Anandamide Inhibits Secretion of Oxytocin and Vasopressin from Rat Neurohypophysis.

DE LAURENTIIS, A; PRESTIFILIPPO,JP; MOHN, CE; FERNANDEZ-SOLARI,J; ZORRILLA ZUBILETE, MA; RETTORI, V

Washington DC, USA

Congreso; 91st Annual Meeting Endocrine Society; 2009

Endocrine Society

The cannabinoid receptors and their endogenous ligands that belong to the family of eicosanoids, called "endocannabinoids" (EC) are present in brain and peripheral tissues and play broad physiological roles (1). EC were found to be released from the hypothalamic supraoptic nucleus (2) where also cannabinoid receptors type 1 (CB1) are localized (3) suggesting, that EC could modulate oxytocin (OT) and vasopressin (VP) secretion. It was recently reported that tetrahydrocannabinol downregulates OT expression (4), however the participation of EC on OT and VP release has not been dilucidated. The rat neurohypophysis (NH) is a very rich region in the enzyme that synthesizes nitric oxide (NOS) and there is evidence that NO reduces both, OT and VP secretion from NH (5). The aim of the present work was to determine the effect of the EC anandamide (AEA) on in vitro OT and VP release from NH and to study if NO is involved in this action.NH from adult male Sprague Dawley rats were pre-incubated 15 min, the medium was replaced by fresh one containing the substances to be tested and incubated for 30 min. OT and VP were determined by radioimmunoassay. Our results indicate that AEA (10-11-10-8 M) significantly decreased OT and VP secretion from NH at all doses tested, being 10-9 M the most effective [OT= C:13.43}1.62; AEA (10-9 M): 7.71}0.68 ng/NH, n=10-12, p<0.01. VP= C:2.74}0.26; AEA (10-9 M): 1.35}0.17 ng/NH, n=10-12, p<0.01, ANOVA, DunnettLs test]. The inhibitory effect of AEA on OT and VP secretion seems to be mediated by CB2 and type I vanilloid receptors, since CB2 receptor antagonist (AM630, 10-5M) and vanilloid receptor antagonist (capsazepine, 10-5 M) both block inhibitory effects of AEA. CB1 receptor antagonist, AM251 (10-5M) had no effect. Moreover, CB1 receptor mRNA in NH measured by RT-PCR was almost undetectable. AEA (10-9 M) significantly stimulated NOS activity in NH determined by radioconversion of [C14]Arginine to [C14]Citrulline [C: 0.8392 } 0.101; AEA(10-9M): 1.527 } 0.159 pmol NO/NH/min; n=6; p<0.01, StudentLs t test]. Furthermore, hemoglobin (40ƒÊg/ml) a scavenger of NO and L-NAME (1mM) an inhibitor of NOS, prevented the inhibitory action of AEA on OT and VP secretion. In conclusion: AEA acting through CB2 and vanilloid receptors inhibits OT and VP release from NH by a mechanism that involves NO showing for the first time the inhibitory action of an endocannabinoid on oxytocin and vasopressin secretion.(1) Felder et al., Mol Int 2006; 6:149.(2) Di et al., Endocrinology 2005;146:4292.(3) Herkenham et al., J Neurosci 1991;11:563.(4) Butovsky et al., Mol Cell Neurosci 2006 ;31:795.(5) Lutz-Bucher et al., Neurosci Lett 1994;165:48Supported by CONICET PIP 6149, ANPCyT 06-00258.