Evidence for a paracrine role of endogenous adrenomedullary galanin in the regulation

Previous investigations have shown that rat adrenocortical cells are provided with galanin receptors, and galanin stimulates glucocorticoid secretion from dispersed cells. The present study aimed to clarify the possible role of galanin in the physiological regulation of rat adrenal secretory activity. Reverse transcription-polymerase chain reaction detected galanin mRNA expression in the adrenal medulla, but not in the cortex. Sizeable concentrations of galanin-immunoreactivity were measured by radioimmune assay only in the adrenomedullary tissue. Galanin raised norepinephrine, but not epinephrine, release from adrenomedullary tissue. Galanin immunoneutralization (obtained with concentrations of anti-galanin antibody able to block the galanin glucocorticoid secretagogue effect on dispersed adrenocortical cells) decreased basal corticosterone production from adrenal slices containing adrenomedullary tissue, without affecting that from dispersed adrenocortical cells. The ß-adrenoceptor antagonist l-alprenolol partially prevented galanin-stimulated corticosterone secretion from adrenal slices, without per se altering basal secretion. Taken together, our findings allow us to conclude that endogenous galanin, produced in adrenal medulla, is involved in the regulation of adrenocortical glucocorticoid secretion acting via a two-fold paracrine mechanism: i) direct activation of adrenocortical galanin receptors; and ii) stimulation of adrenomedullary release of catecholamines, which in turn activate ß-adrenoceptors located on adrenocortical cells. Introduction Galanin is a regulatory peptide, which is widely distributed in the central and peripheral nervous system, where it acts as a neuromodulator (reviewed in ref. 1). Recent findings showed that galanin enhances glucocorticoid (corticosterone), but not mineralocorticoid (aldosterone) secretion from dispersed rat inner adrenocortical cells, acting via GAL-R1 and GAL-R2 receptors coupled to the adenylate cyclase-dependent signaling cascade (2). Evidence indicates that adrenomedullary cells express the galanin gene (3-5), and radioimmune assay (RIA)-measurable galanin immunoreactivity (IR) was detected in fresh rat adrenal medulla (6,7). These observations could suggest a role for galanin in the regulation of adrenomedullary functions, but in vitro investigations on the effect of this peptide on catecholamine secretion are lacking. Therefore, it seemed worthwhile to examine in vitro the effects of galanin on catecholamine secretion, and to ascertain whether, as in the case of other regulatory peptides contained in medullary chromaffin cells (reviewed in ref. 8), the possible interactions of galanin with adrenomedullary cells may concur to the secretagogue action of this peptide on the adrenal cortex. Materials and methods Animals and reagents. Male Sprague-Dawley rats (200-250 g body weight) were provided by Charles-River (Como, Italy). Rats were decapitated, and their adrenals were promptly removed and cleaned of adherent fat. The protocol of the experiment was approved by the local Ethics Committee for Biomedical Studies. Rat galanin and anti-rat galanin antibody were purchased from Phoenix Pharmaceuticals (Belmont, CA). Medium 199 was obtained from Difco (Detroit, MI). Human serum albumin (HSA), l-alprenolol, and all other chemicals and laboratory reagents were provided by SigmaAldrich Corporation (St. Louis, MO). Reverse transcription (RT)-polymerase chain reaction (PCR). Total RNA was extracted from the frozen adrenal cortex and medulla, and reverse transcribed to cDNA (9-11). INTERNATIONAL JOURNAL OF MOLECULAR MEDICINE 19: 511-515, 2007 511 Evidence for a paracrine role of endogenous adrenomedullary galanin in the regulation of glucocorticoid secretion in the rat adrenal gland PAOLA G. ANDREIS1, CINZIA TORTORELLA1, AGNIESKA ZIOLKOWSKA2, RAFFAELLA SPINAZZI1, LUDWIK K. MALENDOWICZ2, GIULIANO NERI1 and GASTONE G. NUSSDORFER1 1Department of Human Anatomy and Physiology, Section of Anatomy, University of Padua, I-35121 Padua, Italy; 2Department of Histology and Embryology, Poznan School of Medicine, PL-60781 Poznan, Poland Received October 13, 2006; Accepted November 24, 2006 _________________________________________ Correspondence to: Professor G.G. Nussdorfer, Department of Human Anatomy and Physiology, Section of Anatomy, University of Padua, Via Gabelli 65, I-35121 Padua, Italy E-mail: gastone.nusdorfer@unipd