THE EFFECTS OF DOPAMINERGIC AND ADRENERGIC-DRUGS ON TWITCH RESPONSE OF GUINEA-PIG COMMON BILE-DUCT

1. Effects of various doses of bromocriptine and apomorphine, dopamine receptor agonists, on electrically evoked contractile responses of gu inea pig common bile duct (CBD) were investigated in this study. 2. Br omocriptine and apomorphine produced a concentration-dependent reducti on of the twitch heights. IC50 values for bromocriptine and apomorphin e were 2.75 +/- 0.715 x 10(-6) M, and 1.69 +/- 0.11 x 10(-5) M, respec tively, 3. Pretreatment with sulpiride, 0.1 and 1.0 mu M, prevented br omocriptine-and apomorphine-induced inhibition. pA(2) values of sulpir ide against bromocriptine and apomorphine were 8.26 and 6.29, respecti vely. 4. Clonidine, 0.1-100 mu M, produced 49.3 +/- 2.5% inhibition of twitch responses. Its effect was partially antagonized by 1 mu M of y ohimbine. 5. It would appear that both dopamine D-2- and alpha(2)-adre nergic presynaptic receptors are present on the guinea-pig CBD choline rgic nerve. (C) 1997 Elsevier Science Inc.