Possible subdivisions among alpha-adrenoreceptors in various isolated tissues

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 x 10(-5) M), tropolone (3 x 10(-5) M) and (+/-)-propranolol (5 x 10(-7) to 5 x 10(-5) M). The values obtained fall into 3 distinct and statistically different groups. Firstly, a high group comprising (mean +/- s.e.) mouse vasdeferens (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 thirdlya 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 vase 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 conderning the nature of the alpha-adrenoreceptor in these tissues. In spite of the absence of any significant difference between the potency of the alpha-adrenoreceptor blocking agents in the two species it is suggested that alpha-adernoreceptors may not belong to a single homogenous population but may vary in their characteristics from tissue to tissue.