Effect of nitric oxide inhibition on kidney function in experimental renovascular hypertension

We examined the effect of acute systemic blockade of nitric oxide (NO) synthesis on blood pressure and renal function in rats with angiotensin II dependent two-kidney, one-clip Goldblatt hypertension. Hypertensive animals had significantly higher blood pressures, plasma NO metabolite concentrations and urinary NO metabolite excretion rates than control rats. Intravenous administration of N(G)-nitro-L-arginine methylester (L-NAME) (10 mg/kg) increased mean arterial pressure in both hypertensive and control animals with the magnitude of increase being greater in hypertensive than control rats (32 +/- 3 vs. 20 +/- 2 mmHg, p < 0.05). L-NAME did not affect glomerular filtration rates of normal and clipped kidneys but significantly decreased non-clipped kidney glomerular filtration rate (1.1 +/- 0.1 vs. 0.7 +/- 0.1 ml/min per g kidney wt, p < 0.05). Blood flow to normal and non-clipped kidneys fell in response to L-NAME. Percent reduction in renal blood flow produced by L-NAME was significantly greater in non-clipped than normal kidneys (38 +/- 3 vs. 24 +/- 2%, p < 0.05). In contrast, clipped kidney blood flow increased after L-NAME (3.3 +/- 0.2 vs. 4.0 +/- 0.2 ml/min per g kidney wt, p < 0.05). An identical improvement in clipped kidney blood flow occurred when arterial pressure was raised with aortic constriction indicating that the systemic pressor effect of L-NAME was responsible for this finding. These results indicate that NO plays an important role in systemic and non-clipped kidney hemodynamics in renovascular hypertension. Because NO has little influence on stenotic kidney function, the stimulus for increased NO system activity in this disease appears to be vascular shear stress rather than elevated circulating or intrarenal angiotensin II concentrations.     

Angiotensin II type 2 receptors and nitric oxide sustain oxygenation in the clipped kidney of early Goldblatt hypertensive rats

Angiotensin-converting enzyme inhibitors (ACEIs) decrease the glomerular filtration rate and renal blood flow in the clipped kidneys of early 2-kidney, 1-clip Goldblatt hypertensive rats, but the consequences for oxygenation are unclear. We investigated the hypothesis that angiotensin II type 1 or angiotensin II type 2 receptors or NO synthase mediate renal oxygenation responses to ACEI. Three weeks after left renal artery clipping, kidney function, oxygen (O(2)) use, renal blood flow, renal cortical blood flow, and renal cortical oxygen tension (Po(2)) were measured after acute administration of an ACEI (enalaprilat) and after acute administration of ACEI following acute administration of an angiotensin II type 1 or angiotensin II type 2 receptor blocker (candesartan or PD-123,319) or an NO synthase blocker (N(G)-nitro-L-arginine methyl ester with control of renal perfusion pressure) and compared with mechanical reduction in renal perfusion pressure to the levels after ACEI. The basal renal cortical Po(2) of clipped kidneys was significantly lower than contralateral kidneys (35+/-1 versus 51+/-1 mm Hg; n=40 each). ACEI lowered renal venous Po(2), cortical Po(2), renal blood flow, glomerular filtration rate, and cortical blood flow and increased the renal vascular resistance in the clipped kidney, whereas mechanical reduction in renal perfusion pressure was ineffective. PD-123,319 and N(G)-nitro-L-arginine methyl ester, but not candesartan, reduced the Po(2) of clipped kidneys and blocked the fall in Po(2) with acute ACEI administration. In conclusion, oxygen availability in the clipped kidney is maintained by angiotensin II generation, angiotensin II type 2 receptors, and NO synthase. This discloses a novel mechanism whereby angiotensin can prevent hypoxia in a kidney challenged with a reduced perfusion pressure.     

The Antagonism of Aldosterone Receptor Prevents the Development of Hypertensive Heart Failure Induced by Chronic Inhibition of Nitric Oxide Synthesis in Rats

