The role of antihypertensive drugs in counteracting adverse influence on large arteries

Potential Protective Role of Blood Pressure-Lowering Drugs on the Balance between Hemostasis and Fibrinolysis in Hypertensive Patients at Rest and During Exercise

In patients with hypertension, the triad represented by endothelial dysfunction, platelet hyperactivity, and altered fibrinolytic function disturbs the equilibrium between hemostasis and fibrinolysis and translates into a hypercoagulable state, which underlies the risk of thrombotic complications. This article reviews the scientific evidence regarding some biological effects of antihypertensive drugs, which can protect patients from the adverse consequences of hypertensive disease, improving endothelial function, enhancing antioxidant activity, and restoring equilibrium between hemostatic and fibrinolytic factors. These protective effects appear not to be mediated through blood pressure reduction and are not shared by all molecules of the same pharmacological class.

The effects of low calcium dialysate on arterial compliance and vasoactive substances in patients with hemodialysis

BACKGROUND

Considering that dialysate calcium concentration is potentially a main determinant of the serum ionized calcium level and vasoconstriction is associated with the blood calcium concentration, we conducted a study to evaluate the interdialytic effects of treatment with a low calcium dialysate (LdCa, 1.25 mmol/L) on the changes in arterial compliance (AC), blood pressure (BP), biochemical parameters and vasoactive substances.

METHODS

Eight hemodialysis (HD) patients (mean age: 46.8 +/- 13.7 years, 4 men and 4 women) were included in the study. AC, systolic blood pressure (SBP), diastolic blood pressure (DBP), pulse pressure (PP), mean arterial pressure (MAP), serum ionized Ca, intact-PTH, serum nitric oxide and aldosterone were compared after 10 sessions of treatment with LdCa. Right carotid artery diameter was measured 3 times using a real time B-mode ultrasound imager (Hewlett-Packard Sonos 2000) and AC was calculated using the Hayoz method.

RESULTS

1) AC was recorded as 0.140 (0.080-0.170) mm2/kPa at the baseline (1.75 mmol/L calcium dialysate), 0.170 (0.050-0.290) mm2/kPa after LdCa treatment (p < 0.05 versus baseline), and 0.140 (0.070-0.250) mm2/kPa following the HdCa treatment (p < 0.05 versus LdCa data). 2) MAP and PP were calculated at 114.12 +/- 10.56 mmHg and 63.50 +/- 10.87 mmHg at the baseline; 98.37 +/- 15.14 mmHg and 56.50 +/- 5.95 mmHg after LdCa treatment (p < 0.05 versus baseline); and 115.75 +/- 9.64 mmHg and 62.00 +/- 15.71 mmHg following HdCa treatment (p < 0.05 versus LdCa data). 3) Serum ionized Ca and intact-PTH were measured at 4.66 +/- 0.40 mg/dL and 25.08 +/- 16.44 pg/mL at the baseline; 4.45 +/- 0.28 mg/dL and 90.71 +/- 27.03 pg/mL after LdCa treatment (p < 0.05 versus baseline); and 4.65 0.43 mg/dL and 24.08 +/- 15.44 pg/mL following HdCa treatment (p < 0.05 versus LdCa data). 4) Serum aldosterone concentration was 300.8 (65.5-836.1) pg/mL at the baseline, and 220.2 (42.8-527.9) pg/mL after LdCa treatment (p < 0.05).

CONCLUSION

There were favorable changes in AC, BP, biochemical parameters after treatment with LdCa. These changes may be associated with the reduction in serum ionized calcium and decreased serum aldosterone concentration.

Intradialytic and interdialytic effects of treatment with 1.25 and 1. 75 Mmol/L of calcium dialysate on arterial compliance in patients on hemodialysis

