The effects of oestrogens on spontaneous activity and responses to phenylephrine of the mammalian urethra.

The electrical and mechanical activity of strips of urethral smooth muscle from female ovariectomized rabbits were studied. Results were compared with strips from guinea-pigs, dogs and Tammar wallabies and with anaesthetized rabbits. From pressure recordings in intact animals and contractile responses of strips it was concluded that in the urethra of the rabbit both cholinergic and alpha-adrenergic receptors were excitatory. Urethral strips from rabbits and wallabies had continuous spontaneous mechanical activity that was reduced by pre-treatment with oestrogen. In dogs spontaneous activity was transient and in guinea-pigs was usually absent. The alpha-adrenergic agonist, phenylephrine, produced a dose-related contraction of urethral strips from all species. Pre-treatment with oestrogen produced no significant change in the rabbit and guinea-pig but increased sensitivity in the dog and wallaby. Electrical activity was recorded with micro-electrodes from smooth muscle cells of rabbit and guinea-pig urethra. In both species pre-treatment with oestrogen produced slight depolarization. In rabbits regular spike activity was recorded from all animals but there was a tendency for double spikes and reduced amplitude following oestrogen treatment. In guinea-pigs bursts of spikes occurred in control animals; after hormone treatment there was often incomplete recovery of spikes within the burst. The results indicate that oestrogens can influence the smooth muscle of the urethra by modifying both spontaneous activity and the responses to stimulation of alpha-adrenoceptors.