Synergism between systemic corticotropin-releasing factor and XXXX on adrenocorticotropin release in vivo varies as a function of gestational age in the ovine fetus.

@entity701 @entity1831 @entity5463 @entity742
In @entity742 , parturition is associated with maturation of fetal pituitary-adrenal function, and with rises in the concentrations of ACTH and @entity701 (F) in fetal plasma. We examined the hypothesis that pituitary ACTH output in response to @entity5463 ( @entity1831 ) and CRF separately and together might change during late pregnancy as a function of fetal age. Fetal @entity742 were chronically catheterized, and bolus iv injections of equimolar AVP, CRF, AVP plus CRF, or saline (controls) were given on days 110-115, 125-130, and 135-140 of gestation. AVP evoked significant rises in plasma ACTH on days 110-115 and 125-130, but not on days 135-140. After AVP, the peak plasma concentrations of ACTH were attained at 5-10 min, and basal (preinjection) values were reestablished by 30-60 min. After CRF treatment, plasma ACTH rose progressively throughout the 240 min of the study. Evidence was obtained in support of an increase in pituitary responsiveness to CRF between days 110-115 and 125-130 and a decrease in response on days 135-140, when basal F concentrations were higher. The ACTH response to AVP, relative to that to CRF, was greatest in the youngest fetuses. On days 110-115 only, CRF and AVP showed a synergistic response in ACTH output, especially during the first 30 min after agonist injection. Plasma F rose in response to the changes in endogenously released ACTH in a manner consistent with progressive fetal adrenal maturation between days 110-140 of pregnancy. We conclude that in vivo the ovine fetal pituitary responds separately and synergistically to AVP and CRF on days 110-115 of gestation, but the relative role of AVP in stimulating ACTH release decreases with progressive gestational age.
