β-Adrenoceptor Function in White Blood Cells from Newborn Infants: No Relation to Plasma Catecholamine Levels

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Abstract
The maturity of β-adrenoceptors in newborn infants was studied in relation to the catecholamine surge during labor. Umbilical blood was collected at birth from 12 infants delivered vaginally and 13 infants delivered by elective cesarean section. Granulocytes and lymphocytes were isolated. Receptor numbers and binding affinity were determined in the granulocytes by incubation with 125Iiodohydroxybenzylpindolol. Receptor responsiveness was tested by assessing isoproterenol-induced cyclic AMP accumulation in lymphocytes. Significantly higher plasma noradrenaline, adrenaline, and dopamine concentrations were found in infants born vaginally (108; 8.9; 0.9 nmol/ liter, respectively, median values) as compared with those delivered by cesarean section (11.0; 2.4; 0.2 nmol/liter). No significant differences in β-adrenoceptor binding sites (receptor number: 39.2 ± 2.6 versus 44.7 ± 5.9 fmol/mg protein and binding affinity: 66.6 ± 7.8 versus 65.0 ± 6.2 pM) or responsiveness (maximal isoprenaline induced cAMP formation 52.4 ± 10.3 versus 40.6 ± 8.9 pmol/106 cells) were found between the two groups of infants. Lymphocyte β-adrenoceptor sensitivity was similar to that found in adults.The β-adrenoceptors on whole blood cells seem to be mature at birth and have the same responsiveness as in adults. The higher catecholamine surge during vaginal delivery as compared to elective cesarean section does not seem to affect β-adrenoceptor function. Our results do not support the idea that reduced β-adrenoceptor function is the cause of the previously observed inappropriately small cardiovascular and metabolic responses to the exceptionally high plasma catecholamine concentrations at birth.