Urocortin 1 exhibits potent inhibition of cardiac sympathetic nerve activity in conscious sheep

Exposure to Cold Unmasks Potential Biomarkers of Fibromyalgia Syndrome Reflecting Insufficient Sympathetic Responses to Stress

OBJECTIVES

Fibromyalgia syndrome (FMS) is a chronically painful condition whose symptoms are widely reported to be exacerbated by stress. We hypothesized that female patients with FMS differ from pain-free female controls in their sympathetic responses, a fact that may unmask important biomarkers and factors that contribute to the etiology of FMS.

MATERIALS AND METHODS

In a pilot study, blood pressure (BP), skin temperature, thermogenic activity, circulating glucose, and pain sensitivity of 13 individuals with FMS and 11 controls at room temperature (24°C) were compared with that after exposure to cold (19°C).

RESULTS

When measured at 24°C, BP, skin temperature, blood glucose, and brown adipose tissue (BAT) activity, measured using F-fluorodeoxyglucose positron-emission tomography/computed tomography, did not differ between controls and individuals with FMS. However, after cold exposure (19°C), BP and BAT activity increased in controls but not in individuals with FMS; skin temperature on the calf and arm decreased in controls more than in individiuals with FMS; and circulating glucose was lower in individiuals with FMS than in controls. Pain sensitivity did not change during the testing interval in response to cold.

DISCUSSION

The convergence of the effect of cold on 4 relatively simple measures of thermogenic, cardiovascular, and metabolic activity, each regulated by sympathetic activity, strongly indicate that individuals with FMS have impaired sympathetic responses to stress that are observable and highly significant even when measured in extraordinarily small sample populations. If insufficient sympathetic responses to stress are linked to FMS, stress may unmask and maximize these potential clinical biomarkers of FMS and be related to its etiology.

Systemic angiotensin II does not increase cardiac sympathetic nerve activity in normal conscious sheep

While it is well established that centrally injected angiotensin II (Ang II) has potent actions on sympathetic nervous activity (SNA), it is less clear whether peripheral Ang II can immediately stimulate SNA. In particular, the contribution of cardiac sympathetic nerve activity (CSNA) to the acute pressor response is unknown. We therefore examined the effect of incremental doses of intravenous Ang II (3, 6, 12, 24, and 48 ng/kg/min each for 30 min) on CSNA in eight conscious sheep. Ang II infusions progressively increased plasma Ang II up to 50 pmol/l above control levels in dose-dependent fashion (P<0.001). This was associated with the expected increases in mean arterial pressure (MAP) above control levels from <10 mmHg at lower doses up to 23 mmHg at the highest dose (P<0.001). Heart rate and cardiac output fell progressively with each incremental Ang II infusion achieving significance at higher doses (P<0.001). There was no significant change in plasma catecholamines. At no dose did Ang II increase any of the CSNA parameters measured. Rather, CSNA burst frequency (P<0.001), burst incidence, (P=0.002), and burst area (P=0.004) progressively decreased achieving significance during the three highest doses. In conclusion, Ang II infused at physiologically relevant doses increased MAP in association with a reciprocal decrease in CSNA presumably via baroreceptor-mediated pathways. The present study provides no evidence that even low-dose systemic Ang II stimulates sympathetic traffic directed to the heart, in normal conscious sheep.

Low-dose B-type natriuretic peptide raises cardiac sympathetic nerve activity in sheep

The reported effects of atrial natriuretic peptide (ANP) on sympathetic nerve activity (SNA) are variable, dependent on concomitant hemodynamic actions, and likely to be regionally differentiated. There are few reports of the effect of B-type natriuretic peptide (BNP) on SNA and none have measured cardiac SNA (CSNA) by direct microneurography. We measured the effects of low-dose ANP and BNP (2.4 pmol·kg−1·min−1 infused for 120 min) on CSNA and hemodynamics in conscious sheep ( n = 8). While there was a trend for mean arterial pressure and cardiac output to fall with both ANP and BNP, changes were not significant compared with vehicle control. However, BNP did significantly reduce systolic arterial (97 ± 4.2 vs. 107 ± 6.8 mmHg during control; P = 0.043) and pulse pressures (0.047) and increase heart rate (110 ± 6.7 vs. 96 ± 7.3 beats/min; P = 0.044). Trends for these hemodynamic parameters to change with ANP did not achieve statistical significance. ANP also had no significant effect on any CSNA parameters measured. In contrast, BNP induced a rise in both CSNA burst frequency (∼20 bursts/min higher than control, P = 0.011) and burst area (∼40% higher than control, P = 0.013). BNP-induced rises in burst incidence (bursts/100 beats), and burst area per 100 beats, however, were not significant. In conclusion, BNP infused at low doses that only had subtle effects on hemodynamics increased CSNA burst frequency and burst are per minute. This increase in CSNA may in large part be secondary to an increase in heart rate as CSNA burst incidence and burst area per 100 beats were not significantly increased. This study provides no evidence for inhibition of CSNA by natriuretic peptides.

Targeting urocortin signaling pathways to enhance cardioprotection: is it time to move from bench to bedside?

