Binding of [3H]befunolol to β-adrenoceptors in cardiac muscles of fetal and neonatal rat

Abstract

Characterization of β-adrenoceptors was studied in heart muscles of rat fetus and neonate. The results of binding assay with [3H]befunolol, a β-adrenergic partial agonist, to membrane fractions from rat heart muscles indicate that β-adrenoceptors contain two different affinity sites. In the presence of 5′-guanylylimidodiphosphate, the low affinity site was reduced, while the high affinity site was not affected. The dissociation constants for both sites did not change during pre- and post-natal development. But the maximum binding sites for both sites decreased slightly but significantly (p < 0.05) during development. A 10-fold decrease in norepinephrine sensitivity and isoprenaline sensitivity during pre- and post-natal development was not explained by the slight decrease in the maximum binding sites.