Orexins (Hypocretins) A and B Modify Orexin 1 Receptor Expression and Gonadotropins Secretion in Anterior Pituitary Cells of Proestrous Rats.

NI CATALDI, VA LUX-LANTOS AND C LIBERTUN

S. Diego, California

Congreso; The Endocrine Society (USA). 92th Annual Meeting; 2010

The Endocrine Society

[P2-302] Orexins (Hypocretins) A and B Modify Orexin 1 Receptor Expression and Gonadotropins Secretion in Anterior Pituitary Cells of Proestrous Rats.NI Cataldi, VA Lux-Lantos, C Libertun. Inst de Biol y Med Experimental-CONICET, Buenos Aires, Argentina; Fac of Med, Univ of Buenos Aires, Buenos Aires, ArgentinaOrexins A (OXA) and B (OXB) 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). In previous works in vivo, we demonstrated that in the physiological neuroendocrine condition of proestrus leading to ovulation, information of the orexinergic system acts on the anterior pituitary (1, 2).Here, we investigate whether OXA and OXB are involved in the modulation of the OX1 receptor expression at the mRNA level, and the effect on FSH and LH secretion, in an in vitro system using adenohypophyseal cell from proestrous rats.Regular cycling Sprague-Dawley rats were sacrificed in the morning of proestrus, a critical period according to our previous results (1, 3) and pituitary cell cultures done as described (4). After 72 h of incubations with OXA (10-9M) or OXB (10-9M) in absence (OXA-Ab or OXB-Ab), or presence (OXA-Pr or OXB-Pr) of the selective OX1 antagonist SB334867A (1mM, Tocris Bioscience; MO), cells were obtained and OX1 and OX2 receptors was determined by real-time RT-PCR as in (1, 3). Medium LH and FSH were determined by RIA (NHPP, NIDDK). Results were expressed as means ± SE and considered significant when p<0.05. Data were analyzed by one-way analysis of variance.OXA decreased the expression of OX1 in absence or presence of SB334867A [C, control medium only, Arbitrary Units: 1 (n: 6) vs. OXA-Ab: 0.692±0.092 (n: 5); OXA-Pr: 0.706±0.046 (n: 6); p<0.05] and increased gonadotropins in medium, while SB334867A blocked this hormonal effect [LH (ng/ml); C: 19.04±1.86 (n: 7); OXA-Ab: 33.73±2.74 (n: 8); OXA-Pr: 20.38±1.59 (n: 8), p<0.05; FSH (ng/ml): C: 73.37±4.62 (n: 8) ; OXA-Ab: 146.67±17.54 (n: 7); OXA-Pr: 85.14±5.90 (n: 8); p<0.05]. OXB produced similar actions to OXA, i.e., decreased OX1 expression and increased LH and FSH release, while SB334867A blocked hormone release but not OX1 expression. SB334867A by itself did not alter the expression of OX1 or any hormonal parameter.Both orexins decreased expression of the OX1 receptor in pituitary cell cultures while increasing gonadotropins release, this hormonal effect was blocked by SB334867A. The present in vitro results confirm previous in vivo studies about the participation of orexins on pituitary reproductive function, showing a direct effect of both neuropeptides on the gland.1. Silveyra P et al., Am J Physiol, Endocrinol Metab 2007; 292: E8202. Silveyra P et al., Regul Pept 2009; 15:1213. Silveyra P et al., Am J Physiol, Endocrinol Metab 2007; 293: E9774. Fernández M et al., Environ Health Perspect 2009; 117:757Sources of Research Support: Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET); Agencia Nacional de Promoción Científica y Tecnológica; Universidad de Buenos Aires. Argentina.