Despite the exponential growth in medical knowledge, cardiovascular diseases (CVDs) contribute to more than one-third of worldwide morbidity and mortality. A range of therapies already exist for established CVDs, although there is significant interest in further understanding their pathogenesis. The urocortins (Ucns) are peptide members of the corticotrophin-releasing factor family, a group of evolutionary conserved peptides with homologues in fish, amphibians and mammals and considered to play a pivotal role in energy homeostasis and local tissue repair. A number of preclinical studies in vitro, in-vivo and ex-vivo have defined a multifaceted effect of Ucns on the cardiovascular system. Different G-protein coupled signaling and protein-kinase pathways have been shown to be activated by Ucns, together with different transcriptional and translational effects, all of which preferentially converge on the mitochondria, where the modulation of apoptosis is considered their principal action. It has been demonstrated in experimental models, and consequentially suggested in human diseases, that Ucn-mediated inhibition of apoptosis can be exploited for the improvement of both therapeutic and preventative strategies against CVDs. Specifically, some unavoidable iatrogenic ischemia/reperfusion (I/R) injuries, e.g. during cardiac surgery or percutaneous coronary angioplasty, may greatly benefit from the anti-apoptotic effect of Ucns. However, few studies on the topic have been employed in humans to date. Therefore, this review will focus on the different intra-cellular mechanisms of action of Urocortins, and detail the different Ucn-mediated pathways identified so far. It will also highlight the limited evidence already existing in human clinical and surgical settings, as well as emphasize the potential uses of Ucns in human cardiac pathology.

Urocortin 3 inhibits cardiac sympathetic nerve activity in conscious sheep

There is an increasing body of evidence suggesting a role for the urocortin (Ucn) peptides in blood pressure regulation and in the pathophysiology of cardiovascular disease. Both Ucn1 and Ucn2 have recently been shown to inhibit cardiac sympathetic nerve activity (CSNA) in sheep. However, there are few studies reporting the effects of Ucn3 on the sympathetic nervous system. Hence, this study performed in normal conscious sheep examines the effects of Ucn3 on CSNA. Intravenous Ucn3 (administered at doses of 25 and 100 μg) caused transient falls in arterial pressure (P = 0.025), more prolonged rises in heart rate (P < 0.001), and falls in stroke volume (P < 0.001) and peripheral resistance (P = 0.018). CSNA, measured as burst area and burst incidence, fell in a dose-dependent manner after Ucn3 bolus (all P < 0.001). CSNA burst frequency tended to be reduced after high-dose Ucn3. Ucn3 had no significant effect on plasma catecholamine levels. In conclusion, this study reports for the first time that Ucn3 induces potent inhibition of sympathetic traffic directed toward the heart. This provides further support for a role for Ucn3 in pressure and volume homeostasis and suggests that further investigation of potential therapeutic applications for Ucn3 in cardiovascular disease is warranted.

Distribution of urocortins and corticotropin-releasing factor receptors in the cardiovascular system

Urocortins are human homologues of urotensin I, a fish corticotropin-releasing-factor- (CRF-) like peptide secreted from the urophysis. There are three urocortins: urocortin 1, urocortin 2, and urocortin 3 in mammals. We have shown that urocortin 1 and urocortin 3 are endogenously synthesized in the myocardial cells of human heart and may act on CRF type 2 receptor (CRFR2) expressed in the heart. Expression levels of urocortin 1 in the heart and plasma urocortin 1 levels are elevated in patients with heart failure. Recent studies have shown that urocortins have various biological actions in the cardiovascular system, such as a vasodilator action, a positive inotropic action, a cardioprotective action against ischemia/reperfusion injury, and suppressive actions against the renin angiotensin system and the sympathetic nervous system. Urocortins and CRFR2 may therefore be a potential therapeutic target for cardiovascular diseases, such as congestive heart failure, hypertension, and myocardial infarction.

Novel neurohormonal insights with therapeutic potential in chronic heart failure

Despite considerable therapeutic advances over recent years, chronic heart failure remains associated with significant morbidity and mortality. Further improvements in the treatment of this syndrome are therefore needed and this will require advances in the understanding of its underlying pathophysiology. This article reviews the literature regarding recently identified neurohormonal pathways that are declaring themselves as potential therapeutic targets in chronic heart failure.

Urocortin: a protective peptide that targets both the myocardium and vasculature

The urocortins are a family of endogenously produced peptide hormones that show great promise as potential drugs for the treatment of heart disease. They can increase contractility and cardiac output without causing changes in mean arterial blood pressure. As expected, the receptor for these peptides is present in cardiomyocytes, and they can bind and protect these cells from simulated ischemia and reperfusion in vitro. The receptor is present, however, in much higher density in the endothelial cells that form a continuous lining of the coronary vasculature. Functionally, the urocortin peptides have been shown to have potent local vasodilatory effects, and may affect other aspects of vascular function. In this review, we will attempt to distinguish the "cardio" from the "vascular" effects of urocortin and its homologues, including the archetypal family member, corticotrophin releasing hormone.