Temporality of two-way functional coupling between FSH and follicles in heifers.

Abstract The intervals from removal of FSH suppressants by follicle ablation to an increase in FSH and from an increase in FSH to an increase in follicle diameter were determined hourly during follicular wave 1 in a follicles-intact group ( n  = 7) and a follicles-ablated group ( n  = 20). Follicles other than the largest subordinate follicle of wave 1 (SF1) were ablated when the dominant follicle of wave 1 (DF1) was about 11 mm (hour 0) and FSH concentration was basal. In an ablated-regressed subgroup ( n  = 5), SF1 diameter decreased constantly during hours 0 to 8. In an ablated-maintained subgroup ( n  = 15), SF1 decreased for 2 or 3 hours and then increased ( n  = 11) or increased constantly ( n  = 4). Average diameter of SF1 during 8 hours was greater (P  n  = 11), the SF1 increase was preceded by an FSH increase. The interval from hour 0 (removal of source of FSH suppressants) to the beginning of an increase in FSH was 0.8 ± 0.3 hours. The interval from the beginning of an FSH increase to the beginning of an SF1 diameter increase was 2.8 ± 0.4 hours. The immediate coupling and decoupling between follicles and FSH may be essential aspects of follicle deviation during selection of DF1 by impeding the growth rate of the future SF1 before it can attain the developmental stage needed for continued growth during low FSH.