Propranolol and beta-adrenergic receptor blocking drugs in the treatment of hypertension

Screening for Serotonin Receptor 4 Agonists Using a GPCR-Based Sensor in Yeast

More than 30% of all pharmaceuticals target G-protein-coupled receptors (GPCRs). Here, we present a GPCR-based screen in yeast to identify ligands for human serotonin receptor 4 (5-HTR₄). Serotonin receptor 4 agonists are used for the treatment of irritable bowel syndrome with constipation. Specifically, the HTR₄-based screen couples activation of 5-HTR₄ on the yeast cell surface to luciferase reporter expression. The HTR₄-based screen has a throughput of one compound per second allowing the screening of more than a thousand compounds per day.

The sympathetic/beta-adrenergic pathway mediates irisin regulation of cardiac functions in zebrafish

Irisin is a 23 kDa myokine encoded in its precursor, fibronectin type III domain containing 5 (FNDC5). The exercise-induced increase in the expression of peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1-α) promotes FNDC5 mRNA, followed by the proteolytic cleavage of FNDC5 to release irisin from the skeletal or cardiac muscle into the blood. Irisin is abundantly expressed in skeletal and cardiac muscle and plays an important role in feeding, modulates appetite regulatory peptides, and regulates cardiovascular functions in zebrafish. In order to determine the potential mechanisms of acute irisin effects, in this research, we explored whether adrenergic or muscarinic pathways mediate the cardiovascular effects of irisin. Propranolol (100 ng/g B·W) alone modulated cardiac functions, and when injected in combination with irisin (0.1 ng/g B·W) attenuated the effects of irisin in regulating cardiovascular functions in zebrafish at 15 min post-injection. Atropine (100 ng/g B·W) modulated cardiovascular physiology in the absence of irisin, while it was ineffective in influencing irisin-induced effects on cardiovascular functions in zebrafish. At 1 h post-injection, irisin downregulated PGC-1 alpha mRNA, myostatin-a and myostatin-b mRNA expression in zebrafish heart and skeletal muscle. Propranolol alone had no effect on the expression of these mRNAs in zebrafish and did not alter the irisin-induced changes in expression. At 1 h post-injection, irisin siRNA downregulated PGC-1 alpha, troponin C and troponin T2D mRNA expression, while upregulating myostatin a and b mRNA expression in zebrafish heart and skeletal muscle. Atropine alone had no effects on mRNA expression, and was unable to alter effects on mRNA expression of siRNA. Overall, this research identified a role for the sympathetic/beta-adrenergic pathway in regulating irisin effects on cardiovascular physiology and cardiac gene expression in zebrafish.

Dissection of heterocellular cross-talk in vascularized cardiac tissue mimetics

Cellular specialization and interaction with other cell types in cardiac tissue is essential for the coordinated function of cell populations in the heart. The complex interplay between cardiomyocytes, endothelial cells and fibroblasts is necessary for adaptation but can also lead to pathophysiological remodeling. To understand this complex interplay, we developed 3D vascularized cardiac tissue mimetics (CTM) to study heterocellular cross-talk in hypertrophic, hypoxic and fibrogenic environments. This 3D platform responds to physiologic and pathologic stressors and mimics the microenvironment of diseased tissue. In combination with endothelial cell fluorescence reporters, these cardiac tissue mimetics can be used to precisely visualize and quantify cellular and functional responses upon stress stimulation. Utilizing this platform, we demonstrate that stimulation of α/β-adrenergic receptors with phenylephrine (PE) promotes cardiomyocyte hypertrophy, metabolic maturation and vascularization of CTMs. Increased vascularization was promoted by conditioned medium of PE-stimulated cardiomyocytes and blocked by inhibiting VEGF or upon β-adrenergic receptor antagonist treatment, demonstrating cardiomyocyte-endothelial cross-talk. Pathophysiological stressors such as severe hypoxia reduced angiogenic sprouting and increased cell death, while TGF β2 stimulation increased collagen deposition concomitant to endothelial-to-mesenchymal transition. In sum, we have developed a cardiac 3D culture system that reflects native cardiac tissue function, metabolism and morphology - and for the first time enables the tracking and analysis of cardiac vascularization dynamics in physiology and pathology.

