ALPHA-1-ADRENOCEPTOR SUBTYPES INVOLVED IN NORADRENALINE-INDUCED CONTRACTION OF SNAKE (BOTHROPS-JARARACA) ISOLATED AORTA

The effects of chloroethylclonidine (CEC) and calcium channel antagoni sts on noradrenaline-induced contractions of Bothrops javaraca aorta w ere investigated, in order to characterize the alpha-1 adrenoceptor su btypes present in this preparation, CEC (5 x 10(-5) or 10(-4) M) displ aced to the right, in the same order of magnitude, the concentration-r esponse curve of noradrenaline without affecting its maximum response, The residual response was blocked by prazosin (10(-8) M) but not by i dazoxan (10(-5) M), Nifedipine (10(-5) M) or diltiazem (10(-5) M), in the absence of cocaine, did not have any effect on the concentration-r esponse curve of noradrenaline; however, in the presence of cocaine, b oth the drugs were equipotent in displacing the curve, though diltiaze m produced a non-parallel displacement, These results suggest the pres ence of two distinct alpha-1 adrenoceptor subtypes in Bothrops jararac a aorta: one CEC-sensitive (alpha-1B-like) and another CEC-insensitive , though the possibility of the presence of a single but different sub type cannot be excluded.