Summary Aldosterone promotes cardiovascular inflammation and remodeling, both of which are characteristic changes in hypertensive and failing hearts. Since chronic inhibition of nitric oxide (NO) synthase with N^ω-nitro-L-arginine methyl ester (L-NAME) induces systemic hypertension associated with cardiovascular inflammation and remodeling, we examined the potential role of aldosterone in this process using eplerenone, a selective aldosterone receptor antagonist. Ten-week-old male Wistar-Kyoto rats were randomly divided into 3 groups: the control group (no treatment), the L-NAME group (received L-NAME 1 g/L in drinking water), and the L-NAME+Eplerenone group (L-NAME plus eplerenone at 100 mg/kg/day). After 8 weeks of the treatment, the L-NAME group showed significantly higher systolic blood pressure than the control group (198 ± 7 vs. 141 ± 3 mmHg, P < 0.05). Eplerenone did not affect the increase in blood pressure caused by L-NAME (189 ± 12 mmHg). Chronic inhibition of NO synthesis increased the plasma aldosterone concentration and CYP11B2 mRNA in adrenal glands. Cardiac inflammation and fibrosis were detected in the L-NAME group, while both changes were completely prevented by eplerenone. Cardiac hypertrophy was induced in L-NAME group, but was partially prevented by eplerenone. In the L-NAME group, left ventricular fractional shortening (LVFS: 27 ± 2 vs. 38 ± 1%) and E/A ratio (1.7 ± 0.1 vs. 2.1 ± 0.1) were significantly lower and LV end-diastolic pressure (LVEDP) was higher (4.9 ± 0.6 vs. 13.9 ± 0.5 mmHg) without LV enlargement, compared with those in the control group (P < 0.05). Eplerenone completely normalized LVFS (36 ± 2%), E/A ratio (2.2 ± 0.1), and LVEDP (6.2 ± 0.7 mmHg). These results suggest that chronic inhibition of NO synthesis induces cardiac inflammation and dysfunction via an aldosterone receptor-dependent mechanism.     

Effects of Mast-Cell Stabilization in Cerulein-Induced Acute Pancreatitis in Rats

Summary Aim. In this study we aimed to clarify the role of mast cells in the development and progression of inflammation in cerulein-induced acute pancreatitis (AP) in rats. We have also examined the effects of ketotifen; a mast-cell stabilizing agent in the treatment of acute pancreatitis and its relation with nitric oxide (NO) synthesis. Methods. In the first part of the study we planned to examine the effects mast cell stabilization in acute pancreatitis, while the second part was focused on examining the relation between NO synthesis and the potential effects of ketotifen in AP. Wistar albino rats were randomly divided into 6 groups (n: 10). In the first part of the study, AP was induced by four subcutaneous (sc) injections of 20 μg/kg body weight of cerulein at hourly intervals in Groups A and B while Group C was treated with saline as the control group. Group B was pretreated with ketotifen 1 mg/kg (ip). In the second part, the study design was similar except for the inhibition of nitric oxide synthesis by N-nitro L-arginine methyl ester (L-NAME) 30 mg/kg (ip) in Groups D, E and F. Group D was treated with L-NAME and cerulein and Group E was treated with ketotifen, L-NAME and cerulein. Group F was treated with L-NAME and saline as the control group. Serum amylase activity and pancreatic myeloperoxidase activity (MPO) were measured. Pancreatic histology and mast-cell count in pancreatic tissue were evaluated. Results. Mast cell count was found to be increased in the pancreatic tissue in cerulein-induced AP. (2.93±0.26 vs 1.98±0.26; p<0.001). Ketotifen treatment significantly reduced cerulein induced edema (1.30±0.21 vs 0.70±0.15; p<0.001), neutrophil infiltration (1.50±0.16 vs 0.60±0.16; p<0.001) and attenuated the increase in amylase (4394.0±149.5 U/L vs 3350.5±216.9 U/L; p<0.05) and MPO activity (1.14±0.13 U/gr tissue vs 0.54±0.08 U/gr tissue; p<0.001). Mast-cell count in pancreatic tissue was also decreased significantly with ketotifen pretreatment (2.93±0.26 vs 1.70±0.21; p<0.05). Inhibition of NO synthesis with L-NAME treatment decreased the beneficial effects of ketotifen. Conclusion. It seems likely that mast cell activity may play an important role in the initiation and progression of acute pancreatitis. Ketotifen treatment may reduce the severity of AP in rats. The protective action of ketotifen in cerulein-induced acute pancreatitis is most probably owing to mast cell stabilization and stimulation of NO synthesis.     

Intra-uterine environment influences glomerular number and the acute renal adaptation to experimental diabetes

Aims/hypothesis. We sought to test the hypothesis of whether low birth weight rats would have reduced glomerular number, higher systolic blood pressure and an altered acute response to streptozotocin diabetes compared to normal birth weight rats. Methods. Female offspring of Wistar rats fed an isocaloric diet containing either 6 % casein (LPD) or 18 % casein (NPD) in utero were studied. Birth weight, body weight, systolic blood pressure and urine albumin excretion were measured before and after streptozotocin diabetes. Glomerular number and volume were estimated after one week of diabetes. Results. The LPD rats were of low birth weight (5.4 ± 0.5 g vs 6.4 ± 0.8 g, p < 0.0001) with higher systolic blood pressure (137 ± 9 mmHg vs 120 ± 7 mmHg, p < 0.0001) and reduced glomerular number (17 435 ± 2074 vs 24 846 ± 1864, p < 0.0001). The LPD rats had smaller kidneys (0.925 ± 0.009 g vs 1.200 ± 0.173 g, p = 0.041) but similar glomerular volume to NPD control rats (1.11 ± 0.15 · 10⁶μm³ vs 1.08 ± 0.17 · 10⁶μm³). After 1 week of diabetes LPD rats had a greater proportional increase in renal size (diabetes 50 ± 12 % vs control 20 ± 4 %, p = 0.003). Insulin suppressed renal hypertrophy in both LPD and NPD rats but failed to suppress glomerular hypertrophy in LPD rats (1.48 ± 0.21 · 10⁶μm³ vs 1.03 ± 0.23 · 10⁶μm³ p = 0.015). Conclusion/interpretation. Abnormal intra-uterine environment reduces both renal size and glomerular number and influences the acute renal adaptation to experimental diabetes. [Diabetologia (2001) 44: 721–728] Received: 25 September 2000 and in revised form: 26 February 2001     

