Effects of neuromedin-U on immature rat adrenocortical cells: in vitro and in vivo studies.

Neuromedin U (NMU) is a brain-gut peptide, that in the peripheral organs and tissues acts via a G protein-coupled receptor, called NMUR1. Reverse transcription-polymerase chain reaction showed the expression of NMUR1 mRNA in either cortex and medulla or dispersed zona glomerulosa and zona fasciculata-reticularis cells of the immature rat adrenals. Accordingly, immunocytochemistry demonstrated the presence of NMUR1-like immunoreactivity in the cortex and medulla of immature adrenals. NMU8 administration to immature rats was found to raise aldosterone, but not corticosterone, plasma concentration, without altering adrenal growth. Conversely, the exposure to NMU8 markedly enhanced the proliferative activity of immature rat inner adrenocortical cells in primary in vitro culture, without significantly affecting their corticosterone secretion. Collectively, our findings suggest that adrenals of immature rats may be a target for circulating NMU. However, the physiological significance and relevance of the adrenal effects of NMU remain to be ascertained.