In vitro administration of 17 beta-estradiol inhibits drug-induced contractions of the rat isolated seminal vesicle.

1. The rat isolated seminal vesicle responded to noradrenaline (NA), acetylcholine (ACh), potassium chloride (KCl) and barium chloride (BaCl2) with reproducible contractions. 2. 17 beta-estradiol (17 beta E) cumulatively added in the isolated organ bath reduced the number of contractions with all agonists used in the rank order of potency: BaCl2 > or = KCl > ACh > NA. The dose-response curves constructed in the presence of 17 beta E (2 x 10(-5) mol/l) produced a rightward shift and a reduction in the maximum response showing inhibitory activity. 3. When the calcium content in the normal Krebs medium (2.5 mmol/l) was reduced to half, the inhibitory activity of 17 beta E was potentiated. The maximum inhibition rates to KCl (phasic and tonic), BaCl2 and ACh were significantly (P < 0.05) different from each other. 4. The inhibitory effects of 17 beta E against all agonists tested were found to be similar in their responses to verapamil, but were much lower in potency. 5. The inhibitory effects of 17 beta E was seen only when the hormone was present in the tissue environment and was readily reversible as soon as the tissue was washed with the Krebs medium, suggesting that the effect of 17 beta E is localized. 6. It is suggested that the in vitro application of 17 beta E on the rat isolated seminal vesicle interferes with the process of translocation of calcium ions from the extracellular medium.