Calcitonin gene-related peptide (CCRP), but not tachykinins, causes relaxation of small arteries from the rainbow trout gut

Possible vasoactive effects on small diameter arteries from the rainbow trout gut of calcitonin gene-related peptide (CGRP-chicken) and different fish tachykinins; substance P (SP-trout), neurokinin A (NKA-trout), scyliorhinin I and IT (SCY I and SCY LI-dogfish), were investigated. CGRP relaxed precontracted arteries with a pD(2) value of 8.3 +/- 0.2. Relaxation to CGRP 10(-8) M was reduced by 86.4 +/- 5.2% by the CGRP-1 receptor antagonist CGRP(8-37) (10(-6) M), but unaffected by N-G-nitro-L-arginine (10(-4) M), indomethacin (10(-6) M) and by removal of the endothelium, suggesting no involvement of nitric oxide, prostaglandins or endothelium-derived factors. A low number of CGRP immunoreactive fibers were present in the arterial wall. The tachykinins (10(-12)-10(-6) M) occasionally contracted the relaxed vessel. No synergistic action of SP on the CGRP-induced response was found. A dense plexus of tachykinin-containing fibers without coexisting CGRP innervated the arterial wall. Tachykinins or CGRP had no effect on small diameter veins, and no such immunoreactivity was found in these vessels. In conclusion, CGRP-and tachykinin-containin,rr fibers innervate trout gut arteries. CGRP probably is vasodilatory, while the function of the tachykinin fibers is unknown. (C) 1998 Elsevier Science Inc.