A52-75-2007E.pdf - AgroMedia International Inc

Reproduction3Follicular fluid concentration of transforming growth factor-β1 isnegatively correlated with estradiol and follicular size at the earlystage of development of the first-wave cohort of bovine ovarianfolliclesCorresponding AuthorCarrière, P.D.Université de MontréalCollaboratorsOuellette, Y.Université de MontréalPrice, C.A.Université de MontréalDomestic Animal Endocrinology (2005) Vol. 29 p. 623-633.In a cow experiencing regular estrous cycles, ovulation occurs when anoocyte (egg) is released from a dominant ovarian follicle. This dominantfollicle is one of several that began to develop from a so-called wave ofgrowing follicles that emerge from the ovary at regular intervals throughoutthe estrous cycle. Within about 3 days of the beginning of this ‘wave’of development, one of the follicles will begin to become dominant and,under the influence of follicle stimulating hormone (FSH) and other factors,will start to produce more estradiol than the others. The amount of estradiolproduced by each follicle is influenced by signalling molecules whichaffect the responsiveness of its estradiol-secreting cells to FSH. Transforminggrowth factor beta (TGF-β) is a class of signalling molecules which includes3 unique variations: β1, β2 and β3. The objective of this study wasto determine whether TGF-β1 is involved in determining which follicle willbecome dominant by modulating the effect of FSH on estradiol production.In one experiment, estradiol and TGF-β1 concentrations were measuredin follicular fluid from 3 or 4 of the largest follicles at several stagesof development of the follicle wave. Early in the wave, as follicles grew andestradiol levels rose, TGF-β1 concentrations declined. In a second experiment,the addition of TGF-β1 to follicle cells maintained in tissue culturecaused a dose-dependent decrease in FSH-stimulated estradiol secretion.These findings underline the importance of inhibitory mechanisms thatcontrol ovarian follicle growth and suggest that a reduction of TGF-β1 inhibitionof estradiol production may play a role in the mechanism by whichthe dominant follicle is selected.108 Highlights in Canadian Dairy Cattle Research - 2007