title: Changes in adrenocorticotropin and cortisol responsiveness after repeated partial umbilical cord occlusions in the late gestation ovine fetus.
abstract: Despite many studies reporting fetal ACTH and cortisol (F) responses to acute fetal hypoxemia induced by several methods, effects of repeated short-term fetal hypoxia produced by umbilical cord occlusion (UCO) on ACTH and F are unknown. We examined fetal ACTH and F responses to repeated, controlled, 50% reductions in common umbilical arterial blood flow (CUBF) produced by an inflatable cord occluder. Ten sheep fetuses were instrumented at 123-128 days gestation (dGA) with arterial, venous, and amniotic catheters. A common umbilical artery transit-time ultrasound flow probe was implanted to measure CUBF. An inflatable occluder was placed around the proximal portion of the umbilicus. In five fetuses (group I) at 131 +/- 1 dGA (mean +/- SEM), 12 UCOs (CUBF reduced by 50%), each lasting 5 min separated by 15 min recovery, were performed. 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 fetuses 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 baseline within 5 min. A modest fall in fetal arterial PO2 and arterial pH (21.2 +/- 0.2 to 16.8 +/- 0.2 mmHg and 7.33 +/- 0 to 7.29 +/- 0, respectively) 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 preocclusion fetal ACTH concentrations increased by the 12th UCO, F remained unchanged. Fetal ACTH increased after the 1st, 6th, and 12th UCOs. Fetal F increased after the 1st and 6th UCOs but not after the 12th UCO. Fetal plasma ACTH and F remained unchanged throughout the experiments in group II fetuses. We conclude that: 1) partial reductions in CUBF induce significant activation of the fetal anterior pituitary-adrenocortical axis in late-gestation fetal sheep; 2) after repeated UCOs, fetal ACTH responsiveness is maintained, but fetal F responses become attenuated.
authors.affiliation: Department of Physiology, New York State College of Veterinary Medicine, Cornell University, Ithaca 14853-6401, USA.
authors.forename: N
authors.initials: N
authors.lastname: Unno
authors.forename: D A
authors.initials: DA
authors.lastname: Giussani
authors.forename: W K
authors.initials: WK
authors.lastname: Hing
authors.forename: X Y
authors.initials: XY
authors.lastname: Ding
authors.forename: J H
authors.initials: JH
authors.lastname: Collins
authors.forename: P W
authors.initials: PW
authors.lastname: Nathanielsz
mesh_terms: D000324:Adrenocorticotropic Hormone / Q000097:blood*; D000818:Animals; D002245:Carbon Dioxide / Q000097:blood; D005260:Female; D005312:Fetal Blood / Q000737:chemistry*; D006854:Hydrocortisone / Q000097:blood*; D006863:Hydrogen-Ion Concentration; D010100:Oxygen / Q000097:blood; D011247:Pregnancy; D012039:Regional Blood Flow; D012756:Sheep; D014470:Umbilical Cord / Q000502:physiology*
chemical_list: D002245:Carbon Dioxide; D000324:Adrenocorticotropic Hormone; D010100:Oxygen; D006854:Hydrocortisone