Changes of autonomic receptors following castration and estrogen administration in the male rabbit urethral smooth muscle.

Effects of castration and estrogen administration on the distribution of autonomic receptors in the male rabbit urethral smooth muscle were examined. Thirty-eight mature Japanese white rabbits were used. Eight rabbits were used as untreated control. The other 30 rabbits were castrated and 10 of them were administered intramuscularly with 5 mg/kg estrogen 3 times a week for 4 weeks from 12 weeks after castration. Autonomic receptor densities in the urethral smooth muscle were measured by radioligand binding techniques. alpha 1-Adrenergic and muscarinic cholinergic receptor densities decreased significantly after castration and were not affected by estrogen administration. alpha 2-Adrenergic receptor density increased slightly after castration and markedly after estrogen administration. beta-Adrenergic receptors were not affected either by castration or estrogen administration. No significant changes were observed in any receptor affinities. These results demonstrate the effects of castration and estrogen administration on the autonomic receptors in the male rabbit urethral smooth muscle.