Activity of Angiotensin‐Converting Enzyme After Treatment with L‐Arginine in Renovascular Hypertension

The renin‐angiotensin system plays a role in the pathophysiology of renovascular hypertension. In addition, some studies have demonstrated a beneficial effect of L‐arginine (L‐Arg), the precursor of nitric oxide (NO), in this model of hypertension. This study was designed to investigate the effects of L‐Arg on cardiovascular parameters and on the activity of the angiotensin‐converting enzyme (ACE), after 14 days of renovascular hypertension. The experiments were performed on conscious male Wistar rats. Two‐kidney, one‐clip renovascular hypertension (2K1C) was initiated in rats by clipping the left renal artery during 14 days, while control rats were sham‐operated. One group was submitted to a similar procedure and treated with L‐Arg (10 mg/ml; average intake of 300mg/day) from the 7th to the 14th day after surgery, whereas the respective control group received water instead. At the end of the treatment period, the mean arterial pressure (MAP) was measured in conscious animals. The rats were sacrificed and the ACE activity was assayed in heart and kidneys, using Hip‐His‐Leu as substrate. In a separate group, the heart was removed, the left ventricle (LV) was weighed and the LV/body weight ratios (LV/BW) were determined. We observed significant differences in MAP between the L‐Arg‐treated and untreated groups (129 ± 7 vs. 168 ± 6 mmHg; P < 0.01). The cardiac hypertrophy described for this model of hypertension was attenuated in the 2K1C‐L‐Arg‐treated group (14th day, wet LV/BW: 2K1C‐L‐Arg = 1.88 ± 0.1; 2K1C = 2.20 ± 0.1 mg/g; P < 0.05). L‐Arg administration caused an important decrease in cardiac ACE activity (2K1C‐L‐Arg: 118 ± 15; 2K1C: 266 ± 34 µmol/min/mg; P < 0.01). L‐Arg also decreased the ACE activity in the clipped kidney by 47% (P < 0.01), but not in the nonclipped kidney. These data suggest that increased NO formation and reduced angiotensin II formation are involved in the anthihypertensive effect of orally administered L‐arginine.     

Arterial pressure and renal function in two-kidney, one clip Goldblatt hypertensive rats maintained on a high-salt intake

Arterial blood pressure and renal function of both clipped and non-clipped kidneys of benign two-kidney, one clip (2K1C) Goldblatt hypertension were evaluated in order to determine whether high-salt intake alters the course of the development and magnitude of hypertension or influences renal function. The administration of 0.9% sodium chloride as a drinking solution for 3 weeks suppressed plasma renin activity (PRA) and kidney renin content of the clipped kidney to normal values. Despite suppression of PRA and kidney renin content, the saline-drinking clipped rats still developed hypertension of the same magnitude as the water-drinking clipped rats. However, the onset of hypertension was delayed by 4 days. Urine flow, glomerular filtration rate (GFR) and sodium excretion rate from the clipped kidneys of the saline-drinking clipped rats were higher than the corresponding values in the water-drinking rats, and approached those observed in control animals. Thus, the high-salt intake which was associated with suppression of the activity of the renin-angiotensin system delayed the onset of, but not the final magnitude of, the hypertension. In addition, kidney function in the clipped kidneys of saline-drinking clipped rats was enhanced compared with that observed in the water-drinking clipped rats.     

The Effect of an Angiotensin Converting Enzyme Inhibitor on Skin Microvascular Hyperaemia in Microalbuminuric Insulin-dependent Diabetes Mellitus

