AN in vitro COMPARISON OF β‐ADRENOCEPTOR STIMULANTS ON POTASSIUM‐DEPOLARIZED UTERINE PREPARATIONS FROM GUINEA‐PIGS

Abstract

1 A comparison of six β-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 EC₅₀ 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 β-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 pA₂ 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 β-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 β-adrenoceptors in guinea-pig uterus and trachea in the same sub-group (β₂).