Impact of proestrous milieu on expression of orexin receptors and preproorexin in rat hypothalamus and hypophysis: Actions of Cetrorelix and Nembutal

Orexins and their receptors OX₁ and OX₂ regulate energy balance and the sleep-wake cycle. We studied the expression of prepro-orexin (PPO), OX₁, and OX₂ in brain and pituitary under the influence of the hormonal status in adult rats. Primarily, PPO, OX₁, and OX₂ expression was determined in Sprague-Dawley female cycling rats during proestrus and in males. Animals were killed at 2-h intervals. Anterior (AH) and mediobasal (MBH) hypothalamus, anterior pituitary (P), and frontoparietal cortex (CC) were homogenized in TRIzol, and mRNAs were obtained for screening of PPO, OX₁, OX₂ expression by semiquantitative RT-PCR. Main findings were confirmed and extended to all days of the cycle by quantitative real-time RT-PCR. Hormones and food consumption were determined. Finally, OX₁, OX₂, and PPO were measured by real-time RT-PCR in tissues collected at 1900 of proestrus after treatments at 1400 with ovulation-blocking agents Cetrorelix or pentobarbital. OX ₁ and OX₂ expression increased at least threefold in AH, MBH, and P, but not in CC, between 1700 and 2300 of proestrus, without variations in estrus, diestrus, or in males. PPO in AH and MBH showed a fourfold or higher increase only during proestrus afternoon. Cetrorelix or pentobarbital prevented increases of OX₁ and OX₂ only in the pituitary and blunted gonadotropin surges, but left OX₁, OX₂, and PPO brain expression unchanged. Reproduction, energy balance, and sleep-wake cycle are integrated. Here, we demonstrate that, in the physiological neuroendocrine condition leading to ovulation, information to the orexinergic system acts in hypothalamus and pituitary by different mechanisms.