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Steroid Regulation of Retinol-Binding Protein in the Ovine Oviduct¹

^a Department of Animal Science, The University of Tennessee, Knoxville, Tennessee 37901

Two studies were conducted to identify retinol-binding protein (RBP) expression in the ovine oviduct and to determine the role of ovarian steroids in its regulation. Ewes were salpingectomized on Days 1, 5, or 10 of their respective estrous cycles, and oviducts were homogenized for RNA analysis, fixed for immunocytochemistry (ICC), or cultured for 24 h for protein analysis. ICC localized RBP to the epithelium of all oviducts. RBP synthesis was demonstrated by immunoprecipitation of radiolabeled RBP from the medium of oviductal explant cultures. Explant culture medium from oviducts harvested on Day 1 contained significantly more RBP than medium from oviducts collected on Days 5 or 10. Slot-blot analysis demonstrated that steady-state RBP mRNA levels were significantly higher on Day 1 than Day 5 or 10. In the second experiment, ovariectomized ewes were treated with estradiol-17ß (E₂), progesterone (P₄), E₂+P₄ (E2+P4), or vehicle control, and oviducts were analyzed as above. P₄ alone or in combination with E₂ significantly reduced steady-state RBP mRNA levels compared to those in E₂-treated animals. Oviductal explants from E₂- and E2+P4-treated animals released 3- to 5-fold more RBP into the medium than control and P₄ treatments as determined by ELISA. RBP synthesis of metabolically labeled RBP was increased by E₂ and E2+P4 treatments. This study demonstrates that P₄ applied on an estradiol background negatively regulates RBP gene expression in the oviduct whereas estradiol appears to stimulate RBP synthesis and secretion.

¹ This work was supported, in part, by USDA NRI CGP #93-37201-8980 and The Tennessee Agricultural Experiment Station.

² Correspondence. FAX: 423 974 4359; jgodkin{at}utk.edu

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