1 Increased renal vascular resistance is one renal functional abnormality that contributes to hypertension, and alpha(1)-adrenoceptors play a pivotal role in modulating this renal vascular resistance. This study investigates the functional contribution of alpha(1)-adrenoceptor subtypes in the renal cortical vasculature of Wistar-Kyoto rats on a normal sodium diet (WKYNNa) compared with those given saline to drink for 6 weeks (WKYHNa). 2 The renal cortical vascular responses to the adrenergic agonists noradrenaline (NA), methoxamine (ME) and phenylephrine (PE) were measured in WKYHNa and WKYNNa rats either in the absence (the control phase) or presence of chloroethylclonidine (CEC), an alpha(1B)-adrenoceptor antagonist, 5-methylurapidil (5-MeU), an alpha(1A) antagonist, or BMY7378, an alpha(1D) antagonist. 3 Results showed a greater renal cortical vascular sensitivity to NA, PE and ME in the WKYHNa compared with WKYNNa rats (P < 0.05). Moreover, 5-MeU and BMY7378 attenuated adrenergically induced renal cortical vasoconstriction in WKYHNa and WKYNNa rats; this response was largely blunted in CEC-treated WKYHNa rats (all P < 0.05) but not in CEC-treated WKYNNa rats. 4 The data suggest that irrespective of dietary sodium content, in Wistar-Kyoto rats alpha(1A)- and alpha(1D)-subtypes are the major alpha(1)-adrenoceptors in renal cortical vasculature; however, there appears to be a functional involvement of alpha(1B)-adrenoceptors in the WKYHNa rats.

A double-blind, placebo-controlled, crossover study on the effects of 4 months' growth hormone (GH) treatment was carried out in 22 GH-deficient adults (8 women, 14 men; mean [SEM] age 23.8 [1.2] years). 1 patient was withdrawn because of oedema. Mean total body weight of the other 21 did not change, whereas mean muscle volume of the thigh, estimated by computerised tomography (CT), was significantly higher after GH than after placebo (70.0 [3.7] vs 66.3 [3.1] ml/0.8 cm cross-sectional slice). The mean adipose tissue volume of the thigh and subscapular skinfold thickness fell significantly during GH treatment. Growth hormone caused a small increase in the isometric strength of the quadriceps muscles and a significant rise in exercise capacity (60.8 [7.2] vs 54.2 [6.6] kJ). The heart rate both at rest and after maximum exercise was low during the placebo period and increased significantly during GH treatment. Blood pressure and echocardiographic wall mass of the left ventricle did not change during the study. Growth hormone increased both mean glomerular filtration rate and renal plasma flow from a subnormal level on placebo to a level comparable with that of an age-matched control group. The filtration fraction did not change. Urinary albumin excretion was in the low normal range and was not affected by GH treatment. Finally, GH treatment normalised mean circulating levels of insulin-like growth factor 1 (IGF-1), which were low after the placebo period (96 [9] micrograms/l placebo; 224 [28] micrograms/l GH). These findings suggest that GH, in a conventional replacement dose, has several potentially beneficial effects in GH-deficient adults and therefore encourage future long-term trials.

Recent studies have indicated that acute inhibition of nitric oxide biosynthesis in the rat promotes arterial hypertension and renal vasoconstriction. We evaluated the renal and systemic effects of 4-6 weeks of nitric oxide blockade in Munich-Wistar rats receiving the nitric oxide inhibitor nitro-L-arginine orally. Age-matched untreated rats were used as controls. In an additional seven rats, nitric oxide blockade was carried out in conjunction with oral administration of the novel angiotensin II antagonist losartan potassium. Tail-cuff pressure rose progressively in nitro-L-arginine-treated rats, reaching 164 +/- 6 mm Hg at 4-6 weeks, compared with 108 +/- 3 mm Hg in controls. In rats concomitantly receiving losartan, tail-cuff pressure reached 125 +/- 6 mm Hg, still elevated compared with rats receiving losartan alone (98 +/- 3 mm Hg). Nitro-L-arginine-treated rats presented marked renal vasoconstriction and hypoperfusion, as well as a 30% fall in glomerular filtration rate and a 39% increase in filtration fraction. Treatment with Losartan normalized glomerular filtration rate, but not filtration fraction or renal vascular resistance. Plasma renin activity was elevated after nitro-L-arginine treatment. Renal histological examination revealed widespread arteriolar narrowing, focal arteriolar obliteration, and segmental fibrinoid necrosis in the glomeruli. In a separate group of rats, nitro-L-arginine administered for 1 week induced hypertension that was partially reversed by acute L-arginine, but not D-arginine or L-glycine, infusions. We conclude that chronic nitric oxide blockade may constitute a new model of severe arterial hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)

