Neuromedin-U stimulates enucleation-induced adrenocortical regeneration in the rat

Neuromedin-U (NMU) is a brain-gut peptide, which has been previously found to stimulate hypothalamic-pituitary-adrenal axis in the rat. Enucleation-induced adrenal regeneration in rats with contralateral adrenalectomy is a well-established model of adrenal growth, that not only depends on the compensatory ACTH hypersecretion, but is also modulated by several regulatory peptides. Hence, we investigated whether NMU may be included in this group of bioactive molecules. Reverse transcription-polymerase chain reaction and immunocytochemistry showed that regenerating rat adrenocortical cells at days 5 and 8 after surgery express the NMU receptor NMUR1 as mRNA and protein. NMU8 administration to rats bearing regenerating adrenals markedly raised the plasma concentration of corticosterone and notably enhanced proliferative activity of adrenocortical cells. ACTH blood level was unchanged at day 5 and significantly decreased at day 8. The conclusion is drawn that NMU stimulates regeneration of rat adrenal cortex, via a mechanism independent of pituitary ACTH and involving the activation of NMUR1 located on adrenocortical cells.