Sympathetic control of the cardiovascular response to acute hypoxemia in the chick embryo

• Published in: American journal of physiology. Regulatory, integrative and comparative physiology integrative and comparative physiology, 2002-04, Vol.282 (4), p.1156-R1163
• Main Authors: Mulder, A. L. M, Miedema, A, De Mey, J. G. R, Giussani, D. A, Blanco, C. E
• Format: Article
• Language: English
• Subjects: Acute Disease; Animals; Cardiac Output - drug effects; Cardiac Output - physiology; Chick Embryo; Epinephrine - blood; Ganglionic Blockers - pharmacology; Hexamethonium - pharmacology; Hypoxia - physiopathology; Norepinephrine - blood; Sympathetic Nervous System - drug effects; Sympathetic Nervous System - physiology
• ISSN: 0363-6119; 1522-1490
• DOI: 10.1152/ajpregu.00634.2001

1  Department of Pediatrics, Research Institute Growth and Development, and 2  Department of Pharmacology and Toxicology, Cardiovascular Research Institute Maastricht, Maastricht University, 6202 AZ Maastricht, The Netherlands; and 3  Department of Physiology, University of Cambridge, Cambridge CB2 3EG, United Kingdom In response to an acute hypoxemic insult, the mammalian fetus shows a redistribution of the cardiac output in favor of the heart and brain. Peripheral vasoconstriction contributes to this response and is partly mediated by the release of catecholamines. Two mechanisms of catecholamine release in the fetus are reported: 1 ) neurogenic sympathetic stimulation and 2 ) a nonneurogenic mechanism via a direct effect of hypoxemia on chromaffin tissues. In the present study, the effects of sympathetic blockade on plasma catecholamine release and cardiac output distribution in response to acute hypoxemia were studied in the chick embryo at different stages of incubation. Only at the end of the incubation period, sympathetic blockade markedly attenuated the increase in plasma catecholamine concentrations and resulted in a greater fraction of the cardiac output distributed to the carcass. However, these effects did not prevent a significant increase in cardiac output to the brain and heart during acute hypoxemia. These data imply that in the chick embryo the contribution of neurogenic mechanisms to the catecholaminergic response to acute hypoxemia becomes greater by the end of the incubation period. fetus; hexamethonium; hypoxia; catecholamines; avian