Calcitonin gene-related peptide in the rat uterus: presence in nerves and effects on uterine contraction

The influence of calcitonin gene-related peptide (CGRP) on rat uterine activity was examined in concert with the anatomical distribution of CGRP-like immunoreactivity in the uterus. CGRP-like immunoreactivity was localized in nerve fibers; these peptide-containing nerves were abundant throughout the mesometrium of the uterine horn and appeared to innervate mesometrial smooth muscle and vascular smooth muscle. In the uterine wall, CGRP-like immunoreactive fibers were prevalent in the myometrium, endometrium and the endocervix. Fibers in the endometrium and endocervix appeared to form a plexus subjacent to the epithelium and some fibers penetrated the epithelium as an intraepithelial plexus. The action of CGRP (10(-9) to 10(-6) M) on acetylcholine (10(-6) or 10(-5) M)-stimulated uterine activity was examined in vitro. Exogenously applied CGRP induced a dose-dependent relaxation of acetylcholine-stimulated uterine contractions. CGRP had no effect on basal uterine tension. The localization of CGRP-like immunoreactivity in nerves and the relaxing effect of CGRP suggests a role for CGRP-containing nerve fibers in the regulation of uterine activity.