Orexin B, rat, mouse (Rat orexin B) TFA is an endogenous orexin receptor agonist. Orexin B, rat, mouse TFA binds and activates two closely related orphan G protein-coupled receptors OX1-R and OX2-R. Orexin B, rat, mouse TFA stimulates food intake and energy expenditure and plays a significant role in sleep-wakefulness regulation[1][2][3].
OX2 receptor is indeed a high-affinity receptor for human orexin B, with an IC50 of 36 nM in the binding assay and an EC50 of 60 nM in the [Ca2+]i transient assay. Human Orexin B has significantly lower affinity for the human OX1: the calculated IC50 in the competitive binding assay and the EC50 in the [Ca2+]i transient assay are 420 nM and 2500 nM for human orexin-B, respectively[2].
Orexin-B modulates the activity of rod bipolar cells (RBCs) located in the outer retina of rat. Intravitreal injection of orexin-B increased the amplitude of the scotopic electroretinographic b-wave, a reflection of RBC activity, recorded in vivo[4].
[1]. Smart D, et al. Orexins: a new family of neuropeptides. Br J Anaesth. 1999 Nov;83(5):695-7.
[2]. Sakurai T, et al. Orexins and orexin receptors: a family of hypothalamic neuropeptides and G protein-coupled receptors that regulate feeding behavior. Cell. 1998 Feb 20;92(4):573-85.
[3]. Ziolkowska A, et al. Orexin B inhibits proliferation and stimulates specialized function of cultured rat calvarial osteoblast-like cells. Int J Mol Med. 2008;22(6):749-755.
[4]. Zhang G, et al. Orexin-B modulates synaptic transmission of rod bipolar cells in rat retina. Neuropharmacology. 2018;133:38-50.