The effect of intravenous insulin infusion on kidney function in insulin-dependent diabetes mellitus

Mechanisms of Diabetic Nephropathy Not Mediated by Hyperglycemia

Diabetes mellitus (DM) is characterized by the appearance of progressive kidney damage, which may progress to end-stage kidney disease. The control of hyperglycemia is usually not sufficient to halt this progression. The kidney damage is quantitatively and qualitatively different in the two forms of diabetes; the typical nodular fibrosis (Kimmelstiel Wilson nodules) appears mostly in type 1 DM, whereas glomerulomegaly is primarily present in type 2 obese DM. An analysis of the different metabolites and hormones in type 1 and type 2 DM and their differential pharmacological treatments might be helpful to advance the hypotheses on the different histopathological patterns of the kidneys and their responses to sodium/glucose transporter type 2 inhibitors (SGLT2i).

The Association of Background Medications on Initial eGFR Change and Kidney Outcomes in Diabetic Patients Receiving SGLT2 Inhibitor

BACKGROUND

To determine whether background medications modify the effects of sodium-glucose cotransporter-2 inhibitor (SGLT2i) on the eGFR and kidney outcomes among patients with type 2 diabetes.

METHODS

We used medical data from a multicenter health care facility in Taiwan and included 10,071 patients who received SGLT2i treatment from June 1, 2016, to December 31, 2018. Direct comparisons for use versus no use of specific background drugs were conducted after adjusting for baseline characteristics through propensity score matching. Patients were followed up until the occurrence of composite kidney outcomes (two-fold increase in the serum creatinine level or the development of end-stage kidney disease), mortality, or the end of the study period.

RESULTS

Patients exhibited an initial mean (SEM) decline of -2.72 (0.10) ml/min per 1.73 m 2 in eGFR dip from baseline to a mean treatment duration of 8.1±3.1 weeks after SGLT2i initiation. The eGFR trajectory stabilized 24 weeks after SGLT2i treatment with a mean (SEM) slope of -1.36 (0.25) ml/min per 1.73 m 2 per year. Compared with no drug use, the use of background renin-angiotensin inhibitor ( n =2073), thiazide diuretics ( n =1764), loop diuretics ( n =708), fenofibrate ( n =1043), xanthine oxidase inhibitor ( n =264), and insulin ( n =1656) was associated with a larger initial decrease in eGFR, while background metformin treatment ( n =827) was associated with a smaller initial decrease in eGFR after SGLT2i treatment. The only drugs associated with the long-term composite kidney outcome during SGLT2i treatment were renin-angiotensin inhibitor (hazard ratio [HR], 0.61; 95% confidence interval [CI], 0.40 to 0.95) and loop diuretics (HR, 1.88; 95% CI, 1.19 to 2.96).

CONCLUSIONS

Several background medications were associated with the initial eGFR dip after SGLT2i initiation. Most drugs were not associated with long-term composite kidney outcomes among patients treated with SGLT2i, except for renin-angiotensin system inhibitor associated with favorable outcomes and loop diuretics associated with worse composite kidney outcomes.

Blockade of the renin-angiotensin system and renal tissue oxygenation as measured with BOLD-MRI in patients with type 2 diabetes

AIM

To assess whether blockade of the renin-angiotensin system (RAS), a recognized strategy to prevent the progression of diabetic nephropathy, affects renal tissue oxygenation in type 2 diabetes mellitus (T2DM) patients.

METHODS

Prospective randomized 2-way cross over study; T2DM patients with (micro)albuminuria and/or hypertension underwent blood oxygenation level-dependent magnetic resonance imaging (BOLD-MRI) at baseline, after one month of enalapril (20 mgqd), and after one month of candesartan (16 mgqd). Each BOLD-MRI was performed before and after the administration of furosemide. The mean R₂* (=1/T₂*) values in the medulla and cortex were calculated, a low R₂* indicating high tissue oxygenation.

RESULTS

Twelve patients (mean age: 60 ± 11 years, eGFR: 62 ± 22 ml/min/1.73 m(2)) completed the study. Neither chronic enalapril nor candesartan intake modified renal cortical or medullary R₂* levels. Furosemide significantly decreased cortical and medullary R₂* levels suggesting a transient increase in renal oxygenation. Medullary R₂* levels correlated positively with urinary sodium excretion and systemic blood pressure, suggesting lower renal oxygenation at higher dietary sodium intake and blood pressure; cortical R₂* levels correlated positively with glycemia and HbA1c.

CONCLUSION

RAS blockade does not seem to increase renal tissue oxygenation in T2DM hypertensive patients. The response to furosemide and the association with 24 h urinary sodium excretion emphasize the crucial role of renal sodium handling as one of the main determinants of renal tissue oxygenation.

