Ovary

The Effect of the Manipulation of Follicle-Stimulating Hormone (FSH)-Peak Characteristics on Follicular Wave Dynamics in Sheep: Does an Ovarian-Independent Endogenous Rhythm in FSH Secretion Exist?

Abstract
We designed three experiments to examine the relationship between FSH peaks and ovarian follicular waves, and to see if an endogenous rhythm of FSH peaks exists in sheep. In experiment 1, anestrous ewes were treated with oFSH or vehicle (6 ewes per group) at the expected time of an endogenous FSH peak, to double the FSH-peak amplitude in treated ewes. In experiment 2, anestrous ewes were treated with either oFSH or vehicle (6 ewes per group) at the expected time of two consecutive inter-peak nadirs, such that the treated ewes had five FSH peaks in the time frame of three FSH peaks in control ewes. In experiment 3, daily blood samples, to measure FSH concentrations, were collected from 5 cyclic ewes for a control period during the estrous cycle and then for three 17-d periods after ovariectomy. Daily blood samples were collected from another group of 8 ovariectomized ewes that were treated with estradiol-releasing implants and intravaginal progestogen sponges. Doubling the FSH-peak amplitude did not alter the characteristics of the following follicular wave. Increasing the frequency of FSH peaks stimulated the emergence of additional follicular waves, but did not alter the rhythmic occurrence of FSH peaks and follicular wave emergence. Endogenous follicular waves in oFSH-treated ewes emerged and grew in the presence of the growing largest follicle of the induced follicular waves. Finally, based on the observation of serum FSH concentrations in ovariectomized ewes, it appears that there exists an endogenous rhythm for peaks in daily serum FSH concentrations, which is, at least in part, independent of regulation by ovarian follicular growth patterns.

Key words: Ovary • Pituitary • Estradiol • Follicle • Follicle-stimulating hormone

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