Stimulation of distal airspace fluid clearance in guinea pigs involves bumetanide-sensitive ion transport

Objective This study was undertaken to test the hypothesis that β-adrenoceptor stimulation of fetal lung fluid absorption in near-term guinea pig fetuses involves bumetanide-sensitive ion transport. Study design Fetuses were obtained from timed-pregnant guinea pigs at 61 to 69 daysʹ gestation with and without oxytocin-induced preterm labor. The fetuses were placed on continuous positive airway pressure oxygenation, and an isosmolar 5% albumin solution was instilled into the lungs. Distal airspace fluid clearance was measured over 1 hour from the increase in distal airspace protein concentration as fluid was reabsorbed with and without the Cl− transport inhibitor bumetanide. Results Fetal lungs began to absorb distal airspace fluid at 64 to 66 daysʹ gestation, and at birth, distal airspace fluid clearance rapidly quadrupled. Labor induction by oxytocin stimulated distal airspace fluid clearance. Distal airspace fluid clearance, when present, was sensitive to propranolol-inhibition and depended on β-adrenoceptor stimulation. Fluid secretion at 61 daysʹ gestation was reduced by bumetanide instillation. Bumetanide addition was only inhibitory when distal airspace fluid clearance was propranolol-sensitive. Conclusion β-adrenoceptor stimulation from endogenous fetal epinephrine increased fetal distal airspace fluid clearance and involved bumetanide-sensitive ion transport.