Adrenomedullin and vascular endothelium growth factor genes are overexpressed in the regenerating rat adrenal cortex, and AM and VEGF reciprocally enhance their mRNA expression in cultured rat adrenocortical cells

Adrenomedullin (AM) is an endogenous regulatory peptide, which exerts growth promoting and neoangiogenic actions in several normal and neoplastic tissues. Evidence has been provided that AM and the pro-angiogenic peptide vascular endothelium growth factor (VEGF) are expressed in the adrenal gland, and we investigated whether their gene transcription is modified in a model of rapid rat adrenal growth, namely regeneration after enucleation and contralateral adrenalectomy. Real-time polymerase chain reaction (PCR) showed that AM and VEGF mRNAs were significantly increased in regenerating adrenals with respect to the intact adrenocortical tissue of sham-operated control rats. Subsequent studies were carried out on dispersed rat adrenocortical cells cultured in vitro for 72 h. Conventional PCR demonstrated that cultured cells expressed AM and VEGF mRNAs. Moreover, real-time PCR showed that 24 h exposure to 10-8 M AM or 50 ng/ml VEGF significantly raised the expression of VEGF and AM, respectively, without affecting that of their own mRNA, suggesting the occurence of autocrine-paracrine up-regulatory mechanisms. Taken together, our findings allow us to conceive that the coordinate up-regulation of AM and VEGF expression may favor cell proliferation and neoangiogenesis, thereby leading to a rapid restoration of morphology and function of regenerating adrenals.