Expression of prepro-ghrelin and related receptor genes in the rat adrenal gland and evidences that ghrelin exerts a potent stimulating effect on corticosterone secretion by cultured rat adrenocortical cells

Abstract

The orexigenic peptide ghrelin (GHREL) and obestatin (OBS) originate from the same peptide precursor, preproghrelin (ppGHREL). Apart from orexigenic effect, GHREL also regulates neuroendocrine function. We investigated GHREL and OBS effects on corticosterone secretion by freshly isolated and cultured rat adrenocortical cells. Classic RT-PCR revealed the presence of ppGHREL, GHS-R1a, GPR39v1 and GPR39v2 and GOAT4 (ghrelin O-acyl transferase) mRNAs in rat adrenals and cultured for 4 days rat adrenocortical cells. Expression of ppGHREL, GHS-R1a, and GOAT genes was notably higher in the cortex than in medulla. High expression level of GOAT gene was found in the zona glomerulosa, while expression level of both GPR39v1 and GPR39v2 genes was similar in adrenal cortical zones and in medulla. In freshly isolated cells neither GHREL nor OBS had an effect on corticosteroid output. Prolonged exposure of cultured cells to GHREL resulted in a potent, comparable to ACTH, stimulating effect of GHREL on corticosterone secretion. Prolonged exposure to OBS was ineffective. Neither GHREL nor OBS had any effect on proliferation of studied cells, while ACTH notably lowered it. GHREL down regulated GHS-R1a gene expression while both ACTH and GHREL stimulated expression level of GPR39v1 gene. Expression of CYP11A1 gene was notably stimulated and that of StAR gene remained unaffected by ACTH or GHREL. Thus, our study is the first to demonstrate direct stimulating effect of GHREL on corticosterone output by cultured rat adrenocortical cells. This stimulating action differs from that evoked by ACTH and is not dependent on the presence of functional ACTH receptor.