A nitric oxide donor NOC 7 suppresses renal responses induced by norepinephrine and angiotensin II in the NO-depleted denevated rabbit kidney

Interaction of Endothelial Nitric Oxide and Angiotensin in the Circulation

Discovery of the unexpected intercellular messenger and transmitter nitric oxide (NO) was the highlight of highly competitive investigations to identify the nature of endothelium-derived relaxing factor. This labile, gaseous molecule plays obligatory roles as one of the most promising physiological regulators in cardiovascular function. Its biological effects include vasodilatation, increased regional blood perfusion, lowering of systemic blood pressure, and antithrombosis and anti-atherosclerosis effects, which counteract the vascular actions of endogenous angiotensin (ANG) II. Interactions of these vasodilator and vasoconstrictor substances in the circulation have been a topic that has drawn the special interest of both cardiovascular researchers and clinicians. Therapeutic agents that inhibit the synthesis and action of ANG II are widely accepted to be essential in treating circulatory and metabolic dysfunctions, including hypertension and diabetes mellitus, and increased availability of NO is one of the most important pharmacological mechanisms underlying their beneficial actions. ANG II provokes vascular actions through various receptor subtypes (AT1, AT2, and AT4), which are differently involved in NO synthesis and actions. ANG II and its derivatives, ANG III, ANG IV, and ANG-(1-7), alter vascular contractility with different mechanisms of action in relation to NO. This review article summarizes information concerning advances in research on interactions between NO and ANG in reference to ANG receptor subtypes, radical oxygen species, particularly superoxide anions, ANG-converting enzyme inhibitors, and ANG receptor blockers in patients with cardiovascular disease, healthy individuals, and experimental animals. Interactions of ANG and endothelium-derived relaxing factor other than NO, such as prostaglandin I2 and endothelium-derived hyperpolarizing factor, are also described.

Facilitatory role of NO in neural norepinephrine release in the rat kidney

We examined modulation by nitric oxide (NO) of sympathetic neurotransmitter release and vasoconstriction in the isolated pump-perfused rat kidney. Electrical renal nerve stimulation (RNS; 1 and 2 Hz) increased renal perfusion pressure and renal norepinephrine (NE) efflux. Nonselective NO synthase (NOS) inhibitors [N(omega)-nitro-L-arginine methyl ester (L-NAME) or N(omega)-nitro-L-arginine], but not a selective neuronal NO synthase inhibitor (7-nitroindazole sodium salt), suppressed the NE efflux response and enhanced the perfusion pressure response. Pretreatment with L-arginine prevented the effects of L-NAME on the RNS-induced responses. 2-(4-Carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (carboxy-PTIO), which eliminates NO by oxidizing it to NO(2), suppressed the NE efflux response, whereas the perfusion pressure response was less susceptible to carboxy-PTIO. 8-Bromoguanosine cGMP suppressed and a guanylate cyclase inhibitor [4H-8-bromo-1,2,4-oxadiazolo(3,4-d)benz(b)(1,4)oxazin-1-one] enhanced the RNS-induced perfusion pressure response, but neither of these drugs affected the NE efflux response. These results suggest that endogenous NO facilitates the NE release through cGMP-independent mechanisms, NO metabolites formed after NO(2) rather than NO itself counteract the vasoconstriction, and neuronal NOS does not contribute to these modulatory mechanisms in the sympathetic nervous system of the rat kidney.

Interaction between norepinephrine release and intrarenal angiotensin II formation during renal nerve stimulation in dogs

We examined possible interactions between intrarenal angiotensin II (ANG II) formation and norepinephrine (NE) release during renal sympathetic nerve stimulation (RNS) in anesthetized dogs. During 10 min of continuous RNS (1.5-2 Hz), the ANG II formation rates (ANG II-FR) and NE secretion rates (NE-SR) were determined at 1 and 10 min. Under control conditions, almost the same extent of increase in the NE-SR was observed at 1 and 10 min of RNS, whereas a significant increase in ANG II-FR was observed at 10 min but not at 1 min. During intrarenal arterial infusion of enalaprilat or losartan, the increase in NE-SR and reduction in renal blood flow at 10 min of RNS were suppressed, whereas the NE release and vasoconstriction responses at 1 min remained unaffected. The RNS-induced increases in ANG II-FR were completely abolished during infusion of enalaprilat. These results suggest that NE release on continuous RNS is enhanced by concomitantly formed ANG II, and this interaction depends on the time-related changes in intrarenal ANG II formation during RNS in the canine kidney.

