Foliculogênese em ovelhas: fatores de estímulo e inibição do crescimento folicular

The regulatory mechanisms of females´ reproduction are crucial to the success of conventional or assisted breeding. The follicle is the functional unit of the ovary of the female mammal species, being its major functions the growth and maturation of oocytes, as well as the production of steroid hormones. Several factors act jointly on the regulation of these activities through endocrine, autocrine and pa­racrine mechanisms stimulating the mitogenic activity of quiescent oocytes and also steroidogenic activity of the theca cells and of the granulosa. Among the regulatory factors, there are some that act in a stimulant way, such as the receptor of the binding protein (c-KITL), the system of growth factors related to insulin (IGF’s), the activin and follistatin complex, and the super family of growth-β transforming factor (TGF-β). Other agents are inhibitory, such as inhibin, the retinoblastoma protein, expressed in oocytes, as the Wilms’ gene (WTI). This paper aims to review the regulatory mecha¬nisms of folliculogenesis and its importance in the reproductive physiology of ewes.