RELATIONSHIPS AMONG CONCENTRATIONS OF STEROIDS, INSULIN-LIKE GROWTH-FACTOR-I, AND INSULIN-LIKE GROWTH-FACTOR BINDING-PROTEINS IN OVARIAN FOLLICULAR-FLUID OF BEEF-CATTLE
Se. Echternkamp et al., RELATIONSHIPS AMONG CONCENTRATIONS OF STEROIDS, INSULIN-LIKE GROWTH-FACTOR-I, AND INSULIN-LIKE GROWTH-FACTOR BINDING-PROTEINS IN OVARIAN FOLLICULAR-FLUID OF BEEF-CATTLE, Biology of reproduction, 51(5), 1994, pp. 971-981
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.