RELATIONSHIPS AMONG CONCENTRATIONS OF STEROIDS, INSULIN-LIKE GROWTH-FACTOR-I, AND INSULIN-LIKE GROWTH-FACTOR BINDING-PROTEINS IN OVARIAN FOLLICULAR-FLUID OF BEEF-CATTLE

The relationship between ovarian follicular steroidogenesis and insuli n-like growth factor binding protein (IGFBP) activity was evaluated du ring the follicular phase of the bovine estrous cycle. In experiment 1 , follicles were collected from cyclic cows (n = 11) slaughtered at 48 h after administration of prostaglandin F-2 alpha (PGF; 35 mg i.m.). In experiment 2, cows were injected twice daily with saline (control) or FSH (FSH cows; total dosage = 42 mg) from Day 2 to Day 6 (estrus = Day 0) and with PGF (35 mg i.m.) on Day 7; follicles were collected fr om control cows (n = 20) slaughtered at 0, 24, 48, or 72 h and from FS H cows (n = 8) at 0 and 48 h after PGF. Follicular fluid was assayed f or estradiol (E(2)), androstenedione (A(4)), progesterone (P-4), and i nsulin-like growth factor-I (IGF-I) by RIA and for IGFBP activity by l igand blotting and densitometry. Intensities of the 34-kDa (IGFBP-2), 29-27-kDa, and 22-kDa IGFBP bands in follicular fluid were nondetectab le or were lower (p < 0.01) in the fluid of large (greater than or equ al to 8 mm) E-active (E-A; E(2) > 50 ng/ml and > P-4) follicles than i n large E-inactive (E-I), medium (5-7 mm), or small (< 5 mm) follicles . IGFBP-3 (44-40-kDa doublet) was unaffected by follicle stage in expe riment 1, but IGFBP-3 was lower (p < 0.01) in follicular fluid of E-A vs. E-I large follicles in experiment 2. Profiles of IGFBP activity we re similar in follicular fluid of small, medium, and E-I large follicl es. In experiment 2, E(2) concentrations in large E-A follicles increa sed (p < 0.01) from 0 to 48 h after the PGF injection for control cows but decreased (P < 0.01) for FSH cows, whereas follicular fluid IGFBP -2 binding activity decreased from 0 to 48 h after PGF in controls and increased in FSH cows (treatment X time, P < 0.05). IGFBP-3 binding w as unaffected by FSH treatment or time after administration of PGF. Pr ofiles of IGFBP activity in homogenates of granulosa or theca cells we re similar to follicular fluid profiles except for the absence of IGFB P-3 binding activity. The disappearance of binding activities for IGFB P-2 and smaller-molecular-mass IGFBPs in E-A follicles suggests a poss ible regulatory role for IGFBPs in follicular maturation and on aromat ase activity. Likewise, the elevated E(2) secretion in large follicles recruited by FSH in vivo coincided with a reduction in binding activi ty of IGFBPs (i.e., less than or equal to 34 kDa) in the follicular fl uid.