Fetal and neonatal cardiopulmonary response to histamine.
Effects of intravenous histamine and its H1 receptor blocker (Benadryl) were investigated in near-term fetal and in newborn lambs. Fetuses were studied before and after closure of the ductus arteriosus. Newborn lambs were chronically instrumented and the same animal was tested periodically from 3 to 70 days old. The results show that a) in the fetus whose pulmonary vascular resistance is already high, histamine produces a profound pulmonary vasodilation; b) in contrast, in the neonate with reduced pulmonary vascular resistance, histamine produces pulmonary vasoconstriction similar to that of the adult; c) both responses can be attenuated by Benadryl indicating that they are mediated by the same receptor; d) in the fetus, histamine produces marked constriction of the ductus arteriosus which could be partly attributed to the pulmonary vasocilatation; and e) when neonatal pulmonary vascular resistance was raised by hypoxia, histamine elicited a biphasic response, part of which was blocked by Benadryl. These findings are discussed in terms of their possible role in cardiovascular and pulmonary changes that occur after birth.
D000818:Animals; D000831:Animals, Newborn; D001011:Aorta / Q000187:drug effects; D001794:Blood Pressure / Q000187:drug effects; D004155:Diphenhydramine / Q000494:pharmacology*; D004373:Ductus Arteriosus / Q000187:drug effects; D005260:Female; D005333:Fetus / Q000187:drug effects*; D006632:Histamine / Q000494:pharmacology*; D000860:Hypoxia / Q000503:physiopathology; D011247:Pregnancy; D011651:Pulmonary Artery / Q000187:drug effects; D011652:Pulmonary Circulation / Q000187:drug effects*; D011955:Receptors, Drug / Q000187:drug effects*; D012756:Sheep; D014655:Vascular Resistance / Q000187:drug effects*
D011955:Receptors, Drug; D006632:Histamine; D004155:Diphenhydramine