Human and rat alpha-CGRP but not calcitonin cause mesenteric vasodilatation in rats

A single gene encodes both calcitonin and the calcitonin gene-related peptide (CGRP). Human and rat alpha-CGRP were compared with sodium nitroprusside in the rat and rabbit isolated mesenteric vascular preparation perfused at constant flow. In the presence of the vasoconstrictor noradrenaline (10(-5) M), rat alpha-CGRP was about 10 times as potent as either human alpha-CGRP or sodium nitroprusside as a vasodilator in the rat mesenteric vasculature. In the rabbit mesenteric vasculature the order of potency was rat alpha-CGRP greater than human alpha-CGRP greater than sodium nitroprusside. Human and salmon calcitonin showed no vasodilator activity at doses 100 times greater than human alpha-CGRP. These results show that human and rat alpha-CGRP are potent vasodilators in the mesenteric vasculature, an effect not mimicked by the alternative gene product, the plasma calcium lowering hormone calcitonin.