Reserpine non-selectively inhibits rat uterus contraction in vitro.

1. Reserpine produced a direct in vitro non-selective inhibitory effect on smooth muscle contraction of endometrium-free rat uterus. 2. Reserpine uptake into uterine muscle and its antagonistic effect on contraction had a similar time course. 3. Reserpine had a relaxing effect similar to that of trifluoperazine and different from that of verapamil or papaverine, and also failed to exert any inhibitory effect on 45Ca uptake rate. 4. Both reserpine and trifluoperazine but not verapamil inhibited the acetylcholine-induced contraction when present during the Ca-release from intracellular stores. 5. It is hypothesized that reserpine exerts its inhibitory action intracellularly on the activation of smooth muscle contraction by sarcoplasmic Ca2+.