The plasma catecholamine response to parturition was studied in two groups of chronically catheterized fetal sheep. Group I consisted of full term pregnancies with a mean gestation of 147 days at delivery. Group II was comprised of fetal sheep infused with cortisol to induce premature delivery at a mean gestational age of 135 days. Plasma catecholamine concentrations were measured in group I mothers and fetuses and group II fetuses by radioenzymatic assay using 50 μ1 samples. Uterine contractions began 4–14 h before delivery in both groups. Significant increases in fetal plasma norepinephrine (NE) concentrations occurred within 3 h of delivery in both groups. Group I plasma epinephrine (E) and group I and II plasma dopamine levels were significantly increased within 1 h of delivery. Only plasma E levels differed in group I and II fetuses; there was no significant rise in plasma E concentrations in cortisol-infused (group II) fetuses. Maternal plasma NE and E concentrations were increased 2–3 h before delivery in group I animals. Maternal plasma dopamine concentrations were only elevated 30 min before delivery when plasma NE and E levels were highest.
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