease in humans.     

Effect of chronic growth hormone administration on diabetic nephropathy in the rat

Indirect data exist which implicate elevated growth hormone (GH) as a factor in the development of diabetic nephropathy. The administration of somatostatin (SRIH) has been shown to reverse many of the changes found in early diabetic nephropathy; however, it is unknown whether SRIH causes these effects by the suppression of GH or by other unspecified factors. To study directly the possible effect of excess GH in the development of diabetic nephropathy, either ovine growth hormone (0.2 mg oGH) or diluent buffer was administered IM daily for 19 weeks to diabetic rats and to controls. Severity of nephropathy was assessed by 24 hour urine albumin excretion (UAE), relative kidney weight, and kidney histology. Results showed that diabetic rats overall had elevated UAE and kidney weight vs non-diabetic rats (46.2 +/- 8.6 vs 5.4 +/- 1.3 mg per day and 5.7 +/- 0.2 vs 2.7 +/- 0.1 mg per g of body weight, respectively, p < 0.001). However, no differences were detected between diabetic rats treated with GH compared to control diabetic rats. Additionally, diabetic rats had histopathologic changes consistent with early diabetic nephropathy, but no difference in severity scores was found between diabetic groups. These data provide evidence against GH as an etiologic factor in the development of diabetic nephropathy and it is speculated by the authors that SRIH exerts its protective renal effects in diabetes by mechanisms other than GH suppression.     

Effect of pancreas transplantation on the prevention of nephropathy in alloxan-induced diabetic rats

We studied the effects of pancreas transplantation on kidney lesions of rats with alloxan-induced diabetes. Ninety inbred male Lewis rats were randomly assigned to 3 experimental groups: group NC included 30 non-diabetic control rats, group DC included 30 alloxan-induced diabetic control rats, and group PT included 30 alloxan-induced diabetic rats that received pancreas transplants from normal donor Lewis rats. Each group was further divided into 3 subgroups of 10 rats which were sacrificed at 1, 3, and 6 months of follow-up, respectively. Clinical and laboratory parameters during these periods were documented. The kidneys of 5 rats in each subgroup were studied and 50 glomeruli and tubules from each kidney were analyzed by light microscopy by two different investigators in a double-blind study. There was progressive glomerular basement membrane thickening (GBMT), mesangial enlargement (ME), and Bowman's capsule thickening (BCT) in kidneys of rats in the 3 experimental groups during follow-up. These alterations were significantly higher in DC rats (GBMT: 1.99 +/- 0.31; ME: 2.00 +/- 0.33; BCT: 1.88 +/- 0.27) when compared to NC (GBMT: 1.54 +/- 0.30; ME: 1.56 +/- 0.47; BCT: 1.36 +/- 0.35) and PT rats (GBMT: 1.49 +/- 0.29; ME: 1.57 +/- 0.36; BCT: 1.35 +/- 0.28) at 6 months (P < 0.01). The extent of GBMT, ME, and BCT observed in DC rats at 1 and 3 months was not significantly different from NC and PT rats. The amount of kidney lesions in PT rats was similar to that of NC rats and lower than those of DC rats at 6 months (P < 0.01). In addition, Armanni-Ebstein lesions of the tubules (AE) and tubular lumen protein (PRO) observed in DC rats were not present in NC or PT rats. We conclude that pancreas transplantation in alloxan-induced diabetic rats prevents the development of kidney lesions beginning at 6 months after transplantation.     

Does the presence of diabetic nephropathy in parents influence the metabolic response in the offspring?

