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The aim of our studies was to examine whether IGF-binding protein (IGFBP)-4 is involved in the control of the secretion of various ovarian substances and also the mediation of the effects of several hormones and growth factors on this secretion. For this purpose, we carried out the transfection of porcine granulosa cells with a cDNA sense construct, increasing IGFBP-4 synthesis. We then compared the release of IGFBP-3, progesterone, oxytocin and IGF-I by control and transfected cells cultured with and without porcine LH (100 ng/ml), porcine GH (100 ng/ml), IGF-I (10 ng/ml), oxytocin (10 ng/ml) and estradiol-17beta (100 ng/ml). The concentration of IGFBP-4 produced was assessed using ligand blotting, and the release of progesterone, oxytocin, IGF-I and IGFBP-3 was evaluated using RIA/IRMA techniques. It was observed that GH, IGF-I, estradiol, LH and oxytocin alter the progesterone, oxytocin, IGF-I and IGFBP-3 release by porcine ovarian granulosa cells. Transfection of these cells with an IBFBP-4 cDNA expression construct significantly increased the IGFBP-4 accumulation in cell-conditioned medium. Furthermore, this transfection significantly reduced progesterone, oxytocin and IGFBP-3 release, and increased IGF-I output in cells cultured in the absence or presence of GH, IGF-I, estradiol and LH. The addition of oxytocin, but not of other tested substances, fully or partially prevented the effects of IGFBP-4 overexpression on IGFBP-3, IGF-I, but not on progesterone release. The present results suggested that IGFBP-4, as well as GH, IGF-I, estradiol, LH and oxytocin, is a potent regulator of porcine ovarian steroid (progesterone), nonapeptide hormone (oxytocin), growth factor (IGF-I) and growth factor-binding protein (IGFBP-3) release. IGFBP-4 is an inhibitor of basal progesterone, oxytocin and IGFBP-3 release and a stimulator of IGF-I output by porcine ovarian cells. The action of IGFBP-4 on the ovary can be mediated by (1) inhibition of oxytocin release, (2) suppression of receptor/postreceptor events induced by other hormones and IGF-I and (3) stimulation of IGF-I release.

The aim of our in vitro experiments was to examine if IGF binding protein (IGFBP)-3 is involved in control of bovine ovarian secretory activity. For this purpose we performed the transfection of bovine granulosa cells with cDNA sense and antisense constructs increasing or inhibiting IGFBP-3 synthesis. The release of IGFBP-3, progesterone, oxytocin, IGF-I and prostaglandins F (PGF) and E (PGE) by control and transfected cells was compared. The transfected ovarian cells were cultured with and without bLH (100 ng/ml), bGH (100 ng/ml), IGF-I (10 ng/ml), oxytocin (10 ng/ml) and oestradiol-17beta (100 ng/ml). The concentration of IGFBP-3 produced was assessed using ligand and western blotting and secretion of progesterone, oxytocin, IGF-I, PGF and PGE was evaluated using RIA/IRMA techniques. Transfection of cells with the sense IGFBP-3 cDNA construct resulted in the expected increase in IGFBP-3 release, whereas the antisense IGFBP-3 construct induced the expected reduction in IGFBP-3 output. The granulosa cells transfected to overexpress IGFBP-3 had an increase in IGF-I, PGF and PGE release, and a decrease in basal and hormone- or growth factor-induced accumulation of progesterone and oxytocin. The granulosa cells transfected to have reduced IGFBP-3 expression gave primarily significant opposite findings. The present results suggest the involvement of IGFBP-3 in control of bovine ovarian steroid, peptide hormone, growth factor and prostaglandin release. IGFBP-3 is a physiological stimulator of IGF-I and prostaglandin release and an inhibitor of steroid and peptide hormone output.