Up-regulation of the fetal baboon hypothalamo-pituitary-adrenal axis in intrauterine growth restriction: coincidence with hypothalamic glucocorticoid receptor insensitivity and leptin receptor down-regulation

Abstract

Intrauterine growth restriction (IUGR) is an important fetal developmental problem resulting from 2 broad causes: maternal undernutrition and/or decreased fetal nutrient delivery to the fetus via placental insufficiency. IUGR is often accompanied by up-regulation of the hypothalamo-pituitary-adrenal axis (HPAA). Sheep studies show fetal HPAA autonomy in late gestation. We hypothesized that IUGR, resulting from poor fetal nutrient delivery, up-regulates the fetal baboon HPAA in late gestation, driven by hypothalamo-pituitary glucocorticoid receptor (GR) insensitivity and decreased fetal leptin in peripheral plasma. Maternal baboons were fed as ad libitum controls or nutrient restricted to produce IUGR (fed 70% of the control diet) from 0.16 to 0.9 gestation. Peripheral ACTH, cortisol, and leptin were measured by immunoassays. CRH, arginine vasopressin (AVP), GR, leptin receptor (ObRb), and pro-opiomelanocortin peptide expression were determined immunohistochemically. IUGR fetal peripheral cortisol and ACTH, but not leptin, were increased (P < .05). IUGR increased CRH peptide expression, but not AVP, in the fetal hypothalamic paraventricular nucleus (PVN) and median eminence (P < .05). PVN ObRb peptide expression, but not GR, was decreased (P < .05) with IUGR. ObRb and pro-opiomelanocortin were robustly expressed in the anterior pituitary gland, but ∼1% of cells showed colocalization. We conclude that (1) CRH, not AVP, is the major releasing hormone driving ACTH and cortisol secretion during primate IUGR, (2) fetal HPAA activation was aided by GR insensitivity and decreased ObRb expression in the PVN, and (3) the anterior pituitary is not a site for ObRb effects on the HPAA.

Figure 1.

ACTH and cortisol concentrations in peripheral plasma of fetal baboons (A and B) and cortisol from their mothers (C) that were fed as ad libitum controls (filled bars; n = 7) or IUGR (open bars, mothers fed 70% CTR diet; n = 6) from 0.16 to 0.9 gestation with blood collected at cesarean section or necropsy at 0.9 gestation (165 dG). Data are expressed as means ± SEM. *, P < .05 vs CTR.

Figure 2.

Photomicrographs (A and B) and data summary (C) of CRH peptide expression (black product) in neuronal perikarya (black arrows) and beaded neuronal fibers (open arrows) in the hypothalamic PVN of baboon fetuses from mothers fed as ad libitum fed controls (A, CTR; C, CTR, filled bars; n = 7) or IUGR (B, mothers fed 70% CTR diet; C, IUGR, open bars; n = 6) from 0.16 to 0.9 gestation with cesarean section/tissue collection at 0.9 gestation (165 dG). Data are expressed as means ± SEM. *, P < .05. Scale bar applies to both micrographs.

Figure 3.

Photomicrographs (A and B) and summary (C) of AVP peptide expression (black product) in neuronal perikarya (thin arrows) and neuronal fibers (black arrows) in the hypothalamic PVN of baboon fetuses from mothers fed as ad libitum controls (A, CTR; C, CTR, filled bars; n = 7) or IUGR (B, mothers fed 70% CTR diet; C, IUGR, open bars; n = 6) from 0.16 to 0.9 gestation with cesarean section/tissue collection at 0.9 gestation (165 dG). Data are expressed as means ± SEM. No difference (P ≫ .05) was seen between groups in AVP expression. Scale bar applies to both micrographs.

Figure 4.

Photomicrographs (A and B) and summary (C) of CRH peptide expression (black product) in terminal axons of the median eminence external zone (EZ) from baboon fetuses of mothers fed as ad libitum controls (A, CTR; C, CTR, filled bars; n = 7) or IUGR (B, mothers fed 70% CTR diet; C, IUGR [MNR], open bars; n = 6) from 0.16 to 0.9 gestation with cesarean section/tissue collection at 0.9 gestation (165 dG). IZ, internal zone of median eminence; EZ, external zone; CZ, capsule. Data are expressed as means ± SEM. *, P < .05; †, P = .05. Scale bar applies to both micrographs.

Figure 5.

Photomicrographs (A and B) and summary (C) of AVP peptide expression (black product) in terminal axons of the median eminence external zone (EZ) from baboon fetuses of mothers fed as ad libitum controls (A, CTR, filled bars; n = 7) or IUGR (B, mothers fed 70% CTR diet; C, IUGR [MNR], open bars; n = 6) from 0.16 to 0.9 gestation with cesarean section/tissue collection at 0.9 gestation (165 dG). IZ, internal zone of median eminence; EZ, external zone; CZ, capsule. Data are expressed as means ± SEM. *, P < .05; †, P = .05. Scale bar applies to both micrographs.

Figure 6.

Photomicrographs (A and B) and summary (C) of leptin long form receptor peptide expression (black product) in neurons of the hypothalamic PVN from baboon fetuses of mothers fed as ad libitum controls (A, CTR, filled bars; n = 7) or IUGR (B, mothers fed 70% CTR diet; C, IUGR [MNR], open bars; n = 6) from 0.16 to 0.9 gestation with cesarean section/tissue collection at 0.9 gestation (165 dG). Data are expressed as means ± SEM. *, P < .05; †, P = .05. Scale bar applies to both micrographs. D, Photomicrograph of leptin long form receptor peptide expression (black product) in endothelial cells (arrows) of a small hypothalamic blood vessel from a baboon fetus with cesarean section/tissue collection at 0.9 gestation (165 dG).