Non-insulin dependent (Type 2) diabetes mellitus (NIDDM) and long-term complications such as nephropathy have a strong genetic predisposition. Insulin resistance is thought to be a pathogenetic factor, predisposing genetically prone individuals to develop the microvascular complications of diabetes. To test these hypotheses, two groups of young individuals were studied: 28 offspring of parents having NIDDM and diabetic nephropathy (group 1) aged 29.5 +/- 6.1 years, BMI 25.2 +/- 4.7 kg m(-2) and 31 offspring of diabetic parents with no history of nephropathy, aged 31.6 +/- 4.1 years and BMI 26.3 +/- 4.9 kg m(-2) (group 2). All underwent a standard oral glucose tolerance test with measurement of serum insulin levels and serum lipid profile. Urine albumin:creatinine ratio (A/C ratio) and blood pressure were also recorded. Diabetes was detected in 2/28 (7.1%) and 3/31 (9.7%) and IGT was detected in 5/28 (25%) and 8/31 (25%) of groups 1 and 2, respectively. These differences were not statistically significant, but were higher than in a group of non-diabetic controls with healthy parents. Comparison of the normoglycaemic subjects (19 and 20 in group 1 and 2, respectively) showed no significant differences between blood pressure readings, fasting and 2 h plasma glucose, and lipid profiles. Plasma insulin values, fasting and 2 h, and the area under the graph were also similar in both groups, indicating an absence of higher insulin response in group 1 in comparison with group 2. These values were also not different from those in the non-diabetic controls. A delay in insulin response to glucose was noted in many of the offspring as indicated by a low deltaI/deltaG at 30'. We conclude that offspring of diabetic parents with nephropathy do not show higher risk of glucose intolerance or insulin resistance compared to those with diabetic parents without nephropathy. The relatively high plasma glucose values in the presence of normal insulin secretion in both groups of offspring of diabetic parents suggest the presence of insulin resistance.     

Effects of thyroid hormone on the sorbitol pathway in streptozotocin-induced diabetic rats

Sorbitol accumulation plays an important role in diabetic complications involving the kidney, nerves, retina, lens and cardiac muscle. To investigate the influence of thyroid hormone on the sorbitol pathway, we studied the effects of thyroid hormone on polyol metabolism in normal and diabetic rats. Rats were divided into three groups: controls, streptozotocin (STZ)-induced diabetic euthyroid rats (DM) and STZ-induced diabetic hyperthyroid (thyroxine-injected) rats (DM+HT). The sorbitol (Sor) concentrations in the kidney, liver and sciatic nerve (2.53+/-0.74, 0.97+/-0.16 and 24.0+/-5.1 nmol/mg protein, respectively) of the DM rats were significantly higher than those (1.48+/-0.31, 0.58+/-0.13 and 3. 1+/-0.6 nmol/mg protein) of the control rats. The Sor concentrations in the kidney and sciatic nerve of the DM+HT rats (1.26+/-0.29 and 9. 40+/-1.2 nmol/mg protein) were significantly lower than those in the DM rats. These values were reduced in the liver, unchanged in the kidney, and increased in the sciatic nerve from the hyperthyroid rats without diabetes. Thyroid hormone reduced the aldose reductase (AR) activities in the kidney, liver and sciatic nerve of the DM rats, and similarly reduced AR in the kidney and liver, but not in the sciatic nerve, of the non-diabetic rats. The sorbitol dehydrogenase (SDH) activities were decreased by thyroid hormone in the kidney and liver but not the sciatic nerve of DM rats. In the non-diabetic rats, this enzyme activity was decreased in liver, but not in kidney or sciatic nerve. A positive correlation between the Sor concentration and AR activity was observed in the kidney and liver but not in the sciatic nerve from control, DM and DM+HT rats. A negative correlation was observed between the Sor concentration and SDH activities in the same organs. These data suggest that thyroid hormone affects the sorbitol pathway, but the detailed mechanism whereby this hormone reduces the sorbitol content (especially in diabetic rats) remains to be clarified.     

Upregulation of osteopontin expression in renal cortex of streptozotocin-induced diabetic rats is mediated by bradykinin