Salt sensitivity of nitric oxide generation and blood pressure in mice with targeted knockout of the insulin receptor from the renal tubule

To elucidate the role of the insulin receptor (IR) on kidney nitric oxide generation and blood pressure (BP) control, we generated mice with targeted deletion of renal tubule IR using loxP recombination driven by a Ksp-cadherin promoter. Male knockout (KO) and wild-type (WT) littermates (~4 mo old) were transitioned through three 1-wk treatments: 1) low-NaCl diet (0.085%); 2) high-NaCl diet (HS; 5%); and 3) HS diet plus 3 mM tempol, a superoxide dismutase mimetic, in the drinking water. Mice were then switched to medium-NaCl (0.5%) diet for 5 days and kidneys harvested under pentobarbital anesthesia. Twenty-four-hour urinary nitrates plus nitrites were significantly higher in the WT mice under HS (2,067 ± 280 vs. 1,550 ± 230 nmol/day in WT and KO, respectively, P < 0.05). Tempol attenuated genotype differences in urinary nitrates plus nitrites. A rise in BP with HS was observed only in KO mice and not affected by tempol (mean arterial pressure, dark period, HS, 106 ± 5 vs. 119 ± 4 mmHg, for WT and KO, respectively, P < 0.05). Renal outer medullary protein levels of nitric oxide synthase (NOS) isoforms by Western blot (NOS1-3 and phosphorylated-S1177-NOS3) revealed significantly lower band density for NOS1 (130-kDa isoform) in the KO mice. A second study, when mice were euthanized under HS conditions, confirmed significantly lower NOS1 (130 kDa) in the KO, with an even more substantial (>50%) reduction of the 160-kDa NOS1 isoform. These studies suggest that the loss of renal IR signaling impairs renal nitric oxide production. This may be important in BP control, especially in insulin-resistant states, such as the metabolic syndrome.

Long-term follow-up of patients with type 1 diabetes transplanted with neonatal pig islets

Pancreas transplantation is an option to achieve better metabolic control and decrease chronic complications in patients with diabetes. Xenotransplantation becomes an important alternative. In this study, we show the clinical outcome of patients with type 1 diabetes transplanted with neonatal pig islets without immunosuppression. In a longitudinal study of 23 patients with type 1 diabetes, who received porcine islets between 2000 and 2004, we registered demographic and clinical characteristics every 3 months and chronic complications evaluation yearly. Porcine C-peptide was measured in urine samples under basal conditions and after stimulation with l-arginine. More than 50% were female, median current age was 20·8 years, median diabetes duration at transplantation 5·5 years, median current diabetes duration 11 years and median time post-transplantation 5·7 years. Their media of glycosylated haemoglobin reduced significantly after the first transplantation. Insulin doses remain with a reduction greater than 33% in more than 50% of the patients. Before transplantation, 14 of the 21 patients presented mild chronic complications and currently only two patients presented these complications. Porcine C-peptide was present in all urine samples under basal conditions and increased post-stimulation with l-arginine. These patients achieved an excellent metabolic control after the first transplantation. This could explain, as well as the remaining function of transplanted cells, the low frequency of chronic complications compared to patients with similar diabetes duration and age.

Serum C peptide level and renal function in diabetes mellitus

C peptide is an active peptide hormone with potentially important physiological effects. C peptide has the capacity to diminish glomerular hyperfiltration and reduce urinary albumin excretion in both experimental and human type 1 diabetes. The present study is aimed at correlating the serum C peptide level with that of renal clearance, urinary albumin excretion and duration of diabetes. This is a prospective cross sectional study. Patients with diagnosis of type 2 diabetes mellitus were evaluated for their baseline clinical and laboratory profile. Both males and females above the age of 18 years were included in the study. The laboratory investigations include fasting serum C peptide, HbA(1C), serum creatinine, blood urea nitrogen, urine albumin and creatinine. Creatinine clearance was calculated using modification of diet in renal disease formula from serum creatinine value. A total of 168 patients were included in the study, among them 90 were females (53.57%) and 78 males (46.43%). Mean age of the patients was 57.64 years. Pearson correlation test showed negative correlation of serum C peptide level with creatinine clearance, though statistically not significant. Negative correlation was also seen between serum C peptide, and urine albumin, urine albumin creatinine ratio, HbA(1C) and duration of diabetes. Mean urine albumin was higher in patients with subnormal C peptide level. Duration of disease was more in patients with lower serum C peptide level. The study has shown weak association of serum C peptide level with microalbuminuria and creatinine clearance. Risk of albuminuria is more in patients with low serum C peptide level.

Reduction of glomerular hyperfiltration by dopamine D(2)-like receptor blockade in experimental diabetes mellitus

BACKGROUND

Dopamine D(2)-like receptors are involved in the physiological response of renal haemodynamics to amino-acid infusion. The present study was performed to investigate whether domperidone, a D(2)-like receptor antagonist, modulates the pathological hyperfiltration in experimental diabetes mellitus.

