Echternkamp S E, Roberts A J, Lunstra D D, Wise T, Spicer L J
USDA, ARS, Roman L. Hruska U.S. Meat Animal Research Center, Clay Center, NE 68933-0166, USA.
J Anim Sci. 2004 Feb;82(2):459-71. doi: 10.2527/2004.822459x.
Comparisons of numbers of antral ovarian follicles and corpora lutea (CL), of blood hormone concentrations, and of follicular fluid steroid concentrations and IGFBP activity were conducted between cows selected (twinner) and unselected (control) for twin births to elucidate genetic differences in the regulation of ovarian follicular development. Ovarian follicular development was synchronized among cows by a single i.m. injection of PGF2alpha on d 18 of the estrous cycle; six cows per population were slaughtered at 0, 24, 48, and 72 h after PGF2alpha. Jugular vein blood was collected from each animal at PGF2alpha injection and at 24-h intervals until slaughter. Ovaries of twinner cows contained more small (< or = 5 mm in diameter, P < 0.05), medium (5.1 to 9.9 mm, P < 0.05), and large (> or = 10.0 mm, P < 0.01) follicles and more (P < 0.01) CL than ovaries of controls. Follicular fluid concentrations of estradiol, androstenedione, testosterone, and progesterone reflected the stage of follicular development and were similar for twinner and control follicles at the same stage. Earlier initiation of follicular development and/or selection of twin-dominant follicles in some twinner cows resulted in greater concentrations of estradiol in plasma at 0, 24, and 48 h and of estradiol, androstenedione, and testosterone in follicular fluid of large follicles at 0 h after PGF2alpha for twinner vs. control cows (follicular status x time x population, P < 0.01). Binding activities of IGFBP-5 and -4 were absent or reduced (P < 0.01) in follicular fluid of developing medium and large estro-gen-active (estradiol:progesterone ratio > 1) follicles but increased with atresia. Only preovulatory Graafian follicles lacked IGFBP-2 binding, suggesting a possible role for IGFBP-2 in selection of the dominant follicle. Concentrations of IGF-I were twofold greater (P < 0.01), but GH (P = 0.10) and cholesterol (P < 0.05) were less in blood of twinners. Three generations of selection of cattle for twin ovulations and births enhanced ovarian follicular development as manifested by increased numbers of follicles within a follicular wave and subsequent selection of twin dominant follicles. Because gonadotropin secretion and ovarian steroidogenesis were similar for control and twinner cattle, enhanced follicular development in twinners may result from decreased inhibition by the dominant follicle(s), increased ovarian sensitivity to gonadotropins, and/or increased intragonadal stimulation, possibly by increased IGF-I.
为阐明卵巢卵泡发育调控中的遗传差异，对选择用于双胎分娩的奶牛（双胎牛）和未选择的奶牛（对照牛）的窦状卵巢卵泡数量、黄体数量、血液激素浓度、卵泡液类固醇浓度以及胰岛素样生长因子结合蛋白（IGFBP）活性进行了比较。通过在发情周期的第18天单次肌肉注射前列腺素F2α（PGF2α）使奶牛的卵巢卵泡发育同步；每组六头奶牛在注射PGF2α后的0、24、48和72小时屠宰。在注射PGF2α时以及直至屠宰前每隔24小时从每头动物采集颈静脉血。双胎牛的卵巢比对照牛的卵巢含有更多的小卵泡（直径≤5毫米，P<0.05）、中等卵泡（5.1至9.9毫米，P<0.05）和大卵泡（直径≥10.0毫米，P<0.01）以及更多的黄体（P<0.01）。卵泡液中雌二醇、雄烯二酮、睾酮和孕酮的浓度反映了卵泡发育阶段，并且在相同阶段双胎牛和对照牛的卵泡相似。一些双胎牛中卵泡发育和/或双胎优势卵泡选择的提前启动导致双胎牛与对照牛相比，在PGF2α注射后0、24和48小时血浆中雌二醇浓度更高，在0小时时大卵泡的卵泡液中雌二醇、雄烯二酮和睾酮浓度更高（卵泡状态×时间×群体，P<0.01）。在发育中的中等大小和大的具有雌激素活性（雌二醇：孕酮比率>1）的卵泡的卵泡液中，IGFBP - 5和 - 4的结合活性缺失或降低（P<0.01），但随着卵泡闭锁而增加。只有排卵前的格拉夫卵泡缺乏IGFBP - 2结合，表明IGFBP - 2在优势卵泡选择中可能起作用。双胎牛血液中IGF - I的浓度高两倍（P<0.01），但生长激素（P = 0.10）和胆固醇（P<0.05）较低。经过三代选择用于双排卵和双胎分娩的牛，卵巢卵泡发育增强，表现为卵泡波内卵泡数量增加以及随后双胎优势卵泡的选择。由于对照牛和双胎牛的促性腺激素分泌和卵巢类固醇生成相似，双胎牛卵泡发育增强可能是由于优势卵泡抑制作用降低、卵巢对促性腺激素的敏感性增加和/或可能由于IGF - I增加导致的性腺内刺激增加。
