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Because environmental temperature falls when the fetus is delivered from the uterus, the role of cold in stimulating cardiovascular and sympathoadrenal responses at the time of birth was examined in fetal lambs. In eight fetuses (gestational age 140 +/- 2 d), catheters were inserted into hind-limb and neck arteries and veins, and into an umbilical vein. After returning the fetus to the uterus and administering a muscle relaxant (succinylcholine chloride), blood gases, glucose and lactate concentrations, and plasma catecholamine and atrial natriuretic peptide concentrations were measured. Fetal combined ventricular output and organ blood flows were measured by the radionuclide-labeled microsphere technique. Measurements were repeated after delivering the fetus into a warm water bath (40 degrees C) and at 15 and 30 min after the bath temperature was cooled to 25 degrees C. Fetal cooling stimulated a sympathoadrenal response, which was manifested by an immediate increase in heart rate and arterial blood pressure, a rise in atrial natriuretic peptide, and modest increase in norepinephrine concentration. Contrary to earlier reports that investigated the effect of cold on fetal lambs using an intrauterine cooling coil, we did not find a decrease in fetal arterial oxygen tensions and pH, an increase in plasma glucose and lactate concentrations, or changes in fetal oxygen consumption. Combined ventricular output did not increase with cooling, and blood flow to most organs did not change significantly; however, blood flow to the skin decreased markedly, particularly in the lower body.(ABSTRACT TRUNCATED AT 250 WORDS)

Sympathoadrenal, Metabolic, and Regional Blood Flow Responses to Cold in Fetal Sheep