IMMATURE RAT OVARIES BECOME REVASCULARIZED RAPIDLY AFTER AUTOTRANSPLANTATION AND SHOW A GONADOTROPIN-DEPENDENT INCREASE IN ANGIOGENIC FACTOR GENE-EXPRESSION

When the ovaries of 23-day-old juvenile rats are transplanted to an ec topic site, they recover within 1 week the ability to control gonadotr opin secretion via steroid negative feedback. Vascular corrosion casti ng followed by scanning electron microscopy revealed that the transpla nted ovary becomes profusely revascularized within 48 h after transpla ntation. Vascular ingrowth was accompanied by a 40- to 60-fold increas e in expression of the genes encoding two angiogenic factors, vascular endothelial growth factor (VEGF) and transforming growth factor-beta( 1) (TGF beta(1)), as assessed by RNA blot hybridization of the corresp onding mRNAs. Although TGF beta(3) mRNA levels also increased, no chan ges in the levels of mRNAs encoding other putative angiogenic factors, such as TGF alpha, basic fibroblast growth factor, and TGF beta(2), w ere observed. Hybridization histochemistry demonstrated that in intact ovaries, VEGF mRNA is mainly expressed in granulosa cells of the cumu lus oophorus and thecal cells of large antral follicles. Transplantati on is followed by an increase in mRNA abundance and a dramatic shift i n cellular localization, so that the mRNA becomes predominantly expres sed in cells of the outer ovarian cortex. In intact ovaries, low level s of TGF beta(2) mRNA were detected in thecal-interstitial cells; afte r transplantation, its expression also became more predominant in the ovarian outer cortex, but this change was not as marked as in the case of VEGF. Because ovarian autotransplantation is followed by a rapid i ncrease in serum gonadotropin levels, experiments were conducted to de termine the importance of this rise in the activation of VEGF and TGF beta(1) gene expression. After transplantation, some animals were trea ted with the LHRH antagonist Nal-Glu LHRH (50 mu g/rat, once a day for 2 days) to prevent the posttransplantation rise in serum gonadotropin s. Quantitation of VEGF and TGF beta(1) mRNA by RNase protection assay 48 h later showed that suppression of gonadotropin secretion diminish ed the increase in both VEGF and TGF beta(1) gene expression. Concomit ant treatment with PMSG (8 IU/rat, single injection), which mainly byp asses the suppression of endogenous FSH levels, restored the TGF beta( 1) mRNA response, but had no effect on VEGF mRNA. The results suggest that the increase in gonadotropin secretion following ovarian transpla ntation contributes to revascularization of the graft by up-regulating the gene expression of two major angiogenic factors.