B. Richardson et al., REGIONAL BLOOD-FLOW AND THE ENDOCRINE RESPONSE TO SUSTAINED HYPOXEMIAIN THE PRETERM OVINE FETUS, Pediatric research, 40(2), 1996, pp. 337-343
To determine the circulatory response of the preterm fetus to a sustai
ned hypoxic insult, regional blood how was measured (microsphere techn
ique) in 12 unanesthetized fetal sheep (0.75 gestation) during a normo
xic control period, after 1 h and 8 h of sustained hypoxemia, and afte
r a l-h recovery period. Associated endocrine changes which might rela
te to organ-specific changes in blood flow were also assessed. Myocard
ial and cerebral blood flow were increased by 240 and 90%, respectivel
y, such that oxygen delivery to the heart was well maintained througho
ut the study, whereas that to the brain was significantly decreased by
8 h of hypoxic study. Regional blood flows for all structures within
the brain showed similar percent increases, except that for the pituit
ary gland, where the increase was much smaller, and that for the choro
id plexus, where blood how actually fell. Whereas blood flow to upper
body muscle showed no significant change throughout the study, that to
the thyroid was increased by 70% by 1 h of hypoxic study but fell the
reafter. Adrenal cortical blood flow relative to that of the medulla w
as increased 3-fold by 8 h of hypoxic study, indicating a differential
effect of sustained hypoxia on these vascular beds. Although pituitar
y and thyroid blood flows showed no relationship to respective trophic
and/or secretory hormones measured, values for adrenal cortical flow
relative to medullary flow were well correlated with plasma concentrat
ions of ACTH. It is concluded that the ''centralization'' of blood flo
w to vital organs in response to a sustained hypoxic insult is qualita
tively similar for both the preterm and near term ovine fetus and that
hypoxic regulatory mechanisms may be better protective of the heart.
Additionally, a role for the functional activation of the adrenal glan
d in its blood flow response to sustained hypoxemia is suggested.