Catecholamine concentrations in plasma and organs of the fetal guinea pig during normoxemia, hypoxemia, and asphyxia.

To examine the responses of the sympatho-adrenal system to reduced oxygen supply we studied plasma and tissue concentrations of catecholamines during normoxemia, hypoxemia, and asphyxia in 22 fetal guinea pigs near term. Fetal blood was obtained by cardiopuncture in utero under ketamine/xylazine-anesthesia. Catecholamines were determined in plasma and tissue of 15 organs and 14 brain parts by HPLC-ECD. During normoxemia (SO2 54 +/- 4 (SE) %, pH 7.36 +/- 0.02, n = 5) plasma catecholamine levels were low (norepinephrine 447 +/- 53, epinephrine 42 +/- 12, dopamine 44 +/- 6 pg/ml). During hypoxemia (SO2 27 +/- 3%, pH 7.32 +/- 0.01, n = 6) and asphyxia (SO2 24 +/- 2%, pH 7.23 +/- 0.02, n = 11) tissue catecholamine concentrations changed with changing blood gases and with increasing plasma catecholamines. Norepinephrine concentrations increased in both skin and lung and decreased in liver, pancreas, and scalp; those of epinephrine increased in the heart, lung liver, and scalp and decreased in the adrenal. There were only minor changes in brain catecholamine concentrations except for a 50% reduction in dopamine in the caudate nucleus. Concentrations of dopamine catabolite 3,4-dihydroxyphenylacetic acid decreased in many brain parts, suggesting that cerebral catecholamine metabolism was affected by hypoxemia and asphyxia. We conclude that the sympatho-adrenal system of fetal guinea pigs near term is mature and that its stimulation by reduced fetal oxygen supply leads to changes in both plasma and tissue catecholamine concentrations.