The right drug and the right dose

The goal of antihypertensive treatment is to reduce both blood pressure and other risk factors for cardiovascular disease. There are currently six major classes of antihypertensive drugs that are available for the initial lowering and maintenance of blood pressure, including beta-blockers, alpha-adrenoceptor blockers, calcium channel blockers, diuretics, angiotensin-converting enzyme inhibitors and angiotensin-II receptor antagonists. All these classes of antihypertensive drugs are equally effective in reducing high blood pressure. To select the right antihypertensive drug, characteristics other than efficacy should be used to distinguish the different classes. According to the Sixth Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure, the selection of initial antihypertensive drug should consider patient risk-factor profile and co-morbidity, as well as the safety and tolerability profile of the drug. When these factors are considered, an effective and well-tolerated drug regimen can be tailored to an individual patient. An initial drug regimen should consist of a low dose of a long-acting, once-daily drug that is titrated upward if blood pressure is not adequately controlled. Low-dose combinations of two antihypertensive drugs may also be considered. Results from comparative studies with different classes of antihypertensive drugs suggest that different populations of patients, such as those with diabetes, left-ventricular dysfunction, or lipid disorders, may benefit from taking different antihypertensive drugs.

A risk-benefit assessment of carvedilol in the treatment of cardiovascular disorders

Carvedilol is a nonselective beta-adrenoceptor blocking vasodilator drug that may be a promising new agent in the management of cardiovascular disease. The rationale for the development of agents of this type is that the alpha-blocking component may overcome the direct vasoconstrictor consequence of beta 2-blockade, whilst the beta-blocker component may inhibit the reflex tachycardia that occurs following alpha-blockade. In clinical trials published to date, carvedilol has been demonstrated to be effective as an antihypertensive agent as monotherapy and also as additional therapy in those patients whose blood pressure cannot be controlled on other standard agents. It is also effective in the management of angina. Carvedilol has beneficial haemodynamic effects in patients with congestive heart failure. beta-Blocker vasodilator drugs of this type may be particularly useful in this condition as the vasodilator component of the drug may overcome the initial negative inotropy of the beta-blocker. In addition, carvedilol possess potentially useful pharmacological actions. In particular, the drug has antimitogenic and free radical scavenging effects that may make it a useful therapy in the long term management of atherosclerotic vascular disease. Its metabolic profile is also favourable, presumably on the basis of its alpha-blocking properties. Thus, beta 2-mediated adverse effects on peripheral vascular tone, glycaemic control and lipid status appear to be offset by the alpha-blocking property of the drug. Carvedilol thus far appears to be well tolerated, with postural dizziness the major adverse effect, especially in the elderly. As with nonselective beta-blockers, carvedilol is contraindicated in patients with asthma.

A risk-benefit assessment of celiprolol in the treatment of cardiovascular disease

Celiprolol is a third-generation beta-adrenoceptor blocker with selective beta 1-antagonist, partial beta 2-agonist and mild alpha 2-antagonist actions. It seems to be as effective as other beta-blockers in the treatment of hypertension and angina pectoris. beta-Blockers have many cardioprotective effects and have been shown to reduce the morbidity and mortality from coronary artery disease in a number of trials. However, there is no good clinical evidence that celiprolol itself has specific cardioprotective properties other than those attributable to this class of drugs. Because of its pharmacological profile, celiprolol is less likely to cause bradycardia, deterioration in cardiac function and other adverse effects mainly caused by beta 2-blockade. Unlike most other beta-blockers, celiprolol has no adverse effects on plasma lipids. It seems to be well tolerated in diabetic patients and patients with renal dysfunction.