METHODS

Renal function was studied in anaesthetized rats 2 weeks after induction of moderate diabetes mellitus by streptozotocin, and in non-diabetic controls. Rats in both groups continuously received domperidone or vehicle via drinking water. Following infusion of Ringer's saline for measurement of baseline values, an i.v. amino-acid load was applied to investigate the renal functional reserve.

RESULTS

In vehicle-treated diabetic rats baseline glomerular filtration rate and renal plasma flow were significantly higher compared with controls (1.10+/- 0.04 vs. 0.83+/-0.02 (P<0.004) and 4.83+/-0.26 vs 3.32+/-0.24 ml/min/100 g body weight (bw) (P<0.001) respectively). Domperidone completely normalized glomerular filtration rate and renal plasma flow in diabetic rats to values observed in vehicle-treated controls (0.81+/-0.07 (P=0.740) and 3.35+/- 0.30 ml/min/100 g bw (P=0.889) respectively). In the clearance experiments, arterial blood pressure, urinary flow rate and sodium excretion did not significantly differ when comparing the four groups. However, in conscious rats, urinary flow rate and sodium excretion were significantly higher in diabetic rats compared with non-diabetic controls. In both non-diabetic groups, amino-acid infusion induced a significant glomerular hyperfiltration that was completely absent in diabetic rats, and restored by domperidone treatment. In conscious vehicle-treated diabetic rats urinary albumin excretion was enhanced (449.0+/-47.7 vs. 185.7+/- 18.1 microg/24 h in non-diabetic rats (P<0.001)) and significantly lowered in diabetic rats by domperidone treatment (109.8+/-15.4 microg/24 h (P<0.001)).

CONCLUSION

The data suggest that dopaminergic mechanisms are involved in the changes in renal haemodynamics during early experimental diabetes mellitus in rats.

Relaxing effect of insulin in renal arteries from diabetic rats

Abnormal renal vasomotor tone exists in the early stages of diabetes mellitus. Insulin has been proposed to modulate renal function and to possess vasodilatory effects. The present study was initiated in order to evaluate the direct effect of insulin on isolated renal arteries. Twelve insulin-treated streptozotocine diabetic rats with diabetes for 50 days were compared with 15 weight-matched control rats. The contractile responses to 60 mM K+ and 10(-4) M noradrenaline, and the insulin- (0.8-6.4 I.U./ml) induced relaxation of vessels precontracted with noradrenaline, were similar in diabetic and control rats. There was a tendency towards greater relaxation in diabetic (71%) than in control rats (54%). Nw-nitro-L-arginine methyl ester (L-NAME) (10(-4) M) given before noradrenaline tended to attenuate the insulin-induced relaxation, while addition of L-arginine (10(-6) M) to L-NAME attenuated the relaxation in diabetic but increased it in control rats (P < 0.05). The effect of insulin was tested further in control rats and was not influenced by administration of a single dose (10(-6) M) of indomethacin or propranolol given instead of L-NAME. The effect of a single dose of methylene-blue, given before noradrenaline, was tested in control rats in varying doses between 2 x 10(-6) and 2 x 10(-4) M. In the highest concentration it made no difference whether insulin was given or not and there was a similar relaxing effect in diabetic and control arteries. In conclusion, the present study showed that insulin per se has a relaxing effect on renal arteries. There was a tendency to greater relaxation in diabetic than in control rats, an effect which was attenuated by in-vitro-pretreatment with L-NAME as well as with L-NAME and L-arginine in diabetic vessels, while relaxation was increased in control vessels. This may indicate that the effect of insulin may be mediated through nitric oxide in diabetic but not in control rats. The effects of insulin in control vessels were not modified in vitro by indomethacin, propranolol or methylene-blue.

Treatment with acarbose, an alpha-glucosidase inhibitor, reduces increased albumin excretion in streptozotocin-diabetic rats

1. We examined the effect of the alpha-glucosidase inhibitor acarbose on urinary albumin excretion (UAE) in streptozotocin diabetic rats. 2. Treatment with acarbose for 8 weeks after induction of diabetes prevented the significant increase in UAE observed in untreated diabetic rats relative to nondiabetic controls. 3. Acarbose significantly reduced integrated glycemia, which correlated with albumin excretion rates, and exerts a salutary effect on diabetic renal dysfunction.

Does C-peptide have a physiological role?