The model of streptozotocin (STZ)-induced diabetes in Wistar rats was used to study the expression of osteopontin during development of diabetic nephropathy. Diabetes was confirmed by serum glucose levels exceeding 16 mmol/l during the experimental period of 12 weeks. During this period of time, diabetic nephropathy developed, as characterized by a reduced glomerular filtration rate (2.7 +/- 0.3 ml/min in controls vs. 1.7 +/- 0.1 ml/min in diabetic rats) and proteinuria (8.3 +/- 1.7 mg/24 h in controls vs. 22.0 +/- 4 mg/24 h in diabetic rats). Northern blot analysis revealed a time-dependent upregulation of renal cortical osteopontin expression reaching 138 +/- 6% of control levels after 2 weeks and 290 +/- 30% (mean +/- SE, n = 6-9) after 12 weeks. By immunostaining, the increased osteopontin expression could be located to the tubular epithelium of the renal cortex. Chronic treatment of animals with ramipril (3 mg/kg) during the 12-week experimental period led to a further increase in osteopontin mRNA expression in diabetic animals, amounting to 570 +/- 73% (mean +/- SE, n = 6) of controls. Increased levels of osteopontin were not associated with accumulation of monocyte/macrophages that were identified by the cell type specific monoclonal antibody ED-1. The increased osteopontin expression in ramipril-pretreated rats was abolished by application of the bradykinin B2-receptor antagonist, icatibant (0.5 mg/kg). In addition, increased osteopontin expression in diabetic rats, which did not receive any treatment after STZ injection, could as well be reduced by icatibant given for the final 2 weeks of the experimental period. These data suggest that a strong bradykinin B2-receptor-mediated upregulation of osteopontin occurs during the pathogenesis of experimental diabetic nephropathy in rats.     

Improvement of impaired glucose tolerance by oral administration of vanadyl sulfate by gavage in streptozotocin-induced diabetic rats

We examined the effect of oral administration of vanadyl sulfate by gavage on the levels of blood glucose and plasma insulin during oral glucose tolerance test (OGTT) in diabetic rats. Diabetes was induced by intravenous injection of streptozotocin at the dose of 32 mg/kg. Nondiabetic control animals were injected with an equal volume of saline. Vanadyl sulfate at a dose of 25, 50, or 75 mg/kg was given orally by gavage for 2 weeks, starting 12 hours after streptozotocin injection. When vanadyl sulfate was given twice a day, half of the one-day-dosage was given in the morning and the remaining half in the evening. Glucose tolerance test with 5 g/kg of glucose was carried out 2 weeks after administration of vanadyl sulfate. The fasting the blood glucose level in the diabetic rats was higher than that in the non-diabetic rats, whereas the plasma insulin level in the diabetic rats was lower. An increase in blood glucose seen in the glucose tolerance test was significantly greater in the diabetic rats than in the non-diabetic rats. The level of plasma insulin was increased by glucose tolerance test in the non-diabetic rats, while it was not changed in diabetic rats. Oral administration of vanadyl sulfate by gavage significantly improved the impaired glucose tolerance in the the diabetic rats in a dose-dependent manner without any change in plasma insulin level. In conclusion, oral administration of vanadyl sulfate by gavage is effective on impaired glucose tolerance in streptozotocin-induced diabetic rats.     

Streptozotocin-induced diabetes lowers retinol-binding protein and transthyretin concentrations in rats

Retinol-binding protein (RBP) and transthyretin (TTR) in the plasma, liver and kidney, retinol in plasma, and total vitamin A in the liver were measured in rats 6 weeks after diabetes mellitus had been induced by streptozotocin (STZ). The diabetic rats gained 83% less weight despite consuming 45% more feed than the non-diabetic controls. Plasma and kidney concentrations of RBP and TTR were significantly lower in diabetic than in the non-diabetic control rats. Unlike the retinol carrier proteins, plasma albumin concentrations remained unaffected. Plasma concentrations of retinol were decreased while its hepatic levels increased in the diabetic animals. The depressed circulatory levels of retinol may reflect an altered metabolism of its transport proteins.     