Patients with longstanding insulin-dependent (Type 1) diabetes mellitus (IDDM) are reported to have microvascular complications in most capillary beds. The microvascular hyperaemia of the skin in normoalbuminuric and microalbuminuric IDDM patients and healthy volunteers was measured with laser Doppler flowmetry. The effect of 3 and 9 months of treatment with captopril, an angiotensin converting enzyme inhibitor, on hyperaemia in the microalbuminuric patients was studied. Mean (±SD) pretreatment duration of skin postocclusive reactive hyperaemia was longer in microalbuminuric than in both normoalbuminuric patients and healthy volunteers (118.2 ± 34.4 vs 57.8 ± 16.0 vs 63.3 ± 18.3 sec, respectively, p < 0.00001). After 3 and 9 months of captopril treatment the prolonged hyperaemia was shortened to 78.6 ± 45.6 s (p < 0.01) and 62.3 ± 55.6 s (p < 0.03), respectively. Urinary albumin excretion decreased from 63.9 ± 43.5 to 33.4 ± 28.1 mg 24 h⁻¹ at 3 months treatment (p < 0.002) and 43.1 ± 38.5 mg 24 h⁻¹ at the end of the study period (p <0.02). A positive correlation between changes in urinary albumin excretion and the shortening of the skin postocculsive reactive hyperaemia was found. Blood pressure remained in the same range throughout. These results show that captopril affects skin blood flow, independent of its hypotensive effect. This action may reflect the influence of angiotensin converting enzyme inhibitor on vascular beds other than those of the kidneys. © 1997 by John Wiley & Sons, Ltd.     

ETA receptor blockade induces fibrosis of the clipped kidney in two-kidney-one-clip renovascular hypertensive rats

BACKGROUND: In two kidney-one clip renovascular hypertension (2K1C), blood flow is reduced in the clipped kidney leading to ischaemia. The non-clipped kidney is characterized by increased shear stress. Circulating Ang II is elevated. All these factors are stimuli of the paracrine renal endothelin system. Indeed, we demonstrated an activation of the renal endothelin system in the 2K1C rat model. METHODS: We analysed the effects of chronic treatment with the ETA receptor antagonist BQ-123 on blood pressure, heart rate, plasma renin activity, and on the progression of glomerulosclerosis, interstitial fibrosis and vascular remodeling in the clipped and non-clipped kidney. RESULTS: Long-term treatment with BQ-123 led to a fibrotic atrophy of the clipped kidney characterized by a significantly reduced weight of the clipped kidney compared to the clipped kidney of the placebo-treated group. Computer-aided image analysis revealed a markedly enhanced interstitial fibrosis of these clipped kidneys after long-term ETA blockade. The effects of ETA receptor antagonists on the non-clipped kidney were less pronounced. Neither blood pressure nor plasma renin activity were significantly altered by BQ-123 treatment. CONCLUSIONS: The present study indicates that long-term blockade of the activated endothelin system in the clipped kidney of rats with renovascular hypertension using an ETA receptor antagonist led to a fibrotic atrophy of the clipped kidney.     

Inhibition of nitric oxide synthesis increases apoptotic cardiomyocyte death and myocardial angiotensin-converting enzyme gene expression in ischemia/reperfusion-injured myocardium of rats

Cardiomyocyte apoptosis is an important pathogenic mechanism in myocardial ischemia/reperfusion (I/R) injury. It has been shown that nitric oxide (NO) and the renin–angiotensin system (RAS) are closely related, and both systems regulate apoptotic cell death. However, the effects of NO modulation on myocardial apoptotic cell death and changes in the RAS in the I/R-injured myocardium have not been studied. Female Sprague–Dawley rats were randomized into three groups: NO synthesis inhibitor, N^G-nitro-l-arginine-methyl ester (l-NAME, 10 mg/kg); NO precursor, l-arginine (540 mg/kg); and vehicle. The rats were then subjected to 45 min coronary occlusion followed by 4 h reperfusion. The TdT-mediated in situ nick and labeling (TUNEL) indices were 39.9% ± 0.8% at the border and 30.9% ± 1.2% at the center of the I/R area in the vehicle group. L-NAME administration significantly increased these TUNEL-positive cells to 45.3% ± 1.9% and 37.9% ± 1.3%, respectively (P < 0.05 each). L-arginine administration reduced the TUNEL index at the border zone with marginal significance (P = 0.08 vs vehicle group). I/R injury significantly reduced the angiotensin-converting enzyme (ACE) mRNA expression in the left (ventricular) free wall of vehicle group rats. However, ACE mRNA expression was 1.9 times greater in the L-NAME group than that in the vehicle group (P < 0.05). This study showed that the inhibition of NO synthesis increased apoptotic cardiomyocyte death and local ACE mRNA expression in the I/R-injured myocardium. Our observations indicate that NO, ACE, and apoptotic cardiomyocyte death are related to each other during I/R injury. Received: July 9, 2001 / Accepted: August 17, 2001     

The effect of intrauterine environment and low glomerular number on the histological changes in diabetic glomerulosclerosis

