CORTICOTROPIN REGULATES VASCULAR ENDOTHELIAL GROWTH-FACTOR EXPRESSIONIN HUMAN FETAL ADRENAL-CORTICAL CELLS

The human adrenal cortex has a complex vasculature that is essential f or growth, organ maintenance, and access of secreted hormones to the c irculation. Growth and function of the adrenal cortex are regulated by corticotropin (ACTH), the actions of which are in part mediated by lo cally produced growth factors. As cortical growth and vascularization must increase in a coordinated manner, we hypothesized that ACTH also influences adrenal cortical angiogenesis by stimulating the local expr ession of specific angiogenic factors. Vascular endothelial growth fac tor (VEGF) is a potent endothelial cell-specific angiogenic peptide, t he expression of which has been detected in adrenal cortical cells. Th erefore, we examined the localization of VEGF expression in the midges tation (16-20 weeks) human fetal adrenal cortex and determined whether VEGF expression and secretion by isolated human fetal adrenal cortica l cells arts regulated by ACTH. By immunohistochemical analysis, stron g cytoplasmic staining for VEGF was detected in scattered clusters of fetal zone (inner cortical compartment) cells. In contrast, cells in t he outer, definitive zone of the cortex stained. only weakly for VEGF. The predominant staining for VEGF in the fetal zone correlated with t he extensive vasculature of this zone as detected by immunohistochemic al staining for von Willebrand factor, which is specific for endotheli al cells. In primary cultures of human fetal adrenal cortical cells, A CTH (1 nmol/L) and forskolin (10 mu mol/L) increased the abundance of messenger ribonucleic acid transcripts encoding VEGF, as assessed by N orthern and slot blot analyses. The stimulatory effect of ACTH and for skolin on VEGF gene expression occurred within 2 h of agonist exposure and persisted for at least 24 h. ACTH and forskolin also increased VE GF protein secretion by fetal adrenal cortical cells, as assessed by e nzyme-linked immunosorbent assay for VEGF in fetal adrenal cortical ce ll-conditioned medium. A significant (P < 0.05) increase in VEGF secre tion was detected as early as 8 h after ACTH or forskolin treatment. B y 24 h after the addition of ACTH or forskolin, VEGF secreted from iso lated human fetal adrenal cells was increased 5- to 6-fold. These data demonstrate that the human fetal adrenal cortex, particularly the cel ls of the inner fetal zone, express VEGF and that VEGF expression and secretion by these cells are directly regulated by ACTH and the activa tion of adenylate cyclase. Thus, VEGF may be a local regulator of adre nal cortical angiogenesis and an important mediator of the tropic acti on of ACTH, ensuring the coordination of ACTH-stimulated cortical grow th and vascularization.