Short-term administration of physiological amounts of C-peptide to patients with insulin-dependent diabetes was found to reduce the glomerular hyperfiltration in these patients as well as augment whole body glucose utilization. It could also be shown that C-peptide administration increases blood flow, oxygen uptake and capillary diffusion capacity of exercising forearm muscle in IDDM patients, probably by increasing capillary recruitment in the working muscle. Studies under in vitro conditions have shown that C-peptide stimulates glucose transport in skeletal muscle with its maximal effect within the physiological concentration range. The findings in a clinical study in which IDDM patients were given C-peptide and insulin or insulin alone for 4 weeks in a double-blind randomized study design, indicate that C-peptide improves renal function by reducing urinary albumin excretion and glomerular filtration, decreases blood retinal barrier leakage and improves metabolic control. Preliminary findings suggest that C-peptide administration on a short-term basis (3h) may ameliorate autonomic neuropathy by restoring to near normal the heart rate variability in response to expiration and inspiration. Insight into a possible mechanism of action of C-peptide is provided by the finding that C-peptide stimulates Na+K(+)-ATPase activity in renal tubular segments. In conclusion, the present results suggest that, contrary to the prevailing view, C-peptide possesses important physiological effects.

Impact of initial treatment on renal function in newly-diagnosed type 2 (non-insulin-dependent) diabetes mellitus

The impact of improved glycaemic control on renal function in newly-presenting Type 2 (non-insulin-dependent) diabetic patients has not been adequately researched. Consequently, glomerular filtration rate and effective renal plasma flow and urinary albumin excretion rates were determined in 76 subjects (age (mean (SD)): 54 (9.5) years; 50 male) of an original cohort of 110 newly-presenting normotensive non-proteinuric Type 2 diabetic patients following 6 months treatment with diet alone (n = 42) or with oral hypoglycaemic agents (n = 34). Significant reductions were observed in (presentation vs 6 months): body mass index (p < 0.001); fasting plasma glucose (p < 0.001); glycated haemoglobin (HbA1) (p < 0.001); systolic blood pressure (p < 0.01); and diastolic blood pressure (p < 0.001). Glomerular filtration rate declined from 117 (22) to 112 (21) ml.min-1 (p < 0.01), with unchanged effective renal plasma flow (534 (123) vs 523 (113) ml.min-1) and filtration fraction (22.4 (3.0) vs 21.8 (3.4)%). Albumin excretion rate (median (range)) declined from 1.1 (0.1-34.7) to 0.5 (0.1-29.9) micrograms.min-1 (p < 0.01). Changes in glomerular filtration rate (delta values) were inversely correlated with presentation values (p < 0.001), and positive relationships were observed with delta effective renal plasma flow (p < 0.01), and delta glycated haemoglobin (p < 0.05). Type 2 diabetic patients with glomerular filtration rate values at presentation over 120 ml.min-1 demonstrated significant reduction in glomerular filtration rate (n = 31; p < 0.001), whilst those with original values less than 120 ml.min-1 remained unchanged (n = 45).(ABSTRACT TRUNCATED AT 250 WORDS)

Urinary protein/creatinine index in follow up of patients with Wilms' tumour after nephrectomy

The protein/creatinine index (p/c) was determined in early morning urine (EMU) samples from available patients with Wilms' tumour who had had a nephrectomy and whose diagnosis had been made between January 1970 and December 1989. Clinical details were obtained by case note review. Results were obtained from 36 boys and 40 girls. The mean interval between nephrectomy and measurement of the EMUp/c was 9.0 years (2-23). Eleven patients had a EMUp/c greater than 20 mg/mmol (normal range less than 20). Of the 11 patients with proteinuria, there were in addition to nephrectomy other adverse features including bilateral tumours, treatment with nephrotoxic drugs, and dysplastic kidneys. Renal dysfunction seems most likely to occur where there are adverse factors in addition to unilateral nephrectomy. There was a significant correlation between the glomerular filtration rate and the EMUp/c, and it is thought that this is a simple tool which can be used for the regular monitoring of renal function in these patients.

The influence of human C-peptide on renal function and glucose utilization in type 1 (insulin-dependent) diabetic patients

The possible influence of C-peptide administration on renal function and whole body glucose utilization was examined in 11 patients (Group 1) with Type 1 (insulin-dependent) diabetes mellitus. They were given an i.v. insulin infusion during the night before the study and were euglycaemic at the time of examination. The glomerular filtration rate and effective renal plasma flow were measured by clearance techniques using constant-rate infusions of inulin and sodium para-aminohippurate. After baseline measurements C-peptide was infused during two periods of 60 min at rates of 5 and 30 pmol.kg-1.min-1. In a control study 0.9% NaCl was infused during two 60 min periods in ten Type 1 diabetic patients (Group 2). Glomerular filtration rate decreased by 7% (p less than 0.001), effective renal plasma flow increased by 3%, (p less than 0.05) and whole-body glucose utilization rose by approximately 25% (p less than 0.05) above basal during low-dose C-peptide infusion. Group 2 showed an unaltered glomerular filtration rate, effective renal plasma flow and glucose utilization during 60 min of NaCl infusion. The differences between Group 1 and Group 2 in glomerular filtration rate and glucose utilization were statistically significant. It is concluded that short-term administration of C-peptide in physiological amounts to patients with Type 1 diabetes may reduce the glomerular filtration rate and increase whole-body glucose utilization. The results suggest the possibility that short-term C-peptide administration may exert a regulatory influence on renal function and stimulate glucose utilization in Type 1 diabetic patients.

