The precise effect of low estrogen levels on urinary bladder contractility remains controversial. The present study was designed to analyze the effect of 17beta-estradiol in bladder smooth muscle contractility and the involvement of specific estrogen receptor stimulation in this effect. Castrated male and female pig detrusor strips were mounted for tension recording in an organ bath, superfused with Krebs solution at 37 degrees C and stimulated electrically and pharmacologically. In order to verify the acute effect of 17beta-estradiol on muscle contractility, the strips were incubated with different concentrations of the hormone. Muscle contractions were induced by potassium chloride, acetylcholine chloride and electrical field stimulation. The involvement of the estrogen receptor in the effects of 17beta-estradiol was assessed by incubation of some strips with the selective estrogen receptor antagonist ICI 182.780 before estradiol was applied. Estradiol at a dose of 30 micromol/l elicited a lower amplitude of contractions induced by EFS, Ach and KCl in female as well as in castrated male pig bladder smooth muscle strips. The effects of 17beta-estradiol were stronger in contractions induced by potassium chloride than those induced by other forms of stimulation. Pre-treatment with the pure estrogen receptor antagonist had no effect on 17beta-estradiol-induced inhibition of muscle contractility. These observations suggest that 17beta-estradiol induces lower amplitude of contraction of female as well as castrated male pig detrusor which is not mediated by the classic estrogen receptor. Furthermore, we can conclude that estradiol has a stronger inhibitory effect on the depolarization of muscle cell membrane compared to a muscarinic receptor-induced contraction.