Increased sensitivity to alpha-adrenoceptor stimulation but intact purinergic and muscarinergic effects in prehypertensive cardiac hypertrophy of spontaneously hypertensive rats

Ubrogepant, erenumab, and eptinezumab antagonize positive inotropic effects of the calcitonin gene-related peptide in the isolated human atrium

The calcitonin gene-related peptide (CGRP) is an endogenous peptide that is known to be involved in the development of a migraine. CGRP is also present in the human heart, acts via CGRP receptors, and has been shown to increase the force of contraction (FOC) in isolated, electrically driven human atrial preparations (HAP) from adult patients obtained during open-heart surgery. Here, the hypothesis was tested that the positive inotropic effect (PIE) of CGRP could be attenuated by three anti-migraine drugs, namely ubrogepant, erenumab (both CGRP receptor antagonists), and eptinezumab (a CGRP antagonist). CGRP, cumulatively applied at concentrations ranging from 1 to 100 nM, increased the FOC. In the presence of cilostamide, an inhibitor of phosphodiesterase III, CGRP was more potent and effective than in the absence of cilostamide. Furthermore, when 100 nM CGRP was administered, subsequent application of ubrogepant (1 nM), erenumab (2 nM), and eptinezumab (6 nM) led to a reduction of FOC in HAP. In a more effective way, 1 µM carbachol and 1 µM (-)-N6-phenylisopropyladenosine (PIA) attenuated the PIE of CGRP in the presence of cilostamide. Conversely, when we applied first ubrogepant (1 nM), erenumab (2 nM), or eptinezumab (6 nM), then, this pre-incubation attenuated the PIE in HAP of cumulatively applied CGRP compared to CGRP given alone. We conclude that ubrogepant, erenumab, and eptinezumab are functional antagonists of CGRP in HAP at therapeutic concentrations of these anti-migraine drugs. Further investigation is necessary to determine whether this reduction in FOC is beneficial or detrimental for migraine patients.

Effect of renal denervation on left ventricular mass and function in patients with resistant hypertension: data from a multi-centre cardiovascular magnetic resonance imaging trial

AIMS

Sympathetic stimulation induces left ventricular hypertrophy and is associated with increased cardiovascular risk. Catheter-based renal denervation (RDN) has been shown to reduce sympathetic outflow and blood pressure (BP). The present multi-centre study aimed to investigate the effect of RDN on anatomic and functional myocardial parameters, assessed by cardiac magnetic resonance (CMR), in patients with resistant hypertension.

METHODS AND RESULTS

Cardiac magnetic resonance was performed in 72 patients (mean age 66 ± 10 years) with resistant hypertension (55 patients underwent RDN, 17 served as controls) at baseline and after 6 months. Clinical data and CMR results were analysed blindly. Renal denervation significantly reduced systolic and diastolic BP by 22/8 mm Hg and left ventricular mass index (LVMI) by 7.1% (46.3 ± 13.6 g/m(1.7) vs. 43.0 ± 12.6 g/m(1.7), P < 0.001) without changes in the control group (41.9 ± 10.8 g/m(1.7) vs. 42.0 ± 9.7 g/m(1.7), P = 0.653). Ejection fraction (LVEF) in patients with impaired LVEF at baseline (<50%) significantly increased after RDN (43% vs. 50%, P < 0.001). Left ventricular circumferential strain as a surrogate of diastolic function in the subgroup of patients with reduced strain at baseline increased by 21% only in the RDN group (-14.8 vs. -17.9; P = 0.001) and not in control patients (-15.5 vs. -16.4, P = 0.508).

CONCLUSIONS

Catheter-based RDN significantly reduced BP and LVMI and improved EF and circumferential strain in patients with resistant hypertension, occurring partly BP independently.

Therapeutic potential of renal sympathetic denervation in patients with chronic heart failure

Chronic heart failure is associated with sympathetic activation characterised by elevated circulating norepinephrine levels linked to cardiovascular morbidity and mortality. Norepinephrine induces phenotype changes of the cardiomyocyte, fibrosis and β-adrenergic signal transduction defects implicated in the dysregulation of contractility. Renal denervation reduces left ventricular hypertrophy and improves diastolic dysfunction, partly blood pressure independently. Also, exercise tolerance and cardiac arrhythmias are positively influenced. Furthermore, there is evidence that common comorbidities like sleep apnoea, metabolic disease and microalbuminuria are improved following renal denervation. The available evidence suggests performing randomised controlled trials to scrutinise whether renal sympathetic denervation might be able to improve morbidity and mortality in chronic heart failure with preserved or reduced ejection fraction.

