NCBI Summary:
This gene encodes a hypothalamic neuropeptide precursor protein that gives rise to two mature neuropeptides, orexin A and orexin B, by proteolytic processing. Orexin A and orexin B, which bind to orphan G-protein coupled receptors HCRTR1 and HCRTR2, function in the regulation of sleep and arousal. This neuropeptide arrangement may also play a role in feeding behavior, metabolism, and homeostasis. [provided by RefSeq, Jan 2010]
General function
Ligand
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Cellular localization
Secreted
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Ovarian function
Steroid metabolism
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Interaction between orexin A and bone morphogenetic protein system on progesterone biosynthesis by rat granulosa cells. Fujita S et al. (2018) The involvement of orexins in reproductive function has been gradually uncovered. However, the functional role of orexins in ovarian steroidogenesis remains unclear. In the present study, we investigated the effects of orexin A on ovarian steroidogenesis by using rat primary granulosa cells that express both OX1 and OX2 receptors for orexins. Treatment with orexin A enhanced progesterone, but not estradiol, biosynthesis induced by FSH, whereas it did not affect basal levels of progesterone or estradiol. In accordance with the effects on steroidogenesis, orexin A increased the mRNA levels of progesterogenic enzymes, including StAR, P450scc and 3βHSD, but not P450arom, and cellular cAMP synthesis induced by FSH. Under the condition of blockage of endogenous BMP actions by noggin or BMP-signaling inhibitors, orexin A failed to increase levels of progesterone synthesis induced by FSH treatment, suggesting that endogenous BMP activity in granulosa cells might be involved in the enhancement of progesterone synthesis by orexin A. Treatment with orexin A impaired Smad1/5/9 activation as well as Id-1 mRNA expression stimulated by BMP-6 and BMP-7, the latter of which was reversed by treatment with an OX1 antagonist. It was also found that orexin A suppressed the mRNA expression of both type-I and -II receptors for BMPs and increased that of inhibitory Smad6 and Smad7 in granulosa cells. On the other hand, treatments with BMP-6 and -7 suppressed the expression of OX1 and OX2. Collectively, the results indicated that orexin A enhances FSH-induced progesterone production, at least in part, by downregulating BMP signaling in granulosa cells. Thus, a new role of orexin A in facilitating progesterone synthesis and functional interaction between the orexin and BMP systems in granulosa cells were revealed.//////////////////
Serum orexin-A (OXA) level decreases in policystic ovarian syndrome. Yilmaz E et al. Abstract Aim: In the current study, we aimed to investigate whether serum orexin-A (OXA) levels are different in polycystic ovary syndrome (PCOS) subjects. Materials and methods: Thirty-six women with PCOS and 40 healthy, age and body mass index-matched controls were included in the prospective cross-sectional study. All subjects underwent venous blood draws during the early follicular phase after overnight fasting. Serum OXA levels were measured with an enzyme immunoassay (EIA). The relationships between the serum OXA levels and the anthropometric and metabolic parameters were also assessed. Results: The serum OXA levels were lower in the women with PCOS compared to the control group. The serum OXA levels were correlated negatively with systolic blood pressure, the Ferriman-Gallway score and LH and free testosterone levels. Conclusion: Our results indicate that serum OXA levels decrease in the serum of women with PCOS.
Effects of Orexins A and B on Expression of Orexin Receptors and Progesterone Release in Luteal and Granulosa Ovarian Cells. Cataldi NI et al. Orexin-A and Orexin-B are neuropeptides controlling sleep-wakefulness, feeding and neuroendocrine functions via their G protein-coupled receptors, Orexin-1R and Orexin-2R. They are synthesized in the lateral hypothalamus and project throughout the brain. Orexins and orexin receptors have also been described outside the brain. Previously we demonstrated the presence of both receptors in the ovary, their increased expression during proestrous afternoon and the dependence on the gonadotropins. Here we studied the effects of orexins on the mRNA expression of both receptors, by quantitative real-time PCR, on luteal cells from superovulated rat ovaries and granulosa cells from diethylstilbestrol-treated rat ovaries. Effects on progesterone secretion were also measured. In luteal cells, 1 nM of either Orexin-A or Orexin-B decreased progesterone secretion. Orexin-A treatment increased expression of both Orexin-1R and Orexin-2R mRNA. The effect on Orexin-1R mRNA expression was abolished by an Orexin-1R selective receptor antagonist SB-334867 and the effect on Orexin-2R mRNA expression was abolished by a selective Orexin-2R antagonist JNJ-10397049. Orexin-B did not modify Orexin-1R mRNA expression, but increased Orexin-2R mRNA expression. The effect of Orexin-B on Orexin-2R was abolished by a selective Orexin-2R antagonist. Neither the expression of orexin receptors nor progesterone secretions by granulosa cells were affected by orexins. FSH, as positive control, increased both steroid hormones secretion, but did not induce the expression of OX receptors in granulosa cells isolated from late preantral/early antral follicles.. Finally in ovaries obtained immediately after sacrifice, the expression of Orexin-1R and Orexin-2R was higher in superovulated rat ovaries compared to control or diethylstilbestrol treated rat ovaries. A selective presence and function of both orexinergic receptors in luteal and granulosa cells is described, suggesting that the orexinergic system may have a functional role in the ovary.
