An in vitro comparison of beta-adrenoceptor stimulants on potassium-depolarized uterine preparations from guinea-pigs.

1 A comparison of six beta-adrenoceptor stimulants has been carried out on in vitro preparations of guinea-pig uterus which were depolarized in K(+)-Krebs solution. Results have also been obtained on uterine preparations in which contractions to acetylcholine were inhibited. The establishment of the conditions for the K(+)-depolarized preparations are described.2 There was no significant difference between potency values (mean neg log EC(50) values) for any of the drugs on the two types of uterine preparation i.e. the preparations had the same sensitivity to the drugs.3 There was a less than two-fold difference between the relative potency values for the beta-adrenoceptor stimulants on the two types of uterine preparation. The relative potency values (isoprenaline = 100) on the K(+)-depolarized preparation were fenoterol 74.1, salbutamol 15.1, rimiterol 13.5, terbutaline 8.2 and orciprenaline 5.6.4 The relative potency values obtained on uterine preparations were less than three-fold different from those previously found for guinea-pig trachea (after inhibition of extraneuronal uptake).5 The pA(2) value for propranolol on the K(+)-depolarized uterine preparations was 9.13.6 It is concluded that the K(+)-depolarized guinea-pig uterine preparation can be used for quantitative studies on beta-adrenoceptor stimulant drugs. It lacks spontaneous activity, drugs can be added cumulatively and several drugs can be compared on a single preparation. In addition, the results obtained support the classification of the beta-adrenoceptors in guinea-pig uterus and trachea in the same sub-group (beta(2)).