The role of activation of the sympathetic nervous system in the central pressor action of calcitonin gene-related peptide in conscious rats.

The effects of intracerebroventricular (i.c.v.) administration of calcitonin gene-related (CGRP) on blood pressure and heart rate (HR), and the underlying mechanisms were studied in conscious rats. CGRP (0.1-3.0 nmol i.c.v.) increased mean arterial blood pressure (MABP) and HR. CGRP (3.0 nmol i.c.v.) also significantly increased both plasma norepinephrine and epinephrine concentrations. Pretreatment with 16.5 nmol i.c.v. CGRP(8-37), a specific CGRP receptor antagonist, significantly inhibited the i.c.v. CGRP (1.0 nmol)-induced increases in MABP and HR. Phenoxybenzamine inhibited the i.c.v. CGRP-induced increase in MABP, while propranolol suppressed the tachycardiac response to i.c.v. CGRP. Chemical sympathectomy by 6-hydroxydopamine inhibited the increases in MABP and HR produced by i.c.v. CGRP. These results suggest that the central pressor and tachycardiac effects of i.c.v. CGRP are mediated by catecholamine release due to stimulation of sympathetic nervous system activity, possibly via specific CGRP receptors in the central nervous system.