Acidemia potentiates the plasma catecholamine response to hypoxemia in fetal sheep

Though hypoxemia has been shown to stimulate adrenal medullary catecholamine (CA) release and raise plasma CA concentrations, the extent to which concomitant acidosis influences the magnitude of this response is unclear. Eleven chronically catheterized late gestation (0.8 term) fetal lambs in utero were investigated during a baseline control period and following the onset of umbilical cord constriction-induced hypoxemia (PO2 = 5-15 Torr). Plasma CA rose in response to hypoxemia in all animals but was potentiated by the development of acidemia. Baseline norepinephrine (NE = 487 +/- 113 pg/cm3 and increased to 1,386 +/- 127 pg/cm3 (p less than 0.001) in response to hypoxemia. Hypoxemia combined with acidemia promoted an even greater rise in NE to 6,726 +/- 1,289 pg/cm3 (p less than 0.05). Plasma epinephrine (E) = 99 +/- 36 pg/cm3 during baseline observations and increased to 512 +/- 81 pg/cm3 (p less than 0.001) in response to hypoxemia. However, an additional 9-fold increase (p less than 0.05) was noted when hypoxemia was combined with acidemia (E = 4,311 +/- 1,449 pg/cm3). Thus, acidosis significantly potentiates the magnitude of the plasma CA response to hypoxemia in the late gestation fetus.