Expression regulated by
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Ovarian localization
Granulosa, Theca, Luteal cells
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Expression of orexins and their precursor in the porcine ovary and the influence of orexins on ovarian steroidogenesis in pigs. Nitkiewicz A 2014 et al.
Orexins A and B are hypothalamic neuropeptides associated with homeostasis and the reproductive system. The aim of the study was to compare the expression of the prepro-orexin gene and the intensity of orexins immunoreactivity in the porcine ovary (corpora lutea, granulosa and theca interna cells) during four different stages of the oestrous cycle (days: 2-3, 10-12, 14-16 and 17-19) and to examine the in vitro effect of orexins on the secretion of steroid hormones by porcine luteal, granulosa and theca interna cells. The highest expression of prepro-orexin mRNA was observed in theca interna cells on days 17-19 of the oestrous cycle. The highest content of immunoreactive orexin A was noted in corpora lutea on days 10-12 and the highest level of immunoreactive orexin B on days 14-16 of the cycle. Immunoreactive orexin A concentrations were higher in theca interna cells than in granulosa cells, whereas similar levels of immunoreactive orexin B were observed in both cell types. Under in vitro conditions, at the concentration of 10nM, orexins A and B inhibited FSH-induced oestradiol secretion by granulosa cells. The obtained results suggest that the pattern of orexin peptide expression in the porcine ovary is related to the animals' hormonal status. Our findings imply that orexins can affect porcine reproductive functions through modulation of ovarian steroidogenesis.
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Ohkubo T, et al reported
cDNA cloning of chicken orexin receptor and tIssue distribution: sexually dimorphic expression in chicken gonads.
Orexin-A and -B are known to stimulate food intake in mammals. However, the critical roles of orexins in birds are not fully understood, since orexins have no stimulatory effect on food intake in the chicken. To understand the physiological role(s) of orexins in birds, we have cloned chicken orexin receptor (cOXR) cDNA by RT-PCR, and analysed the tIssue distribution of OXR mRNA in the chicken. The cOXR cDNA is 1869 bp long and encodes 501 amino acids. The cloned cDNA for cOXR corresponds to the type 2 OXR in mammals, and shows approximately 80% similarity to those of mammals at the amino acid level. Expression analysis by RNase protection assay revealed OXR mRNA was distributed widely in brain regions, and expression in the cerebrum, hypothalamus and optic tectum were abundant. In peripheral tIssues, OXR mRNA was expressed in the pituitary gland, adrenal gland and testis, but no mRNA expression was observed in other tIssues examined. Furthermore, we found that the amount of cOXR mRNA was different between testis and ovary, while prepro-orexin mRNA is equally expressed in the gonads of both sexes in the chicken. These data indicate that the orexins have neuroendocrine actions in chickens, which are mediated through hypothalamic receptors as has been observed in mammals. In addition, orexin may have specific role(s) in the regulation of gonadal function in which sex-dependent mechanisms could be involved.
Follicle stages
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Orexin A Expression in the Ovary of Dog and Cat. Levanti M et al. (2015) Orexin A and B, also known as hypocretin A and B, are hypothalamic neuropeptides arising from a precursor to the 130 amino acid, called pre-pro orexin. They are synthesized mainly in lateral and posterior hypothalamus and are involved in different functions such as regulation of food intake and energy balance. Orexins and orexin receptors were previously described also in different tissues and organs outside the brain. The aim of this study was to demonstrate by means of the immunofluorescence technique, the presence of orexin A in the ovary of cat and dog, to support the hypothesis of the role of this substance also at the level of the female genital system. The presence of orexin A in the ovary either in dog or in cat is in agreement with previous data on the presence and role of orexins in the female genital system of other species.//////////////////