Calcitonin gene-related peptide-induced relaxation in isolated small superior mesenteric arteries from adult stroke-prone spontaneously hypertensive rats.

1. The relaxant responses to calcitonin gene-related peptide (CGRP) of the 3rd order branches of the superior mesenteric arteries (SMA) from 6 month old stroke-prone spontaneously hypertensive rats (SHRSP) and age-matched Wistar-Kyoto (WKY) rats were studied in vitro. 2. Cumulative addition of CGRP (10(-11)-10(-7) mol/L) caused endothelium-independent relaxation of arterial rings precontracted with noradrenaline (10(-6) mol/L). A markedly increased response to CGRP was observed in SHRSP. 3. There was no significant difference between SHRSP and WKY in relaxation produced by forskolin, dibutyryl cyclic AMP and 3-isobutyl-1-methylxanthine. 4. Pretreatment with glibenclamide (10(-6) mol/L) did not affect CGRP-induced relaxation in either SHRSP or WKY. 5. These results indicated that CGRP-induced vasodilation was increased in the small branches of SMA from SHRSP, and that this increase did not seem to be associated with an augmented response to cyclic AMP or with increased involvement of ATP-sensitive potassium channels.