Glucose-induced changes in renal haemodynamics in proteinuric type 1 (insulin-dependent) diabetic patients: inhibition by acetylsalicilic acid infusion

The effect of hyperglycaemia on renal function in diabetic nephropathy remains poorly understood. We investigated the renal haemodynamic response to an acute plasma glucose rise from sustained euglycaemia to sustained hyperglycaemia in eight persistently proteinuric Type 1 (insulin-dependent) diabetic patients. Studies were performed in a double-blind cross-over manner after i.v. injection of 450 mg lysine acetylsalicilate (equivalent to 250 mg acetylsalicilic acid) or equal volume of 0.9% NaCl (isotonic saline). In the isotonic saline experiments hyperglycaemia produced a significant rise, by approximately 35%, in glomerular filtration rate in all patients from 41.5 +/- 5.2 to 55 +/- 6 ml.min-1.1.73 m-2 (p < 0.005) and an increase in sodium paraminohippurate clearance from 178 +/- 22.7 to 220 +/- 20.0 ml.min-1.1.73 m-2 (p < 0.05). These changes took place within the first 30 min of glucose infusion and were maintained for a 90 min hyperglycaemic period. Filtration fraction did not change significantly. Infusion of lysine acetylsalicilate lowered baseline glomerular filtration rate (isotonic saline vs lysine acetylsalicilate 41.5 +/- 5.2 vs 30.0 +/- 5.7 ml.min-1.1.73 m-2; p < 0.05) and significantly blunted the rise in glomerular filtration rate during hyperglycaemia (glomerular filtration rate increment: saline vs lysine acetylsalicilate: 13.6 +/- 2.8 vs 5.3 +/- 1.8 ml.min-1.1.73 m-2; p < 0.005). The effects on renal plasma flow were similarly blunted. In five additional patients, time- and volume-controlled isotonic saline experiments during sustained euglycaemia showed no significant changes in glomerular filtration rate and sodium paraminohippurate clearance.(ABSTRACT TRUNCATED AT 250 WORDS)     

Quantitative trait loci for blood glucose confirm diabetes predisposing and protective genes, Iddm4 and Iddm5r, in the spontaneously diabetic BB/OK rat

Rats were given a single injection of streptozotocin. They became diabetic with a blood sugar of around 300 mg dL-1. They were divided into three groups of six rats each. Group II was the diabetic control. Each one of group III diabetic rats received daily 2 ml of 2% solution of lysine supplement orally. Group IV received daily 2 ml of a 2% solution of a mixture of amino acids supplement for 120 days. In addition there were 6 rats as normal control (Group I). Periodically ophthalmic examination was done by slit lamp. Blood glucose, proteins, hemoglobin, free amino acids, glycosylated hemoglobin and glycated lens proteins were also analysed. Body weight was recorded. The diabetic controls decreased in body weight. The blood sugar levels were lowered from about 295 mg dL-1 to 99 mg dL-1 in the lysine-fed group and from 268 mg dL-1 to 126 mg dL-1 in the amino acids mixture-fed group. The levels of glycosylated hemoglobin and glycated lens proteins increased in diabetic controls while they were normal in other groups. The free amino acid levels in blood were lower in groups receiving lysine or amino acids than in diabetic controls indicating their better utilization. In diabetic control, all the animals developed cataract in 70-90 days; five out of six did not develop cataract in the lysine supplemented group. Four of six did not develop cataract in the amino acid mixture-supplemented group. None developed cataract in normal controls. Lysine and amino acids have anticataractous and antidiabetic effects.     

The development of overt diabetes in young Zucker Diabetic Fatty (ZDF) rats and the effects of chronic MCC-555 treatment

1. Young (6-week-old) pre-diabetic Zucker Diabetic Fatty (ZDF) rats displaying impaired glucose tolerance (IGT), moderate hyperglycaemia and hyperinsulinaemia were treated with the novel thiazolidinedione, MCC-555, for 28 days, during which time beta-cell failure and progression to overt diabetes occurs. 2. Treated ZDF rats exhibited consistently lower blood glucose levels than vehicle-treated diabetic controls, with a delayed rise and lower plateau levels. MCC-555 maintained plasma insulin levels throughout the treatment period, whereas these fell by 40% in untreated ZDF rats. 3. The rise in body weight was maintained in MCC-555-treated rats, whereas vehicle-treated rats exhibited blunted body weight gain after 8 weeks of age. Daily food intake was higher in diabetic, as compared to non-diabetic rats, but treatment did not modify food intake in diabetic rats. Water intake was lower in treated ZDF rats, concomitant with lowering of blood glucose. 4. The hyperinsulinaemic-euglycaemic clamp technique was applied to all rats after treatment to examine the effects of MCC-555 on insulin sensitivity. The glucose infusion rate to maintain normoglycaemia was lower in diabetic than in non-diabetic rats, demonstrating reduced glucose entry into insulin-sensitive tissues in diabetic rats. Increased glucose infusion rates were required to maintain euglycaemia in treated diabetic rats, demonstrating increased insulin sensitivity in these animals. 5. In conclusion, chronic MCC-555 treatment of young ZDF rats displaying IGT attenuates the development of overt diabetes through improved insulin sensitivity and maintenance of beta-cell function. MCC-555 may thus be beneficial in humans with IGT, to prevent or delay the progression of diabetes.     

