Regulation of gluconeogenesis in hepatocytes from fasted alloxan-diabetic rats

Hepatocytes from fasted, alloxan-diabetic rats were incubated in the absence of gluconeogenic substrates to deplete residual glycogen stores. Glucose production from lactate and pyruvate was enhanced in cells from diabetic rats relative to similarly treated hepatocytes from fasted, nondiabetic control rats. Gluconeogenesis from dihydroxyacetone, fructose, or glycerol was not increased but the formation of lactate plus pyruvate from dihydroxyacetone was decreased. The stimulation of gluconeogenesis by exogenous fatty acids was decreased by diabetes. The rates of gluconeogenesis in the presence of lactate plus pyruvate plus oleate were equal in hepatocytes from diabetic and control rats and indicate that the maximal rate of gluconeogenesis was not increased. With lactate plus pyruvate as substrates, stimulation of gluconeogenesis by norepinephrine or dibutyryl-cAMP was not altered by diabetes. The catecholamine stimulation of gluconeogenesis from glycerol also was unaffected. In contrast, diabetes decreased the maximal stimulation of gluconeogenesis from dihydroxyacetone by dibutyryl-cAMP, glucagon, or norepinephrine and this decrease was proportional to the decreased production of lactate plus pyruvate. The concentrations of glucagon or norepinephrine required for half-maximal stimulation were not altered by diabetes. Thus, the hormonal stimulation of gluconeogenesis from dihydroxyacetone is decreased by diabetes, probably because of decreased pyruvate kinase activity, but the interaction of glucagon and norepinephrine with hepatocytes and the subsequent stimulation of gluconeogenesis from physiologic substrates is not impaired.     

The effect of hemorrhagic stress on liver gluconeogenesis. An isolated rat liver perfusion study with three-carbon units as substrates

This effect of hypovolemic stress on hepatic gluconeogenesis has been studied using isolated perfused organs obtained from starved rats subjected to 60 min hemorrhagic hypotension at 70 mmHg. Four different substrates were used: lactate, pyruvate, glycerol and alanine. The substrates were added without any stress endocrine stimulation in the perfusate. Using a recirculating system and supraoptimal substrate availability, a significant higher rate of gluconeogenesis was confirmed for the stressed donor livers: glycerol (+100%), alanine (+97%), lactate (+64%) and pyruvate (+62%). Glucose accumulation was linear for all control and experimental groups. In the absence of added stress hormones, known to stimulate gluconeogenesis, the findings are concordant with an in vivo hormone activation of key enzymes in the gluconeogenic pathway, persisting for the 60 min duration of the in vitro perfusion.     

Relationship between lactate and glutamine metabolism in vitro by the kidney: differences between dog and rat and importance of alanine synthesis in the dog

Interaction between lactate (1 or 5 mM) and glutamine (1 or 5 mM) metabolism was studied with renal cortical slices incubated at a pH of 7.0 and obtained from acidotic (ammonium chloride) dogs and rats. The effect of aminooxyacetate (0.2 mM), dichloroacetate (3 mM), and fluoroacetate (0.05 mM) was also studied. Significant differences were observed between dog and rat. In the dog, lactate had no effect on glutamine uptake and vice versa, but gluconeogenesis increased. Ammonia production, however, decreased by 13 to 21%, whereas a significant increase in alanine production was noted. In the rat, glutamine extraction and ammonia production dropped by 33% with 5 mM lactate. In contrast to the observation in the dog, no production of alanine was noted, but significant accumulation of glutamate took place. Amino-oxyacetate inhibited alanine production in the dog and reestablished ammoniagenesis, and it led to a marked decrement in the uptake of lactate and glucose production in both species. Dichloroacetate in the dog resulted in a reduction in pyruvate, alanine, glucose, and ammonia production while glutamate accumulation was observed. In both species, fluoroacetate stimulated glutamine uptake and ammonia production. With lactate alone, fluoroacetate decreased lactate uptake and glucose production. With both lactate and glutamine in the medium, fluoroacetate prevented any effect of lactate on ammoniagenesis. The present study demonstrates that lactate has a modest depressing effect on renal ammonia production by dog slices through increased synthesis of alanine and redistribution of nitrogen from glutamine. In the rat, the depressing effect of lactate on ammonia production in the alanine amino-transferase deficient kidney occurs through accumulation of glutamate. The data also reveal that oxidation of lactate to carbon dioxide is greater in the dog than it is in the rat, but that gluconeogenesis from lactate is more important in the rat.     