Control of glomerular hypertension by insulin administration in diabetic rats

Micropuncture studies were performed in Munich Wistar rats made diabetic with streptozotocin and in normal control rats. Diabetic rats received daily ultralente insulin to maintain moderate hyperglycemia (approximately 300 mg/dl). Group 1 diabetic rats studied after routine micropuncture preparation exhibited elevation of the single nephron glomerular filtration rate (SNGFR) due to increases in the glomerular transcapillary hydraulic pressure difference and glomerular plasma flow rate. In group 2 diabetic rats infusion of insulin to achieve acute blood glucose control normalized the glomerular transcapillary pressure gradient while increasing the glomerular ultrafiltration coefficient, so that SNGFR remained elevated. Persistent elevation of SNGFR despite normalization of the transcapillary pressure gradient was also observed in group 3 diabetic rats infused with insulin plus sufficient dextrose to maintain hyperglycemia. These studies indicate that glomerular capillary hypertension in diabetes is an acutely reversible consequence of insulin deficiency and not the result of renal hypertrophy.

Nephropathy in non-insulin-dependent diabetes mellitus

End-stage renal disease develops in about 5 percent of patients with non-insulin-dependent diabetes mellitus (NIDDM). The large majority of diabetic patients have this form of the disease. Thus, end-stage renal disease is an important clinical problem in patients with NIDDM. Moreover, hypertension and its macrovascular sequelae are significant problems in patients with NIDDM and may be linked with renal disease. A review of the problem of nephropathy in NIDDM is attempted, pointing out, where data are available, the clinical and pathophysiologic differences from its presentation in insulin-dependent diabetes. The need for further studies of the impact of renal disease in this maturity onset form of diabetes is emphasized.

Tubular dysfunction and microalbuminuria in insulin dependent diabetes

The nature of microproteinuria in the early years of insulin-dependent diabetes was investigated in a cross sectional study of 80 children with insulin-dependent diabetes and 40 normal children. Urinary excretion of three low molecular weight proteins: alpha-1-microglobulin, beta-2-microglobulin and kappa light chains was used as an index of proximal renal tubular function. The first urine samples of the morning were collected and excretion of proteins measured was expressed as ratio of protein to creatinine. There was a strong correlation between excretion of alpha-1-microglobulin and chi light chains and their excretion was significantly higher in diabetic children indicating decreased proximal tubular reabsorbtion. The excretion of beta-2-microglobulin was found to be an unsatisfactory index of proximal tubular function. Urinary albumin excretion was not significantly raised in diabetic children and did not correlate with urinary alpha-1-microglobulin or chi light chain excretion. Glycaemic control might influence proximal tubular function as both urinary glucose concentration and glycosylated haemoglobin showed correlations with urinary alpha-1-microglobulin excretion and with urinary chi light chain excretion.

Prognostic implications of renal hypertrophy in diabetes mellitus

Early in the course of type 1 diabetes mellitus, hypertrophy of the kidney is a consistent finding that is easily diagnosed using current noninvasive methods, especially ultrasonography. Renal functional changes occur in association with hypertrophy, most notably glomerular hyperfiltration. The structural counterpart of this functional change is an early increase in capillary filtration surface area. In most forms of nondiabetic renal hypertrophy, kidney size is closely linked to GFR. In contrast, in diabetes, persistence of hypertrophy after the clinical onset of overt kidney disease (microalbuminuria, hypertension, decreased GFR, etc.) suggests that sustained release of one or more growth factors may continue even after kidney function declines. The fact that growth factors can act in both an autocrine and paracrine fashion raises the possibility that the local effects of such substances may act as local mediators of kidney growth. Failure of renal hypertrophy to reverse following strict glycemic control for a few months may turn out to be an important prognostic indicator of future progression of the renal disease, but this remains to be established. Prospective studies of kidney size in patients with newly diagnosed type 1 diabetes, using accurate noninvasive methods, may be helpful in establishing whether irreversible ("autonomous") hypertrophy of the kidney is indeed a useful prognostic indicator. As therapies are developed that target the different microvascular complications of diabetes (retinopathy, nephropathy, neuropathy), a noninvasive estimation of kidney size may be a cost-effective method of predicting ultimate renal involvement. Since microalbuminuria occurs relatively late in the disease process, early and persistent hypertrophy of the kidney may become a useful prognostic test in the earliest stages of the disease.

