Webb R, Gong J G, Law A S, Rusbridge S M
AFRC, Institute of Animal Physiology and Genetics Research, Roslin, Midlothian, UK.
J Reprod Fertil Suppl. 1992;45:141-56.
In cattle, ovarian function is controlled by complex local and systemic feedback mechanisms involving gonadotrophins from the pituitary gland and steroids and proteins from the ovaries. This control system ensures that in more than 96% of females, only one follicle will ovulate per oestrous cycle. Follicular growth and development in cattle occurs in a wave-like pattern, with two or three waves of follicles growing and regressing per oestrous cycle. Each wave is characterized by the emergence, from a pool of growing follicles, of a large dominant follicle which reaches a mature stage of development and may be induced to ovulate and form a functional corpus luteum with a single treatment of either human chorionic gonadotrophin (hCG) or gonadotrophin-releasing hormone (GnRH). The growth of this dominant follicle is associated with a marked reduction in both the number and growth of subordinate follicles in both ipsi- and contralateral ovaries, suggesting a systemic exertion of 'dominance'. The dominance concept is further supported by the observation that the subsequent wave of follicular growth cannot be detected until after the start of the regression of the previous dominant follicle. Furthermore, the dominance mechanism does not involve an action of inhibin, as previously proposed. In addition, in cattle, inhibin may not have a primary role in the control of follicle-stimulating hormone (FSH) release, unlike its role in other species such as sheep. Gonadotrophins provide the primary endocrine drive for the growth of follicles > 2 mm in diameter, but it is now becoming evident that other systemic and locally produced factors profoundly influence ovarian function. For example, short-term treatment of cattle with recombinant bovine somatotropin (BST) can double the number of small (< 5 mm) antral follicles without altering the pattern of circulating gonadotrophin concentrations. These follicles appear to be fully functional since they can be stimulated to develop further and ovulate with superovulatory treatment regimens. Dominance also appears to be exerted via a different pathway from that involved in the BST-induced recruitment of small follicles. The identification of the factor responsible for dominance, together with the elucidation of the mechanisms controlling follicular recruitment and growth should ensure that the full benefits ensuing from the precise control of ovarian function in cattle are achieved.
在牛中，卵巢功能受复杂的局部和全身反馈机制控制，这些机制涉及来自垂体的促性腺激素以及来自卵巢的类固醇和蛋白质。该控制系统确保在超过96%的母牛中，每个发情周期只有一个卵泡排卵。牛的卵泡生长和发育呈波浪状模式，每个发情周期有两到三个卵泡波生长和退化。每个卵泡波的特征是从一群生长中的卵泡中出现一个大的优势卵泡，该卵泡达到发育成熟阶段，通过单次注射人绒毛膜促性腺激素（hCG）或促性腺激素释放激素（GnRH），可诱导其排卵并形成功能性黄体。这个优势卵泡的生长与同侧和对侧卵巢中次级卵泡的数量和生长显著减少有关，这表明存在“优势”的全身作用。优势概念进一步得到以下观察结果的支持：直到前一个优势卵泡开始退化后，才能检测到随后的卵泡生长波。此外，优势机制并不涉及如先前提出的抑制素的作用。此外，与在绵羊等其他物种中的作用不同，在牛中抑制素可能在控制促卵泡激素（FSH）释放方面没有主要作用。促性腺激素为直径大于2毫米的卵泡生长提供主要的内分泌驱动，但现在越来越明显的是，其他全身和局部产生的因素对卵巢功能有深远影响。例如，用重组牛生长激素（BST）对牛进行短期治疗可使小（<5毫米）窦状卵泡数量增加一倍，而不会改变循环促性腺激素浓度的模式。这些卵泡似乎功能完全正常，因为通过超排治疗方案可以刺激它们进一步发育并排卵。优势作用似乎也通过与BST诱导小卵泡募集所涉及的途径不同的途径发挥。确定负责优势作用的因素，以及阐明控制卵泡募集和生长的机制，应确保实现精确控制牛卵巢功能所带来的全部益处。
