Abstract
Calcitonin gene-related peptide (CGRP) invariably induced a slow acting but potent relaxation of bovine retinal small arteries contracted with PGF 2α. Maximal relaxation obtained was 93% and 96% with a pD 2-value of 8·97 and 8·86 for rat and human CGRP, respectively; thus the bovine retinal arteries cannot discriminate between CGRP from these two species. The CGRP-induced relaxation was reversible. Substance P was without effect on retinal arteries contracted with PGF 2α. Bradykinin relaxed 4 of 18 vessels tested in the concentration range of 11 −11–10 −8 m whereas the vessels were contracted again at 3 × 10 −8 m. Bradykinin was without effect in the remaining 14 vessels. None of the peptides had a contractile effect on retinal arteries kept relaxed in normal buffer solution. Capsaicin 3 × 10 −5 m induced a relaxation comparable to that obtained by 10 −9 m of CGRP. The capsaicin-induced relaxation was reproducible and it was concentration dependently inhibited by ruthenium red which suggests that capsaicin releases CGRP in the arterial wall. The results indicate that CGRP has a powerful relaxing effect on the retinal vasculature indicating a role for CGRP in ocular blood flow regulation.
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