Rapid effects of estrogen and progesterone on tone and spontaneous rhythmic contractions of the rabbit bladder

Abstract

Previous studies indicate that bladder instability in man may be associated with increased spontaneous rhythmic contractile activity. Ca²⁺ influx plays a central role in smooth muscle contractions, and recent evidence suggests that steroid hormones rapidly affect Ca²⁺ influx. Therefore we tested the hypothesis that estrogen and progesterone modulates spontaneous rhythmic detrusor contractions. Tissues were secured to isometric force (F) transducers in tissue baths and length-adjusted until K⁺-depolarization produced maximum contractions (F_o). Spontaneous rhythmic contractions (SRC) were sampled before and immediately after addition of estradiol or progesterone (10⁻⁵ M) to tissue baths. The average frequency and amplitude of SRC were, respectively, 0.156 Hz and 0.053 F/F_o (n = 24). Estradiol caused an immediate reduction in SRC, such that by 10 min, tone, frequency and amplitude were each reduced by, respectively, 36%, 46% and 47% (n = 7, P < 0.05). However, progesterone caused an immediate weak contraction, and at steady state (10 min), progesterone increased frequency of SRC by 152% but decreased SRC amplitude by 50% (n = 10, P < 0.05). Novel therapies using unique steroids that do not interact with genomic receptors may potentially reduce bladder smooth muscle activity, thereby reducing detrusor instability.