Effect of beta-adrenoceptor antagonist and angiotensin-converting enzyme inhibitor on hypertension-associated changes in adenylyl cyclase type V messenger RNA expression in spontaneously hypertensive rats

Adenylyl cyclase (AC) messenger RNA (mRNA) expression is decreased in failing hearts. Diminished expressions are accompanied by desensitization of beta-adrenergic signal transduction. Factors contributing to such changes in mRNA expression for the major myocardial isoform AC V are not well established. To assess the contributions of hypertension, left ventricular hypertrophy (LVH), the renin-angiotensin-aldosterone system (RAS), and the sympathetic nervous system to these changes, ventricular expression of AC V mRNA was measured at different ages in spontaneously hypertensive rats (SHRs). In addition, the effects on them of angiotensin-converting enzyme inhibitor and beta-adrenoceptor antagonists were determined. Prior to quantitative Northern blotting at ages 5, 9, or 12 weeks, hemodynamic and morphologic variables were measured in SHRs and Wistar-Kyoto rats (WKYs). The SHRs and WKYs were treated with an angiotensin-converting enzyme inhibitor, enalapril (10 mg/kg/d), or a beta(1)-adrenoceptor antagonist, atenolol (100 mg/kg/d), for 8 weeks preceding Northern analysis. Myocardial AC V mRNA expression increased from 5-12 weeks in both SHRs and WKYs. Expression of AC V mRNA in SHRs increased somewhat less than in WKYs at 9 weeks and significantly less at 12 weeks. This was accompanied by development of LVH and hypertension in SHRs. Blood pressure and left ventricular weight relative to body weight were markedly decreased by enalapril and were moderately decreased by atenolol. Expression of AC V mRNA in SHRs at 12 weeks was normalized equally by enalapril and atenolol to the level of WKYs. Thus AC V mRNA expression increases are blunted in the early stages of LVH in SHRs under the influences of beta(1)-adrenergic signal transduction and the RAS.

Alpha-adrenergic signal transduction in renin transgenic rats

The alpha1-adrenoceptor-G protein-phosphoinositide-specific phospholipase C (PLC) signal transduction pathway is assumed to play an important role in the regulation of contractile force and in the pathophysiology of myocardial hypertrophy. In the present study, the components of this pathway were investigated in left ventricles of hearts from hypertensive transgenic rats overexpressing the mouse renin gene [TG(mREN2)27] in comparison to age- and weight-matched Sprague-Dawley control rats. Contractile force was assessed in isolated electrically driven left ventricular papillary muscle strips. Alpha1-adrenoceptor density was measured by radioligand binding using [3H]prazosin, steady state levels of alpha q/11, and G protein beta-subunits by Western blotting. PLC activity was determined by a cell-free assay using exogenous phospholipid vesicles containing [3H]phosphatidylinositol (4,5)-bisphosphate as a substrate. Alpha1-adrenoceptor density was significantly increased (by 80%) in transgenic rats compared with control rats, while the positive inotropic response to the alpha1-adrenoceptor agonist phenylephrine was significantly reduced, suggesting a postreceptor defect in TG(mREN2)27. The expression of alpha q and alpha11 was verified by reverse transcription-polymerase chain reaction, and alpha q/11 steady state protein levels were shown to be similar in transgenic and control rats. Western blotting using a beta-common antibody revealed two bands at approximately 35 and 36 kD. The quantities of both were similar in TG(mREN2)27 compared with those in control rats. In contrast, PLC activity was significantly reduced (by 32%) in transgenic rats. In conclusion, our findings are consistent with a desensitization of the alpha1-adrenergic signal transduction pathway at the level of the effector.

Myocardial alpha1-adrenoceptor: inotropic effect and physiologic and pathologic implications

Alpha1-adrenergic receptors have been found in myocardium of all mammalian species. Although the exact underlying mechanisms have not been conclusively determined, it would appear that the myocardial effects of alpha1-adrenoceptors may vary in importance according to the pathophysiologic process involved. In physiological conditions, this receptor system plays a role in cardiac growth, cardiac contraction, and has both an antiarrhythmic function as well as a role in cardiac adaptation to various situations. This system is also involved in some pathological processes such as ischemia/reperfusion, ischemic preconditioning, and cardiac hypertrophy. The role of alpha1-adrenoceptors in heart failure is somewhat controversial. Experimental evidence suggests that myocardial alpha1-adrenoceptors can have either beneficial or deleterious effects on the heart. It thus seems possible that the development of agents specific to certain subtypes of alpha1-adrenoceptor and a better understanding of their role in pathophysiologic states could be clinically relevant.

