The adrenal secretion of catecholamines during systemic metabolic acidosis in fetal sheep.

This study was undertaken to determine whether or not metabolic acidemia per se stimulates catecholamine (CA) secretion from the adrenal medulla in fetal sheep. The potential confounding effect of low O2 content, occasioned by the right shift in the oxyhemoglobin dissociation curve with acidemia, was taken into account in experimental design. Hemodynamic values, blood gases, O2 content, lactate and glucose concentrations and adrenal CA secretion rates and plasma CA levels were studied in fetal sheep at baseline and during control (saline infusion) and acidemic (15 and 30% lactic acid infusion) periods. Experiments were conducted after recovery from preparative operations performed under general anesthesia. Arterial pH did not change with saline infusion. During 15 and 30% lactic acid infusions, pH fell to 7.23 and 7.09, respectively, as lactate concentrations increased 4.7 and 10 times. Arterial PCO2 increased from 50 to 58 torr during 30% lactic acid infusion. Fetal CA secretion and plasma concentrations did not change during saline, or 15 or 30% lactic acid infusions. Moreover, hemodynamic parameters did not indicate increased CA secretion. In conclusion, we found no evidence for stimulation of adrenal CA secretion by metabolic acidosis.