Role of glutamine in human carbohydrate metabolism in kidney and other tissues

Glutamine is the most abundant amino acid in the human body and is involved in more metabolic processes than any other amino acid. Until recently, the understanding of many aspects of glutamine metabolism was based on animal and in vitro data. However, recent studies using isotopic and balance techniques have greatly advanced the understanding of glutamine metabolism in humans and its role in glucose metabolism in the kidney and other tissues. There is now evidence that in postabsorptive humans, glutamine is an important glucose precursor and makes a significant contribution to the addition of new carbon to the glucose carbon pool. The importance of alanine for gluconeogenesis, viewed in terms of the addition of new carbons, is less than previously assumed. It appears that glutamine is predominantly a renal gluconeogenic substrate, whereas alanine gluconeogenesis is essentially confined to the liver. As shown recently, renal gluconeogenesis contributes 20 to 25% to whole-body glucose production. Moreover, glutamine has been shown not only to stimulate net muscle glycogen storage but also to stimulate gluconeogenesis in normal humans. Finally, in humans with type II diabetes, conversion of glutamine to glucose is increased (more so than that of alanine). The available evidence on the hormonal regulation of glutamine gluconeogenesis in kidney and liver and its alterations under pathological conditions are discussed.     

Obesity and type 2 diabetes impair insulin-induced suppression of glycogenolysis as well as gluconeogenesis

To determine whether the hepatic insulin resistance of obesity and type 2 diabetes is due to impaired insulin-induced suppression of glycogenolysis as well as gluconeogenesis, 10 lean nondiabetic, 10 obese nondiabetic, and 11 obese type 2 diabetic subjects were studied after an overnight fast and during a hyperinsulinemic-euglycemic clamp. Gluconeogenesis and glycogenolysis were measured using the deuterated water method. Before the clamp, when glucose and insulin concentrations differed among the three groups, gluconeogenesis was higher in the diabetic than in the obese nondiabetic subjects (P < 0.05) and glycogenolysis was higher in the diabetic than in the lean nondiabetic subjects (P < 0.05). During the clamp, when glucose and insulin concentrations were matched and glucagon concentrations were suppressed, both glycogenolysis and gluconeogenesis were higher (P < 0.01) in the diabetic versus the obese and lean nondiabetic subjects. Furthermore, glycogenolysis and gluconeogenesis were higher (P < 0.01) in the obese than in the lean nondiabetic subjects. Plasma free fatty acid concentrations correlated (P < 0.001) with glucose production and gluconeogenesis both before and during the clamp and with glycogenolysis during the clamp (P < 0.01). We concluded that defects in the regulation of glycogenolysis as well as gluconeogenesis cause hepatic insulin resistance in obese nondiabetic and type 2 diabetic humans.     

