Role of Orexin-A in Hypertension and Obesity.

Abstract

Hypertension is one of the most challenging health problems inducing cerebrovascular disease and high percentage of death when associated with diabetes, dyslipidemias, and obesity. Orexin/hypocretin is a peptide expressed by a small number of neurons of the dorsolateral hypothalamus, a brain feeding and autonomic "fight-or-flight" regulatory center. According to this function, orexin has been demonstrated to evoke cardiovascular responses, heart rate, hypertension, hyperarousal, hyperphagia, and obesity. The focus of this review is to provide an overview about the mechanism through which orexin regulates food intake and cardiovascular responses and its role in the pathogenesis of obesity and hypertension which could be of great interest to establish possible new therapies. In normal rats and mice, central administration of orexin increases food intake, blood pressure, and sympathetic nerve activity and these effects are blocked by selective orexin receptor antagonist SB-334867 or almorexant. Moreover, upregulation of orexin signaling, in combination with elevation of epinephrine and norepinephrine circulating levels, occurs in rats exposed to chronic stress, in models of spontaneous hypertension (SHR and BPH/2J Schlager mice) and in obese mice (ob/ob or mice fed with high fat diet). Therefore, hyperactivity of orexinergic neurons could be a factor in the development of obesity and essential hypertension. Because of their widespread projections to the brain regions involved in appetite and cardiovascular responses, as far down as sympathetic preganglionic neurons in the spinal cord, orexin evokes sympathetically mediated cardiovascular responses. Lasting upregulation of orexin signaling can lead to hyperphagia, obesity, and hypertensive state. Dual orexin receptor antagonists (DORAs) and selective orexin receptor antagonists (SORAs) have antihypertensive effects that could be of clinical use for regulation of food intake and hypertension, supporting the role of orexinergic neurons as critical checkpoint in the neurogenic control of metabolic and cardiovascular functions.