Responsiveness of the trimmed rat subcutaneous adipose tissue beta-receptors to catecholamines in ontogenesis

In order to estimate the possible changes of the functional state of beta-adrenergic receptors during ontogenesis, the lipid mobilizing effects of isoprenaline (ISO), adrenaline (ADR) and noradrenaline (NA) were studied in trimmed subcutaneous adipose tissue of rats at different stages of postnatal development (5, 14, 21 and 35 days after birth. The release of free acids (FFA) into the incubation medium was measured after addition of increasing concentrations of catecholamines and the dose-response curves were evaluated. In all the studied age groups, ISO produced the highest maximum effect and had the greatest potency. The calculated pD2 values indicate the same potency order ISO much greater than NA = ADR in all age groups and they also demonstrate that there exist no appreciable differences in the affinity single catecholamines at different stages of postnatal development. In comparison with all the other groups, the intrinsic activity of the studied adrenomimetics was relatively low in 14-day-old rats.