Binding sites for IGF-I, insulin, and GH were localized by in situ binding
of I-125-labelled hormones to the different compartments of the sow ovary.
Binding sites for IGF-I were detected in oocytes, granulosa and thecal cell
s of healthy and atretic follicles as well as in the antrum and the stroma.
Competition of I-125-labelled IGF-I with IGF-I, insulin and an analogue of
IGF-I (Long R(3)IGF-I), which allowed discrimination between binding to bi
nding proteins from binding to type-I receptors, suggested that type-I rece
ptors were present in granulosa cells of healthy follicles, whilst binding
in other compartments was mainly due to binding proteins. Binding of insuli
n was revealed in oocytes, granulosa and theca interna cells of healthy pre
antral and antral follicles, and, to a lesser extent, theca externa and str
omal cells, and was still observed in granulosa cells of atretic follicles.
Labelling with I-125-labelled bovine GH was demonstrated in oocytes, granu
losa cells, theca interna cells, and, although less intense, in theca exter
na and stromal cells. It disappeared in granulosa cells during atresia. Bin
ding sites for GH were detected at all follicular stages, from preantral to
preovulatory stages, but the intensity of labelling in granulosa cells was
more intense in preantral than in large follicles. These data support the
participation of insulin, GH and IGF-I in oocyte maturation, follicular gro
wth and stromal cell function in swine.