Insulin resistance and depressed gluconeogenic capability during early hyperglycemic sepsis

The present study was performed to determine whether insulin resistance, independent of the prevailing hormonal milieu, occurs in the liver during sepsis. To determine this, sepsis was produced in rats by cecal ligation and puncture (CLP). Six hours later, when the rats were in the early hypermetabolic phase of sepsis, the livers were isolated and perfused with Krebs-HCO3 buffer using a nonrecirculating system. The effects of various concentrations of insulin on the gluconeogenic response to lactate and phenylephrine stimulation were determined. In the absence of insulin and phenylephrine, there was no difference in the rates of glucose production from lactate between septic and sham-operated rats. The gluconeogenic response to phenylephrine stimulation was, however, significantly depressed in the livers from septic rats. Addition of 50 microU insulin/ml resulted in an inhibition of the phenylephrine-stimulated glucose release from livers from sham-operated rats. This inhibition was maximal at 100 microU insulin/ml. In contrast, significant inhibition of phenylephrine-stimulated glucose release from livers from septic rats was only observed in the presence of 2,000 microU insulin/ml. These results demonstrate that even during the early, hypermetabolic phase of sepsis, depressed hormonally stimulated hepatic gluconeogenic capability occurs. In addition, livers from septic rats exhibited a resistance to the effects of insulin on gluconeogenesis. This resistance may account, at least in part, for accelerated gluconeogenesis in spite of hyperinsulinemia in early sepsis.     

Renin secretion by the spontaneously diabetic rat

Renal function studies and measurements of in vivo plasma renin activity (PRA), kidney renin content, and renin secretion by isolated, perfused kidneys were performed in spontaneously diabetic and nondiabetic BioBreeding/Worcester (BB/W) rats. Diabetic animals evidenced hyperglycemia, glycosuria, and plasma volume expansion. After dietary sodium deprivation, plasma volume fell to levels equivalent to those of sodium-deprived, nondiabetic rats. Dietary sodium deprivation evoked a larger proportional increase in PRA among diabetic than nondiabetic animals, although PRA before sodium restriction was equivalent in the two groups. Basal renin release (RR) was higher from isolated, perfused kidneys from diabetic rats than from nondiabetic kidneys. Diabetic kidneys, moreover, displayed increased kidney renin content (KRC). By contrast, while isoproterenol (10(-5) M) stimulated a nearly fivefold increment in RR from nondiabetic, perfused kidneys, a negligible effect was observed in diabetic kidneys. The dose-response curve of renin secretion (as a proportion of total renal content) in response to isoproterenol was shifted downward. Hence, while KRC and spontaneous RR by isolated, perfused kidneys were increased, the increment in PRA with salt depletion and the renin-secretory response to isoproterenol in vitro were impaired. We propose that specific defects in renin secretion, in particular, the response to beta-adrenergic stimulation, may be operative in diabetes.     

Deletion of MK2 signalling in vivo inhibits small Hsp phosphorylation but not diabetic nephropathy.

It is supposed that some stress-induced heat shock proteins (Hsps) are regulated through e.g. stimulation of the p38MAPK/MK(MAPKAP)-2 signalling pathway. It has been postulated from in vitro experiments that phosphorylation of Hsp25(rodents)/Hsp27(human), the major phosphorylation substrate of MK2, is responsible for mesangial contractility and glomerular hyperfiltration in the diabetic kidney. To verify this hypothesis in vivo we studied the renal function of nondiabetic and streptozotocin (STZ)-induced, diabetic MK2(-/-) mice in comparison to wild-type (WT) control mice. Following 8 weeks of hyperglycaemia, light microscopy showed increased glomerulosclerosis and tubulointerstitial renal fibrosis in both diabetic study groups. Protein analysis demonstrated that Hsp25 phosphorylation is stimulated upon high-glucose condition but inhibited in the diabetic MK2(-/-) mice. However, we found the kidney-body weight ratio significantly increased in diabetic WT and MK2(-/-) mice. No difference regarding the increased expression of the extracellular matrix proteins and TGF-beta1 between both diabetic study groups was observed. Importantly, diabetic MK2(-/-) mice showed no protection against renal hyperfiltration in the diabetic state and the development of diabetic albuminuria. Although activation of p38MAPK has been previously shown in diabetes mellitus, our results indicate that blockade of the downstream MK2/Hsp25 signalling pathway does not interfere with the development of early diabetic nephropathy.     

