Substance P and calcitonin gene-related peptide immunoreactivity in nerves of the rat uterus: Localization, colocalization and effects on uterine contractility

Abstract

Immunoreactivity to the neuropeptides substance P (SP) and calcitonin gene-related peptide (CGRP) was examined in nerves in the rat uterus as a prelude to studying their effects on uterine contractility. With immunocytochemical techniques, SP immunoreactivity (SP-I) and CGRP-I were localized in myometrial nerves throughout the uterine horns, with nerves immunoreactive for CGRP being the more numerous. Immunocytochemical double labeling studies revealed SP coexisted with CGRP in a subpopulation of CGRP-I nerve fibers, i.e., SP-I was not present in all CGRP-I nerves. Effects of these neuropeptides on uterine contractility were examined on in vitro preparations of uterine horns from diethylstilbestrol-treated rats. SP (10 −4 to 10 −8 M) stimulated uterine contraction in a dose-related manner. CGRP(1–37) and CGRP(8–37) had no effect on basal uterine tension. While CGRP(1–37) (10 −7 M) reduced SP-stimulated (10 −5 M) uterine contraction by 56%, CGRP(8–37) had no effect on SP-stimulated uterine contraction. However, CGRP(8–37) (10 −6 M) significantly reduced the ability of CGRP(1–37) (10 −7 M) to inhibit SP-stimulated uterine contraction. These results demonstrate that SP- and CGRP-I are present in, and coexist in some uterine nerves, presumably afferent nerves. The first 7 amino acids are necessary for the inhibitory effect of CGRP(1–37) on stimulated uterine contraction. In addition, CGRP(8–37) acted as an antagonist to this inhibitory action. SP and CGRP could be coreleased from afferent fibers in an “efferent fashion” and influence uterine contractility, SP having a contractile effect and CGRP having a relaxing effect.