Plasma leptin in diabetic and insulin-treated diabetic and normal rats

Adipose tissue leptin mRNA levels are decreased by food deprivation or induction of insulin-deficient diabetes. To determine whether plasma leptin concentrations are similarly affected, whether treatment of diabetes with insulin restores plasma leptin, and whether this requires restoration of body weight (lost as a result of diabetes) and/or normalization of glycemia, we measured plasma leptin concentrations in control, untreated streptozotocin (STZ)-diabetic, and insulin-treated STZ-diabetic rats. Plasma leptin was markedly reduced in untreated STZ-diabetic rats. Insulin treatment for 4 to 17 days increased plasma leptin approximately twofold above control levels. However, despite the hyperleptinemia, insulin-treated diabetic rats gained weight at a rate equal to that of sham-treated controls. Epididymal adipose tissue leptin mRNA levels in 17-day insulin-treated diabetic rats were equal to but did not exceed sham-control levels, unlike plasma leptin. Plasma glucose concentrations in insulin-treated STZ-diabetic rats were lower than in sham controls. Therefore, to determine whether hypoglycemia may be important in increasing plasma leptin, we measured plasma leptin levels in diabetic rats infused with insulin for 3 hours along with a variable-rate glucose infusion targeting glycemia to 200 or 40 mg/100 mL. Plasma leptin rapidly increased in these rats irrespective of target glycemia. Plasma leptin also increased rapidly in normal rats infused with insulin and glucose (target glycemia, 200 mg/100 mL). We conclude that plasma leptin concentrations are markedly reduced under conditions of insulin deficiency and rapidly increased by insulin treatment. The increase in plasma leptin does not require restoration of body weight and, under glucose clamp conditions, does not depend on target glycemia. Hyperleptinemia in insulin-treated diabetic rats is not explained on the basis of steady-state leptin mRNA levels, at least as reflected in epididymal fat.     

Prevention of glomerular dysfunction in diabetic rats by treatment with d-alpha-tocopherol

Because d-alpha-tocopherol (vitamin E) has been shown to decrease diacylglycerol (DAG) levels and prevent the activation of protein kinase C (PKC), which is associated with retinal and renal dysfunctions in diabetes, the study presented here characterized the effect of d-alpha-tocopherol treatment to prevent glomerular hyperfiltration and increased albuminuria as well as PKC activities in streptozotocin (STZ)-induced diabetic rats. Two weeks after the induction of diabetes, total DAG content and PKC activity in glomeruli were significantly increased in diabetic rats by 106.4 +/- 16.8% and 66.4 +/- 8.4%, respectively, compared with control rats. Intraperitoneal injection of d-alpha-tocopherol (40 mg/kg of body weight) every other day prevented the increases in total DAG content and PKC activity in glomeruli of diabetic rats. Glomerular filtration rate (GFR) and filtration fraction (FF) were significantly elevated to 4.98 +/- 0.34 mL/min and 0.36 +/- 0.05, respectively, in diabetic rats, compared with 2.90 +/- 0.14 mL/min and 0.25 +/- 0.02, respectively, in control rats. These hemodynamic abnormalities in diabetic rats were normalized to 2.98 +/- 0.09 mL/min and 0.24 +/- 0.01, respectively, by d-alpha-tocopherol. Albuminuria in 10-wk diabetic rats was significantly increased to 9.1 +/- 2.2 mg/day compared with 1.2 +/- 0.3 mg/day in control rats, whereas d-alpha-tocopherol treatment improved albumin excretion rate to 2.4 +/- 0.6 mg/day in diabetic rats. To clarify the mechanism of d-alpha-tocopherol's effect on DAG-PKC pathway, the activity and protein levels of DAG kinase alpha and gamma, which metabolize DAG to phosphatidic acid, were examined. Treatment with d-alpha-tocopherol increased DAG kinase activity in the glomeruli of both control and diabetic rats, by 22.6 +/- 3.6% and 28.5 +/- 2.3% respectively, although no differences were observed in the basal DAG kinase activity between control and diabetic rats. Because immunoblotting studies did not exhibit any difference in the protein levels of DAG kinase alpha and gamma, the effect of d-alpha-tocopherol is probably modulating the enzyme kinetics of DAG kinase. These findings suggest that the increases in DAG-PKC pathway play an important role for the development of glomerular hyperfiltration and increased albuminuria in diabetes and that d-alpha-tocopherol treatment could be preventing early changes of diabetic renal dysfunctions by normalizing the increases in DAG and PKC levels in glomerular cells.     

