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Two alpha 1-adrenoceptor subtypes (alpha 1A and alpha 1B) have been detected in various tissues by pharmacological techniques, and three distinct cDNAs encoding alpha 1-adrenoceptor subtypes have been cloned. The profile of an increasing number of subtype-selective compounds at cloned and endogenous receptors recently has facilitated alignment between cloned and pharmacologically defined alpha 1-adrenoceptor subtypes. Thus, alpha 1a-adrenoceptors (previously designated alpha 1c), alpha 1b-adrenoceptors and alpha 1d-adrenoceptors (previously designated alpha 1a, alpha 1d or alpha 1a/d) are now recognized. Since the alpha 1d-adrenoceptor shares characteristics with both alpha 1A- and alpha 1B-adrenoceptors, tissues previously reported to express alpha 1A- and/or alpha 1B-adrenoceptors may additionally contain alpha 1d-adrenoceptors. This article reviews the features of all three subtypes and discusses possible pitfalls in their pharmacological identification.

('pA2'= 8.74) compared to blood pressure ('pA2'= 7.51). 6 Data in this study suggest that the a, adrenoceptor mediating noradrenaline-induced contractions of human prostate, whilst having some of the characteristics of an a1A adrenoceptor, cannot be satisfactorily aligned with cloned IxIA, I IB or cID adrenoceptors. In addition, studies in the anaesthetized dog have shown that agents having high affinity and selectivity for prostatic a, adrenoceptors, particularly over the alD subtype, appear to inhibit phenylephrine-induced increases in prostatic pressure selectively compared to blood pressure.

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