Inhibition of fructose 1,6-bisphosphatase reduces excessive endogenous glucose production and attenuates hyperglycemia in Zucker diabetic fatty rats

Gluconeogenesis is increased in type 2 diabetes and contributes significantly to fasting and postprandial hyperglycemia. We recently reported the discovery of the first potent and selective inhibitors of fructose 1,6-bisphosphatase (FBPase), a rate-controlling enzyme of gluconeogenesis. Herein we describe acute and chronic effects of the lead inhibitor, MB06322 (CS-917), in rodent models of type 2 diabetes. In fasting male ZDF rats with overt diabetes, a single dose of MB06322 inhibited gluconeogenesis by 70% and overall endogenous glucose production by 46%, leading to a reduction in blood glucose of >200 mg/dl. Chronic treatment of freely feeding 6-week-old male Zucker diabetic fatty (ZDF) rats delayed the development of hyperglycemia and preserved pancreatic function. Elevation of lactate ( approximately 1.5-fold) occurred after 4 weeks of treatment, as did the apparent shunting of precursors into triglycerides. Profound glucose lowering ( approximately 44%) and similar metabolic ramifications were associated with 2-week intervention therapy of 10-week-old male ZDF rats. In high-fat diet-fed female ZDF rats, MB06322 treatment for 2 weeks fully attenuated hyperglycemia without evidence of metabolic perturbation other than a modest reduction in glycogen stores ( approximately 20%). The studies confirm that excessive gluconeogenesis plays an integral role in the pathophysiology of type 2 diabetes and suggest that FBPase inhibitors may provide a future treatment option.     

Lactate production and pyruvate dehydrogenase activity in fat and skeletal muscle from diabetic rats.

This study was initiated to explore the possibility that an increase in the supply of gluconeogenic precursors contributes to the overproduction of glucose by the liver in NIDDM patients. To address this issue, a form of experimental NIDDM was produced in rats by injecting a low dose (38 mg/kg) of STZ and comparing lactate and alanine production and PDH activity in skeletal muscle and isolated adipocytes from normal and diabetic rats. Skeletal muscle lactate production was measured by using a hindlimb perfusion technique and was significantly greater (P < 0.01) in the diabetic rats compared with two groups of control rats: one perfused at normal glucose levels and the other perfused at glucose concentrations comparable with those observed in diabetic rats. Alanine production by hindlimb from diabetic rats was 46% greater than hindlimbs from control rats perfused at normal glucose levels (P < 0.01) but was not significantly greater than control rats perfused at diabetic glucose levels. The percentage of glucose converted to lactate by muscle from both control groups was 4-5%, significantly lower than the 18% conversion rate observed in diabetic animals (P < 0.001). An increase in the ratio of lactate produced/glucose transport by isolated adipocytes from diabetic rats also was observed when measured in both the basal state (0.65 +/- 0.12 vs. 0.15 +/- 0.03, P < 0.01) and in the presence of maximal amounts of insulin (0.15 +/- 0.02 vs. 0.04 +/- 0.01, P < 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)     

Shor- and long-term effect of a calcium channel blocker, barnidipine, on renal hemodynamics in spontaneously hypertensive, diabetic rats

