Possible subdivisions among α-adrenoceptors in various isolated tissues

Abstract

Abstract The ratio (expressed in log10 units) of the equieffective concentrations of (+)- and (—)-noradrenaline has been measured in a variety of isolated tissues in the presence of cocaine (1 times 10−5m), tropolone (3 times 10−5m) and (±)-propranolol (5 times 10−7 to 5 times 10−5m). The values obtained fall into 3 distinct and statistically different groups. Firstly, a high group comprising (mean ± s.e.) mouse vas deferens (2·78 ± 0·04), rabbit duodenum (2·91 ± 0·07) and ileum (2·86 ± 0·05). Secondly a middle group comprising rabbit vas deferens (2·54 ± 0·04), bladder neck muscle (2·56 ± 0·07) and spleen (2·50 ± 0·02), guinea-pig vas deferens (2·55 ± 0·10) and bladder neck muscle (2·48 ± 0·13) and rat deferens (2·40 ± 0·08) and thirdly, a low group comprising the bladder detrusor muscle from both the rabbit (2·08 ± 0·08) and the guinea-pig (2·07 ± 0·04). Under the same conditions measurement of pA2 values for phentolamine and piperoxan against noradrenaline gave the following values in rat vas deferens (8·22 ± 0·07 and 6·72 ± 0·03 respectively) and mouse vas deferens (8·31 ± 0·05 and 6·53 ± 0·07 respectively). The results are discussed in relation to other findings concerning the nature of the α-adrenoceptor in these tissues. In spite of the absence of any significant difference between the potency of the α-adrenoceptor blocking agents in the two species it is suggested that α-adrenoceptors may not belong to a single homogeneous population but may vary in their characteristics from tissue to tissue.