Pulmonary hypertension and vascular remodeling in fetal sheep

Vascular remodeling is commonly associated with pulmonary hypertension (PH) postnatally, but little is known about its presence in fetuses. In sixteen fetal sheep (126 wk gestation), the ductus arteriosus (DA) was ligated, and the animals were studied at 4, 8, and 14 days after surgery. The uninstrumented twins served as controls. Four days post-DA ligation PH resulted in an increase in the right and left ventricular free wall weight ratio (1.2 +/- 0.1 vs. 1.0 +/- 0.1 in the controls; P < 0.01), with a further progressive increase at 8 (1.4 +/- 0.1 vs. 1.0 +/- 0.1; P < 0.01) and 14 days (1.5 +/- 0.2 vs. 1.0 +/- 0.1; P < 0.01). An increase in vascular percent medial thickness was observed after 4 days of DA ligation and was restricted to small vessels. The large arteries collagen and elastin contents were 28.9 +/- 3.4 and 27.1 +/- 3.4 micrograms/micrograms of DNA, respectively, and were not significantly different from control values even after 14 days DA ligation. We further compared elastin synthesis in fetal and neonatal arteries in vitro. Synthesis in the fetus was greater than the newborn (10.6 +/- 1.4 vs. 4.6 +/- 0.7 cpm.mg wet wt-1.h-1; P < 0.01). Vessel endothelium denudation reduced synthesis to 60 +/- 8% of controls in the fetus, whereas no change was seen in the newborn. After an increase in wall stress, synthesis increased in the fetus (194 +/- 28% of control P < 0.01) and newborn (173 +/- 25%; P < 0.01). Removal of the endothelium abolished the response.(ABSTRACT TRUNCATED AT 250 WORDS)