MUSCARINIC RECEPTOR SUBTYPES IN THE RAT PROSTATE-GLAND

Muscarinic receptor subtypes mediating carbachol-induced contractions of the rat prostatic smooth muscle were determined. The rank order of potency of muscarinic receptor antagonists in blocking the effects of carbachol was (mean pK(B) estimates in parentheses): atropine (8.90) m uch greater than para-fluorohexahydrosiladifenidol (7.75) greater than or equal to hexahydrosiladifenidol (7.62) > methoctramine (6.89) grea ter than or equal to pirenzepine (6.68) greater than or equal to himba cine (6.67). The specific binding of [H-3]quinuclidinyl benzilate to t he rat prostatic homogenates was competitively inhibited by (mean pK(i ) values in parentheses): atropine (8.89) much greater than hexahydros iladifenidol (7.86) > para-fluorohexahydrosiladifenidol (7.28) greater than or equal to himbacine (7.22) > pirenzepine (6.63) greater than o r equal to methoctramine (6.38). These profiles, whilst different, ind icate the probable involvement of muscarinic M-3 receptors in the carb achol-induced contraction. (C) 1998 Elsevier Science B.V.