A primary role for the kidney in the initiation and maintenance of hypertension has long been recognized, but the pathogenetic interactions among renal hemodynamics, hormonal and hereditary factors, and dietary sodium intake remain enigmatic. Reduction in filtration surface area, whether acquired in the course of intrinsic renal disease or after surgical renal ablation, leads to systemic hypertension as well as to progressive renal insufficiency, sequellae made even more severe by dietary sodium excess. Moreover, hypertension and progressive renal disease eventuate in some individuals born with a solitary kidney, as well as in those with more severe degrees of dysgenesis (ie, oligomeganephronia). Hypertension is also commonly observed in certain inbred rat strains in which filtration surface area is congenitally deficient. Based on these and other lines of evidence reviewed herein, we postulate that a renal abnormality that contributes to essential hypertension in the general population is a reduced number of nephrons. The consequences of this abnormality are limitations in the ability to excrete sodium and thus, salt-sensitive hypertension. Finally, congenital variability in filtration surface area may explain why only some, but not all, patients exposed to potentially injurious renal stimuli eventually manifest chronic nephropathy. This may also account for the susceptibility of subsets of Type I and Type II diabetics to develop overt glomerulopathy.

Interlobular arteries and superficial afferent and efferent arterioles were isolated from rabbit kidney, and the effects of intraluminal pressure, norepinephrine (NE), and angiotensin II (ANG II) on lumen diameter were examined. A single microvessel was dissected and one end was cannulated. The other end of the vessel was occluded and lumen diameter was measured at fixed intraluminal pressures. With step increases in intraluminal pressure over the range of 70-180 mmHg, lumen diameters of the interlobular arteries and afferent arterioles remained constant or decreased by up to 11%. In contrast, lumen diameters of efferent arterioles continued to increase as intraluminal pressure was elevated. In all three vessels NE (10(-9) to 10(-5) M) caused a dose-dependent decrease in lumen diameter. However, only the efferent arteriole responded to ANG II (10(-12) to 10(-8) M). The contractile response of the efferent arteriole to NE or ANG II was localized to the first 50-75 micrometers of the vessel as it emerged from the glomerulus. This finding suggests that smooth muscle cells are located only in this portion of the efferent arteriole. It is concluded that at least part of the autoregulation of renal blood flow can be explained by a myogenic mechanism in preglomerular vessels and that ANG II acts primarily on postglomerular segments of the rabbit renal microcirculation.

These studies were conducted in the conscious, chronically catheterized rat to determine whether the endothelial derived relaxing factor (EDRF) controls renal function in the normal state. Administration of the EDRF synthesis inhibitors N-monomethyl-L-arginine (NMA; 100 mg/kg body weight) or N-nitro-L-arginine methylester (NAME; 10 mg/kg body wt) led to a large, sustained rise in blood pressure, a large rise in renal vascular resistance, a fall in renal plasma flow, a relatively slight reduction in glomerular filtration rate, and a consequent rise in filtration fraction. In addition, a marked natriuresis occurred because of a reduction in the fractional reabsorption of sodium. In separate studies, a continuous infusion of excess L-arginine (300 mg/kg body wt bolus followed by 50 mg/kg body wt per min) attenuated the NMA- or NAME-induced rise in blood pressure and reversed the renal hemodynamic effects such that a significant rise in renal plasma flow was seen. L-Arginine alone produced a selective renal vasodilation and large increases in sodium excretion. These observations support earlier suggestions that tonic release of EDRF controls the basal blood pressure and also show that renal function in the normal unstressed rat is markedly influenced by EDRF. These studies suggest that, in addition to controlling renal plasma flow, EDRF may have other, complex actions at the glomerulus. The natriuresis seen after acute inhibition of EDRF with NMA or NAME was probably the result of a pressure natriuretic response to the abrupt rise in blood pressure and also, perhaps, reflects removal of an EDRF influence to directly enhance sodium reabsorption somewhere in the nephron.

The dose-dependent effects of intravenous infusions of nitric oxide (NO) synthesis inhibitor, NG-nitro-L-arginine methyl ester (L-NAME; 0.1, 1, 10, and 50 micrograms.kg-1.min-1), were studied in anesthetized rats to determine whether the inhibitory actions of L-NAME are manifested primarily in alterations of renal function or whether they are the consequences of the increase in systemic blood pressure. Mean arterial pressure (MAP) was not altered by the intravenous L-NAME infusions of 0.1 and 1.0 microgram.kg-1.min-1. However, 0.1 microgram.kg-1.min-1 L-NAME induced a 30% decrease in urine flow rate (UV). The administration of 1.0 microgram.kg-1.min-1 L-NAME, in addition to decreasing UV, also decreased urinary sodium excretion (UNaV) and renal plasma flow (RPF). The intravenous L-NAME infusions of 10.0 and 50.0 microgram.kg-1.min-1 intravenous L-NAME infusions of 10.0 and 50.0 microgram.kg-1.min-1 produced significant increases in MAP that reversed the initial fall in UV and UNaV, despite decreasing RPF and glomerular filtration rate (GFR). The administration of L-arginine alone (10 micrograms.kg-1.min-1) did not modify any of the parameters measured, but it effectively prevented all the hemodynamic and renal changes induced by the infusion of 50 micrograms.kg-1.min-1 L-NAME. These results suggest that the decrease in nitric oxide production induced by the intravenous infusion of L-NAME affects renal excretion of sodium and water in the absence of any significant change in blood pressure. At larger doses, L-NAME also produces hypertension that overrides the initial antinatriuretic effect.

