Role of orexins in the hypothalamic-pituitary-ovarian relationship.

C. LIBERTUN; P. SILVEYRA; N.I. CATALDI; V.A. LUX-LANTOS

University of Oulu, Oulu. Finlandia.

Simposio; 10 Years of Hypocretins/Orexins Physiology and Pathophysiology.; 2008

Acta Scandinavia International Symposium

Role of orexins in the hypothalamic-pituitary-ovarian relationship. C. Libertun1, 2; P. Silveyra1; NI. Cataldi1 and VA. Lux-Lantos1. 1Instituto de Biología y Medicina Experimental-CONICET, Buenos Aires; 2Dep. Physiology, Faculty of Medicine, UBA; Argentina. Appropriate nutritional and vigilance states are needed for reproduction. We hypothesized that orexins may play a role in this integration. We determined the mRNA expression of PPO, OX1 and OX2 in brain areas and pituitary in female cycling rats by Real Time RT-PCR. OX1 and OX2 expression increased only in hypothalamus and pituitary at 17:00 h-23:00 h of proestrus. PPO was also increased in hypothalamus. Cetrorelix or Pentobarbital pretreatments prevented the increases of OX1 and OX2 in pituitary at 19:00 h of proestrus but left OX1, OX2 and PPO in hypothalamus unchanged. Thus we found the influence of the hormonal milieu of proestrus on the orexinergic system. Then PPO, OX1 and OX2 were determined in ovaries. Both receptors expression increased between 17:00 h-23:00 h of proestrus in coincidence with gonadotropins peaks; PPO was not detected. Cetrorelix or Nembutal prevented the increases while blunting gonadotropins. Blocking of OX1 or OX2 decreased serum gonadotropins and reduced ova number the following morning. Thus we found an increased ovarian expression of both receptors only during proestrous afternoon. Finally expression of OX1 was determined by Western Blot at 11:00 h or 19:00 h of proestrus and in ovariectomized (OVX) rats treated with vehicle or estradiol benzoate (E). E treatment restored serum estradiol to values similar to those found during proestrus. OX1 expression increased at 19:00 h of proestrus in hypothalamus and pituitary. OVX rats, treated or not with E, sacrificed at 11:00 h showed OX1 expression similar to 11:00 h of proestrus in hypothalamus and pituitary. At 19:00 h in OVX rats low OX1 expression persisted; E replacement increased OX1 expression to high levels of normal cycling at 19:00 h. Thus we conclude that OX1 expression in hypothalamus and adenohypophysis is under the influence of both estradiol and the time of the day. Information from the hormonal sexual milieu of adult proestrous female rats impacts on the orexinergic system; alertness on this particular time of proestrus would be of importance for successful reproduction. (ANPCYT; CONICET UBA).