Abstract
Prazosin and yohimbine were used to differentiate postjunctional alpha adrenoceptors in the coronaries of the perfused guinea-pig heart. Two postjunctional alpha adrenoceptor subtypes were distinguished by the affinities of the receptor for yohimbine and prazosin. The pA2 for yohimbine were 8.74 against alpha-methylnorepinephrine and 8.98 against BHT-920, and the pA2 for prazosin was 9.84 against phenylephrine. Yohimbine was not very active against the alpha-1 selective agonist as was prazosin against the alpha-2 selective agonists. Alpha-1 and alpha-2 postjunctional adrenoceptors mediate vasoconstriction in the whole coronary bed of the perfused guinea-pig heart.
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