We measured pulmonary vasodilation induced by histamine, H(1) and H(2) antagonists,and H(1) and H(2) agonists in chronically prepared, normally oxygenated fetal sheep in order to study the response of H(1) and H(2) stimulation in late gestation. Blood flow was measured in the left pulmonary artery; pressures were measured in the main pulmonary artery and abdominal aorta. Histamine administered into the left pulmonary artery caused dose-dependent increases in left pulmonary blood flow without changes in either pulmonary arterial or aortic pressures. Cimetidine (H(2) antagonist) and/or diphenhydramine (H(1) antagonist)shifted the histamine dose-response curve to the right. 2-Pyridylethylamine (H(1) agonist)and dimeprit (H(2) agonist) caused vasodilation which was selectively blocked by its respective antagonist. We conclude that both H(1) and H(2) stimulation cause pulmonary vasodilation in the ovine fetus.

Keywords:
Histamine, Antagonist, Agonist, Pulmonary circulation, Receptors, H(1), H(2), Sheep fetus
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1990
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