C-terminal calcitonin gene-related peptide fragments and vasopressin but not somatostatin-28 induce miosis in monkeys

Abstract

The miotic effects of C-terminal calcitonin gene-related peptide (CGRP) fragments, somatostatin-28 and vasopressin have been evaluated with special attention being paid to possible interactions with cholecystokinin (CCK) A receptors. The peptides were injected intracamerally to anesthetized monkeys pretreated with indomethacin and atropine. CGRP-(32–37) induced a miosis with a potency 1000 times lower than that previously found with sulphated CCK-8. Two other fragments, CGRP-(30–37) and CGRP-(31–37), also had miotic properties. The CGRP-(32–37)-induced miosis was antagonized by the CCK A receptor antagonist loxiglumide. No contractile effect was elicited by 67 pmol-7.4 nmol somatostatin-28. Vasopressin (360 pmol) caused a small reduction in pupil size. Loxiglumide pretreatment did not affect the reduction in pupil size but a vasopressin receptor antagonist partly inhibited the response. The results indicate that CGRP-(32–37) is a miotic with low potency but high efficacy in the monkey eye, probably interacting with CCK A receptors, and that vasopressin is a miotic with low potency and efficacy, probably acting via vasopressin receptors.