Central adrenomedullin augments the baroreceptor reflex in conscious rabbits

We examined the roles of central adrenomedullin, proadrenomedullin N-terminal 20 peptide (PAMP), and calcitonin gene-related peptide (CGRP) on the baroreceptor reflex in conscious rabbits. Intracerebroventricular injection of adrenomedullin (0.2 and 1 nmol/80 microL) elicited dose-related increases in arterial pressure and renal sympathetic nerve activity. On the other hand, a subpressor dose of intracerebroventricular infusion of adrenomedullin (1 nmol/300 microL per hour) caused significant increases in baroreflex sensitivities assessed by renal sympathetic nerve activity and heart rate compared with vehicle infusion (Gmax; -14.9+/-1.7 versus -8.0+/-0.7%/mm Hg, P<0.01, and -8.1+/-0.8 versus -5.1+/-0.5 bpm/mm Hg, P<0.01, respectively). Intracerebroventricular infusion of CGRP (1 nmol/300 microL per hour), which is structurally homologous to adrenomedullin, also enhanced the baroreflex controls of renal sympathetic nerve activity and heart rate. However, the intracerebroventricular infusion of PAMP (30 nmol/300 microL per hour) failed to alter the baseline levels of arterial pressure and baroreflex sensitivities. These results suggest that central adrenomedullin and CGRP, but not PAMP, participate in cardiovascular regulation to augment the baroreflex controls of renal sympathetic nerve activity and heart rate in conscious rabbits.