nitroarginine and Hydronephrosis

Proteinase-activated receptors (PARs) are a novel class of G protein-coupled receptors that respond to signals through endogenous proteinases. PAR activation involves enzymatic cleavage of the extracellular NH(2)-terminal domain and unmasking of a new NH(2) terminus, which serves as an anchored ligand to activate the receptor. At least four PAR subtypes have been identified. In the present study, we used the in vitro perfused hydronephrotic rat kidney to examine the effects of activating PAR-2 on the afferent arteriole. The synthetic peptide SLIGRL-NH(2), which corresponds to the exposed ligand sequence and selectively activates PAR-2, did not alter basal afferent arteriolar diameter but caused a concentration-dependent vasodilation (3-30 microM) of arterioles preconstricted by angiotensin II (0.1 nM). A modified peptide sequence (LSIGRL-NH(2), inactive at PAR-2) had no effect. This vasodilation was characterized by an initial transient component followed by a smaller sustained response. A similar pattern of vasodilation was seen when SLIGRL-NH(2) was administered to isolated perfused normal rat kidney. The sustained component of the PAR-2-induced afferent arteriolar vasodilation was eliminated by nitric oxide (NO) synthase inhibition (100 microM nitro-L-arginine methyl ester). In contrast, the transient vasodilation persisted under these conditions. This transient response was not observed when afferent arterioles were preconstricted with elevated KCl, suggesting involvement of an endothelium-derived hyperpolarizing factor. Finally, RT-PCR revealed the presence of PAR-2 mRNA in isolated afferent arterioles. These findings indicate that PAR-2 is expressed in the afferent arteriole and that its activation elicits afferent arteriolar vasodilation by NO-dependent and NO-independent mechanisms.

Topics: Acetylcholine; Angiotensin II; Animals; Anti-Inflammatory Agents, Non-Steroidal; Arterioles; Enzyme Inhibitors; Hydronephrosis; Ibuprofen; Kidney; Male; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Oligopeptides; Potassium Chloride; Rats; Rats, Sprague-Dawley; Receptor, PAR-2; Receptors, Thrombin; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Vasodilation

To define the role of endothelium-derived relaxing factor (EDRF) in the regulation of renal hemodynamics in the hydronephrotic kidney.. Experiments were performed in control rats and in rats that had undergone unilateral ureteral ligation 6 weeks before. Renal blood flow was monitored before and after inhibition of EDRF synthesis in the control and hydronephrotic animals. Videomicroscopy was also performed in hydronephrotic animals to observe directly the effect of inhibition of EDRF synthesis on the renal microcirculation.. Inhibition of EDRF synthesis resulted in a 61% decrease in renal blood flow in the control animals compared with only a 27% decrease for the hydronephrotic animals. The videomicroscopy studies demonstrated that inhibition of EDRF synthesis results in significant vasoconstriction of the preglomerular and postglomerular resistance vessels.. Although EDRF continues to play a significant role in the maintenance of renal blood flow in the chronically obstructed kidney, EDRF synthesis by the renal vascular endothelium may be reduced in this setting, contributing to ischemic renal atrophy.

Topics: Acetylcholine; Animals; Arginine; Chronic Disease; Disease Models, Animal; Dose-Response Relationship, Drug; Endothelium, Vascular; Hemodynamics; Hydronephrosis; Male; Microcirculation; Microscopy, Video; Nitric Oxide; Nitroarginine; Rats; Rats, Wistar; Renal Circulation; Vasoconstriction

Renal autoregulation curves are reset toward higher renal arterial pressure in spontaneously hypertensive rats (SHR) compared with those in Wistar-Kyoto rats (WKY). We previously demonstrated that myogenic afferent arteriolar constriction is shifted to higher renal arterial pressure. To investigate whether nitric oxide participates in the regulation of myogenic tone, we examined the effect of nitro-L-arginine on myogenic afferent arteriolar constriction in kidneys from SHR and WKY, using the isolated perfused hydronephrotic kidney. Elevating pressures from 40 to 80 mm Hg caused increases in afferent arteriolar diameter in WKY (from 18.2 +/- 0.4 to 19.0 +/- 0.3 micron) and SHR (from 17.3 +/- 0.6 to 18.4 +/- 0.6 micron). Further pressure elevation elicited constriction at 100 mm Hg in WKY (17.9 +/- 0.3 micron), but significant constriction was observed at 120 mm Hg in SHR (17.3 +/- 0.6 micron), indicating a resetting in myogenic responses to higher pressures. In WKY, after treatment with 10 mumol/L nitro-L-arginine, afferent arterioles exhibited pressure-dependent constriction, with a threshold pressure for constriction at 80 mm Hg. The addition of 100 mumol/L nitro-L-arginine had no further effect on myogenic responsiveness in WKY. In contrast, in SHR, nitro-L-arginine dose-dependently shifted the myogenic responses toward lower renal arterial pressure, with threshold pressures for constriction observed at 100 mm Hg (10 mumol/L) and 80 mm Hg (100 mumol/L).(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Arginine; Arterioles; Homeostasis; Hydronephrosis; Hypertension; Kidney; Male; Nitric Oxide; Nitroarginine; Nitroprusside; Perfusion; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Receptors, Vasopressin; Vasoconstriction

Acetylcholine (ACh) elicits vasodilation by releasing a number of endothelium-derived relaxing factors (EDRFs). We used the isolated perfused hydronephrotic rat kidney to examine the characteristics of ACh-induced vasodilation of renal afferent arterioles during different types of underlying vasoconstriction. Basal arteriolar tone was increased by either elevating perfusion pressure to 180 mm Hg (myogenic), administering 0.3 mumol/L norepinephrine (NE), or elevating medium potassium concentration to 30 mmol/L (KCl). ACh (10 mumol/L) completely reversed myogenic and NE-induced vasoconstriction and reversed KCl-induced vasoconstriction by 80 +/- 5%. However, whereas ACh produced a sustained vasodilation during KCl- and NE-induced vasoconstriction, only a transient reversal of myogenic vasoconstriction was observed, and myogenic tone recovered within 5 to 10 minutes. ACh-induced vasodilation of arterioles preconstricted with KCl was markedly inhibited by either indomethacin (100 mumol/L) or nitro-L-arginine (100 mumol/L) and was completely abolished by pretreatment with both inhibitors. In contrast, indomethacin and nitro-L-arginine had no effect on the transient response to ACh observed during pressure-induced vasoconstriction. In vessels preconstricted with NE, nitro-L-arginine converted the normally sustained response to ACh to a transient vasodilation, which was refractory to both nitric oxide synthase and cyclooxygenase inhibition. Since this component was not observed during KCl-induced vasoconstriction, it may reflect the actions of an, as yet unidentified, endothelium-derived hyperpolarizing factor (EDHF). Our findings thus suggest that prostanoids, nitric oxide, and EDHF all contribute to ACh-induced renal afferent arteriolar vasodilation and that the relative contributions of these individual EDRFs depends on the nature of the underlying renal vascular tone.

Topics: Acetylcholine; Animals; Arginine; Arterioles; Biological Factors; Hydronephrosis; In Vitro Techniques; Indomethacin; Kidney; Male; Microcirculation; Muscle, Smooth, Vascular; Nitroarginine; Norepinephrine; Potassium Chloride; Rats; Rats, Sprague-Dawley; Renal Circulation; Vasoconstriction; Vasodilation