We studied the efficacy of the ACE inhibitor lisinopril in treating overt proteinuria in comparison with the NSAID indomethacin, and evaluated some of the conditions that could influence this antiproteinuric effect. In 12 patients with a proteinuria varying from 3.2 to 10.5 g/24 hr, a diastolic BP ranging from 64 to 105 mm Hg, and a GFR varying from 34 to 127 ml/min, the effect of different lisinopril doses and of changing dietary sodium intake was evaluated. Proteinuria fell by 27 +/- 20% from 6.1 +/- 2.1 to 4.5 +/- 1.9 g/24 hr on a low dose (median 5 mg/day) lisinopril and by 50 +/- 17% to 3.1 +/- 1.4 g/24 hr on a higher dose (median 10 mg/day), irrespective of initial proteinuria, BP, or GFR. This antiproteinuric effect was abolished by increasing salt intake from 50 to 200 mmol/day, and was recovered again by re-instituting the sodium restricted diet. The antiproteinuric effect of 10 mg/day lisinopril was comparable to the reduction in proteinuria (by 57 +/- 21% to 2.8 +/- 2.0 g/24 hr) on 150 mg/day indomethacin, while adverse effects were less and renal hemodynamic effects were more favorable during lisinopril. In some patients it took several weeks before the effect of the ACE inhibitor on proteinuria was stabilized. Thus, the antiproteinuric effect of the ACE inhibitor lisinopril appears to be dose and time related, and is strongly dependent on dietary sodium restriction, whereas it does not depend on initial proteinuria, BP, or GFR. The effect is comparable to that of indomethacin, while adverse effects are less.

The endogenous cannabinoid receptor agonist anandamide is present in central and peripheral tissues. As the kidney contains both the amidase that degrades anandamide and transcripts for anandamide receptors, we characterized the molecular components of the anandamide signaling system and the vascular effects of exogenous anandamide in the kidney. We show that anandamide is present in kidney homogenates, cultured renal endothelial cells (EC), and mesangial cells; these cells also contain anandamide amidase. Reverse-transcriptase PCR shows that EC contain transcripts for cannabinoid type 1 (CB1) receptors, while mesangial cells have mRNA for both CB1 and CB2 receptors. EC exhibit specific, high-affinity binding of anandamide (Kd = 27.4 nM). Anandamide (1 microM) vasodilates juxtamedullary afferent arterioles perfused in vitro; the vasodilation can be blocked by nitric oxide (NO) synthase inhibition with L-NAME (0.1 mM) or CB1 receptor antagonism with SR 141716A (1 microM), but not by indomethacin (10 microM). Anandamide (10 nM) stimulates CB1-receptor-mediated NO release from perfused renal arterial segments; a similar effect was seen in EC. Finally, anandamide (1 microM) produces a NO-mediated inhibition of KCl-stimulated [3H]norepinephrine release from sympathetic nerves on isolated renal arterial segments. Hence, an anandamide signaling system is present in the kidney, where it exerts significant vasorelaxant and neuromodulatory effects.

The present study was designed to test whether altered renovascular reactivity is associated with the increased risk of radio-contrast nephropathy (RCN) in diabetics. We studied 50 patients (24 diabetics, 26 nondiabetics) with chronic renal insufficiency undergoing cardiac catheterization. Patients were randomized to receive either saline, or one of three renal vasodilator/diuretic drugs--dopamine, atrial natriuretic peptide (ANP), or mannitol--by intravenous infusion during cardiac catheterization. Renal blood flow (RBF) was measured by thermodilution at various time points during cardiac catheterization. RCN was defined as an increase in PCr of at least 25% over baseline within 48 hours of cardiac catheterization. Baseline PCr and creatinine clearance were similar in diabetics and nondiabetics (2.6 +/- 0.2 mg/dl vs. 2.4 +/- 0.1 mg/dl, and 32 +/- 3 ml/min vs. 34 +/- 3 ml/min, respectively), but baseline RBF was significantly lower in diabetics (154 +/- 21 ml/min/kidney vs. 277 +/- 36 ml/min/kidney, P < 0.05). Diabetic patients exposed to the three vasodilator/diuretic drugs had the greatest increase in RBF throughout cardiac catheterization. The incidence of RCN among the diabetics receiving those drugs was 83%, 83% and 75%, in the dopamine, ANP and mannitol groups, respectively. In contrast, among the nondiabetics in each of those groups the incidence of RCN was zero (all P < 0.05, diabetics vs. nondiabetics). In the saline control group the rates of RCN in the diabetics and nondiabetics were 43% and 38%, respectively (NS). In conclusion, the increased risk of RCN among diabetics was associated with exaggerated renovascular reactivity: baseline vasoconstriction and enhanced vasodilation with vasodilator/diuretic drugs. These same drugs, however, reduced the risk of RCN in nondiabetic patients.