The vasorelaxing effect of CGRP and natriuretic peptides in isolated bovine retinal arteries.
OBJECTIVE
To study the vasorelaxing effect of calcitonin gene-related peptide (CGRP) and natriuretic peptides on isolated bovine retinal arteries (BRAs) and to evaluate the possibility of the unidentified retinal relaxing factor (RRF) being one of these peptides.


METHODS
Retinal arteries were isolated from bovine eyes and mounted in a wire myograph for isometric tension recording. Concentration-response curves were generated by cumulative addition of the peptides to the organ bath.


RESULTS
In BRAs, CGRP-induced relaxation was significantly reduced by removal of the endothelium or by application of the nitric oxide synthase (NOS) inhibitor N(omega)-nitro-l-arginine (l-NA) or the soluble guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ). The nonselective K(+) channel blocker tetraethylammoniumchloride (TEA) and the voltage-dependent K(+) channel blocker 4-aminopyridine significantly reduced the CGRP response, whereas the Ca(2+) activated K(+) channel blockers apamin plus charybdotoxin, the inward rectifier K(+) channel blocker Ba(2+), and the adenosine triphosphate (ATP)-sensitive K(+) channel blocker glibenclamide had no effect. The CGRP receptor antagonist CGRP 8-37 caused a small, but not significant, rightward shift in the concentration-response curve for CGRP, whereas the AM-receptor antagonist AM 22-52 had no effect. The natriuretic peptides did not induce relaxation in isolated retinal arteries.


CONCLUSIONS
Endothelium-derived NO, voltage-dependent K(+) channels, and possibly also CGRP(1) receptors are involved in the CGRP response in BRAs. The natriuretic peptides do not induce vasorelaxation in isolated BRAs. No evidence was found that CGRP or a natriuretic peptide is the as yet unidentified RRF.
Boussery
Koen
K
Department of Physiology and Pathophysiology, Ghent University, Belgium.
Delaey
Christophe
C
Van de Voorde
Johan
J
D000818:Animals; D015740:Calcitonin Gene-Related Peptide / Q000494:pharmacology*; D000077221:Calcitonin Gene-Related Peptide Receptor Antagonists; D002417:Cattle; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007537:Isometric Contraction / Q000502:physiology; D009126:Muscle Relaxation / Q000187:drug effects*; D009131:Muscle, Smooth, Vascular / Q000502:physiology*; D045265:Natriuretic Peptides / Q000494:pharmacology*; D019335:Nitroarginine / Q000494:pharmacology; D010069:Oxadiazoles / Q000494:pharmacology; D010446:Peptide Fragments / Q000494:pharmacology; D026902:Potassium Channel Blockers / Q000494:pharmacology; D015221:Potassium Channels / Q000502:physiology; D011810:Quinoxalines / Q000494:pharmacology; D012039:Regional Blood Flow / Q000502:physiology; D012161:Retinal Artery / Q000502:physiology*; D014664:Vasodilation / Q000502:physiology*
C095284:1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one; D000077221:Calcitonin Gene-Related Peptide Receptor Antagonists; D004791:Enzyme Inhibitors; D045265:Natriuretic Peptides; D010069:Oxadiazoles; D010446:Peptide Fragments; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D011810:Quinoxalines; C058636:calcitonin gene-related peptide (8-37); D019335:Nitroarginine; D015740:Calcitonin Gene-Related Peptide