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INCREASED SECRETION OF PROGESTERONE FROM THE OVARY OF THE EWE DURING THE PREOVULATORY PERIOD

A.R.C. Animal Breeding Research Organisation, King's Buildings, West Mains Road, Edinburgh EH9 3JQ, and MRC Unit of Reproductive Biology, 39 Chalmers Street, Edinburgh EH2 9ER

(Received 10th April 1975)

The new CL is formed from the granulosa cells of the preovulatory follicle. This process involves well-characterized changes in the morphology of the granulosa cells that are usually accompanied by an increase in progesterone secretion (functional luteinization). In many animals, morphological luteinization of the granulosa cells is apparent some hours before the rupture of the follicle (Baird et al., 1975). Functional luteinization at this time can be inferred from an increase in the concentration of progesterone in the peripheral plasma in women (Yussman & Taymor, 1970). These changes are coincident with, and dependent on, the preovulatory surge of LH. Although the morphology of the granulosa cells in the ewe changes after the onset of oestrus and immediately before the rupture of