Aims/hypothesis We tested the hypothesis that diabetic glomerulosclerosis would develop more rapidly in animals with fewer glomeruli. Methods We studied the female offspring of Wistar rats that had been fed a low-protein diet (LPD) containing 6% protein or a normal-protein diet (NPD) containing 18% protein during pregnancy. Streptozotocin diabetes was induced at 12 weeks and animals were killed at 40 weeks. Results Non-diabetic LPD offspring were of lower birthweight than the NPD offspring (5.19±0.64 vs 6.45±0.67 g, p<0.001) and had fewer glomeruli (27,402±3,137 vs 34,203±6,471, p<0.05). Glomerular volume correlated inversely with glomerular number (r=−0.64, p=0.035), but total glomerular filtration surface area was reduced in the LPD animals (4,770±541 vs 5,779±1,302 mm², p=0.05). Other renal structural and functional parameters were similar. In LPD and NPD diabetic animals, glomerular volume and basement membrane width were significantly increased compared to their respective controls. Podocyte density was lowest in the LPD diabetic animals (not significant), and the area covered by each podocyte was greater in the LPD diabetic group (2.40±0.693 ×10⁻³ mm²) than in the LPD control group (1.68±0.374 ×10⁻³ mm², p<0.001) and in the NPD diabetic animals (1.71±0.291 ×10⁻³ mm², p<0.05). There was no difference in any other structural or functional parameter between the LPD and NPD diabetic animals. Conclusions/interpretation A decrease in glomerular number was not deleterious to renal structure and function over 40 weeks in this animal model. Further work in models with progressive renal impairment and hypertension is necessary to clarify the impact of glomerular number on the development of renal disease.     

Relative contribution of vasopressin and angiotensin II to the altered renal microcirculatory dynamics in two-kidney Goldblatt hypertension

The renal microcirculation was assessed in non-clipped kidneys of 23 Munich-Wistar rats with two-kidney one-clip Goldblatt hypertension. Four weeks after placement of a renal arterial clip, mean systemic arterial pressure averaged 163 +/- 5 mm Hg in hypertensive rats as compared to 108 +/- 2 in sham-operated controls (n = 6 rats). Non-clipped kidneys in hypertensive rats were characterized by higher glomerular capillary hydraulic pressures, single nephron glomerular filtration rate, and afferent arteriolar resistance. The glomerular capillary ultrafiltration coefficient was significantly reduced in hypertensive rats. In 10 of these rats, intravenous infusion of the angiotensin antagonist, saralasin, or the converting enzyme inhibitor, SQ20881, led to significant reductions in systemic arterial pressure and in afferent and efferent arteriolar resistance, on average by 8 +/- 3%, 15 +/- 4%, 28 +/- 5%, respectively. These changes were associated with significant increase in glomerular plasma flow, while ultrafiltration coefficient remained unaffected. In the presence of saralasin or SQ20881, infusion of a specific antagonist of the vascular action of arginine vasopressin led to significant systemic but not renal vasodilation. Thus, whereas systemic arterial pressure fell further, on average by 23 +/- 2%, renal arteriolar resistance remained constant, resulting in marked reduction in glomerular capillary hydraulic pressures (by 18 +/- 2%) and glomerular plasma flow rate (by 28 +/- 10%). Because of these pronounced reductions in glomerular pressures and flows induced by vasopressin antagonist, single nephron glomerular filtration rate fell markedly in hypertensive rats (by 34 +/- 6%) despite normalization of ultrafiltration coefficient. When hypertensive rats (n = 7) were treated with vasopressin antagonist alone, a modest fall in systemic arterial pressure was again observed in the absence of changes in renal arteriolar resistance. Due to this selective extrarenal vasodilatory action of vasopressin antagonist, glomerular capillary hydraulic pressure, plasma flow rate, and single nephron glomerular filtration rate again fell markedly. When these vasopressin antagonist pre-treated hypertensive rats were given saralasin or SQ20881, marked reductions in renal arteriolar resistance were observed in association with a significant increase in glomerular plasma flow rate. These observations made during acute inhibition of angiotensin II and vasopressin indicate that both of these vasopressin hormones may play important roles in maintaining systemic hypertension in hypertensive rat. By virtue of its preferential constrictor effects on extrarenal rather than renal vasculature vasopressin serves to maintain high glomerular pressures and flows in the non-clipped kidney of Goldblatt hypertensive rats.     

Systemic and splanchnic hemodynamic changes in patients with hepatic schistosomiasis

Abstract: Although hepatic schistosomiasis is a common cause of portal hypertension, only a few hemodynamic studies, in humans, have been published on this subject. The aim of this study was to determine the systemic and splanchnic hemodynamic changes in hepatic schistosomiasis and to evaluate the influence of liver fibrosis on these changes. A retrospective analysis of a series of 13 patients with hepatic schistosomiasis who had undergone hemodynamic studies was performed. Portal or perisinusoidal fibrosis was present at liver biopsy in 8 patients. The control group included 22 patients with chronic hepatitis and normal hepatic venous pressure gradients. Patients with schistosomiasis exhibited high cardiac index (4.11±1.15 1 · min^-1 · m^-2 vs 2.99±0.85 1 · min^-1 · m^-2; p<0.05) and low systemic vascular resistance (1039±316 dyn · s · cm^-5 vs 1334±336 dyn · cm^-5; p<0.05). The hepatic venous pressure gradient and hepatic blood flow were normal. Azygos blood flow was markedly increased (0.90±0.66 1 · min^-1 vs 0.13±0.04 1 · min^-1; p<0.05). Hemodynamic values were not significantly different between patients with liver fibrosis and those without fibrosis at liver biopsy. In conclusion, patients with hepatic schistosomiasis had a hyperkinetic systemic and splanchnic circulation. In patients with esophageal varices, a normal hepatic venous pressure gradient confirmed presinusoidal portal hypertension. The presence of portal or perisinusoidal fibrosis did not influence hyperdynamic splanchnic state.     

