Cardiovascular, renal and endocrine responses to graded volume
expansion in lambs during maturation.
Smith, Francine G., Oliva J. McWeeny, Jean E. Robillard.
Department of Medical Physiology, The University of Calgary,
Calgary, Alberta, CANADA, The Department of Pediatrics, The
University of Iowa, Iowa City, Iowa, USA
APStracts 2:0464H, 1995.
To further investigate the maturation of the cardiopulmonary
baroreflex, we measured the effects of a 45 min blood volume
expansion to an increase in right atrial pressure of 4 mmHg in
chronically instrumented newborn (n=17) and older lambs (n=14).
Measurements included various parameters of endocrine, cardiovascular
and renal function and concomitant recording of renal sympathetic
nerve activity (RSNA). During blood volume expansion, RSNA was
inhibited to a similar extent in newborns and in older lambs when
atrial pressures were increased by 4 mmHg. A sympatho-inhibition
persisted in newborns but was only transient in older lambs. In
newborn lambs, heart rate decreased in response to blood volume
expansion; heart rate remained constant after blood volume expansion
in older lambs. The renal and endocrine responses to blood volume
expansion were, however, similar in newborns and older lambs. These
data provide evidence that when atrial pressures are matched, the
renal and endocrine responses to blood volume expansion are similar,
but there are differential cardiovascular and RSNA responses. Any
reduced ability of the newborn kidney to excrete a volume load is
therefore probably related to maturational differences in its
distribution between the capacitance vessels and the heart.
Received 5 May 1995; accepted in final form 25 September 1995.
APS Manuscript Number H427-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 November 95