Pathogenesis of diabetic glomerulopathy: hemodynamic considerations

Early stages of diabetes mellitus are characterized by glomerular hyperfiltration in humans and experimental animals. In diabetic rats, single nephron hyperfiltration results from elevations in the glomerular capillary plasma flow rate and hydraulic pressure, which are in turn associated with progressive albuminuria and morphologic injury. Interventions that ameliorate these hemodynamic adaptations afford protection against structural injury. Dietary protein restriction, which lowers glomerular filtration, perfusion, and hydraulic pressure, retards glomerular injury and limits capillary basement membrane thickening in both the glomerular and retinal circulatory beds. Alternatively, selective control of glomerular capillary hypertension using angiotensin I converting enzyme inhibitor therapy limits glomerular injury in this model as well. Each of these interventions is effective even in the absence of improved metabolic control, implying that hemodynamic factors per se are important in this pathogenic process. The pathophysiologic mechanisms of diabetic hyperfiltration remain incompletely elucidated. Recent studies invoke a potential role for atrial natriuretic peptide (ANP). Strict metabolic control abolishes the elevations of glomerular filtration rate and of plasma ANP levels in moderately hyperglycemic diabetic rats. Moreover, infusion of a specific ANP antibody reverses hyperfiltration in diabetic rats. Thus, hyperglycemia-induced chronic volume expansion may trigger ANP release, which in turn contributes to diabetic hyperfiltration. Hemodynamic factors may play an important role in the pathogenesis of extrarenal microangiopathy as well. Elevated peripheral capillary blood flows and/or hydraulic pressure may be found in many peripheral capillaries, in association with thickening of the capillary basement membrane. Dietary protein restriction, which lowers blood flow to many organs, limits retinal as well as glomerular basement membrane thickening in diabetic rats, suggesting that hemodynamically mediated structural injury is a diffuse phenomenon in the diabetic state.

Hyperglycemia with and without glycosuria: effect on inulin and para-amino hippurate clearance

The response of the clearance of inulin (Cin) and para-amino hippurate (CPAH) to acute hyperglycemia with and without glycosuria was investigated in ten, healthy non-diabetic subjects. Standard methodology (UV/P) was used, with a mean clearance calculated from three, 15-minute urine collection periods. Each subject was studied at three levels of blood glucose (mmol/liter) concentration, mean (SE): Level 1, fasting, 4.5 (0.1); Level 2, hyperglycemia below renal threshold for glucose, 7.2 (0.1); Level 3, hyperglycemia with glycosuria, 12.6 (0.5). There was a significant rise in mean Cin (ml/min/1.73 m2) when changing from Level 1 (112[3]) to Level 2 (121[5]), with no further increase on changing to Level 3 (122[4]). With glycosuria Cin fell in some subjects. Mean CPAH (ml/min/1.73 m2) increased through Level 1 (560[27]) to Level 3 (603[34]), with consequently no change in mean filtration fraction at the three levels of glycemia. Our observations show a rise in glomerular filtration rate with mild hyperglycemia below renal threshold, with no further increase during hyperglycemia sufficient to produce glycosuria.

Elevated plasma atrial natriuretic peptide levels in diabetic rats. Potential mediator of hyperfiltration

Infusion of atrial natriuretic peptide (ANP) increases the glomerular filtration rate (GFR), and ANP is released from cardiac myocytes in response to extracellular fluid volume expansion. Since diabetes mellitus is associated with glomerular hyperfiltration and volume expansion, we investigated the relationship between ANP and GFR in diabetic rats given insulin to achieve stable moderate hyperglycemia or normoglycemia. At 2 wk after induction of diabetes, moderately hyperglycemic diabetic rats exhibited elevations of plasma ANP levels averaging 281 +/- 28 pg/ml vs. 158 +/- 15 pg/ml in normoglycemic diabetic rats. In hyperglycemic rats, the GFR was also elevated on average to 2.24 +/- 0.28 ml/min as compared with 1.71 +/- 0.13 ml/min in normoglycemic diabetic rats. To test further the relationship between ANP and GFR in diabetes, moderately hyperglycemic diabetic rats were infused either with a specific ANP antiserum or with nonimmune serum. The infusion of specific ANP antiserum uniformly reduced the GFR on average from 2.38 +/- 0.1 ml/min to 1.60 +/- 0.1 ml/min, whereas the infusion of nonimmune serum was without effect. It is concluded that elevated endogenous ANP levels contribute to the hyperfiltration observed in early diabetes in the rat.