Forearm Substrate Exchange during Hyperinsulinaemic Hypoglycaemia in Normal Man

To assess muscle substrate exchange during hypoglycaemia, 8 healthy young male subjects were studied twice during 2 h of hyperinsulinaemic euglycaemia followed by 4 h of (1) hypoglycaemia (plasma glucose < 2.8 mmol l^?1), and (2) euglycaemia. Insulin was infused at a rate of 1.5 mU kg^?1 min^?1 throughout. When compared to euglycaemia, hypoglycaemia was associated with: (1) increment in circulating glucagon (65 ± 8 vs 23 ± 4 ng l^?1, p < 0.05), growth hormone (19.9 ± 3.6 vs 2.6 ± 1.3 μg l^?1, p < 0.05), adrenaline (410 ± 88 vs 126 ± 32 ng l^?1, p < 0.05) and increased suppression of C-peptide (0.5 ± 0.1 vs 1.0 ± 0.1 μg l^?1, p < 0.05) along with a modest lowering of insulin (103 ± 10 vs 130 ± 13 mU l^?1, p < 0.05); (b) decrease in plasma glucose level (3.0 ± 0.07 vs 5.0 ± 0.12 mmol l^?1 p < 0.05), forearm glucose uptake (0.21 ± 0.09 vs 1.21 ± 0.21 mmol l^?1, p < 0.05) and requirement for exogenous glucose (5.6 ± 1.1 vs 13.2 ± 0.9 mg kg^?1 min^?1 p < 0.005) together with an impaired suppression of isotopically determined endogenous glucose production (0.34 ± 0.5 vs ?2.3 ± 0.3 mg kg^?1 min^?1, p < 0.05); (3) exaggerated increase in blood lactate (1680 ± 171 vs 1315 ± 108 μmol l^?1, p < 0.05) and a decrease in alanine (215 ± 18 vs 262 ± 19 μmol l^?1, p < 0.05). Forearm release of lactate (130 ± 43 vs 12 ± 31 μmol l^?1, p = 0.09) tended to be increased, whereas alanine balance (18 ± 6 vs 17 ± 5 μmol l^?1) was unchanged. (4) Total forearm blood flow increased similarly during both studies (4.4 ± 0.6 vs 4.2 ± 0.5 ml 100 ml^?1 min^?1). These data suggest that the human forearm is not a major site for glucose uptake nor for lactate production during protracted hypoglycaemia; the fact that forearm glucose uptake is reduced sixfold during hypoglycaemia further suggests that restriction of glucose uptake in muscles plays a frontline role in the defence against hypoglycaemia.     

Low birth weight – is it associated with few and small glomeruli in normal subjects and NIDDM patients?

Summary These studies were undertaken to ascertain if there is any association between low birth weight, and low kidney weight, few and/or small glomeruli, in kidneys from a control group and a group of non-insulin-dependent diabetic (NIDDM) patients. The background for this study comes from findings suggesting a correlation between low birth weight and the development of NIDDM and high blood pressure. Furthermore, Brenner has postulated that humans born with a low number of glomeruli, thereby having a low glomerular filtration surface area, have a greater tendency to develop high blood pressure. We examined 79 autopsy kidneys, with known weight from normal and NIDDM patients, which had previously been used for studies of glomerular number and volume. In the archives of the Danish midwives we were able to find birth weight for 26 NIDDM patients and an age- and sex-matched sample of 19 control persons. The kidney weight (g) (Control: 137 ± 36; NIDDM: 150 ± 38; 2p = 0.26), glomerular number (10³) (Control: 670 ± 176; NIDDM: 673 ± 200; 2p = 0.95), glomerular volume (10⁶μm³) (Control: 6.25 ± 1.48; NIDDM: 5.71 ± 1.74; 2p = 0.28) or birth weight (g) (Control: 3577 ± 400; NIDDM: 3489 ± 429; 2p = 0.49) were not different between the groups. There was no significant correlation between birth weight and glomerular number (Control: 2p = 0.80; r = 0.06 and NIDDM: 2p = 0.10; r = –0.33), glomerular volume (Control: 2p = 0.43; r = 0.19 and NIDDM: 2p = 0.78; r = 0.06) or kidney weight (Control: 2p = 0.56; r = 0.14 and NIDDM: 2p = 0.81; r = 0.05). Our results on a limited number of subjects in Denmark do not support the hypothesis that there is any association between low birth weight and low kidney weight or low birth weight and few and/or small glomeruli in NIDDM patients. [Diabetologia (1996) 39: 1634–1637]     