Background The purpose of this study was to examine the short- and long-term effects of the calcium channel blocker, barnidipine, on renal hemodynamics and urinary albumin excretion in spontaneously hypertensive rats with streptozotocin-induced diabetes. Methods Diabetic and nondiabetic spontaneously hypertensive rats and nonhypertensive rats were treated with barnidipine or placebo (vehicle). In the short-term experiment, barnidipine was given as a single bolus injection (3 μg/kg); in the long-term experiment, barnidipine was administered orally (15 mg/kg per day) for 16 to 20 weeks. Results Renal hyperfiltration was observed in both hypertensive and nonhypertensive rats at 1 to 2 weeks after induction of diabetes, without changes in renal blood flow. Although short-term administration of barnidipine significantly decreased mean arterial pressure and renal vascular resistance, barnidipine did not affect renal blood flow or glomerular filtration rate in hypertensive, diabetic rats. At 16 to 20 weeks after induction of diabetes, renal hyperfiltration and increased urinary albumin excretion were still observed in hypertensive rats given placebo, compared to values for hypertensive nondiabetic rats given placebo. Long-term administration of barnidipine to hypertensive, diabetic rats suppressed the increase in both glomerular filtration rate and urinary albumin excretion, and reduced systolic blood pressure without any change in renal blood flow, renal vascular resistance, or filtration fraction. Conclusions These results indicate that in hypertensive, diabetic rats short-term administration of barnidipine, despite reducing renal vascular resistance, is less effective than long-term administration in restoring normal renal filtration, although long-term administration may normalize renal filtration and reduce urinary albumin excretion.     

Serum C-peptide concentrations poorly phenotype type 2 diabetic end-stage renal disease patients

BACKGROUND: A homogeneous patient population is necessary to identify genetic factors that regulate complex disease pathogenesis. In this study, we evaluated clinical and biochemical phenotyping criteria for type 2 diabetes in end-stage renal disease (ESRD) probands of families in which nephropathy is clustered. C-peptide concentrations accurately discriminate type 1 from type 2 diabetic patients with normal renal function, but have not been extensively evaluated in ESRD patients. We hypothesized that C-peptide concentrations may not accurately reflect insulin synthesis in ESRD subjects, since the kidney is the major site of C-peptide catabolism and would poorly correlate with accepted clinical criteria used to classify diabetics as types 1 and 2. METHODS: Consenting diabetic ESRD patients (N = 341) from northeastern Ohio were enrolled. Clinical history was obtained by questionnaire, and predialysis blood samples were collected for C-peptide levels from subjects with at least one living diabetic sibling (N = 127, 48% males, 59% African Americans). RESULTS: Using clinical criteria, 79% of the study population were categorized as type 1 (10%) or type 2 diabetics (69%), while 21% of diabetic ESRD patients could not be classified. In contrast, 98% of the patients were classified as type 2 diabetics when stratified by C-peptide concentrations using criteria derived from the Diabetes Control and Complications Trial Research Group (DCCT) and UREMIDIAB studies. Categorization was concordant in only 70% of ESRD probands when C-peptide concentration and clinical classification algorithms were compared. Using clinical phenotyping criteria as the standard for comparison, C-peptide concentrations classified diabetic ESRD patients with 100% sensitivity, but only 5% specificity. The mean C-peptide concentrations were similar in diabetic ESRD patients (3.2 +/- 1.9 nmol/L) and nondiabetic ESRD subjects (3.5 +/- 1.7 nmol/L, N = 30, P = NS), but were 2.5-fold higher compared with diabetic siblings (1.3 +/- 0.7 nmol/L, N = 30, P < 0.05) with normal renal function and were indistinguishable between type 1 and type 2 diabetics. Although 10% of the diabetic ESRD study population was classified as type 1 diabetics using clinical criteria, only 1.5% of these patients had C-peptide levels less than 0.20 nmol/L, the standard cut-off used to discriminate type 1 from type 2 diabetes in patients with normal renal function. However, the criteria of C-peptide concentrations> 0.50 nmol/L and diabetes onset in patients who are more than 38 years old identify type 2 diabetes with a 97% positive predictive value in our ESRD population. CONCLUSIONS: Accepted clinical criteria, used to discriminate type 1 and type 2 diabetes, failed to classify a significant proportion of diabetic ESRD patients. In contrast to previous reports, C-peptide levels were elevated in the majority of type 1 ESRD diabetic patients and did not improve the power of clinical parameters to separate them from type 2 diabetic or nondiabetic ESRD subjects. Accurate classification of diabetic ESRD patients for genetic epidemiological studies requires both clinical and biochemical criteria, which may differ from norms used in diabetic populations with normal renal function.     

