ANALYSIS OF THE ANTAGONISM BY ATROPINE AND PIRENZEPINE OF ACETYLCHOLINE AND METHACHOLINE-INDUCED CONTRACTIONS OF THE RAT URINARY-BLADDER

The interaction between the muscarinic receptor agonists, acetylcholin e (ACh) and methacholine, and antagonists, atropine and pirenzepine wa s studied on the rat isolated urinary bladder preparation. ACh (4.36 x 10(-8)-1.35 x 10(-6)M) and methacholine (5.5 x 10(-8)-6.8 x 10(-6)M) induced contractions were reversibly antagonised by atropine (1.9 x 10 (-9)-4.8 x 10(-8)M) and pirenzepine (2.8 x 10(-7)-7.0 x 10(-6)M). The PA(2) values were atropine: 8.56 +/- 0.36 and 9.03 +/- 0.12; and piren zepine: 6.93 +/- 0.06 and 7.25 +/- 0.14 for ACh and methacholine respe ctively. The results suggest that in the rat urinary bladder, the musc arinic receptors are homogenous and non-differentiated.