Acute effects of the superoxide dismutase mimetic tempol on split kidney function in two-kidney one-clip hypertensive rats

OBJECTIVE: To investigate the acute effects of the superoxide dismutase mimetic 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (tempol) on split kidney function, and renal haemodynamics, in two-kidney, one-clip (2K1C) hypertensive rats. METHODS: Three weeks after clipping, or the sham procedure, the effects of intravenous tempol (200 micromol/kg per h) were evaluated on thiobutabarbital anaesthetized Sprague-Dawley rats. RESULTS: Mean arterial pressure (MAP; 152 +/- 3 versus 122 +/- 3 mmHg, P < 0.001), plasma renin activity (28.7 +/- 3.0 versus 9.5 +/- 0.6 ng/ml per h, P < 0.001) and urinary 8-iso-prostaglandin F2alpha excretion (124 +/- 4 versus 92 +/- 10 pmol/24 h, P = 0.003) were significantly elevated in 2K1C rats compared with sham. Tempol reduced MAP by 15 +/- 1% compared with baseline (P < 0.001) in 2K1C rats. In clipped kidneys, tempol increased the glomerular filtration rate (GFR; +50 +/- 15% from baseline) and the effective renal plasma flow (ERPF; +37 +/- 13%, from baseline), and reduced renal vascular resistance (RVR; -32 +/- 6% from baseline) compared with saline-treated controls (P < 0.05). In non-clipped kidneys, tempol reduced RVR (-24 +/- 5% from baseline) compared with saline-treated controls (P = 0.001). In sham-operated rats, tempol produced a modest reduction in MAP (-8 +/- 2% from baseline, P = 0.003), but did not significantly affect renal haemodynamics or function. CONCLUSION: Tempol reduced MAP and RVR in both clipped and non-clipped kidneys of 2K1C hypertensive rats. In addition, tempol increased ERPF and GFR in the clipped kidney. These findings suggest important roles for superoxide in the regulation of renal haemodynamics during the early maintenance phase of renovascular hypertension.     

Modulation of Nitric Oxide Synthase Activity in Brain,Liver, and Blood Vessels of Spontaneously Hypertensive Rats by Ascorbic Acid: Protection from Free Radical Injury

End organ damage in essential hypertension has been linked to increased oxygen free radical generation, reduced antioxidant defense, and/or attenuation of nitric oxide synthase (NOS) activity. Ascorbic acid (AA), a water-soluble antioxidant, has been reported as a strong defense against free radicals in both aqueous and nonaqueous environment. In this study we examined the hypothesis that antioxidant ascorbic acid may confer protection from increased free radical activity in brain, liver, and blood vessels of spontaneously hypertensive rats (SHR). Male SHRs were divided into groups: SHR + AA (treated with AA, 1 mg/rat/day; for 12 weeks) or SHR (untreated). Wister-Kyoto rats (WKY) served as the control. Mean systolic blood pressure (SBP) in treated and untreated SHR was 145 ± 7 mmHg and 142 ± 8 mmHg, respectively. AA treatment prevented the increase in systolic blood pressure in SHR by 37 ± 1% (p < 0.05). NOS activity in the brain, liver, and blood vessels of WKY rat was 1.82 ± 0.02, 0.14 ± 0.003, and 1.54 ± 0.06 pmol citruline/mg protein, respectively. In SHR, total NOS activity was significantly reduced by 52 ± 1%, 21 ± 3%, and 44 ± 4%, respectively. AA increased NOS activity in brain, liver, and blood vessels of SHR from 0.87 ±.03, 0.11 ±.01, and 0.87 ±.08 pmol citruline/mg protein to 0.93 ± 0.01, 0.13 ± 0.001, and 1.11 ± 0.03 pmol citruline/mg protein (p < 0.05), respectively. Lipid peroxides in the brain, liver, and blood vessels from WKY rats were 0.87 ± 0.06, 0.11 ± 0.005, and 0.47 ± 0.04 nmol MDA equiv/mg protein, respectively. In SHR, lipid peroxides in brain, liver, and blood vessels were significantly increased by 40 ± 3%, 64 ± 3%, and 104 ± 13%, respectively. AA reduced lipid peroxidation in liver and blood vessels by 17 ± 1% and 34 ± 3% but not in brain. Plasma lipid peroxides were almost doubled in SHR (p < 0.01) together with a reduction in total antioxidant status (6 ± 0.1%; p < 0.05), nitrite (53 ± 2%; p < 0.05) and superoxide dismutase (SOD) activity (36 ± 2%; p < 0.05). AA treatment reduced plasma lipid peroxide (p < 0.001), and increased TAS (p < 0.001), nitrite (p < 0.001), and SOD activity (p < 0.001). From this study, we conclude that brain, liver, and blood vessels in SHR are susceptible to free radical injury, which reduces the availability of NO either by scavenging it or by reducing its production via inhibiting NOS. In addition, brain, liver, and blood vessels in SHR; may be protected by antioxidant, which improves total antioxidant status, and SOD thus may prevent high blood pressure and its complications.     