Lack of insulin resistance in the Lyon hypertensive rat

Genetically hypertensive rats (LH) of the Lyon strain, compared to their normo-tensive (LN) controls associate, in a unique manner, high blood pressure with increases in body weight and in plasma lipids and insulin/glucose ratio. The present work investigated the development of insulin resistance with age in this model. At the age of 22 and 52 weeks, LH and LN fasted male rats were submitted to an intravenous glucose tolerance test, allowing measurement of the elimination rate of the glucose and the area under the curve of the insulin response. Insulin sensitivity was calculated as the ratio of these two parameters. It was observed that insulin sensitivity coefficient decreased with age in all the animals and that LH rats did not significantly differ from LN controls (from 62.6 +/- 3.3 and 69.1 +/- 4 at 22 weeks to 42.1 +/- 4.4 and 49.5 +/- 12.8 at 52 weeks for LH and LN rats, respectively). It is concluded that 1) elevated plasma insulin/glucose ratio does not mean insulin resistance and 2) hypertension can develop without being associated, even in aged rats, to a true insulin resistance.     

Urinary albumin excretion rate and glomerular filtration rate in single-kidney type 2 diabetic patients

OBJECTIVE: To evaluate the urinary albumin excretion rate (UAER) and the glomerular filtration rate (GFR) of single-kidney type 2 diabetic patients (SKD) and of single-kidney non-diabetic patients (SKN). RESEARCH DESIGN AND METHODS: Patients who had only one kidney for at least 5 years, with no renal disease or hypertension at the time of the nephrectomy and with no calculus or systemic disease at the time of the evaluation, were included in this controlled cross-sectional study A total of 20 SKD (8 men, age 62 +/- 9 years; diabetes duration 8.5 +/- 7 years), 17 SKN (2 men, age 57 +/- 13 years), and 184 type 2 diabetic patients who were matched to the single-kidney diabetic group for age, sex, and BMI were studied. UAER was measured by immunoturbidimetry in timed 24-h sterile urine, and GFR was determined by the 51Cr-EDTA single-injection method. RESULTS: SKD patients presented a higher proportion (8 of 20, 40%) of microalbuminuria (UAER 20-200 microg/min) than SKN patients (3 of 17, 17.6%) and type 2 diabetic patients (37 of 184, 20%). SKD patients presented a higher proportion of macroalbuminuria (UAER >200 microg/min; 6 of 20, 30%) than SKN patients (1 of 17, 6%) but were similar to type 2 diabetic patients (43 of 184, 23%). The GFRs of normoalbuminuric SKN (71.7 +/- 21.4 ml x min(-1) x 1.73 m(-2)) and SKD patients (73.0 +/- 21.5 ml x min(-1) x 1.73 m(-2)) were similar but higher than the one-kidney GFR (GFR / 2) of the age-, sex-, and BMI-matched normal individuals (50.5 +/- 9.0 ml x min(-1) x 1.73 m(-2)) and normoalbuminuric type 2 diabetic patients (54.0 +/- 11.6 ml x min(-1) x 1.73 m(-2)). CONCLUSIONS: Increased GFR related to single-kidney status confers an increased risk of developing renal disease in the presence of diabetes.     

