Plasma catecholamines in foetal and adult sheep.

Abstract

1. Foetal and maternal plasma catecholamine concentrations were measured during and after hypoxia (mean maternal Pa,02 44mmHg) in chronically catheterized sheep, 118–141 days pregnant. 2. In most foetuses the initial plasma catecholamines were smaller than 0.07 ng/ml. During hypoxia plasma adrenaline and noradrenaline always rose; there was a rise in arterial pressure and a fall in heart rate. 3. The initial catecholamine concentration in the ewes was smaller than 0.05–2.3 ng/ml. During hypoxia there was no consistent change; the maternal plasma concentrations were less than the foetal. 4. Infusion of adrenaline at 0.3 mug kg(−1) min(−1) to the ewe resulted in plasma catecholamine concentrations higher than those observed during hypoxia. There was a rise in heart rate but no consistent change in arterial pressure. 5. Infusion of adrenaline 0.4 mug kg(−1) min(−1) into the foetal jugular vein caused a rise in plasma concentration similar to that seen during hypoxia. There was a rise in heart rate but no significant change in arterial pressure. 6. The half‐life of adrenaline and of noradrenaline in the maternal and foetal circulation was 0.25‐1 min. There was no evidence of transfer of labelled catecholamine across the placenta.