Calcitonin gene-related peptide innervation and binding sites in rat aorta during development.

Indirect immunohistochemistry performed on whole mounts of arch and thoracic part of the rat aorta at six developmental stages (from embryonic day 17 to 6 months, in males and females) revealed that calcitonin gene-related peptide (CGRP) innervation is highest in the arch. The highest density of innervation is found at the three first postnatal ages investigated (day 1, day 3 and 5 weeks; 2.6 +/- 0.6 intercepts/mm in the arch at 1 day); however, all values are low compared to other arteries. The innervation grows from a few short isolated fibres in the embryo to a more complex meshwork in older animals. No striking differences were noticed between males and females. Autoradiographic studies were performed on serial sections at several levels of the aorta but did not reveal binding sites for CGRP in the vascular wall. This might be due to the technique which does not allow visualization of low density of binding sites, or to binding sites of weak affinity. We discuss the possible importance of CGRP in rat aortic smooth muscle development.