1. Binding sites for calcitonin-gene-related peptide were localized and characterized in porcine coronary arteries using quantitative autoradiography, and the density of binding sites was compared between large epicardial and small intramyocardial coronary arteries.
2. A single class of binding sites for calcitonin-gene-related peptide with a dissociation constant of 2.1 ± 0.2 nmol/l was detected in both the large and small coronary arteries. The density of specific binding sites was higher (maximum binding site density 231 ± 14 fmol/mg of protein) in the small coronary arteries than in the large epicardial coronary arteries (maximum binding site density 108 ± 5 fmol/mg of protein). β-Human calcitonin-gene-related peptide showed higher affinity than α-human calcitonin-gene-related peptide for the binding sites. Most of the specific binding sites for both peptides in the large coronary artery were localized in the intima and media.
3. In coronary artery from patients with coronary heart disease, there were more binding sites for calcitonin-gene-related peptide in the smooth muscle layer of atheromatous segments (7.2 ± 0.7 amol/mm2) than in that of normal segments (3.0 ± 0.3 amol/mm2, P < 0.002).
4. The present findings lend further support to the theory of regional variation in the vasodilator response to calcitonin-gene-related peptide in porcine coronary arteries, which seems to be due to different densities of a single type of receptor for calcitonin-gene-related peptide.