RESUMO
Selection of a single dominant follicle is morphologically manifested by diameter deviation between the future dominant follicle (F1) and the future largest subordinate follicle (F2). Conventional deviation is defined as F2≥7â¯mm when F1 reaches â¼8.5â¯mm whereas, undersized deviation is if F2<7â¯mm when F1 reaches â¼8.5â¯mm. Greater frequency of undersized deviation has been temporally associated with greater circulating progesterone (P4) and greater FSH but reduced LH in observational studies. Experiment 1 was conducted to directly test if elevating P4 increased the likelihood of undersized deviation and altered circulating concentrations of LH and FSH. Experiment 2 was conducted to test if increasing LH action by treatment with exogenous porcine LH or human chorionic gonadotropin (hCG) in the presence of elevated P4, would stimulate growth of F2 and increase the likelihood of conventional deviation. Ovaries were evaluated by ultrasound and blood samples collected every 12â¯h after development of a new wave following follicle ablation on D6 (D0â¯=â¯ovulation). Data were normalized to F1≥7.5â¯mm and compared using SAS software. In experiment 1 (nâ¯=â¯20), the CL was regressed by prostaglandin F2α treatment and heifers were randomized on D6 into control (no P4 treatment) or P4 treatment (75â¯mg every 12â¯h for 5.5â¯d) beginning when F1 reached â¼3â¯mmâ¯(P4-3â¯mm group) or â¼6â¯mmâ¯(P4-6â¯mm group). The P4 treatment significantly increased the frequency of undersized deviation from 0% (controls) to 54%, decreased LH by 44%, and increased FSH by 32%. In experiment 2 (nâ¯=â¯27) heifers were randomized on D6 into control (saline) or treatment with the LH analogs - pLH (1.25â¯mg porcine LH/12â¯h) or hCG (160 IU initially and subsequently 96 IU/24â¯h). Treatment with LH analogs significantly increased P4 (control, 4.6⯱â¯0.3â¯ng/mL; pLH, 6.6⯱â¯0.4â¯ng/mL; and hCG, 8.9⯱â¯0.4â¯ng/mL) and decreased FSH (control, 0.46⯱â¯0.03â¯ng/mL; combined-pLH/hCG, 0.34⯱â¯0.02â¯ng/mL). However, F1 and F2 diameter and frequency of conventional (37%) and undersized (48%) deviations were similar between the control and combined-pLH/hCG groups. In conclusion, elevated P4 was directly linked to undersized deviation but the P4 effect on decreasing F2 diameter occurred independently of the P4 effects on FSH and LH concentrations.
Assuntos
Bovinos/fisiologia , Hormônio Foliculoestimulante/sangue , Hormônio Luteinizante/sangue , Folículo Ovariano/efeitos dos fármacos , Progesterona/farmacologia , Animais , Bovinos/sangue , Bovinos/metabolismo , FemininoRESUMO
Follicle diameter deviation has been identified as the pivotal morphological manifestation of follicle selection, however, many of the hormonal mechanisms leading to this key event and regulating variation between individual follicular waves remain undefined. This study compared circulating FSH, LH, and P4 with the follicular dynamics during three different physiological conditions. We hypothesized that these end-points would: 1) be similar for a spontaneous wave 2 vs one induced by follicular aspiration, 2) but would differ between wave 1 and 2, and 3) between conventional (F2â¯>â¯7.0 mm at deviation) vs undersized (F2â¯<â¯7.0 mm) deviations in either wave. Holstein dairy heifers (Nâ¯=â¯24) were studied daily during an interovulatory interval. All heifers were evaluated during wave 1 and randomized 6 days after ovulation into an induced wave 2 and a spontaneous wave 2. Values were normalized to the day of expected diameter deviation (day 0) and compared for day -2 to 0 and 0 to 2. Hypothesis 1 was supported that an induced wave 2 from ablation of follicles of wave 1 and spontaneous wave 2 have similar follicle dynamics. However, the peak FSH surge was more prominent at emergence of an induced wave 2 (Pâ¯<â¯0.003). Hypothesis 2 was supported that waves 1 and 2 differ in follicle and hormone dynamics. Circulating P4 was lower and LH was greater (Pâ¯<â¯0.01) with no difference in diameter of F1 but with a greater (Pâ¯<â¯0.01) diameter of F2 on day 0 in wave 1 (7.3⯱â¯0.2â¯mm) than in wave 2 (6.6⯱â¯0.2â¯mm). Differences between waves were not found when each follicular wave was categorized into conventional vs undersized deviation and analyzed separately. Hypothesis 3 was supported as there were differences in circulating hormones between conventional and undersized deviations. Growth rate of F2 differed (Pâ¯<â¯0.0005) during days -2 to 0 (conventional, 2.6⯱â¯0.2â¯mm/2d; undersized, 1.4⯱â¯0.3â¯mm/2d). However, circulating FSH and P4 concentration on days -1 and 0 tended to be greater (Pâ¯<â¯0.06) in undersized than conventional deviations. In conclusion, the effect of different hormonal conditions on follicle dynamics was observed for F2 and not for F1. Furthermore, understanding the physiology that produces conventional vs undersized deviations is crucial since these categories explained most differences in follicular dynamics and circulating FSH observed in these different physiological conditions. In addition, future studies of wave 2 may be facilitated by using an induced wave 2 since it was similar to a spontaneous wave 2.