title: Estradiol-17 beta has a biphasic effect on oxytocin secretion by bovine granulosa cells.
abstract: The peptide hormone oxytocin (OT) and its mRNA are synthesized by bovine granulosa cells. Bovine granulosa cells isolated before the preovulatory LH/FSH surge secrete low amounts of OT and respond to gonadotropins with an increase in OT secretion. After the LH/FSH surge, basal OT secretion increases 20-fold. At the same time, dramatic changes in steroidogenesis occur in the preovulatory follicle. Estradiol-17 beta production is high before and declines after the LH surge. The objective of this study was to determine whether steroid hormones, particularly estradiol-17 beta, influence OT secretion by bovine granulosa cells. Heifers (n = 5) were injected with prostaglandin F2 alpha (PGF2 alpha) on Day 7 of the estrous cycle to induce luteolysis. Preovulatory follicles were obtained during the ensuing follicular phase, 24 h after PGF2 alpha injection (about 24-36 h before the expected time of the preovulatory LH/FSH surge). Granulosa cells were isolated and cultured for 5 days in defined medium containing graded doses (0, 0.001, 0.01, 0.1, 1, 10 micrograms/ml) of estradiol-17 beta, testosterone, or progesterone. Media were collected daily and assayed for OT by radioimmunoassay. Addition of 0.001 or 0.01 micrograms estradiol-17 beta/ml stimulated OT secretion by granulosa cells by about 75% during the last 2 days of culture (p < 0.01). In contrast, estradiol-17 beta at high doses (1 and 10 micrograms/ml) inhibited OT secretion by 45-85% (p < 0.01). Therefore, estradiol-17 beta had a biphasic effect on OT secretion by granulosa cells.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Physiology, College of Veterinary Medicine, Cornell University, Ithaca, New York 14853.
authors.forename: A K
authors.initials: AK
authors.lastname: Voss
authors.forename: J E
authors.initials: JE
authors.lastname: Fortune
mesh_terms: D000818:Animals; D002417:Cattle; D002478:Cells, Cultured; D015237:Dinoprost / Q000494:pharmacology; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D005640:Follicle Stimulating Hormone / Q000378:metabolism / Q000494:pharmacology; D005498:Follicular Phase; D006107:Granulosa Cells / Q000187:drug effects / Q000378:metabolism*; D007986:Luteinizing Hormone / Q000378:metabolism; D010121:Oxytocin / Q000378:metabolism*; D011374:Progesterone / Q000494:pharmacology; D013739:Testosterone / Q000494:pharmacology
chemical_list: D013739:Testosterone; D011374:Progesterone; D004958:Estradiol; D010121:Oxytocin; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone; D015237:Dinoprost