Supplementation of equine early spring transitional follicles with luteinizing hormone stimulates follicle growth but does not restore steroidogenic activity
ABSTRACT This study was conducted to test the hypothesis that supplementation of growing follicles with LH during the early spring transitional period would promote the development of steroidogenically active, dominant follicles with the ability to respond to an ovulatory dose of hCG. Mares during early transition were randomly assigned to receive a subovulatory dose of equine LH (in the form of a purified equine pituitary fraction) or saline (transitional control; n = 7 mares per group) following ablation of all follicles >15 mm. Treatments were administered intravenously every 12 h from the day the largest follicle of the post-ablation wave reached 20 mm until a follicle reached >32 mm, when an ovulatory dose of hCG (3000 IU) was given. Saline-treated mares during June and July were used as ovulatory controls. In a preliminary study, injection of this pituitary fraction (eLH) to anestrus mares was followed by an increase in circulating levels of LH (P < 0.01) but not FSH (P > 0.6). Administration of eLH during early transition stimulated the growth of the dominant follicle (Group x Day, P < 0.00001), which attained diameters similar to the dominant follicle in ovulatory controls (P > 0.1). In contrast, eLH had no effect on the diameter of the largest subordinate follicle or the number of follicles >10 mm during treatment (P > 0.3). The numbers of mares that ovulated in response to hCG in transitional control, transitional eLH and ovulatory control groups (2 of 2, 3 of 5 and 7 of 7, respectively) were not significantly different (P > 0.1). However, after hCG-induced ovulation, all transitional mares returned to an anovulatory state. Circulating estradiol levels increased during the experimental period in ovulatory controls but not in transitional eLH or transitional control groups (Group x Day, P = 0.013). In addition, although progesterone levels increased after ovulation in transitional control and transitional eLH groups, levels in these two groups were lower than in the ovulatory control group after ovulation (Group, P = 0.045). In conclusion, although LH supplementation of early transitional waves beginning after the largest follicle reached 20 mm promoted growth of ovulatory-size follicles, these follicles were developmentally deficient as indicated by their reduced steroidogenic activity.
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ABSTRACT: There is evidence in several species that high circulating LH concentrations can interfere with normal follicle development and ovulation. In the mare, high LH levels after induction of luteolysis with PGF(2α) have been temporally associated with an increased incidence of anovulatory follicles. We hypothesized that a premature increase in LH levels during a follicular wave in mares would disrupt normal follicle maturation leading to ovulatory dysfunction. In experiment 1, all follicles >10 mm were ablated at midestrous cycle in pony mares followed by twice daily administration of equine LH (eLH; 1.6 μg/kg body weight) or saline (vehicle; N = 8 mares per group). When a dominant follicle reached >32 mm, an ovulatory dose of hCG was given. Treatment with eLH had no effects on ovulatory responses or progesterone levels during the posttreatment luteal phase. In experiment 2, after follicle ablation, mares were treated with eLH or vehicle (as above) or were given a single injection of PGF(2α) (N = 7 mares per group), followed by aspiration of a dominant follicle when it reached >32 mm. Administration of eLH induced an increase in circulating LH levels similar to that after PGF(2α) injection. Neither PGF(2α) nor eLH administration had significant effects on follicle growth or total number of follicles in the postablation wave. However, compared with mares treated with vehicle, the preovulatory follicle in the eLH and PGF(2α) groups had lower levels of androstenedione (P = 0.03) and higher levels of insulin-like growth factor I (P = 0.03). Further, levels of prostaglandin E2 in preovulatory follicles tended to be lower in the eLH and PGF(2α) groups (P = 0.06). In conclusion, exposure of developing follicles to high LH in mares did not have apparent effects on ovulation but it induced changes in follicular fluid factor levels which might reflect a disruption in follicle and/or oocyte maturation, indicating the need to further study the implications of using PGF(2α) for the control of fertility in farm animals.Theriogenology 11/2012; 79(3). DOI:10.1016/j.theriogenology.2012.08.017 · 1.85 Impact Factor
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ABSTRACT: Previous evidence from in vitro studies suggests specific roles for a subset of miRNAs, including miR-21, miR-23a, miR-145, miR-503, miR-224, miR-383, miR-378, miR-132 and miR-212, in regulating ovarian follicle development. The objective of this study was to determine changes in the levels of these miRNAs in relation to follicle selection, maturation and ovulation in the monovular equine ovary. In Experiment 1, follicular fluid was aspirated during ovulatory cycles from the dominant (DO) and largest subordinate (S) follicles of an ovulatory wave, and the dominant (DA) follicle of a mid-cycle anovulatory wave (n=6 mares). Follicular fluid levels of progesterone and estradiol were lower (P<0.01) in S follicles than in DO follicles, whereas mean levels of IGF1 were lower (P<0.01) in S and DA follicles than in DO follicles. Relative to DO and DA follicles, S follicles had higher (P≤0.01) follicular fluid levels of miR-145 and miR-378. In Experiment 2, follicular fluid and granulosa cells were aspirated from dominant follicles before (DO) and 24h after (L) administration of an ovulatory dose of hCG (n=5 mares/group). Relative to DO follicles, L follicles had higher follicular fluid levels of progesterone (P=0.05) and lower granulosa cell levels of CYP19A1 and LHCGR (P<0.005). Levels of miR-21, miR-132, miR-212 and miR-224 were increased (P<0.05) in L follicles; this was associated with reduced expression of the putative miRNA targets, PTEN, RASA1 and SMAD4. These novel results may indicate a physiological involvement of miR-21, miR-145, miR-224, miR-378, miR-132 and miR-212 in the regulation of cell survival, steroidogenesis and differentiation during follicle selection and ovulation in the monovular ovary.Reproduction 06/2013; DOI:10.1530/REP-13-0107
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ABSTRACT: Relatively little is known about the physiological roles of microRNAs (miRNAs) during follicular development. Previous evidence from in vitro studies suggests specific roles for a subset of miRNAs, including miR-21, miR-23a, miR-145, miR-503, miR-224, miR-383, miR-378, miR-132, and miR-212, in regulating ovarian follicle development. The objective of this study was to gain insight on the involvement of these miRNAs during follicle maturation. Follicular fluid was aspirated from dominant follicles (>32 mm) during the ovulatory season (July to October) and the anovulatory season (January to March) in each of 5 mares, and the levels of steroids, IGF1, and miRNAs were analyzed by immunoassays and quantitative PCR. Levels of progesterone, testosterone, and IGF1 were lower (P ≤ 0.05) in anovulatory than in ovulatory follicles. Relative to ovulatory follicles, anovulatory follicles had higher (P < 0.05) mean levels of miR-21, miR-23b, miR-378, and miR-202 and tended to have higher (P = 0.06) levels of miR-145. Levels of miR-224 and miR-383 could not be detected in follicular fluid. These novel results indicate a physiological association between increases in follicular miRNA levels and seasonal anovulation in mares; further studies should elucidate the precise involvement of miR-21, miR-23b, miR-145, miR-378, and miR-202 in follicle maturation in the mare.Domestic animal endocrinology 07/2013; DOI:10.1016/j.domaniend.2013.06.006 · 1.78 Impact Factor