Functional and structural relationships in the Graafian follicle population of the sheep ovary.

The Graafian follicle population in sheep can be divided into two groups on the basis of the capacity that individual follicle have for secreting oestrogen when isolated from the remainder of the ovary (Moor, 1973). The most developed one or two non-atretic follicle from each animal generally produce large amounts of oestrogen in culture and can thus be classified as steroidogenically 'activated'. The other follicles usually produce very little oestrogen in culture and are accordingly classified as 'non-activated'. In this paper the above classification will be used and the two groups of follicles will be considered separately. In the first section of the paper the response of the non-activated follicles to gonadotrophic stimuli will be described and related to growth and atresia within this population. The steroidogenic potential of the activated follicles at different stages of the cycle will be discussed in the second part of the paper. In the third part, an attempt will be made to relate the ultrastructure of the activated follicles to the functional activity of their component tissues, namely the theca interna and membrana granulosa.