Direct effect of amezinium on rabbit urethra: effect of estrogen and progesterone treatment.

The effect of amezinium, a new anti-hypotensive agent, and hormonal treatment on the female rabbit urethra was investigated. Cumulative dose responses were obtained for amezinium and norepinephrine on strips of muscle from the urethras of ovariectomized female rabbits by means of the tissue-bath system. Amezinium enhanced the response to electrical field stimulation and showed a direct contractile response on the urethra. These responses were only about 20% of the maximum norepinephrine response. The contractile response to amezinium was completely blocked by prazosin. When rabbits were pretreated with estrogen, with or without progesterone, for 4 weeks, the response to amezinium increased to 40% of the maximum norepinephrine response. Although amezinium enhances muscle contractile responses to electrical stimulation, this effect is strong when amezinium is used alone; concurrent estrogen treatment improves the effects of amezinium.