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

Abstract

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 anesthetized rabbits. From pressure recordings in intact animals and contractile responses of strips, 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 estrogen. 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 estrogen 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 estrogen 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 estrogen treatment. In guinea pigs bursts of spikes occurred in control animals; after hormone treatment there was often incomplete recovery of spikes within the burst. Estrogens can influence the smooth muscle of the urethra by modifying both spontaneous activity and the responses to stimulation of .alpha.-adrenoceptors.