PARENT SESSION

(52) THE ROLE OF LH IN CHANGING GENE EXPRESSION DURING SELECTION OF A DOMINANT FOLLICLE IN CATTLE.

Luo, Wenxiang¹, Gumen, Ahmet¹, Wiltbank, Milo ¹, ¹ University of Wisconsin-Madison, Madison, WI

ABSTRACT- At approx. 8.5 mm the future dominant follicle deviates in growth rate from the largest subordinate follicle and is "selected" for continued growth. There is also an abrupt expression of LH receptors (LHr) on granulosa cells (GC) near this time. Abnormalities in pulsatile LH secretion can cause defects in selection and post-selection growth of the dominant follicle in humans, cattle, and other species. In this study, cows were treated with a potent GnRH receptor antagonist, Acyline, just before (approx. 8 h) follicular deviation to investigate the role of pulsatile LH in changes in gene expression during selection of a dominant follicle. Cows (n = 12) on Day 9 of the estrous cycle had a new follicular wave induced by aspiration of all follicles >5 mm. Ovaries were evaluated by ultrasound at 6-12 h intervals and cows were randomly assigned to receive Acyline or Control at the first evaluation when the largest follicle reached ≥7.8 mm. The ovary containing the dominant (DF) and largest subordinate (SF) follicles was removed by colpotomy 12 h after treatment. Real-time PCR was used to determine mRNA concentrations in GC and thecal cells (TC). ELISA was used to measure testosterone (T) and 17-estradiol (E2) in follicular fluid (FF). The FF concentration of E2 but not T was greater in DF than SF of control cows (2.0×); however both E2 and T were dramatically decreased (>76%) in both DF and SF after Acyline treatment. In TC, LHr was slightly greater in DF than SF (1.4×) and Acyline reduced LHr in TC of DF (59%). Acyline also reduced TC mRNA for StAR in both DF (82%) and SF (66%) and mRNA for P45017 in DF (59%). P450scc mRNA did not change after Acyline. In GC, LHr mRNA was much greater in DF than SF (8.3×) and was decreased by Acyline in both DF (87%) and SF (45%). The mRNA for P450 aromatase (2.0×) and PAPP-A (1.4×) tended (P <0.1) to be greater in DF than SF and Acyline tended (P<0.1) to decrease expression of P450 aromatase (47%) and PAPP-A (76%) in DF. FSH receptor mRNA was not different between DF and SF and did not change after Acyline. Thus, induction of LHr in GC and possibly TC is a very early event in selection of a single dominant follicle (possibly before induction of aromatase or PAPP-A) and is acutely (within 12 h) dependent on pulsatile LH. Production of follicular T and E2 are also acutely related to pulsatile LH apparently due to expression of StAR and P45017 in TC.

KEY WORDS: Aycline, LH gene expression, follicle, cattle