Increased prostaglandin production by glomeruli isolated from rats with streptozotocin-induced diabetes mellitus

Abnormalities in glomerular function have been observed frequently in the early stages of both clinical and experimental diabetes mellitus. Because prostaglandins (PGs) are present in the glomerulus and have profound effects on glomerular hemodynamics, and because abnormalities of PG metabolism have been noted in other tissues from diabetics, we studied PG biosynthesis in glomeruli obtained from rats in the early stages of experimental diabetes mellitus. Streptozotocin, 60 mg/kg, was administered intravenously to male Sprague-Dawley rats. Control rats received an equal volume of the vehicle. Glomeruli were isolated 9-23 d later. Production of eicosanoids was determined by two methods: by direct radioimmunoassay after incubation of glomeruli under basal conditions and in the presence of arachidonic acid (C20:4), 30 microM, and by radiometric high-performance liquid chromatography (HPLC) after incubation of glomeruli with [14C]C20:4. When assessed by radioimmunoassay, mean basal production of both prostaglandin E2 (PGE2) and prostaglandin F2 alpha (PGF2 alpha) was twofold greater in the diabetic animals whereas production of thromboxane B2 (TXB2) was not significantly greater than control. In response to C20:4, both PGE2 and PGF2 alpha were also greater in the diabetic animals, but these differences were not statistically significant. The increased rate of basal PG production did not appear to be related directly to the severity of the diabetic state as reflected by the degree of hyperglycemia at the time of sacrifice. In fact, the rates of glomerular PG production in the individual diabetic animals correlated inversely with the plasma glucose concentration. The increased rate of PG synthesis did not appear to be due to a nonspecific effect of streptozotocin inasmuch as glomerular PG production was not increased significantly in streptozotocin-treated rats which were made euglycemic by insulin therapy. Furthermore, addition of streptozotocin, 1-10 mM, to the incubation media had no effect on PGE2 production by normal glomeruli. PGE2 production by normal glomeruli was also not influenced by varying the glucose concentration in the incubation media over a range of 1-40 mM. When metabolism of [14C]C20:4 was evaluated by high-performance liquid chromatography conversion to labeled PGE2, PGF2 alpha, TXB2, and hydroxyheptadecatrienoic acid by diabetic glomeruli was two- to threefold greater compared with that in control glomeruli, whereas no significant difference in conversion to 12- and 15-hydroxyeicosatetraenoic acid occurred. These findings indicate that glomerular cyclooxygenase but not lipoxygenase activity was increased in the diabetic animals. A concomitant increase in glomerular phospholipase activity may also have been present to account for the more pronounced differences in PG production noted in the absence of exogenous unlabeled C20:4. These abnormalities in PG biosynthesis by diabetic glomeruli may contribute to the altered glomerular hemodynamics in this pathophysiologic setting.

Sustained reduction of proteinuria in type 2 (non-insulin-dependent) diabetes following diet-induced reduction of hyperglycaemia

To determine whether sustained control of hyperglycaemia in Type 2 (non-insulin-dependent) diabetic patients would diminish proteinuria, the effect of hypocaloric diet therapy (500 kcal/day) on proteinuria was assessed in obese, Type 2 diabetic patients (n = 24) and compared with results obtained for obese subjects with normal glucose tolerance (n = 7) and impaired glucose tolerance (n = 6). Diet therapy of similar mean duration resulted in similar percentage weight loss (mean percentage of original weight +/- SEM) in diabetic (13.6 +/- 1.6%), glucose intolerant (16.4 +/- 3.3%) and obese non-diabetic (11.0 +/- 1.0%) subjects. Following therapy, plasma glucose concentrations 2h after an oral glucose load declined in the diabetic (18.34 +/- 0.81 to 10.67 +/- 0.50 mmol/l, mean +/- SEM; p less than 0.001) and in the glucose intolerant subjects (10.2 +/- 0.3 to 7.3 +/- 0.4 mmol/l, p less than 0.01) while remaining unchanged in the obese non-diabetic subjects (7.09 +/- 0.23 to 6.77 +/- 0.32 mmol/l, NS). Concentrations of total protein of plasma origin and albumin in 24-h urine collections were quantified by a sensitive immunonephelometric assay using specific antisera. Initially, 24-h excretion of total protein and albumin were elevated in the diabetic [mg protein/24 h; (median +/- 95% confidence limits): 63 (42-138), p less than 0.05; albumin: 26 (14-56), p less than 0.05] and glucose intolerant subjects [protein: 52 (13-92), NS; albumin: 24 (3-61), NS] compared with the non-diabetic subjects [protein: 20 (5-38); albumin: 6.2 (3.5-9.5)].(ABSTRACT TRUNCATED AT 250 WORDS)

Kidney function and size in diabetics before and during initial insulin treatment

