| The afferent renal nerves that contain both Aδ and C fibers are stemmed from intrarenal sensory receptors. Two classes of renal sensory receptors have been identified neurophysiologically: renal mechanoreceptors responding to increases in intrarenal hydrostatic pressure, and renal chemoreceptors responding to renal ischemia and changes in the chemical environment of the renal interstitium. The latter is further classified as R1 and R2 chemoreceptors. Some of the mechanoreceptors have a spontaneous discharge under control conditions. R1 chemoreceptors have no spontaneous activity and respond to renal ischemia. R2 chemoreceptors are spontaneous active. In addition to being activated by ischemia, it can be activated by alterations in the composition of the interstitial or pelvic fluid environment. Thus the afferent renal nerves have a basal discharge under normal physiological conditions and R2 chemoreceptors are the principal source of the ongoing activity observed in multiunit recordings. Although the afferent innervation is not directly involved in the regulation of vascular or tubular phenomena within the kidney, its potential role lies in the initiation of reflex effects that mayparticipate in the reflex control system, such as renorenal reflex and cardiovascular activity regulating reflex ect. Also, the changes in afferent renal nerve activity (ARNA) can induce the release of vasopressin, cortisol and atrial natriuretic peptide. Nitric oxide is an important signaling and effector molecule that plays critical roles in numerous essential physiological processes in virtually every organ. The three types of NO synthases ( NOS ), referred to as neuronal NOS ( nNOS ), inducible NOS, and endothelial NOS ( eNOS ), which have all been found in the kidney. Previous studies have shown that L-arginine, a NO precursor, influences the regulation of renal hemodynamics and glomerular microcirculation in isolated perfusion kidney. At the same time NO is known to function as an inhibitory neurotransmitter regulating the activity of renal afferent arteriole in rats. Capsaicin, the pungent ingredient of hot pepper, is a specific activator of primary afferent C- and Aδ-fibers. The kidney is innervated by sensory nerves, which are sensitive to capsaicin. Studies have shown that vanilloid receptors ( capsaicin receptor, VR ), which induce the excitatory effect of capsaicin, are located in various tissues of the kidney. The present work was undertaken to study the effects of intrarenal artery injection of L-arginine and capsaicin on spontaneous discharges of renal afferent nerve fibers, and further analyze the possible mechanisms.The results obtained are as follows: 1. Intrarenal artery injection of L-arginine inhibits spontaneous activity of renal afferent nerve fibers Fifty-two rabbits were used to determine the effect of intrarenal artery injection of L-arginine on multi- and single-unit spontaneous discharges of renal afferent nerve fibers in anesthetized rabbits. The results obtained are as follows: ( 1 ) Intrarenal artery injection of L-arginine 0.05, 0.24, and 0.48 mmol/kg decreased the ARNA in a dose-dependent manner (from 100% to 83.58 ± 2.06 %, 37.29 ± 4.10 %, and 15.33 ± 2.70 % respectively, P < 0.001 ; lasted for 2 ~ 6 min) with arterial pressure unchanged; ( 2 ) Intrarenal L-arginine 0.24 mmol/kg decreased single-unit discharge of ARNA from 0.19 ± 0.05 to 0.07 ± 0.02 impulse/s ( P < 0.001 ), lasting 3.8 ± 0.3 min; ( 3 ) Pretreatment with a nitric oxide synthase inhibitor L-NAME ( N6-nitro-L-arginine methylester, 0.11 mmol/kg ), completely abolished the effect of L-arginine; (4) Intrarenal artery injection of a NO donor SIN-1 ( 3-morpholinosydnonimine, 3.75 μmol/kg ) also resulted in an inhibition of ARNA (from 0.19 ± 0.06 to 0.05 ± 0.01 impulse/s P < 0.001; lasted for 5.1 ± 0.3 min ). The results suggest that intrarenal artery injection of NO precursor ( L-arginine ) and donor ( SIN-1 ) can inhibit ARNA in anesthetized rabbits.Key words: L-arginine;nitric oxide;...
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