AJP - Heart and Circulatory Physiology, Vol 267, Issue 4 1467-H1475, Copyright © 1994 by American Physiological Society
Cardiopulmonary and arterial baroreflex responses to acute volume expansion during fetal and postnatal development
D. C. Merrill, J. L. Segar, O. J. McWeeny, B. A. Smith and J. E. Robillard
Department of Obstetrics and Gynecology, University of Iowa College of Medicine, Iowa City 52242-1080.
Recent studies demonstrated that renal denervation had no effect on the
natriuretic response to volume expansion (VE) in fetal sheep, suggesting
that the sensitivity of the cardiopulmonary reflex in response to VE is
impaired in the fetus. To test this hypothesis, we investigated the renal
sympathetic nerve activity (RSNA) and heart rate (HR) responses to 20 and
50% intravascular VE in fetal (130-135 days gestation; term 145 days) (n =
7), newborn (n = 8), and 6- to 8-wk-old sheep (n = 9). Despite similar
increases in right atrial pressure (RAP) in the three groups, 20% VE had no
significant effect on RSNA and HR in fetal sheep but significantly
decreased RSNA in newborn (-22.8 +/- 7.3%) and 6- to 8-wk-old sheep (-32.1
+/- 11.7%). Bradycardic responses to VE were also observed in both newborn
(from 237 +/- 6 to 200 +/- 12 beats/min) and 6- to 8-wk-old sheep (from 170
+/- 9 to 140 +/- 9 beats/min). A 50% VE had no significant effect on fetal
RSNA and HR, whereas it increased RAP by 6.8 +/- 0.9 mmHg. In addition, we
tested the hypothesis that interactions between cardiopulmonary and
arterial baroreflexes in response to VE change during development. We found
that 20 and 50% VE shifted the RSNA and HR arterial baroreflex response
curves to the right in the fetus but had no significant effects on the gain
of the arterial baroreflex curves in either fetal, newborn, or 6- to
8-wk-old sheep.(ABSTRACT TRUNCATED AT 250 WORDS)
