Insulin-like Growth Factors (igf), Lh and Igf-i Receptors, And

Objectives of this study were to determine if concentrations of steroids, insulin-like growth factor-I (IGF-I) and IGF-II in follicular fluid, and numbers of LH and IGF-I receptors change during growth of the dominant follicle. Ovarian follicular development was monitored daily via ultrasound in lactating Holstein cows. Animals were bilaterally ovariectomized when the dominant follicle (DF) was first identified or when it stopped growing. Numbers of specific I-hCG/LH binding sites in thecal cells were greater in DF compared with large (LG) and small (SM) follicles of both Early (day 5 post-estrus) and Late (day 10 post-estrus) cows. Numbers of specific I-hCG/LH binding sites in granulosa cells were similar for follicle sizes in Early cows, but in Late cows were greater in DF compared with SM follicles, and were greater in Late DF compared with Early DF. Numbers of receptors for IGF-I in thecal cells were twofold greater in DF and LG compared with SM in Late cows. Numbers of IGF-I receptors in granulosa cells were unaffected by size or growth of follicles, but were greater than in theca cells. Concentrations of estradiol were greater in DF compared with LG and SM in both Early and Late cows. Concentrations of androstenedione in Early cows were greater in DF and SM compared with LG follicles. Concentrations of progesterone and IGF-I did not differ among follicle classes. Concentrations of IGF-II did not differ between Early and Late cows but were greater in SM than DF or LG follicles. We conclude that increased thecal binding sites for hCG/LH and increased estradiol in follicular fluid appear to be related to establishment of the dominant follicle during the first follicular wave in dairy cattle exhibiting regular estrous cycles during late lactation.