Effect of caloric restriction on basal insulin levels and the in vivo lipogenesis and glycogen synthesis from glucose in the Koletsky obese rat

Fasting plasma immunoreactive insulin levels increased with age in hyperinsulinemic Koletsky obese rats, being almost four times as high as in lean siblings at 3 mo (40 +/- 5 muU/ml) and rising steadily to 82 +/- 4 muU/ml at 6 mo (about seven times higher than lean siblings). Restricting the food intake of the obese rats markedly reduced but did not normalize the hyperinsulinemia, which in these rats was accompanied by normal plasma glucose concentrations. The incorporation in vivo of D-U-14C-glucose into tissue lipids and glycogen was measured 1 hr after the intravenous injection of 1 g glucose (containing 100 muDi D-U-14C-glucose) per kg body weight in obese rats eating ad libitum, obese rats after 3 mo on a restricted food intake, and lean siblings. All tissues (heart, diaphragm, skeletal muscle, and adipose tissues and liver) of obese rats exhibited a significantly greater lipogenesis from glucose than those of lean siblings. Dietary restriction of the obese rats reduced the 14C incorporation into lipid to levels not significantly different from lean controls in all tissues except skeletal muscle and liver, where, although greatly reduced, lipogenesis was still significantly higher than in lean rats. Glycogen synthesis tended to be greater in all tissues of obese rats than in lean animals. Dietary restriction of obese rats did not greatly affect glycogen synthesis.     

Lipoic acid reduces glycemia and increases muscle GLUT4 content in streptozotocin-diabetic rats

Alpha lipoic acid (lipoate [LA]), a cofactor of alpha-ketodehydrogenase, exhibits unique antioxidant properties. Recent studies suggest a direct effect of LA on glucose metabolism in both human and experimental diabetes. This study examines the possibility that LA positively affects glucose homeostasis in streptozotocin (STZ)-induced diabetic rats by altering skeletal muscle glucose utilization. Blood glucose concentration in STZ-diabetic rats following 10 days of intraperitoneal (i.p.) injection of LA 30 mg/kg was reduced compared with that in vehicle-treated diabetic rats (495 +/- 131 v 641 +/- 125 mg/dL in fed state, P = .003, and 189 +/- 48 v 341 +/- 36 mg/dL after 12-hour fast, P = .001). No effect of LA on plasma insulin was observed. Gastrocnemius muscle crude membrane GLUT4 protein was elevated both in control and in diabetic rats treated with LA by 1.5- and 2.8-fold, respectively, without significant changes in GLUT4 mRNA levels. Gastrocnemius lactic acid was increased in diabetic rats (19.9 +/- 5.5 v 10.4 +/- 2.8 mumol/g muscle, P < .05 v nondiabetic rats), and was normal in LA-treated diabetic rats (9.1 +/- 5.0 mumol/g muscle). Insulin-stimulated 2-deoxyglucose (2 DG) uptake into isolated soleus muscle was reduced in diabetic rats compared with the control group (474 +/- 15 v 568 +/- 52 pmol/mg muscle 30 min, respectively, P = .05). LA treatment prevented this reduction, resulting in insulin-stimulated glucose uptake comparable to that of nondiabetic animals. These results suggest that daily LA treatment may reduce blood glucose concentrations in STZ-diabetic rats by enhancing muscle GLUT4 protein content and by increasing muscle glucose utilization.     

