Fetal endocrine and renal responses to in utero ventilation and umbilical cord occlusion

Fetal to neonatal transition involves a myriad of endocrine and renal adaptive changes triggered by multiple simultaneous stimuli. We examined the extent to which ventilation and umbilical cord occlusion have an impact on the many endocrine and renal function changes in fetal sheep at 133 +/- 1 day of gestation.

Nine fetuses were chronically prepared with an endotracheal tube, vascular and bladder catheters, and an inflatable umbilical cord occluder. After a 2-hour control period fetuses were treated with commercially prepared surfactant and ventilated with 100% oxygen. One hour after the onset of stable ventilation the umbilical cord was occluded and the animals were monitored for 3-hours.

In response to ventilation fetal arterial PO2 increased (18 +/- 1 to 86 +/- 29 mm Hg) and remained significantly above control values after cord occlusion. Fetal arterial pH, hematocrit, and mean arterial pressure and heart rate did not change during the study. Ventilation alone evoked significant increases in epinephrine and norepinephrine concentrations. Renal responses to ventilation included significant decreases in urine flow rate, fractional sodium excretion, and fractional water excretion. Neither ventilation nor cord occlusion resulted in significant changes in plasma concentrations of atrial natriuretic factor, arginine vasopressin, and angiotensin II or in glomerular filtration rate, urine osmolality, free water, and osmolar clearances.

(1) Mechanical ventilation and oxygenation alone increase circulating fetal catecholamine levels. (2) The addition of umbilical cord ligation has minimal impact on fetal endocrine and renal adaptive responses.