ORIGINAL PAPER Influence of nitric oxide synthase inhibition on vasopressin and corticosterone secretion during water deprivation in rats Bessem Mornagui & Raja Rezg & Abir Grissa & Monique Duvareille & Claude Gharib & Abdelaziz Kamoun & Saloua El-Fazaa & Najoua Gharbi Received: 18 December 2009 / Accepted: 11 June 2010 / Published online: 7 August 2010 # University of Navarra 2010 Abstract Nitric oxide (NO) is a short-lived radical that functions as a neurotransmitter in the central nervous system and plays a physiological role in the regulation of hypothalamic–pituitary–adrenal axis and vasopressi- nergic axis. In the present study, we aimed to investigate the interaction between the generation of NO and vasopressin (AVP) and corticosterone release after 3 days of water deprivation in rats. Animals were previously treated with intraperitoneal (i.p.) saline or L- nitro-arginine methyl ester (L-NAME) injection. L- NAME is a nonspecific inhibitor of nitric oxide synthases. In control rats given i.p. saline or L-NAME, hypothalamic, pituitary, and plasma AVP levels and plasma corticosterone did not change from baseline levels (p >0.05). Three days of water deprivation increased significantly the corticosterone levels in plasma (p <0.01) and AVP levels in hypothalamus and plasma (p <0.01), but not in pituitary, which showed a significant decrease. These variations were concomitant with the elevation of nitrates/nitrates in plasma. L-NAME injection abolished significantly (p < 0.01) the elevation of plasma corticosterone and hypothalamic AVP levels induced by water depriva- tion. These findings showed that in water-deprived rats, nitric oxide synthase inhibition by L-NAME inhibits corticosterone and vasopressin release, sug- gesting a potent stimulatory role of NO. Keywords Dehydration . Nitric oxide . L-NAME . Vasopressin . Corticosterone . Prostaglandins Introduction Arginine vasopressin (AVP) is synthesized in magno- cellular neurons of the supraoptic nucleus (SON) and paraventricular nucleus (PVN) in the hypothalamus, transported axonally, and released into the systemic circulation from the nerve terminals in the posterior pituitary [10]. The release and gene transcription of AVP are regulated physiologically by plasma osmolality and blood volume [15, 26, 40, 49]. Changes in plasma osmolality are sensed at the osmoreceptors, which are believed to exist in the organum vasculosum of the lamina terminalis, and J Physiol Biochem (2010) 66:271–281 DOI 10.1007/s13105-010-0026-6 B. Mornagui : R. Rezg : A. Grissa : A. Kamoun : S. El-Fazaa : N. Gharbi Laboratoire de Physiologie des Agressions, Faculté des Sciences de Tunis, Tunis, Tunisia M. Duvareille : C. Gharib Laboratoire de Physiologie de l’Environnement, Faculté de Médecine Grange-Blanche, Lyon, France B. Mornagui (*) Laboratoire de Physiologie des Agressions, Département de Biologie, Faculté des Sciences de Tunis, Campus universitaire, 2092 El Manar, Tunisie e-mail: bessem.mornagui@fst.rnu.tn