Catecholamine physiology in ovine fetus. II. Metabolic clearance rate of epinephrine

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Abstract
The metabolic clearance rate (MCR) of epinephrine (E) was measured in 13 chronically catheterized fetal lambs between 120 and 145 days gestation. The E-MCR was determined by a constant infusion method at an E infusion rate of 0.1 .mu.g/kg estimated fetal wt. Fetal and maternal arterial blood samples were taken for measurements of catecholamine levels, pH, blood gases and glucose. There was a significant positive correlation between gestational age and E-MCR (r = 0.87, P < 0.001). The E production rate in fetuses < 132 days (n = 6) (1234 .+-. 301 pg/min) was not significantly different from fetuses .gtoreq. 132 days (n = 7) (1195 .+-. 242). Catecholamine infusion resulted in a decrease in pH from a control value of 7.37 .+-. 0.01 to 7.31 .+-. 0.01 by 15 min on infusion, but there were no significant changes in fetal heart rate or blood pressure. The mean fetal plasma glucose concentration increased 45% above base line at 15 and 20 min and 65% above base line by 30 min of catecholamine infusion. After 60 min of infusion plasma norepinephrine (NE) increased from 380 .+-. 60 to 520 .+-. 75 pg/ml and plasma dopamine from 100 .+-. 20 to 240 .+-. 50 pg/ml (both P < 0.05). E-MCR evidently increases with maturation in the absence of a change in basal E production.