Estradiol Modulates Female Hypothalamic and Pituitary Orexin Receptor 1 Expression in a Daytime Dependent Manner.

P SILVEYRA; NI CATALDI; VA LUX-LANTOS; C LIBERTUN

S. Francisco, CA. USA.

Congreso; The Endocrine Society (USA). 90th Annual Meeting.; 2008

The Endocrine Society (USA).

[P1-732] Estradiol Modulates Female Hypothalamic and Pituitary Orexin Receptor 1 Expression in a Daytime Dependent Manner.P Silveyra, NI Cataldi, VA Lux-Lantos, C Libertun, Lab Neuroendocrinoloy, Inst de Biol y Med Experimental-CONICET, Buenos Aires, Argentina; Dept Quimica Biol, FCEN, Univ of Buenos Aires, Buenos Aires, Argentina; Dept Physiology, Facultay of Med, Univ of Buenos Aires, Buenos Aires, ArgentinaOrexins A and B are neuropeptides controlling feeding, sleep, autonomic and neuroendocrine functions. Both are synthesized by neurons of the lateral hypothalamus with projections throughout the brain. They exert their actions interacting with orexin receptors 1 (OX1) and 2 (OX2).Previous results from our laboratory demonstrated that late proestrous hormonal levels modulate hypothalamic and pituitary OX1 and OX2 mRNA expression (1, 2). Here we studied whether estradiol (E2) was involved in the modulation of OX1 protein expression in hypothalamus and andenohypophysis in adult female rats. Expression of OX1 was determined by Western Blot in anterior (AH) and mediobasal hypothalamus (MBH), pituitary (P) and frontoparietal cortex (FC) as control, from regularly cycling Sprague-Dawley rats sacrificed at 11:00 h or 19:00 h of proestrus and expressed relative to -syntaxin. Ovariectomized rats (OVX) and OVX replaced with estradiol benzoate (OVX-EB; 10 g im, 6 doses, during two weeks) were also sacrificed at these times and OX1 expression was determined in the same tissues. EB treatment effectively restored serum E2 (measured by RIA) in both groups of OVX-EB animals (11:00 h and 19:00 h) to values similar to those found during proestrous afternoon. OX1 expression increased at 19:00 h of proestrus in AH [Arbitrary units (AU) 0.69 0.06 vs. 0.44 0.01 at 11:00 h, p<0.05], MBH [AU: 1.02 0.02 vs. 0.48 0.09 at 11:00 h, p<0.05] and P [AU: 0.76 0.16 vs. 0.38 0.02 at 11:00 h, p<0.05] but not in FC [AU: 0.14 0.01 vs. 0.17 0.05 at 11:00 h), in concordance with our previous results using Real Time RT-PCR (1). Both OVX and OVX-EB sacrificed at 11:00 h showed OX1 expression similar to 11:00 h of proestrus in AH, MBH and P. At 19:00 h in OVX animals, low OX1 expression persisted in these areas; in contrast EB replacement in OVX-EB significantly increased OX1 expression to high levels of normal cycling rats at 1900h [AU: 0.74 0.02 in AH, 0.92 0.20 in MBH and 0.80 0.11 in P]. These results suggest that OX1 expression in selected areas, as the hypothalamus and the adenohypophysis, is under the influence of E2 and the time of the day in the female adult rat.1. Silveyra P et al, Am J Physiol, Endocrinol Metab 2007; 292: E8202. Silveyra P et al, Am J Physiol, Endocrinol Metab 2007; 293: E977Supported by Consejo Nacional de Investigaciones Cientificas y Tecnicas; Agencia Nacional de Promocion Cientifica y Tecnologica; Universidad de Buenos Aires. Argentina.