LEVELS OF INSULIN-LIKE GROWTH-FACTOR (IGF) BINDING-PROTEINS, LUTEINIZING-HORMONE AND IGF-I RECEPTORS, AND STEROIDS IN DOMINANT FOLLICLES DURING THE FIRST FOLLICULAR WAVE IN CATTLE EXHIBITING REGULAR ESTROUS CYCLES
Re. Stewart et al., LEVELS OF INSULIN-LIKE GROWTH-FACTOR (IGF) BINDING-PROTEINS, LUTEINIZING-HORMONE AND IGF-I RECEPTORS, AND STEROIDS IN DOMINANT FOLLICLES DURING THE FIRST FOLLICULAR WAVE IN CATTLE EXHIBITING REGULAR ESTROUS CYCLES, Endocrinology, 137(7), 1996, pp. 2842-2850
Objectives of this study were to determine if concentrations of steroi
ds, insulin-like growth factor-I (IGF-I), and IGF binding proteins (IG
FBP) 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. Animal
s underwent bilateral ovariectomy when the dominant follicle was first
identified (days 4-6; estrus = day 0; early; n = 5) or when it stoppe
d growing (days 8-12; late; n = 8). All follicles were classified as d
ominant (DF), large (LG; greater than or equal to 6 mm in diameter, ex
cluding DF) or small (SM; < 6 mm), follicular fluid was aspirated, and
theca and granulosa cells were collected. Levels of IGFBP-2, assessed
via ligand blotting, were greater (P < 0.05) in LG and SM follicles c
ompared with DF in early cows. Levels of IGFBP-3 in follicular fluid w
ere unaffected by follicle class. Numbers of specific I-125-hCG/LH bin
ding sites in thecal cells were greater (P < 0.01) in DF compared with
LG and SM follicles of both early and late cows. Numbers of specific
I-125-hCG/LH binding sites in granulosa cells were similar for follicl
e sizes in early cows, but, in late cows, were greater (P < 0.01) in D
F compared with SM follicles and were severalfold greater (P < 0.01) i
n late DF compared with early DF. Numbers of receptors for IGF-I in th
ecal cells were 2-fold greater (P < 0.05) in DF and LG compared with S
M in late cows. Numbers of IGF-I receptors in granulosa cells were una
ffected by size or growth of follicles, but were severalfold greater t
han in theca cells. Concentrations of estradiol were severalfold great
er (P < 0.01) in DF compared with LG and SM in both early and late cow
s. Concentrations of androstenedione in early cows were greater (P < 0
.05) in DF and SM compared with LG follicles. Concentrations of proges
terone and IGF-I did not differ (P > 0.10) among follicle classes, but
both were greater (P < 0.10) in late LG compared with early LG follic
les. Concentrations of IGF-II in follicular fluid did not differ (P >
0.10) between early and late cows but were greater (P < 0.10) in SM th
an DF or LG follicles. We conclude that low amounts of IGFBP-2 and inc
reased thecal binding sites for hCG/LH appear to be related to establi
shment of the dominant follicle during the first follicular wave in ca
ttle exhibiting regular estrous cycles during late lactation.