Abstract
Vascular endothelial growth factor A (VEGF-A) is one of the most important regulators of ovarian angiogenesis. In this study, we examined the temporal relationship between VEGF-A and luteinizing hormone receptor (LHR) mRNA expression during ligand-induced down-regulation of LHR. Immature female rats were treated with pregnant mare's serum gonadotropin followed by 25 IU hCG 56 h later (day 0). On day 5, treatment with hCG (50 IU) to down-regulate LHR showed a temporal decrease in VEGF-A mRNA and protein levels in parallel with decreasing LHR mRNA. This effect was specific since the expression of CYP11A1 mRNA showed no decline. Examination of VEGF-A mRNA expression, using in situ hybridization histochemistry with (35)S-labeled antisense VEGF-A mRNA probe, showed intense signal in the corpora lutea on day 5. Treatment with 50 IU hCG to down-regulate LHR mRNA showed a decline in the intensity of VEGF-A mRNA in the corpora lutea. VEGF-A mRNA expression returned to control level 53 h later when the expression of LHR mRNA also recovered. These results show that the transient down-regulation of VEGF-A mRNA and protein closely parallels the ligand-induced down-regulation of LHR mRNA. The present study establishes a close association between VEGF-A and LHR mRNA expression, suggesting the possibility that VEGF-A-induced vascularization of the ovary is dictated by the expression of LHR and this might play a regulatory role in ovarian physiology.