AJP - Heart and Circulatory Physiology, Vol 240, Issue 6 848-H854, Copyright © 1981 by American Physiological Society
Role of renin-angiotensin system in response to hemorrhage in fetal sheep
H. S. Iwamoto and A. M. Rudolph
During fetal life, the autonomic nervous system is not fully mature, and it
is likely that hormonal mechanisms play an important role in controlling
cardiovascular function. In chronically instrumented fetal sheep,
hemorrhage increased plasma renin activity and plasma angiotensin
concentration significantly from 6.7 +/- 2.5 to 15.2 +/- 3.1 ng.ml-1.h-1
and from 74 +/- 19 to 182 +/- 43 pg/ml, respectively. Both mean arterial
and venous blood pressures decreased initially from 45 to 35 Torr and from
3.5 to 2.5 Torr, respectively; then both returned to control values. Fetal
heart rate decreased initially from 174 beats/min and then increased to 186
beats/min. To determine whether angiotensin had a role in mediating these
responses to hemorrhage, we hemorrhaged a second group of fetuses before
and during infusion of saralasin, a competitive antagonist of angiotensin.
Hemorrhage during infusion of saralasin decreased heart rat from 170 to 145
beats/min and further decreased mean arterial pressure to 30 Torr. Cardiac
output decreased from 436 +/- 25 to 368 +/- 30 ml.min-1.kg-1, and
umbilical-placental blood flow decreased from 205 +/- 20 to 145 +/- 10
ml.min-1.kg-1. We conclude that the renin-angiotensin system plays a major
role in the response to hemorrhage in fetal sheep.