Effects of nephron loss on glomerular hemodynamics and morphology in diabetic rats

Loss of renal mass in rats with experimental diabetes mellitus leads to exaggerated hypertrophy of remaining nephrons and accelerated diabetic glomerulopathy. To examine factors responsible for glomerular injury in this setting, rats with preexisting diabetes were subjected to unilateral nephrectomy. Micropuncture studies and evaluation of glomerular morphology were performed 2-3 mo later. Nephrectomized diabetic rats demonstrated significant increases in kidney weight, superficial nephron glomerular filtration rate, and superficial nephron plasma flow compared with two-kidney diabetic rats and nephrectomized nondiabetic controls. Glomerular capillary hydraulic pressure was comparable in two-kidney and nephrectomized diabetic rats and was significantly reduced compared with nephrectomized nondiabetic controls. Nephrectomized diabetic rats demonstrated significant albuminuria, mesangial matrix expansion, and focal glomerulosclerosis, whereas two-kidney diabetic rats and nephrectomized nondiabetic controls showed only minimal alterations in glomerular morphology. It is concluded that diabetic rats can undergo glomerular functional compensation in response to nephron loss. Moreover, accelerated glomerular injury caused by nephron loss in diabetic rats could not be attributed to increased glomerular capillary pressure.     

Renal gluconeogenesis in insulin resistance: A culprit for hyperglycemia in diabetes

Renal gluconeogenesis is one of the major pathways for endogenous glucose production. Impairment in this process may contribute to hyperglycemia in cases with insulin resistance and diabetes. We reviewed pertinent studies to elucidate the role of renal gluconeogenesis regulation in insulin resistance and diabetes. A consensus on the suppressive effect of insulin on kidney gluconeogenesis has started to build up. Insulin-resistant models exhibit reduced insulin receptor (IR) expression and/or post-receptor signaling in their kidney tissue. Reduced IR expression or post-receptor signaling can cause impairment in insulin’s action on kidneys, which may increase renal gluconeogenesis in the state of insulin resistance. It is now established that the kidney contributes up to 20% of all glucose production via gluconeogenesis in the post-absorptive phase. However, the rate of renal glucose release excessively increases in diabetes. The rise in renal glucose release in diabetes may contribute to fasting hyperglycemia and increased postprandial glucose levels. Enhanced glucose release by the kidneys and renal expression of the gluconeogenic-enzyme in diabetic rodents and humans further point towards the significance of renal gluconeogenesis. Overall, the available literature suggests that impairment in renal gluconeogenesis in an insulin-resistant state may contribute to hyperglycemia in type 2 diabetes.     

Influence of long-term diabetes on renal glycogen metabolism in the rat

BACKGROUND/AIMS: The effects of acute insulin deficiency on the kidney have been investigated in animal models of experimental diabetes; however, the impact of long-term diabetes has not been determined. METHODS: We measured renal glycogen contents in streptozotocin (STZ)-diabetic rats 3 weeks (n = 12) or 9 months (n = 12) after the induction of diabetes, and in 2 groups of control rats of similar age (n = 16 and n = 12, respectively), in the fed state and after a 24-hour fast. RESULTS: Diabetic rats had high glucose levels, low insulin but normal glucagon concentrations in portal blood. In the fasting state, kidney glycogen content was very low in both young control and young diabetic rats (54 +/- 15 and 189 +/- 26 microg/g, respectively, mean +/- SD); in contrast, glycogen levels were markedly elevated in rats with long-standing diabetes as compared to old nondiabetic animals (2,628 +/- 1,023 +/- and 1,968 +/- 989 microg/g of diabetic rat, fasting and fed, respectively, p < 0.001 vs. 0 +/- 0 and 4 +/- 6 microg/g of control rats). On electron microscopy, large glycogen clusters were localized to the renal tubules. Kidney phosphorylase activity was higher, and synthase activity lower in diabetic than control rats (p < 0.05 for both), whereas kidney glycogen was strongly related to plasma glucose levels, suggesting that the enzyme changes were secondary to glycogen accumulation itself. Renal hexosephosphates and fructose-2,6-bisphosphate contents were both increased in long-term diabetic rats (p < 0.05), implying enhanced fluxes through both glycolysis and gluconeogenesis. CONCLUSION: In chronic, untreated diabetes glycogen accumulates in the renal tubules; prolonged hyperglycemia is the sole driving force for this phenomenon.     

