ADAPTATION OF FETAL PULMONARY BLOOD FLOW TO PHARMACOLOGIC VASODILATORS

Abstract

The normally high resistance of the fetal pulmonary circulation decreases acutely in response to some pharmacologic agents and to increases in fetal PO₂. We have previously observed adaptation of fetal pulmonary blood flow to small increases in fetal PO₂. To determine if adaptation also occurs to pharmacologic stimuli, we infused three known fetal pulmonary vasodilators, acetylcholine (A) and histamine (H) in 5 and bradykinin (B) in 3, chronically prepared fetal sheep. A cuff electromagnetic flow probe measured blood flow to the left lung (QL). Catheters in the main pulmonary artery (PA) and aorta (AO) measured pressure. A catheter was also placed in the left pulmonary artery (LPA) for direct infusion into the left lung thereby minimizing systemic effects. After a 1 hour control period, we infused A or H (0.5 μg.min⁻¹.kg⁻¹) or B (15 ng.min⁻¹.kg⁻¹) through the LPA catheter for 2 hours. After an initial increase, QL (x̄ ± SEM ml.min⁻¹) decreased toward baseline during the remaining infusion period. AO and PA pressures did not change.

We conclude that an adaptive response, as seen previously with small increases in PO₂, is observed in the fetal pulmonary circulation with local infusion of three pharmacologic vasodilators.

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