GFR, RPF, and kidney size were measured in nine young recently diagnosed insulin-dependent diabetics before (days 0) and 3 and 8 days after the beginning of the initial insulin treatment and in comparable control subjects. Kidney function was measured by a constant infusion technique using I-125-iothalamate and 131-I-hippuran. Kidney size was determined by means of ultrasound. Before insulin treatment elevated values for GFR (+44%, P less than 0.01), RPF (+18%, P less than 0.05), and kidney size (+29%, P less than 0.01) were found. Near-normal metabolic control was achieved in all patients using either multiple subcutaneous injections of insulin or an artificial betacell. GFR decreased from 160 +/- 9 SEM to 141 +/- 6 ml/min X 1.73 m2 (P less than 0.01) and further to 133 +/- 5 ml/min X 1.73 m2 (P less than 0.01, compared to day 0). Renal plasma flow was 601 +/- 33 and 588 +/- 44 ml x 1.73 m2 at days 0 and 3, respectively (NS) and decreased to 558 +/- 35 ml/min x 1.73 m2 at day 0 (P less than 0.01). By contrast no statistically significant changes in kidney volume were observed; the results on day 0, 3 and 8 were 145 +/- 7, 162 +/- 11 and 143 +/- 9 ml/1.73 m2, respectively. The present study demonstrates that kidney size and function are elevated at the onset of insulin-dependent diabetes. Near-normal metabolic control; for 8 days induces a reduction but not a complete normalization in kidney function. From the present observations it is suggested that the rapidly reversible part of the elevation in GFR cannot be explained by concomitant changes in kidney and glomerular size (morphological origin) but is probably due to a reduction in renal plasma flow and to a decreased transglomerular pressure (functional origin).

Effect of intravenous glucose infusion on renal function in normal man and in insulin-dependent diabetics

The effect of intravenous glucose infusion on glomerular filtration rate and renal plasma flow (constant infusion technique using 125I-iothalamate and 131I-hippuran) and on urinary excretion of albumin and beta-2-microglobulin were studied in ten normal subjects and seven metabolically well-controlled insulin-dependent diabetics. Following glucose infusion in normal subjects (n = 10) blood glucose increased from 4.7 +/- 0.1 to 10.9 +/- 0.4 mmol/l (SEM) (p less than or equal to 0.01). Glomerular filtration rate increased from 116 +/- 2 to 123 +/- 3 ml/mi x 1.73 m2 (p less than or equal to 0.01), while no change in renal plasma flow was seen - 552 +/- 11 versus 553 +/- 18 ml/min x 1.73 m2. Volume expansion with intravenous saline infusion in six of the normal subjects induced no changes in blood glucose or kidney function. In seven strictly controlled insulin-dependent diabetics, blood glucose values were raised from 4.6 +/- 0.4 to 16.0 +/- 0.6 mmol/l and clamped by means of an 'artificial beta cell'. Glomerular filtration rate increased in all patients, from 133 +/- 5 to 140 +/- 6 ml/min x 1.73 m2 (p less than or equal to 0.02), as did renal plasma flow from 576 +/- 26 to 623 +/- 38 ml/min x 1.73 m2 (p less than or equal to 0.02). Urinary albumin excretion remained unchanged in both normal subjects and diabetics. beta-2-microglobulin excretion rate increased significantly in the diabetics following glucose infusion, while no significant change was seen in the normal subjects. Our results show that hyperglycaemia per se contributes to the increased glomerular filtration rate and renal plasma flow in insulin-dependent diabetes.

Increased kidney size, glomerular filtration rate and renal plasma flow in short-term insulin-dependent diabetics

Glomerular filtration rate (GFR), renal plasma flow (RPF) and kidney volume were measured in thirteen male subjects (mean age 30 years) with short-term insulin-dependent diabetes (mean duration of disease 2.4 years) and fourteen normal male subjects (mean age 29 years). GFR and RPF were measured by constant infusion technique using I125-iothalamate and 131I-hippuran. Kidney size was determined by means of ultrasound. GFR, RPF and kidney volume were increased in the diabetic patients compared to the normal controls, 144 versus 113 ml/min X 1.73 m2 (p less than 0.0005), 627 versus 523 ml/min X 1.73 m2 (p less than 0.0025) and 278 versus 224 ml/1.73 m2 (p less than 0.0005) respectively. Combining results from diabetic patients and controls revealed a positive correlation between kidney size and GFR (r = 0.70, p less than 0.001) and between kidney size and RPF (r = 0.61, p less than 0.001). Within the groups kidney size and RPF correlated significantly in the diabetics (p less than 0.01) and the same was found for kidney size and GFR (0.025 less than p less than 0.05), while no correlations were found in the normal group. GFR and RPF correlated in the diabetics when evaluated separately (r = 0.81, p less than 0.001) and in the controls (r = 0.73, p less than 0.001). The previous and present data suggest that the mechanisms of the elevated GFR in insulin-dependent diabetics are enhanced RPF, increased transglomerular hydrostatic pressure gradient and increased glomerular ultrafiltration coefficient. The increased kidney size is probably the main cause of the above alterations in the GFR determinants.