Late-gestation betamethasone enhances coronary artery responsiveness to angiotensin II in fetal sheep.

Antenatal glucocorticoids are used to promote the maturation of fetuses at risk for preterm delivery. While perinatal glucocorticoid exposure has clear immediate benefits to cardiorespiratory function, there is emerging evidence of adverse long-term effects. To determine if antenatal betamethasone alters vascular reactivity, we examined isometric contraction of endothelium-intact coronary and mesenteric arteries isolated from twin fetal sheep at 121-124 days gestation (term being 145 days).

Inhibition of sympathetic responses at birth in sheep by lesion of the paraventricular nucleus.

Birth is characterized by a surge in sympathetic outflow, heart rate (HR), mean arterial blood pressure (MABP) and circulating catecholamines. The paraventricular nucleus (PVN) of the hypothalamus is an important central regulatory site of sympathetic activity, but its role in the regulation of sympathoexcitation at birth is unknown. To test the hypothesis that the PVN regulates sympathetic activity at birth, experiments were performed in chronically instrumented near-term (137- to 142-day gestation, term 145 days) sheep before and after delivery by cesarean section.

Effects of gestational age on myocardial blood flow and coronary flow reserve in pressure-loaded ovine fetal hearts.

To test the hypothesis that coronary flow and coronary flow reserve are developmentally regulated, we used fluorescent microspheres to investigate the effects of acute (6 h) pulmonary artery banding (PAB) on baseline and adenosine-enhanced right (RV) and left ventricular (LV) blood flow in two groups of twin ovine fetuses (100 and 128 days of gestation, term 145 days, n = 6 fetuses/group). Within each group, one fetus underwent PAB to constrict the main pulmonary artery diameter by 50%, and the other twin served as a nonbanded control. Physiological measurements were made 6 h after the surgery was completed; tissues were then harvested for analysis of selected genes that may be involved in the early phase of coronary vascular remodeling.