Renal substrate metabolism and gluconeogenesis during hypoglycemia in humans

To examine the potential contribution of precursor substrates to renal gluconeogenesis during hypoglycemia, 14 healthy subjects had arterialized hand vein and renal vein (under fluoroscopy) catheterized after an overnight fast. Net renal balance of lactate, glycerol, alanine, and glutamine was determined simultaneously with systemic and renal glucose kinetics using arteriovenous concentration differences and 6-[2H2]glucose tracer dilution. Renal plasma flow was measured by para-aminohippurate clearance and was converted to blood flow using the mathematical value (1-hematocrit). Arterial and renal vein samples were obtained in the postabsorptive state and during a 180-min hyperinsulinemic period during either euglycemia or hypoglycemia. Insulin increased from 49 +/- 14 to 130 +/- 25 pmol/l (hypoglycemia) and to 102 +/- 10 pmol/l (euglycemia). Arterial blood glucose decreased from 4.5 +/-0.2 to 3.0 +/- 0.1 mmol/l during hypoglycemia but did not change during euglycemia (4.3 +/- 0.2 mmol/l). After 150 min, endogenous glucose production reached a plateau value that was higher during hypoglycemia (10.3 +/0.6 micromol x kg(-1) x min(-1)) than during euglycemia (5.73 +/-0.6 micromol x kg(-1) x min(-1), P < 0.001). Hypoglycemia was associated with a rise in renal glucose production (RGP) from 3.0 +/- 0.7 to 5.4 +/- 0.6 micromol x kg(-1) x min(-1) (P < 0.05), although glucose utilization remained the same (2.0 +/- 0.8 vs. 2.1 +/-0.6 micromol x kg(-1) x min(-1)). As a result, net renal glucose output increased from 1.0 +/- 0.3 to 3.3 +/- 0.40 micromol x kg(-1) x min(-1). Elevations in net renal uptake of lactate (2.4 +/- 0.5 to 3.5 +/- 0.7 vs. 2.8 +/- 0.4 micromol x kg(-1) x min(-1)), glycerol (0.6 +/- 0.3 to 1.3 +/- 0.5 vs. 0.4 +/- 0.2 micromol x kg(-1) x min(-1)), and glutamine (0.7 +/- 0.2 to 1.1 +/- 0.3 vs. 0.1 +/- 0.3 micromol x kg(-1) x min(-1)) during hypoglycemia versus euglycemia (P < 0.05) could account for nearly 60% of all glucose carbons released in the renal vein during hypoglycemia. Our data indicate that extraction of circulating gluconeogenic precursors by the kidney is enhanced and responsible for a substantial fraction of the compensatory rise in RGP during sustained hypoglycemia. Increased renal gluconeogenesis from circulating substrates represents an additional physiological mechanism by which the decrease in blood glucose concentration is attenuated in humans.     

