Factors responsible for acetylcholine-induced dilatation in the isolated perfused rat kidney

Both endothelium and afferent nerve endings play a role in acetylcholine-induced renal vasodilation

We investigated the nature and signaling pathways of endothelium- and sensory-nerve ending-derived substances involved in acetylcholine-induced vasodilation in rat isolated perfused kidney. Endothelial denudation by Triton X-100 (0.2%, 0.1 ml) or depletion of afferent nerve endings by capsaicin (10(-6) mol/l) attenuated acetylcholine-induced vasodilation. When these two agents were administered together, the response to acetylcholine was completely inhibited. CGRP1 receptor blocker CGRP 8-37 (10(-7) mol/l) and adenosine A(2) receptor antagonist ZM 241 385 (10(-7) mol/l) inhibited acetylcholine-induced dilation. When indomethacin (10(-5) mol/l), a cyclooxygenase inhibitor, l-NOARG (10(-4) mol/l), a nitric oxide (NO) synthase inhibitor, and potassium chloride (30 mmol/l), to test EDHF response, were perfused simultaneously, the inhibition was greater than that was observed with each agent alone. Guanylate cyclase inhibitor ODQ (10(-5) mol/l) or protein kinase A inhibitor KT 5720 (5x10(-7) mol/l) inhibited acetylcholine-induced dilation. Gap junction uncoupler 18alpha-glycyrrhetinic acid (10(-4) mol/l) caused an uncontrollable increase in basal perfusion pressure making it impossible to test against acetylcholine-induced dilation. Our data suggest that NO, prostanoids, EDHF, and CGRP released from vascular endothelium and afferent nerve endings participate in acetylcholine-induced vasodilation and their signal transduction molecules include protein kinase A and guanylate cyclase.

Mechanism of CGRP-Induced Vasodilation in the Rat Isolated Perfused Kidney

We investigated the intracellular mechanisms involved in calcitonin gene-related peptide (CGRP)-induced vasodilation in rat isolated perfused kidney. CGRP-1 receptor antagonist, CGRP-8-37, abolished the responses. Endothelial denudation by Triton X-100 or nitric oxide (NO) synthase inhibition by NG-nitro-L-arginine attenuated the maximum dilation by about 63 and 55%, respectively. Protein kinase A inhibitor, KT-5720, caused an about 72% inhibition in CGRP-induced maximum dilation. Soluble guanylate cyclase inhibitor, ODQ, and ATP-sensitive potassium channel blocker, glibenclamide, inhibited the CGRP-induced maximum responses by 75 and 55%, respectively. Cyclooxygenase inhibitor, indomethacin, had no effect. Our data suggest that CGRP-1 receptors, endothelium, NO synthase, protein kinase A, soluble guanylate cyclase, and ATP-sensitive potassium channels, but not the cyclooxygenase pathway, may play a role in CGRP-induced vasodilation in rat isolated perfused kidney.

Role of Nitric oxide in the renal and systemic vasodilatory responses to platelet-activating factor in the rat, in vivo

BACKGROUND/AIM

Chemical mediator(s) involved in the renal vasodilatory and systemic hypotensive effects of platelet-activating factor (PAF) remain unresolved. Because nitric oxide (NO) and PAF have many similar cardiovascular actions, we examined whether endogenous NO contributes to the renal and systemic actions of PAF.

METHODS

PAF was administered into the renal arterial or systemic venous circulation of anesthetized rats. The change in renal blood flow (RBF) and/or mean arterial blood pressure (MAP) was recorded in the absence and presence of NO synthase inhibition.

RESULTS

Transient exposure of the renal vacsular bed to intrarenal PAF boluses (1-10 ng kg(-1)) resulted in an immediate increase in RBF that was partially inhibited by the intrarenal administration of a NO synthase inhibitor, whereas the ensuing rapid fall in MAP was unaffected by NO synthase blockade. A sustained exposure to intrarenal PAF infusion (2.5 ng min(-1) kg(-1)) in intrarenal NO synthase inhibitor-treated rats (hypertensive with vasoconstricted kidneys) had no effect on RBF and MAP, which was in contrast to the increase in RBF and modest fall in MAP in control intrarenal vasopressin-treated rats (hypertensive with vasoconstricted kidneys). To dissociate the influence of systemic hypotension on the RBF response, rat kidneys were denervated and MAP elevated by a pressor agent whilst maintaining renal arterial blood pressure constant. Subsequent intrarenal PAF infusion at 2.5 and 10 ng min(-1) kg(-1) resulted in a substantial rise in RBF and modest fall in MAP, responses that were abolished by intrarenal NO synthase inhibition at the lower intrarenal PAF infusion or abolished/attenuated at the higher intrarenal PAF infusion. Additional experiments administered drugs intravenously to exclude the possibility that the modified MAP response by NO synthase inhibition was related to the drugs being administered into the kidney. Intravenous PAF boluses (0.1-1 microg kg(-1)) resulted in a transient fall in MAP that was independent of the NO pathway, whereas the systemic hypotension induced by intravenous PAF infusion (10 ng min(-1) kg(-1)) was greatly attenuated by NO synthase inhibition.

CONCLUSION

NO has a major role in mediating the renal and peripheral vasodilatory responses induced by a sustained exposure to PAF in the rat, whereas NO's overall contribution was less or absent during transient PAF exposure.