Dose-dependent systemic and regional hemodynamic effects of calcitonin gene-related peptide.

The dose-response effects of infused calcitonin gene-related peptide (CGRP), a potent vasodilator, on systemic and regional hemodynamics in the conscious rat remain incompletely defined. The radioactive microsphere technique provided these determinations before and after the intravenous administration of vehicle or 22, 65, 220, and 2200 pmol of CGRP. Neither vehicle nor 22 pmol of CGRP significantly changed any systemic or regional hemodynamic parameter. Starting at the 65-pmol dose, CGRP significantly decreased mean blood pressure and total peripheral resistance, while increasing heart rate without changing cardiac output. CGRP produced selective regional vasodilatory effects, with the coronary circulation being unusually sensitive. In contrast, CGRP caused significant increases in blood flow to the mesenteric and cutaneous circulations only at the two highest doses. CGRP increased plasma norepinephrine, epinephrine, and renin activity significantly at only the 2200-pmol dose. In conclusion, CGRP decreases blood pressure by peripheral vasodilation, with a threshold dose occurring between 22 and 65 pmol. In addition, the coronary circulation appears to be particularly sensitive to the vasodilatory properties of CGRP.