title: Differential effects of sex hormones and phytoestrogens on peak and steady state contractions in isolated rabbit detrusor.
abstract: OBJECTIVE
  Recent evidence suggests that sex steroids may produce rapid inhibition of voltage operated Ca2+ channels (VOCCs). Detrusor smooth muscle is highly dependent upon Ca2+ influx for receptor-activated contractions. Thus, we examined the relative effectiveness of a select group of sex steroids and dietary phytoestrogens to relax detrusor contracted with the muscarinic receptor agonist, bethanechol (BE) and the purinergic P2X receptor agonist, alpha,beta-methylene ATP (alpha,beta-MeATP).
  
  
  METHODS
  Isolated strips of rabbit detrusor were secured to isometric force transducers in a tissue bath and length-adjusted until maximum contractions were achieved. Peak (P) contractile responses were recorded for alpha,beta-MeATP (P(ATP)) and BE (P(BE)) and steady-state (SS) responses were recorded for BE (SS(BE)) in the presence and absence of selected sex steroids and phytoestrogens (10 microM, unless indicated).
  
  
  RESULTS
  The L-type VOCC inhibitor, nifedipine (1 to 10 microM), completely inhibited P(ATP) but reduced SS(BE) by approximately 50%, whereas the VOCC and non-VOCC inhibitor, SKF 96365, inhibited SS(BE) by approximately 95%, suggesting that P(ATP) was entirely dependent on L-type VOCCs, but (BE)-induced contractions depended also on activation of non-VOCCs. 17Beta-estradiol (estradiol) and progesterone inhibited P(ATP) by approximately 60% and 20%, respectively, and 32 microM estradiol and ethinyl estradiol inhibited SS(BE) by approximately 80 and 95%, respectively. Inhibition by estradiol was potentiated, rather than blocked, by the nuclear estrogen receptor antagonist, tamoxifen. Moreover, tamoxifen alone nearly completely relaxed SS(BE). The inactive metabolite of estradiol, 17alpha-estradiol, inhibited both P(ATP) and P(BE) by approximately 40%. Testosterone had no effect on P(ATP) and P(BE). The phytoestrogen and tyrosine kinase inhibitor, genistein, inhibited SS(BE) by 44%, whereas daidzein, a phytoestrogen without tyrosine kinase inhibitory activity, produced only a 7% inhibition. None of the phytoestrogens examined inhibited P(BE), whereas all inhibited P(ATP) by approximately 20 to 35%. A comparison of inhibition of (BE) and alpha,beta-MeATP-induced contractions by selected estrogen isomers showed some distinct differences. For example, estrone did not inhibit P(BE) or SS(BE), but inhibited P(ATP) by approximately 20%, whereas DES inhibited SS(BE) by nearly 90%, but P(ATP) by a lesser degree (approximately 70%).
  
  
  CONCLUSIONS
  Our data support the hypothesis that 17beta-estradiol, ethinyl estradiol, DES, tamoxifen and genistein may relax detrusor contractions by inhibition of both VOCCs and non-VOCCs. Moreover, our data show that genistein, a dietary phytoestrogen with tyrosine kinase inhibitory activity, selectively reduced alpha,beta-MeATP-induced peak and BE-induced steady-state contractions, sparing the maximum response to BE. Lastly, the inactive isomer, 17alpha-estradiol, inhibited both BE- and alpha,beta-MeATP-induced contractions. These data suggest that certain dietary phytoestrogens (for example, genistein) or sex steroids, especially those with weak activity at the nuclear steroid site (for example, 17alpha-estradiol), or tamoxifen may prove therapeutically useful in treating overactive bladder caused by elevated muscarinic and purinergic receptor activation.
authors.affiliation: Department of Physiological Sciences, Eastern Virginia Medical School, Norfolk 23501, USA.
authors.forename: P H
authors.initials: PH
authors.lastname: Ratz
authors.forename: K A
authors.initials: KA
authors.lastname: McCammon
authors.forename: D
authors.initials: D
authors.lastname: Altstatt
authors.forename: P F
authors.initials: PF
authors.lastname: Blackmore
authors.forename: O Z
authors.initials: OZ
authors.lastname: Shenfeld
authors.forename: S M
authors.initials: SM
authors.lastname: Schlossberg
mesh_terms: D000818:Animals; D004305:Dose-Response Relationship, Drug; D004968:Estrogens, Non-Steroidal / Q000494:pharmacology*; D005260:Female; D012739:Gonadal Steroid Hormones / Q000494:pharmacology*; D066298:In Vitro Techniques; D007529:Isoflavones; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects* / Q000502:physiology*; D048789:Phytoestrogens; D028321:Plant Preparations; D010944:Plants; D011817:Rabbits; D001743:Urinary Bladder / Q000187:drug effects* / Q000502:physiology*
chemical_list: D004968:Estrogens, Non-Steroidal; D012739:Gonadal Steroid Hormones; D007529:Isoflavones; D048789:Phytoestrogens; D028321:Plant Preparations