Cholinergic and adrenergic neural control of smooth muscle function in the non-pregnant rat uterine cervix

The isolated circular smooth muscle of the uterine cervix from spayed rats was investigated in vitro. One group of animals was treated with oestrogen. Preparations from these rats showed no spontaneous contractile activity, but responded with contractions to electrical field stimulation. The contractions were blocked by approximately 85% with atropine, scopolamine and tetrodotoxin, but were unaffected by the adrenergic antagonists propranolol, phenoxybenzamine, and yohimbine. This neurogenic effect was potentiated by neostigmine. Noradrenaline inhibited the nerve-induced contractions and also lowered resting tension in a concentration-dependent way. The latter effect of noradrenaline was inhibited by propranolol. The indirect effects of noradrenaline on the electrically induced contractions were also inhibited by propranolol, but potentiated with phenoxybenzamine and, to a less extent, yohimbine. Nerve-induced relaxation was never observed. Acetylcholine contracted the smooth muscle by an effect that was counteracted by atropine. A second group of spayed rats was not given any steroid treatment. The cervix preparations from these animals showed spontaneous activity, which was uninfluenced by atropine, propranolol, phenoxybenzamine, yohimbine, and tetrodotoxin. Noradrenaline inhibited the spontaneous activity. This noradrenergic effect was counteracted by propranolol and potentiated by phenobenzamine. Acetylcholine increased the smooth-muscle tone by an atropine-sensitive action. The results suggest the presence of a cholinergic motor innervation on the non-pregnant rat uterine cervix. The cervix also receives an adrenergic innervation, which may act both post-junctionally (lowering resting tension and inhibiting spontaneous activity) and prejunctionally (modulating the cholinergic nerves) via beta-adrenergic as well as alpha-adrenergic receptors.