Mechanical responses of the rat uterus, cervix, and bladder to stimulation of hypogastric and pelvic nerves in vivo.

Mechanical activities of the uterus, cervix, and bladder were recorded in vivo in anesthetized rats during electrical stimulation of either the hypogastric or pelvic nerve. Ovariectomized controls and hormone-treated groups were used as well as pregnant and postpartum rats. Stimulation of either hypogastric or pelvic nerve produced voltage- and frequency-dependent contractions of the three organs with no evidence of apparent inhibition. All evoked responses were completely abolished by tetrodotoxin, suggesting that these nerves are common pathways of innervation to the three organs. Atropine abolished uterine and cervical responses to both hypogastric and pelvic nerve stimulation, whereas bladder responses were only partly reduced. Hexamethonium almost totally blocked the evoked responses of the uterus and cervix. Phentolamine partly blocked uterine and cervical responses, and propranolol or physostigmine enhanced uterine and cervical responses to both hypogastric and pelvic nerve stimulation. These results suggest that motor innervation to the rat uterus and cervix is predominantly postganglionic cholinergic, with some alpha- and beta-adrenergic components, and that the bladder is innervated by mainly cholinergic and also noncholinergic nerves. Estrogen and estrogen-plus-progesterone pretreatment significantly increased the responses of uterus and cervix but not bladder. Uterine and cervical responses to either hypogastric or pelvic nerve stimulation were markedly reduced late in pregnancy and reappeared within 7 days after delivery.