Ghrelin and growth hormone secretagogue receptor are expressed in the rat adrenal cortex: Evidence that ghrelin stimulates the growth, but not the secretory activity of adrenal cells.
Ghrelin is an endogenous ligand of the growth hormone secretagogue receptor (GHS-R), which has been originally isolated from rat stomach. Evidence has been previously provided that adrenal gland possesses abundant ghrelin-displaceable GHS-Rs, but nothing is known about the possible role of ghrelin in the regulation of adrenocortical function. Reverse transcription-polymerase chain reaction demonstrated the expression of ghrelin and GHS-R in the rat adrenal cortex, and high adrenal concentrations of immunoreactive ghrelin were detected by radioimmune assay (RIA). Autoradiography localized abundant [(125)I]ghrelin binding sites in the adrenal zona glomerulosa (ZG) and outer zona fasciculata (ZF). Ghrelin (from 10(-10) to 10(-8) M) did not affect either basal steroid hormone (pregnenolone, progesterone, 11-deoxycorticosterone, corticosterone, 18-hydroxycorticosterone and aldosterone) secretion from dispersed ZG and zona fasciculata/reticularis (ZF/R) cells (as evaluated by quantitative high pressure liquid chromatography), or basal and agonist-stimulated aldosterone and corticosterone production from cultured ZG and ZF/R cells, respectively (as measured by RIA). Ghrelin (10(-8) and 10(-6) M) raised basal, but not agonist-stimulated, proliferation rate of cultured ZG cells (percent of cells able to incorporate 5-bromo-2'-deoxyuridine), without affecting apoptotic deletion rate (percent of cells able to incorporate biotinylated nucleosides into apoptotic DNA fragments). The tyrosine kinase (TK) inhibitor tyrphostin-23 and the p42/p44 mitogen-activated protein kinase (MAPK) inhibitor PD-98059 abolished the proliferogenic effect of 10(-8) M ghrelin, while the protein kinase A and C inhibitors H-89 and calphostin-C were ineffective. Ghrelin (10(-8) M) stimulated TK and MAPK activity of dispersed ZG cells, and the effect was abolished by preincubation with tyrphostin-23 and PD-98059, respectively. Tyrphostin-23 annulled ghrelin-induced activation of MAPK activity. Taken together, the present findings indicate that (i) ghrelin and GHS-R are both expressed in the rat adrenal cortex, ghrelin binding sites being very abundant in the ZG; (ii) ghrelin does not affect the secretory activity of rat adrenocortical cells, but significantly enhances the proliferation rate of cultured ZG cells, without affecting apoptotic deletion rate; and (iii) the ZG proliferogenic action of ghrelin involves the TK-dependent activation of the p42/p44 MAPK cascade.
Andreis
Paola G
PG
Department of Human Anatomy and Physiology, Section of Anatomy, School of Medicine, University of Padua, Via Gabelli 65, I-35121 Padua, Italy.
Malendowicz
Ludwik K
LK
Trejter
Marcin
M
Neri
Giuliano
G
Spinazzi
Raffaella
R
Rossi
Gian Paolo
GP
Nussdorfer
Gastone G
GG
D000302:Adrenal Cortex / Q000187:drug effects / Q000378:metabolism*; D000305:Adrenal Cortex Hormones / Q000378:metabolism*; D000311:Adrenal Glands / Q000737:chemistry; D000818:Animals; D017209:Apoptosis; D001665:Binding Sites; D002455:Cell Division; D002478:Cells, Cultured; D054439:Ghrelin; D008297:Male; D008954:Models, Biological; D036361:Peptide Hormones / Q000032:analysis / Q000378:metabolism* / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism*; D043562:Receptors, G-Protein-Coupled; D054440:Receptors, Ghrelin; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D014158:Transcription, Genetic; D015384:Zona Glomerulosa / Q000166:cytology / Q000187:drug effects / Q000378:metabolism
D000305:Adrenal Cortex Hormones; D054439:Ghrelin; D036361:Peptide Hormones; D011956:Receptors, Cell Surface; D043562:Receptors, G-Protein-Coupled; D054440:Receptors, Ghrelin