Plasma catecholamines in the hypoxaemic fetal rhesus monkey.
To assess the response of the sympathoadrenal system of the primate fetus to oxygen deprivation, we measured plasma catecholamines in 8 chronically catheterized fetal rhesus monkeys. A range of fetal hypoxaemia was produced by having the mother inspire 15, 10, or 9% oxygen mixtures while tranquilized with ketamine. Catecholamines from fetal carotid and maternal femoral arteries were measured by radioenzymatic assay. Fetal plasma norepinephrine and epinephrine concentrations increased significantly at all levels of hypoxaemia, but dopamine increased only at very low fetal oxygen tensions. Norepinephrine levels exceeded those of epinephrine and dopamine under all conditions. Relatively more severe hypoxaemia was necessary to elevate concentrations of epinephrine above baseline as compared with norepinephrine. A negative exponential correlation (P less than 0.001) was found between both fetal arterial PO2 and oxygen content and plasma norepinephrine and epinephrine, which was qualitatively similar to that observed previously in the sheep fetus. Maternal catecholamines were found to increase during hypoxaemia as well, but to a lesser degree than in the fetus.