Uterine response to nerve stimulation; relation to hormonal status and catecholamines

Immature Dutch rabbits were treated as follows: group 1 , 70 µg estradiol-17s every other day for 4 days; group 2 , 70 µg estradiol-17s every other day for 4 days, then 5 mg progesterone daily for 5 days; group 3 , untreated controls. Uterine muscles with their hypogastric nerves attached were isolated, and the responses of the uterus to hypogastric nerve stimulation were recorded. Nerve stimulation (5–50 pulses/sec) contracted uteri from untreated and estrogen-treated rabbits. Nerve stimulation inhibited the spontaneous contractions of estrogen + progesterone-treated animals. These effects were unchanged by atropine or hexamethonium but were abolished by the adrenergic blocking agents phentolamine (estrogen-treated uteri) and propranolol (estrogen + progesterone-treated uteri). Uterine catecholamine content was unaltered by hormonal treatment. Pretreatment with reserpine greatly diminished uterine catecholamine content as well as the response to nerve stimulation in all animals. The hypogastric nerves therefore contain predominantly postganglionic adrenergic fibers, and the effects of their stimulation on uterine activity depend on the hormonal status of the myometrium.