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1 Department of Obstetrics and Gynecology, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA
2 Center for Perinatal Biology, Loma Linda University School of Medicine, Loma Linda, CA, USA
* To whom correspondence should be addressed. E-mail: cducsay{at}som.llu.edu.
We previously demonstrated altered function of the hypothalamic-pituitary-adrenal axis following secondary stressors in long term hypoxic (LTH) fetal sheep. While ACTH is considered the primary mediator of glucocorticoid production in fetal sheep, proopiomelanocortin (POMC) and 22 kDa proACTH (22 kDa ACTH), have been implicated in the regulation of cortisol production in the ovine fetus. This study was designed to determine if POMC expression and processing are altered following LTH. Pregnant ewes were maintained at high altitude (3,820 m) from day 30 of gestation to near term when the animals were transported to the laboratory. Reduced PO2 was maintained by nitrogen infusion through a maternal tracheal catheter. On day 137-141, fetal anterior pituitaries were collected from normoxic control and LTH fetuses. POMC and corticotrophin releasing factor receptor (CRF1) mRNA were measured using quantitative, real time PCR and Western analysis was used for quantitation of ACTH, ACTH precursor and CRF1 proteins. Plasma ACTH1-39 was measured using a two-site IRMA specific for ACTH1-39. Plasma ACTH precursors were measured by ELISA. Anterior pituitary POMC mRNA was not different between groups while CRF1 levels were significantly higher in the LTH anterior pituitaries compared to control (p<0.05). In contrast, protein levels of POMC, CRF1, 22 kDa ACTH and ACTH1-39 were significantly lower in the LTH group. Plasma concentrations of both ACTH precursors and ACTH1-39 were significantly elevated in LTH fetuses while the ratio of plasma precursors to ACTH was significantly lower. We conclude that LTH results in enhanced POMC processing and/or release to ACTH and increased hypothalamic drive.
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