We have previously shown that both
plasma protein restitution and plasma volume restitution are significantly enhanced in female rats hemorrhaged during the proestrus phase of the estrous cycle.
Estradiol and
progesterone levels are markedly elevated during proestrus and also increase during pregnancy. The present studies were therefore designed to determine whether the ability to restore
plasma protein and blood volume after
hemorrhage is augmented during pregnancy and by chronically elevated
estradiol levels. The response to moderate
hemorrhage (22-23% blood loss) was evaluated in conscious pregnant rats during early and midgestation and compared with that of virgin female rats studied during metestrus. At 22 h posthemorrhage, plasma volume had increased to greater than basal levels, and blood volume was restored to 93 +/- 1% (metestrus), 91 +/- 2% (early pregnancy), and 98 +/- 2% (midgestation) of control (P > 0.05). Animals hemorrhaged during metestrus or early pregnancy restored the same amount of
protein to the plasma as had been removed, whereas those hemorrhaged during midgestation restored nearly 50% more
plasma protein than had been removed (P < 0.01). In ovariectomized animals with chronic
steroid replacement that maintained plasma
progesterone at metestrus levels (15 +/- 2 ng/ml) but raised plasma
estradiol to twofold that of midgestation (22 +/- 3 pg/ml), the blood volume and
plasma protein restitution responses to
hemorrhage did not differ from those of ovariectomized animals with no
steroid replacement. In summary, posthemorrhage restoration of
plasma protein content is significantly augmented during midgestation, but not during early pregnancy. This augmented response cannot be attributed to chronic elevation of plasma
estradiol levels alone.