Muscarinic receptors mediating contraction of female mouse urinary bladder: effects of oestrogen

Muscarinic receptors mediating contraction of bladder detrusor muscle from female mice were examined. Mice were untreated (A) or treated with oestradiol cypionate (200 μg/kg) 24 h (B) or 96 h (C) before experimentation, or were pregnant (day 17) (D). Saturation radioligand binding experiments using [ 3H]quinuclidinyl benzilate ([ 3H] QNB) indicated similar muscarinic receptor densities and affinities in bladders from groups A and B. Neither oestrogen treatment nor pregnancy altered p D 2 estimates for methacholine. Maximum responses to methacholine and high-K + physiological salt solution (KPSS) were significantly greater ( Pmethacholine≈acetylcholine>bethanechol. Antagonist p K B estimates were similar in bladders from groups A and B with a rank order of: atropine≥4-diphenyl acetoxy- N-methyl piperidine methiodide>parafluorohexahydrosiladifenidol≈pirenzepine>himbacine, implicating muscarinic M 1 and/or M 5 as well as muscarinic M 3 receptors in mediating methacholine-induced bladder contraction.