Circadian rhythm disturbance is common postoperatively in older patients with hip fractures, which may contribute to the development of postoperative delirium (POD). As a reliable biomarker of endogenous circadian rhythms, melatonin regulates the sleep-wake cycle and environmental adaptation, and its secretory rhythm may be modified by anaesthesia and surgery. This study compared the impact of subarachnoid anaesthesia (SA) and general anaesthesia (GA), on the peak of melatonin secretion (primary outcome), the circadian rhythm of melatonin, cortisol and sleep, and the POD incidence (secondary outcome). In this prospective cohort observational study, hip fracture surgery patients were enrolled and assigned to receive either SA or GA. Postoperative plasma melatonin and cortisol levels were dynamically measured every six hours on seven time-points, and the circadian rhythm parameters including mesor, amplitude, and acrophase were calculated. Subjective and objective sleep assessments were performed by sleep diaries and sleep trackers, respectively. The Confusion Assessment Method was used twice daily by a specific geriatrician to screen for POD occurrence. In a cohort of 138 patients who underwent hip fracture surgery, the circadian rhythm disruption of the patients in the GA group (n=69) was greater than the SA group (n=69). Compared with SA, GA provided the lower peak concentration, mesor, and amplitude of melatonin secretion on postoperative day 1 (p < 0.05). Patients in the GA group experienced higher awakenings, more sleep deprivation, and poor sleep quality on surgery day (p < 0.05). A proportion of 12 patients in the SA group (17.4%) and 24 patients in the GA group (34.8%) experienced POD (p = 0.020). These results suggest that SA may be superior to GA in elderly patients undergoing hip fracture surgery as SA is associated with less impairment of the melatonin rhythm and sleep patterns, and fewer POD occurrences.

To accomplish concerted physiological reactions, nature has diversified functions of a single hormone at at least two primary levels: 1) Different receptors recognize the same hormone, and 2) different cellular effectors couple to the same hormone–receptor pair [R.P. Xiao,Sci STKE2001, re15 (2001); L. Hein, J. D. Altman, B.K. Kobilka,Nature402, 181–184 (1999); Y. Daaka, L. M. Luttrell, R. J. Lefkowitz,Nature390, 88–91 (1997)]. Not only these questions lie in the heart of hormone actions and receptor signaling but also dissecting mechanisms underlying these questions could offer therapeutic routes for refractory diseases, such as kidney injury (KI) or X-linked nephrogenic diabetes insipidus (NDI). Here, we identified that G_s-biased signaling, but not G_iactivation downstream of EP4, showed beneficial effects for both KI and NDI treatments. Notably, by solving Cryo-electron microscope (cryo-EM) structures of EP3-G_i, EP4-G_s, and EP4-G_iin complex with endogenous prostaglandin E₂(PGE₂)or two synthetic agonists and comparing with PGE₂-EP2-G_sstructures, we found that unique primary sequences of prostaglandin E2 receptor (EP) receptors and distinct conformational states of the EP4 ligand pocket govern the G_s/G_itransducer coupling selectivity through different structural propagation paths, especially via TM6 and TM7, to generate selective cytoplasmic structural features. In particular, the orientation of the PGE₂ω-chain and two distinct pockets encompassing agonist L902688 of EP4 were differentiated by their G_s/G_icoupling ability. Further, we identified common and distinct features of cytoplasmic side of EP receptors for G_s/G_icoupling and provide a structural basis for selective and biased agonist design of EP4 with therapeutic potential.

Avians have a complex system of light sensation and circadian organization. We previously found that light wavelength could affect the circadian expression of clock genes in chick liver, and that melatonin participated in this process. Melatonin functions through membrane and nuclear receptors, but their circadian rhythm and the effect of monochromatic light remain unclear. The effects of different receptors on clock gene expression are also unknown. In this study, 144 newly hatched chicks were divided into sham-operation and pinealectomy groups. They were raised under white (WL), red (RL), green (GL) and blue (BL) light for two weeks, and their livers were sampled at 6 time points with 4 h intervals. Using qPCR and western blot, the mRNA and protein expression of three membrane receptors (Mel1a, Mel1b, Mel1c) and one nuclear receptor (RORα) were measured for circadian rhythm analysis. The results showed that melatonin receptors, especially Mel1a and Mel1b, displayed a significant circadian rhythm. The rhythm mesor and amplitude of the membrane receptors were enhanced by GL and reduced by RL; further, pinealectomy dampened their rhythm and diminished the effect of light wavelength. However, the rhythm of melatonin nuclear receptor contrasted that of the membrane receptors. In vitro experiments involving the addition of different agonists and antagonists into primary chick hepatocytes showed that Mel1a and RORα activation induced the expression of seven clock genes (cClock, cBmal1, cBmal2, cCry1, cCry2, cPer2, cPer3). Similarly, activation of Mel1b and Mel1c induced the expression of five clock genes (except cBmal1 and cCry1). Moreover, melatonin entrained the rhythm of cBmal1 and cPer2 in long-term cultured hepatocytes. Overall, this research elucidates the role of melatonin receptors in regulating clock gene expression, and enhances our understanding regarding the effect of light wavelength on chick circadian rhythm.