Corticotropin-releasing factor receptor expression in the pituitary of fetal sheep after lesion of the hypothalamic paraventricular nucleus

Both the capacity of CRF to release ACTH and the number of binding sites fo r CRF in the anterior pituitary decline during the final weeks of gestation in fetal sheep. The present study examined regulation of pituitary CRF rec eptor expression by the hypothalamic paraventricular nucleus (PVN) during l ate gestation in fetal sheep. Bilateral radiofrequency lesions of the PVN (PVN-Lx; n = 4) or sham lesions (SHAM; n = 5)mere performed in fetal sheep at 118-122 days of gestational age (dGA). Pituitary glands hom PVN-Lx and SHAM fetuses were collected at 1 39-142 dGA (term, approximately 148 dGA). Dual-label in situ hybridization was performed using a digoxigenin-labeled ovine POMC complementary RNA, tog ether with a (35S)-labeled ovine GRF type I(CRF1) receptor complementary RN A, to localize and quantify CRF1 receptor mRNA in POMC-hybridizing cells. B inding of [I-126]-ovine CRF was also examined in the fetal pituitary of bot h PVN-Lx and SHAM fetuses using in situ autoradiography. The hybridization signal for the CRF1 receptor mRNA was primarily restricte d to POMC-expressing cells in the anterior pituitary of both PVN-Lx and SHA M fetuses; no hybridization signal for the CRF1 receptor was observed in th e neurointermediate lobe (NIL) in either group. The hybridization signal fo r CRF1 receptor mRNA in anterior pituitary corticotropes of PVN-Lx fetuses was significantly lower in both the inferior and superior regions of the an terior pituitary, compared with SHAM fetuses (P < 0.05). In the inferior re gion of the anterior pituitary, the percentage of POMC-hybridizing cells co ntaining CRF1 receptor hybridization signal was significantly greater in PV N-Lx (90 +/- 7%; mean + SEM), compared with SHAM (67 +/- 6%; P < 0.05) fetu ses. No differences in the percentage of POMC cells containing CRF1 recepto r hybridization signal were observed in the superior region of the anterior pituitary between PVN-Lx (89 +/- 8%) and SHAM (87 +/- 9%). Binding of [I-1 25]-ovine CRF (oCRF) was significantly greater in anterior pituitaries of P VN-Lx(140 +/- 19 mean arbitrary densitometry U +/- SEM), compared with SHAM (73 +/- 23; P < 0.05) fetuses. For both PVN-Lx and SHAM fetuses, there were no differences within group in [I-125]-oCRF binding between the inferior a nd superior regions of the anterior pituitary .A weak, but significant (P < 0.05), autoradiographic signal for [I-125] -oCRF binding was observed in t he NIL of both SHAM and PVN-Lx fetal sheep. The level of [I-125]-oCRF bindi ng was significantly lower in the NIL, compared with anterior pituitary, fo r both SHAM (P < 0.01) and PVN-Lx fetuses. There were no differences in [I- 125]-oCRF binding in the NIL between SHAM and PVN-Lx fetal sheep. Our findi ngs support a role for the PVN in regulating anterior pituitary CRF1 recept or expression in the late-gestation sheep fetus.