Origin of Aberrant Blood Pressure and Sympathetic Regulation in Diet-Induced Obesity

Abstract

O besity, a state of excessive adipose tissue accumulation, has reached epidemic proportions worldwide, and this increasing global prevalence constitutes a major public health challenge. Obesity is one of the main causes of hypertension. Both human and animal studies present a strong link between bodyweight gain and greater blood pressure.1 Importantly, obesity-related hypertension is caused by an interaction of humoral and neural mechanisms, 2,3 and inappropriate increases in sympathetic tone are thought to be the major cause of the hypertension. [4][5][6] Indeed, clinical data show that when compared with normal subjects, noradrenaline spillover rates are greater among obese individuals. 7 Furthermore, in studies using dog and rat models of obesity, bilateral renal denervation attenuated the hypertension 8,9 and combined α-and β-adrenergic blockade has been shown to prevent high fat diet (HFD)-induced hypertension in conscious rabbits. 10 Although the close link between the obesity and the prevalence of hypertension has been well established, a key focus in the field remains the identification of mechanisms underlying sympathetic overdrive in obesity.The adipokine leptin is a 16-kDa peptide that is secreted primarily by white adipose tissue and found in serum in direct proportion to adiposity. In addition to the weight loss effect, leptin has also been shown to activate sympathetic nerve activity (SNA) in the kidneys, hindlimbs, and adrenal glands, which suggested its potential role in the increased SNA in obesityrelated hypertension. 4 Plasma leptin levels correlate strongly with blood pressure and renal SNA (RSNA) while central administration of leptin increases mean arterial pressure (MAP) in both rats and rabbits via stimulation of the sympathetic nervous system. 3,11 Hence, the effect of increased circulating leptin because of high adiposity is considered a primary link between obesity and increased SNA. 3,12 The central effects of leptin are thought to be mediated primarily through the arcuate nucleus of the hypothalamus from which peripheral signals are relayed downstream to other hypothalamic nuclei via a network of second-order neurons.13 Pro-opiomelanocortin and neuropeptide Y (NPY) neurons in the arcuate nucleus form the main population of neurons expressing the leptin receptor, which propagate leptin signals throughout the hypothalamus Abstract-High fat diet (HFD)-induced hypertension in rabbits is neurogenic and caused by the central action of leptin, which is thought to be dependent on activation of α-melanocortin-stimulating hormone (α-MSH) and neuropeptide Y-positive neurons projecting to the dorsomedial hypothalamus (DMH) and ventromedial hypothalamus (VMH). However, leptin may act directly in these nuclei. Here, we assessed the contribution of leptin, α-MSH, and neuropeptide Y signaling in the DMH and VMH to diet-induced hypertension. Male New Zealand white rabbits were instrumented with a cannula for drug injections into the DMH or VMH and a renal sympathetic nerve activity (RSNA) electrode....

Obesity: sex and sympathetics

“…More specifically, it has been shown that nonspecific blockade of the ArcN and PVN [76,77] both decrease SNA in DIO male rats. While these results may reflect the actions of several sympathoexcitatory factors, other reports indicate that, in obese animals, select blockade of leptin receptors in the ArcN [36], VMH [78], or DMH [69] decreases SNA and/or MAP. Nevertheless, two studies were unable to confirm a role for the DMH in obesity-induced sympathoexcitation [77,78].…”

Leptin as a Mediator of Obesity-Induced Hypertension

“…Other investigators have shown no effect on baseline blood pressure of leptin receptor knockdown in the PVN, but that this prevented an increase in blood pressure after direct injection of leptin into the PVN [48]. On the other hand, injection of a leptin receptor antagonist into the VMH but not the DMH reversed the increases in blood pressure, heart rate, and renal SNA in high fat fed rabbits [49]. Conversely, reactivation of leptin receptors only in the DMH increased blood pressure in high fat fed mice while DMH-restricted administration of a leptin receptor antagonist decreased blood pressure in mice fed a high fat diet [28].…”

Do sodium‐glucose co‐transporter‐2 inhibitors prevent heart failure with a preserved ejection fraction by counterbalancing the effects of leptin? A novel hypothesis

“…Although obese people are resistant to leptin's actions to suppress food intake, the resistance is selective; the adipokine continues to stimulate systems that augment energy expenditures . Leptin can contribute to activation of the sympathetic nervous system and renin‐angiotensin system in obesity and to both sodium retention and cardiac fibrosis . Leptin is not merely a marker of obesity; it exerts important effects, as is evidenced by the fact that the neurohormonal activation and coronary vascular abnormalities in diet‐induced obesity are blocked by synthetic leptin antagonists …”