The relaxant of vasodilator peptides were examined in ring preparations of basilar arteries from stroke-prone spontaneously hypertensive rats (SHRSP) and Wistar-Kyoto (WKY) rats. 2. Vasoactive intestinal peptide and peptide histidine isoleucine produced similar endothelium-independent relaxations in basilar arteries from WKY rats and SHRSP. Calcitonin gene-related peptide (CGRP) elicited endothelium-independent relaxations in both groups and the CGRP-induced relaxation was greater in SHRSP than in WKY rats. Substance P and neurokinin A did nor relax basilar arteries from either group. 3. Both WKY rat and SHRSP basilar arteries were relatively insensitive to atrial natriuretic peptide, brain natriuretic peptide and C-type natriuretic peptide. 4. Bradykinin (BK) potently relaxed basilar arteries with endothelium, but BK produced contractions in endothelium-rubbed arteries in both WKY rats and in SHRSP. There was no significant difference in the relaxant response to BK between WKY rat and SHRSP arteries. 5. Adrenomedullin (AM) produced endothelium-independent relaxations in both groups and the relaxant response to AM was significantly greater in SHRSP than in WKY rats. 6. Human CGRP(8-37;mumol/L), a CGRP receptor antagonist, significantly inhibited both relaxant responses induced by CGRP and AM in WKY rats and in SHRSP arteries. 7. Among various peptides tested, the responses to CGRP and AM were higher in basilar arteries from SHRSP than in those from WKY rats. The relaxation produced by AM may be via CGRP receptors in WKY rat and SHRSP basilar arteries.
