CHANGES IN ADRENOCORTICOTROPIN AND CORTISOL RESPONSIVENESS AFTER REPEATED PARTIAL UMBILICAL-CORD OCCLUSIONS IN THE LATE-GESTATION OVINE FETUS

Despite many studies reporting fetal ACTH and cortisol (F) responses t o acute fetal hypoxemia induced by several methods, effects of repeate d short-term fetal hypoxia produced by umbilical cord occlusion (UCO) on ACTH and F are unknown. We examined fetal ACTH and F responses to r epeated, controlled, 50% reductions in common umbilical arterial blood flow (CUBF) produced by an inflatable cord occluder. Ten sheep fetuse s were instrumented at 123-128 days gestation (dGA) with arterial, ven ous, and amniotic catheters. A common umbilical artery transit-time ul trasound flow probe was implanted to measure CUBF. An inflatable occlu der was placed around the proximal portion of the umbilicus. In five f etuses (group I) at 131 +/- 1 dGA (mean +/- SEM), 12 UCOs (CUBF reduce d by 50%), each lasting 5 min separated by 15 min recovery, were perfo rmed. Changes in fetal arterial blood gases, pH and plasma ACTH, and F concentrations were determined before, during, and after the 1st, 6th , and 12th UCOs. Sham experiments were conducted on the other five fet uses at 130 +/- 1 dGA (group II). In group I, CUBF decreased to 49 +/- 1% (mean +/- SEM of 12 UCOs). After each UCO, CUBF returned to baseli ne within 5 min. A modest fall in fetal arterial PO, and arterial pH ( 21.2 +/- 0.2 to 16.8 +/- 0.2 mmHg and 7.33 +/- 0 to 7.29 +/- 0, respec tively) and a mild increase in fetal PaCO2 (49.9 +/- 0.5 to 54.9 +/- 0 .4 mmHg; mean +/- SEM of 12 UCOs) occurred with each UCO. Whereas preo cclusion fetal ACTH concentrations increased by the 12th UCO, F remain ed unchanged. Fetal ACTH increased after the 1st, 6th, and 12th UCOs. Fetal F increased after the Ist and 6th UCOs but not after the 12th UC O. Fetal plasma ACTH and F remained unchanged throughout the experimen ts in group II fetuses. We conclude that: 1) partial reductions in CUB F induce significant activation of the fetal anterior pituitary-adreno cortical axis in late-gestation fetal sheep; 2) after repeated UCOs, f etal ACTH responsiveness is maintained, but fetal F responses become a ttenuated.