Protective effect of oral L-arginine administration on gentamicin-induced renal failure in rats

We investigated the effects of orally supplemented L-arginine, the substrate of nitric oxide (NO) and N(omega)-nitro-L-arginine methyl ester (L-NAME), a nitric oxide-synthase inhibitor in gentamicin-induced renal failure. Rats were given gentamicin (100 mg/kg/day s.c.), gentamicin and L-arginine (2 g/l, drinking water), gentamicin and L-NAME (100 mg/l, drinking water) or gentamicin plus L-arginine and L-NAME. After 8 days, the gentamicin group developed marked renal failure, characterized by a significantly decreased creatinine clearance and increased blood creatinine, fractional excretion of sodium, fractional excretion of lithium, urine gamma glutamyl transferase, systolic blood pressure and daily urine volume when compared to controls. Renal histological analysis confirmed tubular necrosis. L-arginine administration caused normalization of these parameters, whereas L-NAME led to aggravation of the failure. Concomitant administration of L-NAME and L-arginine to gentamicin-treated rats caused no significant changes when compared to the rats receiving gentamicin alone. We conclude that L-arginine supplementation has beneficial effects in gentamicin-induced renal failure in rats and that these effects are reversed by the NO-synthase inhibitor, L-NAME.

Renal effects of endothelin in anesthetized rabbits

Intrarenal arterial infusion of endothelin-1 (1, 3 and 10 ng/kg per min) reduced renal blood flow, urine flow rate and urinary Na+ excretion without affecting fractional Na+ excretion in anesthetized rabbits. An endothelin ET(A) receptor antagonist (R)2-[(R)-2-[(S)-2-[[1-(hexahydro-1H-azepinyl)]carbonyl]amino-4-me thyl-pentanoyl]amino-3-[3-(1-methyl-1H-indolyl)]propionyl]amino-3-(2-pyr idyl)propionic acid (FR139317, 1 microg/kg per min) attenuated the endothelin-1 (1 ng/kg per min)-induced renal responses. An endothelin ET(B) receptor antagonist N-cis 2,6-dimetylpiperidinocarbonyl-L-gamma-metylleucyl-D-1-met hoxycarbonyltryptophanyl-D-norleucine (BQ-788, 1 microg/kg per min) potentiated the endothelin-1-induced changes in renal blood flow, urine flow rate and urinary Na+ excretion. A nitric oxide (NO) synthase inhibitor Nomega-nitro-L-arginine methyl ester (L-NAME, 50 microg/kg per min) also potentiated the endothelin-1-induced reductions in urine flow rate and urinary Na+ excretion but not the reduction in renal blood flow. Endothelin-1 reduced fractional Na+ excretion in the presence of BQ-788 or L-NAME. A spontaneous NO donor 1-hydroxy-2-oxo-3-(N-methyl-3-aminopropyl)-3-methyl-1-triazene (30 ng/kg per min) slightly attenuated the antinatriuresis but not the vasoconstriction induced by endothelin-1. These results suggest that in the rabbit kidney in vivo endothelin ET(A) receptors mediate endothelin-1-evoked vasoconstriction and tubular Na+ reabsorption, that the concomitant stimulation of endothelin ET(B) receptors by endothelin-1 counteracts both the ET(A) receptor-mediated vascular and tubular actions, and that the tubular action, but not the vascular action, of endothelin-1 is also susceptible to changes in renal NO level.