Adrenoceptors in SHR: alterations in binding characteristics and intracellular signal transduction pathways

There is much data on altered adrenoceptor function in the heart, blood vessel and kidney from spontaneously hypertensive rats (SHR). The enhancement of vascular and renal alpha-adrenoceptor function, i.e. vasoconstriction and retention of water and sodium, may contribute to the development and maintenance of the hypertension, whereas cardiac alpha1-adrenoceptor may be of minor physiological significance. Alpha1-adrenoceptor-mediated signal transduction as a whole is increased in SHR vascular tissues, but the intracellular signaling per receptor in the kidney seems to be decreased despite increased alpha1-adrenoceptor density. On the other hand, cardiac and vascular beta-adrenoceptor responsiveness is attenuated in SHR. Reduced vasorelaxation mediated by beta-adrenoceptors may also contribute to high blood pressure. The impaired cardiovascular beta-adrenoceptor function in SHR does not appear to be necessarily explained by alterations observed at receptor levels. Alterations in signal transduction should be also considered. Limited data on renal beta-adrenoceptor density and its signaling suggest decreased or unaltered cyclic AMP formation per receptor in SHR. We will review alterations in both binding characteristics and each component of intracellular signal transduction pathways in cardiovascular and renal adrenoceptors of SHR.

Peripheral adrenergic receptors in hypertension

Increased sympathoadrenal activity appears to play an important role in the development or maintenance of elevated blood pressure in hypertensive patients and various animal models of hypertension. Alterations of adrenergic receptor number or responsiveness might contribute to this increased activity. We therefore reviewed the data on adrenergic receptor alterations in hypertension with special emphasis on several key cardiovascular tissues (i.e., heart, vascular smooth muscle, and kidney) and on lymphocytes and platelets as human tissues available for such studies. The data suggest that the number of alpha-adrenergic receptors in hypertension is regulated by catecholamines, dietary salt intake, and genetic factors. Increases in renal alpha-adrenergic receptor number may be etiologic in genetic forms of essential hypertension. beta-Adrenergic receptor alterations in states of elevated blood pressure do not appear to be specific for genetic hypertension. Desensitization of beta-adrenergic receptor function in hypertensive animals and patients contrasts with reports of decreased, unchanged, and increased beta-adrenergic receptor number, suggesting that signal transduction of beta-adrenergic (and possibly other) receptors that stimulate adenylyl cyclase is disturbed in hypertension. The mechanisms of such heterologous desensitization in states of elevated blood pressure remain to be elucidated.

Adrenoceptors in experimental hypertension

Cardiac, aortic and renal alpha- and beta-adrenoceptors were examined in three types of experimental hypertension in rats. In spontaneously hypertensive rats (SHR), cardiac alpha 1-adrenoceptor concentration was increased and cardiac and aortic beta-adrenoceptor concentrations were decreased compared with Wistar-Kyoto rats (WKY). A similar decrease in cardiac beta-adrenoceptor concentration was also shown in two-kidney, one clip (2K, 1C) and deoxycorticosterone acetate(DOCA)-salt hypertensive rats. Renal alpha 1- and alpha 2-adrenoceptor concentrations were increased in SHR, but not in 2K, 1C and DOCA-salt hypertension. In contrast, renal beta-adrenoceptor concentration was increased in 2K, 1C and DOCA-salt hypertension, but unchanged in SHR. The observed increase in cardiac alpha 1- and renal alpha 2-adrenoceptor concentrations may partly contribute to the elevation of blood pressure in SHR.

[Cardiac effects of adenosine. Mechanism of action, pathophysiologic and clinical significance]

Adenosine has a negative inotropic effect in cardiac atrial preparations ("direct" negative inotropic effect). This effect is probably due to an activation of a potassium outward current which shortens the action potential duration and hence reduces the force of contraction. A pertussis toxin-sensitive N-protein is involved in the signal transduction from the adenosine receptor to atrial potassium channels. In ventricular cardiac preparations adenosine has no negative or even a weak positive inotropic effect, but it reduces the force of contraction in the presence of cAMP-increasing agents such as isoprenaline ("indirect" negative intropic effect). This effect is due to an inhibition of the slow Ca2+ inward current which has previously been enhanced by an increase in the cellular cAMP content. This "indirect" negative inotropic effect of adenosine is also present in the human heart. Since increased amounts of adenosine are released during cardiac stimulation via beta-adrenoceptors, the "indirect" effect might protect the heart against excessive stimulation by catecholamines. In addition, adenosine has negative chronotropic actions and prolongs AV conduction by an activation of potassium channels or an inhibition of the slow Ca2+ inward current (AV node). Cardiac bradyarrhythmias in hypoxia have been attributed to an increased formation and release of adenosine. Furthermore, adenosine has been shown to terminate supraventricular tachycardias involving the AV node. Since it has a very short duration of action it might prove safe and hence advantageous to conventional therapy in the treatment of supraventricular tachycardias.