Vascular endothelial growth factor (VEGF) is an endothelial cell mitogen and permeability factor the role of which in ovarian angiogenesis has been the subject of increasing interest. It was the objective of this communication to explore the possibility that interleukin (IL)-1 may regulate the in vitro expression of rat ovarian VEGF mRNA, as well as to study the in vivo expression of rat ovarian VEGF transcripts during follicular maturation, ovulation, and corpora lutea formation. Taken together, our findings 1) reaffirm the rat ovary as a site of VEGF expression; 2) document an in vivo increase in VEGF transcripts before ovulation; 3) disclose a marked dependence of VEGF on IL-1β; 4) reveal the IL-1β effect to be receptor mediated and dose and time dependent and to be shared by at least two growth factors—epidermal growth factor and basic fibroblastic growth factor; and 5) demonstrate a lack of VEGF effect on ovarian progesterone biosynthesis as assessed in cultured isolated granulosa cells. It is tempting to speculate that the up-regulatory effect of IL-1β on VEGF transcripts may be relevant to the marked angiogenesis and increased vascular premeability displayed by the hyperemic ovarian Graafian follicle during the terminal stages of follicular development. In this context, VEGF may be joined by other IL-1-dependent angiogenesis promoters such as IL-6 or transforming growth factor β1. Thus, IL-1-mediated VEGF induction may constitute one of several end points through which IL-1 may coordinate and perhaps amplify the ovulatory cascade.

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A growing body of information documents the existence of a complete rat intrafollicular insulin-like growth factor (IGF)-I system replete with a ligand (IGF-I), a receptor (type 1 IGF receptor) IGF binding proteins (4 and 5), and IGFBP-directed endopeptidases (4 and 5). Previous studies have established the ability of IGF-I to promote the elaboration of granulosa cell-derived IGFBP-5 and to suppress the activity of granulosa cell-derived IGFBP-5-directed endopeptidase. It was the purpose of this article to examine the effects of treatment with IGF-I on the other components of the intrafollicular IGF system, i.e., IGF-I itself and the type 1 IGF-receptor. Granulosa cells, obtained by follicular puncture from 25-d-old estrogen-primed rats were cultured in polystyrene tubes for 72 h under serum-free conditions, in the absence or presence of the indicated agents. At the conclusion of each experiment, media were discarded, and RNA was extracted and subjected to an RNase protection assay. Treatment of cultured rat granulosa cells with IGF-I resulted in a significant 1.8-fold increase in the steady-state levels of IGF-I mRNA. No effect was noted on the total cellular DNA content thereby arguing against the possibility that the relative increase in IGF-I transcripts can be ascribed to a possible treatment-induced increase in cell number in culture. The IGF-I effect was apparent (p < 0.05) at IGF-I doses as low as 1 ng/mL, minimal additional increments being noted thereafter. Treatment with insulin and des (1-3) IGF-I proved equally effective, producing 2.0- and 2.6-fold increases, respectively, thereby suggesting that the IGF-I effect may be mediated via the type 1 IGF receptor. Treatment with IGF-I also resulted in a significant (p < 0.005) increase in type 1 IGF receptor expression (2.3-fold increase), the first significant effect being noted at the 30 ng/mL dose level. Similar results obtained for insulin and des (1-3) IGF-I thereby suggest that the ability of IGF-I to upregulate the expression of its own receptor is probably type 1 IGF receptor-mediated. Taken together, these findings indicate that treatment of estrogen-primed granulosa cells with IGF-I will result in upregulation of the steady-state levels of transcripts corresponding to IGF-I itself and to its type 1 IGF receptor. These observations emphasize the importance of positive autoregulatory phenomena as determinants of the intrafollicular content of IGF-I and its receptor.

A growing body of information suggests antigonadotropic and atretogenic roles for granulosa cell-derived insulin-like growth factor binding proteins (IGFBPs) 4 and 5 during ovarian folliculogenesis. Activation of protein kinase-A (PKA) in rat granulosa cells has been shown to modulate the relative expression of IGFBP-4 and -5 transcripts and proteins. In this article, we assess the role of protein kinase-C (PKC) in this regard. Provision of granulosa cells with phorbol 12-myristate 13-acetate (PMA) (but not 4alphaPMA, an inert analogue), a tumor-promoting phorbol ester and an established activator of PKC, was without significant effect on the expression of IGFBP-4 transcripts but resulted in biphasic dose-dependent alterations in IGFBP-5 transcripts and in the accumulation of the IGFBP-4 and -5 proteins. Comparable effects were noted for GnRH, an established PKC agonist. Provision of staurosporine, a potent inhibitor of the catalytic subunit of PKC, produced significant dose-dependent decrements in the relative expression of IGFBP-5 transcripts. Treatment with FSH (presumptively PKA-mediated) markedly attenuated the ability of PMA or GnRH to upregulate the accumulation of the IGFBP-5 (but not IGFBP-4) protein. Taken together, our present findings indicate that the modulation of rat ovarian IGFBP-4 and -5 is PKC as well as PKA dependent and that these two signaling pathways interact in a diametrically opposed and antagonistic fashion.

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