Glomerular filtration and tubular reabsorption of albumin in preproteinuric and proteinuric diabetic rats

Microalbuminuria (26-250 mg/d) is considered to be an indicator of incipient diabetic nephropathy in humans in insulin-dependent diabetes (IDD). However, before microalbuminuria is observed, glomerular alterations, such as glycosylation of the glomerular basement membrane and glomerular hyperfiltration, in IDD may result in increased filtration of albumin before any observed increase in albumin excretion. Glomerular and tubular albumin kinetics were examined in streptozotocin (65 mg/kg body wt, i.v.) diabetic, Munich-Wistar rats at 7-10 (untreated) and 50-70 d (poorly controlled with small doses of insulin) after the onset of diabetes and compared with nondiabetic controls. Additional rats in each condition received acute lysine treatment to prevent tubular protein reabsorption. Urinary albumin excretion and nonvascular albumin distribution volumes were measured in the renal cortex and compared with morphometric measurements of interstitial space and the proximal tubule to assess intracellular uptake of albumin in the proximal tubule. Urinary albumin excretion under anesthesia was not different in 7-10-d IDD versus controls (19 +/- 3 vs. 20 +/- 3 micrograms/min) but increased in the 50-70-d IDD (118 +/- 13 micrograms/min, P < 0.05). Lysine treatment resulted in increased albumin excretion compared with respective nontreatment in 7-10-d IDD (67 +/- 10 micrograms/min, P < 0.05) but not in controls (30 +/- 6 micrograms/min) or in 50-70-d IDD (126 +/- 11 micrograms/min). Glomerular filtration rate was increased both in 7-10-d IDD (2.7 +/- 0.1 ml/min, P < 0.05) and in 50-70-d IDD (2.6 +/- 0.1 ml/min, P < 0.05) compared with control (2.2 +/- 0.1 ml/min). Calculated urinary space albumin concentrations increased early in IDD with 2.5 +/- 0.4 mg% in 7-10-d IDD and 4.9 +/- 0.6 mg% in 50-70-d IDD compared with control (1.4 +/- 0.3 mg%). The increase in filtration of albumin is in excess of that attributable to hyperfiltration before increased albumin excretion early in diabetes. In 50-70-d IDD, absolute tubular reabsorption of albumin is decreased, correlating to the decrease in brush border height of the proximal tubule.     

Increased epinephrine-induced cAMP response in severely diabetic BB/W rat liver

The effect of prolonged diabetes on epinephrine-induced adenosine 3',5'-monophosphate (cAMP) response in the liver was examined in diabetes-prone BB/W rats. Basal and 1 microM epinephrine-induced cAMP release from isolated perfused liver was similar in non-diabetic and diabetic BB/W rats with preserved adipose tissue. In adipose tissue-absent diabetic rats losing intra- and retro-peritoneal adipose tissue completely, both basal and 1 microM epinephrine-induced cAMP release from the liver were enhanced (P<0.01, each case). Plasma epinephrine and norepinephrine were similar in non-diabetic, adipose tissue-preserved and -absent diabetic BB/W rats. The plasma free thyroxine level was similar in non-diabetic and adipose tissue-preserved diabetic BB/W rats, but was lower in adipose tissue-absent diabetic BB/W rats than in non-diabetic rats (P<0.01), but the frequency of lymphocytic thyroiditis was similar in these three groups, although plasma corticosterone was lower in adipose tissue-preserved diabetic BB/W rats (P<0.05) and the lowest in adipose tissue-absent diabetic BB/W rats (P<0.01). Lymphocytic infiltration was not observed in the adrenal or pituitary glands in any group. Plasma total protein and albumin were low in adipose tissue-absent diabetic BB/W rats (P<0.01, each case). In adipose tissue-absent diabetic BB/W rats, liver dysfunction and hepatomegaly, but no apparent histological change in the liver, were observed. Plasma glucose was higher (P<0.01) and plasma insulin lower (P<0.05) in adipose tissue-absent diabetic BB/W rats than in adipose tissue-preserved diabetic BB/W rats. In conclusion, epinephrine-induced cAMP response in the liver was enhanced only in adipose tissue-absent diabetic BB/W rats. Denervation supersensitivity was not likely to be responsible for the enhanced beta-adrenergic response. The observed reductions in plasma thyroxine and corticosterone seemed to result from severe diabetes. Although the severity of diabetes can vary continuously, severe diabetes with loss of adipose tissue appeared to cause significant changes in the metabolism and enhanced beta-adrenergic response in the liver.