title: Involvement of vasopressin in the down-regulation of pituitary corticotropin-releasing factor receptors after adrenalectomy.
abstract: The role of vasopressin (VP) in the regulation of pituitary corticotropin-releasing factor (CRF) receptors was studied by examining the effects of adrenalectomy and VP infusion on pituitary CRF receptors in genetically VP-deficient rats (di/di) and Long-Evans control rats. Binding studies with [125I]Tyr-ovine CRF in 30,000 X g anterior pituitary membrane-rich fractions revealed similar characteristics for the CRF receptors in Long-Evans and di/di rats, with Kd values of 2.4 +/- 0.6 and 1.9 +/- 0.2 nM, respectively, and receptor concentrations of 278 +/- 31 and 286 +/- 43 fmol/mg, respectively. Two days after adrenalectomy, the pituitary CRF receptor concentration decreased by 72 +/- 4.2% in Long-Evans rats, but by only 20.3 +/- 5.6% in di/di rats. CRF receptor affinity was unchanged after adrenalectomy (Kd = 1.7 +/- 0.5 nM; n = 8). To determine whether VP deficiency is responsible for the smaller decrease in CRF receptor in di/di rats, the effect of exogenous VP infusion (100 ng/min) by sc osmotic minipumps was studied in adrenalectomized di/di rats. Two days after adrenalectomy, pituitary CRF receptors were reduced by 21 +/- 8% in control di/di rats, whereas a 77.7 +/- 1.8% decrease was observed in VP-infused di/di rats, comparable to the effect of adrenalectomy in Long-Evans rats. VP infusion also caused a significant 35 +/- 2% decrease in CRF receptors in the pituitaries of sham-operated di/di rats, with no change in CRF receptor affinity. In Sprague-Dawley rats, VP or CRF infusion (100 ng/min) decreased pituitary CRF receptors by 14 +/- 1.9% and 46 +/- 3%, respectively. However, the combined infusion of both peptides caused a 65% +/- 4.2 decrease, similar to that observed after adrenalectomy. In vitro incubation of quartered pituitaries with VP or CRF for 4 h reduced CRF receptors by 23.1 +/- 8.2% and 38.2 +/- 3.8%, respectively, while simultaneous preincubation with both peptides was followed by a decrease of 55.3 +/- 5.3%. These findings indicate that increased hypothalamic release of VP contributes to the down-regulation of pituitary CRF receptors after adrenalectomy.
authors.affiliation: Endocrinology and Reproduction Research Branch, National Institute of Child Health and Human Development, Bethesda, Maryland 20892.
authors.forename: M C
authors.initials: MC
authors.lastname: Holmes
authors.forename: K J
authors.initials: KJ
authors.lastname: Catt
authors.forename: G
authors.initials: G
authors.lastname: Aguilera
mesh_terms: D000315:Adrenalectomy; D000324:Adrenocorticotropic Hormone / Q000097:blood; D000818:Animals; D003346:Corticotropin-Releasing Hormone / Q000378:metabolism*; D007700:Kinetics; D008473:Median Eminence / Q000378:metabolism*; D010903:Pituitary Gland, Anterior / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D018019:Receptors, Corticotropin-Releasing Hormone; D017981:Receptors, Neurotransmitter / Q000378:metabolism*; D013045:Species Specificity; D014667:Vasopressins / Q000502:physiology*
chemical_list: D018019:Receptors, Corticotropin-Releasing Hormone; D017981:Receptors, Neurotransmitter; D014667:Vasopressins; D000324:Adrenocorticotropic Hormone; D003346:Corticotropin-Releasing Hormone