Isolation of calcitonin mRNA initiated studies on the multigene complex encoding a family of peptides: calcitonin, its terminal flanking peptides, calcitonin gene-related peptide (CGRP), and amylin. CGRP is expressed in alpha- and beta-forms that vary by one and three amino acids in rat and humans, respectively. Both alpha- and beta-CGRP are very similar in their biologic activities, therefore the role of duplicating the calcitonin/CGRP gene is unclear. CGRP behaves principally as a regulatory neuropeptide acting locally through interaction with target organ receptors that are either cyclic-AMP dependent, or capable of activating KATP channels of vascular smooth muscle. The dense distribution of CGRP-rich structures and the expression of mRNA in the central nervous system suggests that CGRP has a neuromodulator or neurotransmitter role not limited to vasoregulatory effects only, but like calcitonin, extends its action to physiologic, metabolic, and behavioral functions. Activation of perivascular sensory nerves stimulates the release of neuropeptides, including CGRP, which exerts a potent vasodilatory effect on venous and arterial vasculature. The increased levels of CGRP-like immunoreactivity were observed in volume overload states, in heart failure and myocardial infarction, and in some forms of hypertension. The beneficial effect of CGRP infusions was demonstrated in patients with congestive heart failure and also in subjects with neurological deficits after surgical treatment of subarachnoid hemorrhage. On the other hand, there are experimental studies on the inhibition of increased CGRP activity, in septic and shock conditions, in which the vascular hyperrelaxation could have deleterious effects.(ABSTRACT TRUNCATED AT 250 WORDS)