A comparison of the binding constant (Kd) of 125I-labelled 3-(4-iodophenoxy)-1-isopropylamino-propan-2-ol obtained on β-adrenoceptors in guinea-pig myocardial membranes, with its dissociation constants (Kb) obtained on guinea-pig isolated atria and trachea

Abstract

The dissociation constant of binding (KD) of 125I-labelled 3-(4-iodophenoxy)-1-isopropyl-aminopropan-2-ol (IIP) to guinea-pig myocardial membrane preparations was 2·2 × 10−8m. In pharmacological experiments with the non-labelled material and 60 min contact time, IIP produced a parallel shift in the orciprenaline concentration-response line on guinea-pig isolated tracheal and atrial preparations. The dissociation constant (Kb) of IIP was 2·9 × 10−8m on atria (pA2 7·54) and 3·3 × 10−8m on trachea (pA2 7·48). These values indicate that IIP is not a selective β-adrenoceptor blocking drug. In addition, agreement was found between the affinity constant of this antagonist for β-adrenoceptors as determined by a direct binding study and an indirect pharmacological study.