PARENT SESSION
Follicular Development

MECHANISMS REGULATING THE MID-LUTEAL PHASE INCREASE IN SECRETION OF FOLLICLE STIMULATING HORMONE IN COWS.

Mussard, Martin ¹, West, Louisa ², Zanella, Eraldo¹, Jimenez-Severiano, Hector¹, Nett, Terry², Kinder, James¹, ^{1 2}

ABSTRACT- In cattle, an increase in circulating FSH initiates a wave of ovarian follicular development. The objective of the present study was to evaluate mechanisms involved in the mid-cycle increase of FSH. Follicular aspiration was used to control stage of follicular development. Animals in Groups 1, 2, 3 and 5 were subjected to two injections of prostaglandin F₂ (PGF₂) ten days apart to induce a common day of estrus (estrus = Day 0). Group 4 was synchronized with PGF₂ to induce a common day of estrus among animals on Day -2. The groups (n = 6/group) were: 1) no treatment, 2) beginning on Day 2 and continuing until pituitary collection, aspiration of all follicles > 4 mm, 3) aspiration of all follicles > 4 mm only at 30 hours prior to pituitary collection, 4) induction of a persistent follicle going through atresia at the time of pituitary collection and 5) aspiration of all follicles > 4 mm only at 80 hours prior to pituitary collection. Blood samples were taken every six hours from Day -2 until pituitary collection and analyzed for progesterone and FSH. Pituitaries were collected on Day 7 (Day 9, Group 4) and placed on dry ice. Pituitary tissue was analyzed for amounts of mRNA for activin B, follistatin, GnRH receptor and FSH-. Animals that had follicles aspirated 30 hours prior to pituitary collection had greater amounts of FSH present in circulation than animals in all other groups (p <. 05). Amounts of FSH- mRNA were also greater in animals of Group 3 than other groups (p < .05). Amounts of mRNA for activin B, follistatin, and GnRH receptor were similar among treatments. In conclusion, animals with greater amounts of FSH in circulation have increased amounts of mRNA for FSH- in the anterior pituitary. It remains unclear what effect activin-B, follistatin and GnRH receptor have in modulating the mid-cycle FSH increase in the circulation of cattle.

KEY WORDS: FSH, follicular development, cattle, activin