Calcitonin gene-related peptide is a venous dilator in conscious rats

The effect of calcitonin gene-related peptide (CGRP) on body venous tone is not known. This study examines the dose-response effects of rat alpha CGRP on mean circulatory filling pressure (MCFP), an index of body venous tone, in conscious rats. Dose-response curves of CGRP were constructed in three groups of rats, namely, (I) intact, (III) rats pretreated with the ganglionic blocker hexamethonium and (V) rats pretreated with noradrenaline to raise mean arterial pressure (MAP) and MCFP. Three additional groups, (II), (IV) and (VI), served as time controls and were treated similarly to (I), (III) and (V), respectively, except that they were given saline (0.9% NaCl) in place of CGRP. The infusion of CGRP in intact rats dose dependently decreased MAP, increased heart rate (HR) and slightly reduced MCFP. In ganglionic-blocked rats, CGRP caused similar depressor responses but less tachycardia than in intact rats, however, it also slightly reduced MCFP. In rats given noradrenaline, CGRP dose dependently decreased MAP, MCFP and increased HR. The results show that CGRP has venodilator activities; its venous effect is best revealed at elevated venous tone.