Distribution of calcitonin gene-related peptide-like immunoreactivity in the guinea pig heart.

The distribution of calcitonin gene-related peptide like-immunoreactivity (CGRP-IR) within the heart and adjacent blood vessels of the guinea pig was investigated immunohistochemically by use of the peroxidase-antiperoxidase (PAP) technique. Numerous paravascular and perivascular immunoreactive nerve fibers were localized around the aorta, coronary arteries and their branches down to the terminal vasculature. Arterioles in the atria showed greatest density of immunoreactive varicosities of all blood vessels. The epicardium, endocardium and the conductive system also contained numerous CGRP-IR nerve fibers. In the myocardium the number of immunoreactive varicosities was variable. Many were present in both atria, moderate amounts were seen in the right ventricle and parts of the intraventricular septum, and only a few occurred in the left ventricle. CGRP-IR was infrequently found within intracardial ganglionic cells but was abundantly distributed in the surrounding nerve fibers.