Arginine vasopressin modulation of arterial baroreflex responses in
fetal and newborn sheep.
Nuyt, Anne Monique, Jeffrey L. Segar, Aaron T. Holley, Michael S.
O'mara, Mark W. Chapleau, Jean E. Robillard.
Departments of Pediatrics and Internal Medicine and the
Cardiovascular Center, College of Medicine, University of Iowa, Iowa
City, Iowa 52242
APStracts 3:0260R, 1996.
The present study was designed to test the hypothesis that the
influence of circulating vasopressin (AVP) on the arterial baroreflex
control of renal sympathetic nerve activity (RSNA) and heart rate
(HR) changes during development. To test this hypothesis, we studied
arterial baroreflex mediated control of HR and RSNA in the presence
of increasing plasma levels of AVP in conscious, chronically
-instrumented fetal, newborn and adult sheep. In fetal and newborn
sheep, increasing plasma AVP levels (from <10?[mu]U/ml to
>200?[mu]U/ml) increased resting levels of mean arterial blood
pressure (MABP) and decreased HR and RSNA. HR and RSNA baroreflex
responses to variations of MABP with nitroprusside and phenylephrine
infusion were not modified by elevated AVP levels in either newborn
or fetal sheep, except for a small decrease in maximal HR response to
nitroprusside infusion in the newborn animals. In contrast in adults,
AVP caused bradycardia and a decrease in RSNA without change in MABP,
accompanied by resetting of the arterial baroreflex (decrease in
maximal HR and RSNA, decrease in RSNA gain and shift of HR to lower
pressure). To test the hypothesis that the inability of AVP to reset
the arterial baroreflex early during development was not secondary to
maximal stimulation of V1 receptors during baseline conditions, we
investigated the effect of V1 receptor blockade on baseline
cardiovascular and arterial baroreflex function in newborn lambs.
Administration of a V1 receptor antagonist produced no significant
changes in resting MABP, HR and RSNA, and did not influence arterial
baroreflex mediated changes in HR and RSNA. These results indicate
that, contrary to adults, circulating AVP does not modulate the
arterial baroreflex in fetal and newborn sheep.
Received 8 December 1995; accepted in final form 6 June 1996.
APS Manuscript Number R776-5.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 4 July 96