Regulation of atrial autonomic receptors in experimental cyanotic heart disease
Doshi, R.; Strandness, E.; Bernstein, D.
American Journal of Physiology 261(4 Pt 2): H1135-H1140
1991
ISSN/ISBN: 0002-9513 PMID: 1656786 Document Number: 382970
During chronic hypoxemia, left ventricular .beta.-adrenergic receptor density is decreased and a dissociation occurs between increased chronotropic and decreased inotropic responses to chronically elevated sympathetic tone. To determine whether this dissociation was related to alterations in autonomic receptor population in the right atrium, we studied right atrial cholinergic and .beta.-adrenergic receptors in chronically hypoxemic newborn lambs and in normoxemic controls. Heart rate response was determined by infusing isoproterenol at 0.1 or 0.5 .mu.g .cntdot. kg-1 .cntdot. min-1. Muscarinic receptors were quantified with [3H]quinuclidinyl benzilate and .beta.-adrenergic receptors with [125I]iodocyanopindolol. Competition with ICI 118,551 was used to determine .beta.1- vs. .beta.2-receptor subtypes. In the hypoxemic lambs, isoproterenol resulted in a lesser percentage increase in heart rate (hypoxemic, 46 .+-. 6% vs. control, 89 .+-. 17%, P < 0.05); however, because baseline heart rate was higher in the hypoxemic lambs (213 .+-. 7 vs. 177 .+-. 12 beats/min, P < 0.05), maximal heart rate response were similar (310 .+-. 7 vs. 326 .+-. 6 beats/min, NS). There was no change in receptor density or affinity of either muscarinic or .beta.-adrenergic receptors and no change in the proportion of .beta.1- vs. .beta.2-receptor subtypes. Thus the dissociation between the chronotropic and inotropic responses to chronic hypoxemia may be in part secondary to a differential regulation of .beta.-adrenergic receptors between the left ventricle and the right atrium.