Isolated porcine ovarian follicles as a model for the study of hormone and growth factor action on ovarian secretory activity

Abstract

The aim of our in vitro experiments with isolated porcine ovarian follicles was to study the effects of gonadotropins, GH, IGF-I and oxytocin (OT) on release of ovarian steroid, OT, IGF-I, insulin-like growth factorbinding protein-3 (IGFBP-3), prostaglandin F (PGF), prostaglandin E (PGE) and cAMP.It was found that quarters of ovarian follicles cultured for 8 days produced significant amounts of progesterone, estradiol-17 beta, OT and IGFBP-3 with peaks of accumulation from the 3rd to the 8th day of culture. Addition of serum promoted progesterone, estradiol and OT release, whilst accumulation of IGFBP-3 was maintained to a greater extent in serum-free medium.GH (10 ng/ml or above) was able to inhibit androstenedione, OT, PGF and IGFBP-3, to stimulate IGF-I and cAMP, and to alter testosterone and PGE release by follicles cultured in serum-supplemented and/or serumfree medium. IGF-I (10 ng/ml or more) inhibited androstenedione and PGF secretion, stimulated testosterone, estradiol, OT and cAMP production, but did not influence progesterone, IGFBP-3 or PGE output in these conditions. OT (100 ng/ml) was able to inhibit androstenedione and to stimulate testosterone, IGF-I, PGF and PGE, but not estradiol or IGFBP-3 release. A stimulatory effect of LH on progesterone and OT and an inhibitory influence of LH on estradiol secretion in the serumsupplemented medium were observed. FSH in these conditions stimulated OT, but not progesterone or estradiol secretion.The use of this experimental model suggests the involvement of gonadotropins, OT, GH and IGF-I in the control of ovarian steroid and nonapeptide hormone, growth factor, growth factor-binding protein, prostaglandin and cyclic nucleotide production. The stimulatory effect of GH on IGF-I, and the stimulatory influence of IGF-I on OT, as well as coincidence of the majority of effects of IGF-I and OT, suggest the existence of a GH-IGF-I-OT axis. On the other hand, the different patterns of action of GH and IGF-I on OT, estrogen and IGFBP-3 suggest that part of the GH effect on ovarian cells is IGF-I independent.

Secretory activity of bovine ovarian granulosa cells transfected with sense and antisense insulin-like growth factor (IGF) binding protein-3 and the response to IGF-I, GH, LH, oxytocin and oestradiol

“…This confirms our previous observations (Makarevic & Sirotkin 1996, Sirotkin et al 1998 of the usefulness of serum-supplemented medium for stimulation of basal ovarian secretion and response. Nevertheless, in interpreting the data obtained using serum-supplemented medium, it should be kept in mind that, despite the use of blank controls, serum (which can contain hormones, growth factors and IGFBPs) may affect basal secretory activity and responses of cells, and the metabolism of exogenous and endogenous substances.…”

“…The amounts of these substances produced by cells after the transfection procedures in our experiments are comparable to those described in non-transfected bovine granulosa cells. Ovarian PGE production has been demonstrated previously in other species (Cetta et al 1982, Chang et al 1995, Sirotkin et al 1998, but this seems to be the first demonstration of the release of this substance by bovine ovarian cells.…”

“…GH can be either a stimulator (cow: Sirotkin & Makarevich 1999) or an inhibitor (pig: Sirotkin et al 1998) of IGFBP release by ovarian cells. There are reports on both a stimulatory influence (pig: Grimes et al 1994) and a lack of effect (pig: Sirotkin et al 1998) of IGF-I on ovarian IGFBPs. Both a stimulatory effect (cow: Manikkam & Rajamahedran 1997) and no effect (women: Hamori et al 1991) of progesterone on this process have been reported.…”

“…Prostaglandin F (PGF) treatment can either stimulate (cow: Spicer & Echternkamp 1995) or inhibit (cow: Echternkamp et al 1994) ovarian IGFBP accumulation. Ovarian IGFBP accumulation can be induced by oestradiol (cow: Mihm et al 1997) and dibutyryl cAMP (human: Hamori et al 1991), but not by oxytocin (Sirotkin et al 1998). Thus the ovarian IGFBPs can be both stimulated and inhibited by various substances (gonadotrophins, GH, IGF-I, steroids, PGF, cAMP etc.)…”

“…that are known gonadotrophic substances. There are indirect indications that these regulators can affect ovarian functions through alterations in the local IGFBP-3 concentration (Erickson 1995, Spicer & Echternkamp 1995, Schams et al 1999, Sirotkin et al 1998. Nevertheless, the hypothesis of involvement of IGFBPs in the control of ovarian functions and in the mediation of effects of hormones and other ovarian regulators requires direct confirmation.…”