T-Type calcium channel blockage ameliorates proteinuria and renal extracellular matrix accumulation in experimental diabetic rats

Calcium channels have been shown to play an important role in the pathogenesis of diabetic nephropathy. The purpose of this study is to investigate the effect of T-type calcium channel blockers in uninephrectomized diabetic rats. Two weeks after uninephrectomy, streptozotocin (65 mg/kg) was given to male Sprague-Dawley rats to induce diabetes mellitus. In the succeeding days, four groups of animals were randomized to receive 30 mg/kg mibefradil (Mib, T-type calcium channel blocker), 30 mg/kg amlodipine (Aml, L-type calcium channel blocker), 10 mg/kg cilazapril (Cil, angiotensin converting enzyme inhibitor) or 25 mg/kg Mib + 8 mg/kg Cil (M+C), which were delivered daily by gavage (n = 6-8 for each group). At the fourth week, 24-hour urine, blood and kidney samples were collected for examinations. Renal morphometric analyses and assay for type IV collagen and laminin were performed. Untreated diabetic rats (DM) exhibited overt hyperglycemia, proteinuria and albuminuria when compared with uninephrectomized (UNx) control (17.67 ±4.9 vs 2.97 ±0.72 μg/24 hours, p < 0.05), while Cil and M+C treated rats had significantly reduced urinary protein excretion (Cil: 5.53 ±1.45, M+C: 3.87 ±0.88 vs DM: 17.67 ±4.9 μg/24 hours; p < 0.05, respectively). Mibefradil alone also ameliorated albuminuria in DM rats (7.69 ±1.87 vs 17.67 ±4.9 μg/24 hours, p < 0.05). Histopathological study revealed significantly less glomerular matrix, laminin, type IV collagen and proximal tubule cells (PTC) hypertrophy in the Cil and M+C groups when compared with the DM group (Collagen IV: DM 7.3 ±0.65 vs Mib 4.82 ±0.78, Cil 4.11 ±0.74, M+C 2. 64 ±0.66, UNx 3.71 ±0.99, p < 0.05). Albuminuria, glomerular matrix accumulation and collagen IV deposition were not changed in the Aml treated group. There was, however, significantly lower creatinine clearance and laminin volume in the Aml group. In conclusion, our study demonstrated that T-type calcium channel blockage reduced albuminuria and renal extracellular matrix accumulation in experimental diabetic rats, suggesting an important role for T-type calcium channel in the progression of diabetic nephropathy. Additional benefit can be achieved by combination with an angiotensin converting enzyme inhibitor. The mechanism of action, however, requires further investigation.     

Short-term moderate sodium restriction induces relative hyperfiltration in normotensive normoalbuminuric Type I diabetes mellitus

Aims/hypothesis. Type I (insulin-dependent) diabetes mellitus is associated with an increased extracellular volume. Sodium restriction might seem a logical form of treatment but data on its renal effects is conflicting. We therefore studied the effects of sodium restriction on renal haemodynamics in uncomplicated Type I diabetes mellitus. Methods. Uncomplicated Type I diabetic patients (n = 24) and matched control subjects (n = 24) were studied twice in random order: after a week of 50 mmol or after 200 mmol sodium intake, respectively. The diabetic patients were studied under normoglycaemic clamp conditions. Glomerular filtration rate and effective renal plasma flow were measured as the clearances of iothalamate and hippuran, respectively. Results. During liberal sodium intake, glomerular filtration, effective renal plasma flow and filtration fraction were similar between the diabetic patients and the control subjects. Sodium restriction decreased the effective renal plasma flow in both groups, whereas glomerular filtration rate only decreased in the control subjects. Consequently, in the diabetic patients, the filtration fraction was increased on low sodium (4.1 ± 8.4 %, p < 0.05 vs liberal sodium). As a consequence, filtration fraction (24.0 ± 2.6 vs 22.1 ± 2.0 %, p < 0.05) and glomerular filtration (119 ± 14 vs 110 ± 13 ml/min, p < 0.05) were higher in the diabetic patients than in the control subjects during sodium restriction. Conclusion/interpretation. Short-term moderate sodium restriction induces relative hyperfiltration in uncomplicated Type I diabetes. This could indicate an increased intraglomerular pressure. Sodium restriction could be an unfavourable preventive approach in diabetes mellitus but its long-term effects are not known. [Diabetologia (2002) 45: ▪–▪] Received: 17 September 2001 and in revised form: 7 November 2001