Reduced insulinotropic effects of glucagonlike peptide I-(7-36)-amide and gastric inhibitory polypeptide in isolated perfused diabetic rat pancreas

The pathophysiological role of incretin in diabetes mellitus has not been established. We therefore examined the effects of glucagonlike peptide I-(7-36)-amide (truncated GLP-I) and gastric inhibitory polypeptide (GIP) on insulin and glucagon release from isolated perfused pancreases of diabetic rats (12-14 wk of age, mean +/- SE fasting plasma glucose 8.9 +/- 0.6 mM, n = 25) after an injection of 90 mg/kg streptozocin on the 2nd day after birth and compared the results with those of nondiabetic control rats. In diabetic rats, the infusion of 1 nM GLP-I or GIP in perfusates with varying glucose concentrations (2.8, 5.6, 8.3, 11.1, or 22.2 mM) caused a nearly equal degree of insulin stimulation from a similar basal insulin level. Meanwhile, basal and GLP-I- or GIP-stimulated insulin release increased in correlation with the ambient glucose concentration in nondiabetic rats. The degree of stimulation of insulin release at glucose concentrations of 5.6 mM in diabetic rats was approximately 33% that of nondiabetic rats. The stimulation potency was the same between GLP-I and GIP. The insulin treatment for diabetic rats (5 U/kg NPH insulin at 0900 and 2100 for 6 days) brought only a slight improvement in the glucose dependency of GLP-I-stimulated insulin release. The effects of GLP-I and GIP on glucagon release were completely opposite. GLP-I suppressed release; GIP stimulated it. In diabetic rats, the degree of suppression by GLP-I and stimulation by GIP were almost the same with similar basal glucagon levels in the perfusate with varying glucose concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)     

Underdiagnosis of diabetes mellitus in chronic dialysis patients on the renal transplant waiting list

In diabetic patients long-term patient and graft survival after renal transplantation is reduced compared to nondiabetic graft recipients. Incidence and prevalence of diabetic patients on dialysis is rising continuously; however, there is a surprisingly low prevalence of patients with known diabetes mellitus on our local renal transplant waiting list. In a retrospective study we clarified the underestimation of diabetic dialysis patients on the transplant waiting list. Our local waiting list includes 46 diabetic patients among 377 (12.2%) candidates. Nine patients had type 1 diabetes and 37 type 2 diabetes. Surprisingly, only 20 of 37 patients (ie, 54%) were initially (at the time of wait-listing) classified as (type 2 diabetes mellitus). Primary renal disease in these 17 diabetic patients was classified in only eight patients, whereas the remaining nine were considered as chronic glomerulonephritis (not biopsy-proven and diabetic nephropathy not excluded). We conclude that among uremic patients on the renal transplant waiting list, the prevalence of diabetes mellitus and the number of patients with diabetic nephropathy are notably underdiagnosed.     

Effects of Opuntia megacantha leaves extract on renal electrolyte and fluid handling in streptozotocin (STZ)-diabetic rats.

We previously demonstrated that Opuntia megacantha leaves' extracts can reduce blood glucose levels in diabetes mellitus. For O. megacantha leaves' extracts to have potential in the management of diabetes mellitus, it is necessary to establish its detailed effects on renal function since diabetes is associated with renal fluid and electrolyte disturbances. Therefore, the current study was designed to investigate the influence of the extracts on renal function in male diabetic Sprague-Dawley rats. Rats were made diabetic by an i.p. injection of streptozotocin (STZ, 60 mg/kg in citrate buffer). Vehicle injected animals acted as controls. Separate groups of nondiabetic and diabetic rats were orally administered O. megacantha leaves extracts (20 mg/100 g bw) or normal saline (0.1 ml x 100 g(-1) bw) daily for 5 weeks. Urine volume and total urinary outputs of Na+ and K+ were determined from 24 h samples. O. megacantha leaves' extracts significantly (p < 0.01) increased urinary Na+ output in diabetic and nondiabetic rats resulting in significantly (p < 0.01) low plasma concentration by comparison with untreated animals. Treatment with the extract significantly increased FE(Na+) and GFR in all groups. The urinary K+ outputs in nondiabetic was slightly lowered, but did not reach statistically significance. O. megacantha leaves' extracts did not alter plasma aldosterone and AVP concentrations in diabetic and nondiabetic rats in nondiabetic animals. It is concluded that O. megacantha leaves extracts modulate renal water and sodium handling. The mechanisms are not clear.