Distribution of calcitonin gene-related peptide, atrial natriuretic peptide and neuropeptide Y in the rat heart.

Calcitonin gene-related peptide (CGRP) is a novel neuropeptide, predicted on the basis of structural analysis of the rat calcitonin gene. It is a neurotransmitter which has been suggested to take part in sensory transmission. In this study, we have examined the distribution of this peptide, alpha-atrial natriuretic peptide immunoreactivity (irANP) and neuropeptide Y (NPY) within different regions of the rat heart. Attempts were also made to compare the distributions of these peptides in the regions examined, through different methods of immunocytochemistry and further comparing these results with those obtained through radioimmunoassay. The distributions of the peptides in the atria were similar to results obtained with radioimmunoassay, but there were no myocytes containing irANP in the ventricles with immunocytochemistry as opposed to radioimmunoassay. While the staining obtained for irANP in the atrium was more intense in the right, CGRP and NPY nerve fibres were two to three times more abundant in the left atrium. The high local concentration of a vasoconstrictor peptide in the region of coronary vessels may suggest that it is involved in the control of vascular smooth muscle tone. The method of choice with the immunocytochemical studies was that of the susa wax technique for irANP. Caution should therefore be observed when interpreting results based only on a single staining technique.