Calcitonin gene-related peptide and its specific binding sites in the cardiovascular system of rat

The concentration of calcitonin gene-related peptide in rat cardiovascular tissues was determined by a specific and sensitive radioimmunoassay and the distribution of its specific binding sites was assessed by radioligand binding studies. The binding of [125I]calcitonin gene-related peptide to cardiovascular membranes was rapid, saturable, reversible and specific. In atrial membranes a single binding site with high affinity (Kd 1.5 nM) and low capacity (120 fmol/mg protein) was detected. The highest concentrations of both calcitonin gene-related peptide and its binding sites were found in the peripheral and mesenteric arteries. The immunoreactive calcitonin gene-related peptide levels were lower in major vessels and lowest in the heart. The number of calcitonin gene-related peptide specific binding sites also showed a similar pattern with the exception of a high concentration of binding sites present in the atria. These findings, together with the proven vasodilatory activity of calcitonin gene-related peptide, suggest that this peptide has an important role as a modulator of peripheral vascular tone and perhaps a direct action of the heart.