Gonadotrophic control of follicle growth in the ewe.

Preovulatory follicle growth in the ewe is dependent on FSH although no precise relationship appears to exist between plasma concentrations of FSH and the number of preovulatory follicles which develop or ovulation rate. This may be related to a hitherto unrecognized influence of pulsatile LH on the growth of large follicles. Preovulatory follicle growth is dependent on the presence of basal amounts of LH, but pulsatile LH, while being essential to supply an increase in androgen substrate to the granulosa cells of the follicle, may also play a role in reducing the responsiveness of many large follicles to FSH, in particular during the preovulatory phase when plasma concentrations of FSH are reduced. Thus selection of the preovulatory follicle(s) may involve a previously unrecognized interaction between FSH and pulsatile LH secretion in which pulses of LH act in a negative rather than positive manner.