Multicenter evaluation of the hemodynamic effects of bisoprolol in patients with mild to moderate hypertension

Twenty-six patients with mild-to-moderate essential hypertension participated in a 6-week outpatient, multicenter, randomized, double-blind, placebo-controlled two-way crossover study to assess the hemodynamic effects of bisoprolol (20 mg QD) at steady state. Hemodynamic assessments included sitting blood pressure, heart rate, and left-ventricular ejection fraction by radionuclide ventriculography after 7 days of bisoprolol or placebo at trough (24 h post-dose) and peak (3 h post-dose) values. The group adjusted mean ejection fraction was not significantly different in patients receiving bisoprolol compared with the placebo group at either peak or trough measurements; in fact, means in patients taking bisoprolol were slightly higher than in the placebo group. No symptomatic hypotension was documented. Blood pressure, measured 24 hours after dosing, was significantly lower in those receiving bisoprolol when compared with the placebo group, by 7.7 mm Hg and 9 mm Hg for diastolic and systolic blood pressure, respectively. Similarly, mean values of heart rate were 10 beats/min lower in the bisoprolol patients than in the placebo group. Only headache and insomnia occurred as adverse events. Bisoprolol (20 mg QD) effectively lowered blood pressure over a 24-hour period without significantly reducing ejection fraction or causing adverse clinical or biochemical events.

Effects of long-acting propranolol on blood pressure and heart rate in hypertensive Chinese

In a double-blind, balanced and randomised study we used treadmill exercise to assess the effects of long-acting propranolol (LA propranolol) 160 or 320 mg or placebo, given once daily for 4 weeks, on heart rate (HR) and blood pressure (BP) in 15 Chinese subjects with mild primary hypertension (PHT). We used 24 h ECG monitoring to assess drug effects on HR. Another 18 patients were similarly assessed without exercise. Steady-state plasma propranolol concentrations after LA propranolol 160 and 320 mg were comparable to those after ordinary propranolol 80 and 160 mg daily measured in 11 and 12 separate patients. LA propranolol 160 and 320 mg reduced HR and BP before and during vigorous exercise. LA propranolol 160 and 320 mg reduced HR for 17.6 and 21.4 h of the day, and 320 mg significantly reduced the mean 24 h HR, and the mean maximum HR. The drug effects on BP and HR, and the average plasma propranolol levels after LA propranolol were similar to those reported in European subjects.

Combined alpha- and beta-receptor inhibition in the treatment of hypertension

Both beta- and alpha-adrenergic mechanisms are important in the control of blood pressure; alpha-mediated vasoconstriction is responsible for the regulation of vascular tone, and beta-mediated responses stimulate the heart directly and indirectly by liberating renin and affecting vascular smooth muscle tone. beta-Adrenergic blocking drugs have long been established in the treatment of hypertension. The development of drugs which combine this action with an alpha-blocking effect represents an additional mode of action to lower the blood pressure. Numerous studies have demonstrated that labetalol intravenously or orally gives a rapid fall of blood pressure in essential and renal hypertension. It has also been used intravenously in phaeochromocytoma, tetanus, clonidine withdrawal, and as an adjunct to halothane to produce hypotensive anaesthesia. Intravenously, labetalol is probably best given as a graded infusion or as repeated small bolus injections to assure a smooth fall of blood pressure. Many long term studies have shown it to be effective orally in prolonged treatment of hypertension with studies of over 5 years, showing that tolerance does not develop. Labetalol can be used in combination with diuretics and other drugs when necessary. It can be employed to control the blood pressure in all grades of hypertension. A dosage of 100mg twice daily will often be adequate to control mild hypertension and the use of even lower doses has been reported. However, the dosage can be markedly increased in severe hypertension and while such doses are relatively exceptional, several trials have employed over 2 g per day for the more resistant cases. Studies have demonstrated that blood pressure control with labetalol is equivalent to that with beta-adrenoceptor blocking drugs plus vasodilators, or methyldopa. Labetalol has been used in patients with severe renal impairment and a number of studies suggest that it may now be the drug of choice in raised blood pressure of pregnancy. Side effects can be divided into those related to beta-blockade, those related to alpha-blockade and those not clearly related to either effect. It has been suggested that the side effects attributable to the beta-blocking component are less obtrusive than those seen with pure beta-blocking drugs without alpha-activity because the alpha-blockade modifies the consequences of beta-blockade. Heart failure has been reported, but for haemodynamic reasons would be expected to be less common; careful patient selection should avoid any risk. Similarly labetalol may worsen asthma even if the risks are probably less than with non-selective beta-blockade alone.(ABSTRACT TRUNCATED AT 400 WORDS)