Use of indomethacin to reverse neonatal hypotension

Voltage-gated K(+)-channel activity in ovine pulmonary vasculature is developmentally regulated

To examine mechanisms underlying developmental changes in pulmonary vascular tone, we tested the hypotheses that 1) maturation-related changes in the ability of the pulmonary vasculature to respond to hypoxia are intrinsic to the pulmonary artery (PA) smooth muscle cells (SMCs); 2) voltage-gated K(+) (K(v))-channel activity increases with maturation; and 3) O(2)-sensitive Kv2.1 channel expression and message increase with maturation. To confirm that maturational differences are intrinsic to PASMCs, we used fluorescence microscopy to study the effect of acute hypoxia on cytosolic Ca(2+) concentration ([Ca(2+)](i)) in SMCs isolated from adult and fetal PAs. Although PASMCs from both fetal and adult circulations were able to sense an acute decrease in O(2) tension, acute hypoxia induced a more rapid and greater change in [Ca(2+)](i) in magnitude in PASMCs from adult compared with fetal PAs. To determine developmental changes in K(v)-channel activity, the effects of the K(+)-channel antagonist 4-aminopyridine (4-AP) were studied on fetal and adult PASMC [Ca(2+)](i). 4-AP (1 mM) caused PASMC [Ca(2+)](i) to increase by 94 +/- 22% in the fetus and 303 +/- 46% in the adult. K(v)-channel expression and mRNA levels in distal pulmonary arteries from fetal, neonatal, and adult sheep were determined through the use of immunoblotting and semiquantitative RT-PCR. Both Kv2.1-channel protein and mRNA expression in distal pulmonary vasculature increased with maturation. We conclude that there are maturation-dependent changes in PASMC O(2) sensing that may render the adult PASMCs more responsive to acute hypoxia.

Surgery increases fetal plasma prostacyclin

Pulmonary arterial prostacyclin (as 6-keto-PGF1 alpha) concentrations of near term, fetal lambs and goats were determined following fetal surgery and 24, 48, and 72 hrs later. Blood gases, pH, and arterial pressure were determined also. At the end of 2.5 hrs of surgery including exteriorization of the uterus and fetal thoracotomy, pulmonary arterial concentration of 6-keto-PGF1 alpha was 948 +/- 80 (SEM) pg/ml of blood. Twenty-four hrs later it had fallen to 435 +/- 92 pg/ml and remained constant for the duration of monitoring. Maternal arterial 6-keto-PGF1 alpha concentration was much lower (105 +/- 20 pg/ml of blood). No significant changes in fetal PaO2, PaCO2, pH, or arterial pressure were observed, although PaCO2 appeared to be elevated and pH reduced following surgery. These values normalized within 24 hrs. We conclude that surgical perturbation increases fetal arterial prostacyclin concentration. Increased prostacyclin levels are transient, reaching stable values within 24 hrs following completion of extensive surgery.

Morphologic analysis of the pulmonary vascular bed in infants exposed in utero to prostaglandin synthetase inhibitors

Since the effects of prostaglandin synthetase inhibitors on the developing human fetal pulmonary vasculature are unknown, we studied the lungs of two infants, one whose mother took salicylates and the other whose mother took indomethacin during pregnancy. Lungs were fixed by perfusion and fifth generation (resistance) vessels identified. The infant with chronic exposure to aspirin had premature constriction of the ductus arteriosus, tricuspid insufficiency, increased pulmonary arterial medial width/external diameter ratio due to increased smooth muscle, and a decreased number of pulmonary vessels/cm2 lung tissue. The infant with short-term exposure to indomethacin had hypoxemia, increased pulmonary arterial m/d ratio due to increased smooth muscle, and a normal number of pulmonary vessels/cm2 lung tissue. These abnormalities may be due to the effects of prostaglandin synthetase inhibitor drugs on the ductus arteriosus and/or the pulmonary vessels of the human fetus.