Читать книгу Pathy's Principles and Practice of Geriatric Medicine - Группа авторов - Страница 369

Orexin A and B (hypocretin‐1 and ‐2) are neuropeptides synthesized in the hypothalamus and involved with feeding and sleep. Orexin deficiency causes narcolepsy in animals and humans and hypophagia and weight loss in animals.⁴⁰ Intracerebroventricular orexin injection dose‐dependently increases food intake in rodents, and orexin antibody reduces food intake (reviewed by Kirchgessner⁴¹). Orexin A is the subtype mainly responsible for effects on feeding. The majority of evidence does not support declining orexin activity as a cause of the anorexia of ageing. In a cross‐sectional study of 82 healthy men and women age 23–79, plasma orexin A concentrations increased with age in both men and women, which should favour increased appetite and food intake.⁴⁰ Studies in mice have found no changes or increases in total brain orexin levels and hypothalamic orexin A receptor levels with increasing age, while a decrease in hypothalamic orexin gene expression in ageing rats has been described.⁴² In humans, the effects of normal ageing on the levels of the orexin receptors and sensitivity to the effects of orexin are unknown.