Arterial compliance (AC) is an important determinant of vascular structure, and abnormalities of AC can greatly affect the cardiovascular system. Given the vasoconstrictive properties of increased levels of serum ionized calcium (iCa), we investigated the way that dialysate calcium level can influence AC in the hemodialysis (HD) population. In a crossover randomized design, 19 dialysis patients undergoing regular bicarbonate HD (three times weekly) underwent two cycles of four successive HD sessions each with a low (LdCa; 1.25 mmol/L) and high dialysate calcium concentration (HdCa; 1.75 mmol/L). At the fourth session of each cycle, iCa level and hemodynamic parameters (systolic blood pressure [SBP], diastolic blood pressure, mean arterial pressure [MAP], pulse pressure [PP], heart rate, and AC) were measured pre-HD and post-HD. AC was measured noninvasively at the brachial artery by arterial pulse waveform analysis. The dialysate calcium level was a significant determinant of both pre-HD (r = 0.335; P < 0.05) and post-HD iCa level (r = 0.767; P < 0.001). Pre-HD AC increased significantly (P < 0.05) by 0.01+/- 0.02 mL/mm Hg (7% +/- 19%) on switching from HdCa to LdCa treatment. Multiple regression analysis showed that both pre-HD PP and iCa level were major inverse determinants of pre-HD AC in both the LdCa (R(2) = 0.65; P < 0.001) and HdCa (R(2) = 0.51; P < 0.01) treatment groups. AC increased by 32% (P < 0.01) and 37% (P < 0.05) during LdCa and HdCa dialysis, respectively. Intradialytic changes in AC were inversely correlated with changes in SBP and PP. In the HdCa group, changes in iCa level related significantly to MAP (r = 0.464; P < 0.05). The results show that changes in AC during HD are mainly mediated through concurrent changes of systemic hemodynamics, which are largely affected by dialysate calcium level through parallel changes in iCa level. Interdialytically, a significant, blood pressure-independent, inverse relationship between AC and iCa level exists. Therefore, HD with LdCa, by reducing the incidence of HD-induced hypercalcemia, may have a beneficial role in preventing the ongoing reduction of AC in HD patients and thus improving cardiovascular prognosis.

The importance of arterial compliance in cardiovascular drug therapy

Arterial compliance, defined as a change in dimension in response to a given change in stress, is becoming an increasingly important clinical parameter. Related concepts, such as distensibility, elasticity, and stiffness, and more traditional concepts such as resistance, afterload, and impedance need to be differentiated from compliance, although they are frequently (inappropriately) used interchangably. Many studies cannot differentiate between compliance changes due to a drug's effect on blood pressure and those due to a drug's effect on vessel wall integrity. This differentiation is important because a more physiologic therapy, one that benefits pulsatile and nonpulsatile flow, should be of greater clinical benefit than a therapy that only lowers blood pressure. A number of methods have been used to estimate compliance, but to date there is no generally agreed-on best method. There also are no longitudinal studies that relate abnormal compliance and drug effects to outcome. Nonetheless, patients at risk from a variety of disease states, such as hypertension, diabetes mellitus, and hypercholesterolemia, may benefit from earlier recognition of abnormal compliance. Earlier recognition may lead to interventions that would reduce their risk. This review includes a discussion of compliance and related estimates of blood vessel function and attempts to summarize the data currently available regarding the effects of cardioactive drugs on arterial compliance.

The renin-angiotensin system and vascular hypertrophy

In addition to its vasoconstrictor and aldosterone-stimulating action, angiotensin II also drives cell growth and replication in the cardiovascular system, which may result in myocardial hypertrophy and hypertrophy or hyperplasia of conduit and resistance vessels in certain subjects. These actions are mediated through angiotensin II receptors (subtype AT1), which activate the G protein, phospholipase C, diacylglycerol and inositol trisphosphate pathway, to increase the expression of certain protooncogenes (c-fos, c-myc and c-jun) and growth factors (platelet-derived growth factor-A-chain, transforming growth factor-beta 1 and basic fibroblast growth factor). The cellular responses to angiotensin II in vascular smooth muscle have been shown in different hypertensive vessels to be either hypertrophy alone, hypertrophy and DNA synthesis without cell division (polyploidy) or DNA synthesis with cell division (hyperplasia). In genetic hypertension, the altered structure of small arteries is due to either cellular hyperplasia or remodeling, whereas in renovascular hypertension there is hypertrophy of vascular smooth muscle cells. Angiotensin II also increases synthesis of some matrix components, activates blood monocytes and is thrombogenic. Angiotensin-converting enzyme (ACE) inhibitors prevent or reverse vascular hypertrophy in animal models of hypertension; this seems to be a class effect, shared to some extent with calcium channel blocking agents. In human hypertension, ACE inhibitors reduce the increased media/lumen ratio of large and small arteries in hypertension and increase arterial compliance. These properties are also shared by losartan, the first of the new class of angiotensin II receptor (AT1) antagonists. The clinical implications of these findings need to be tested through rigorous and prospective clinical trials.

Acute changes in forearm haemodynamics produced by cigarette smoking in healthy normotensive non-smokers are not influenced by propranolol or pindolol

The aim of the present study was to examine the effect of cigarette smoking in healthy non-smokers on blood pressure and forearm haemodynamics after acute oral administration of non-selective beta-adrenoceptor blockers with and without intrinsic sympathomimetic activity, viz. pindolol 15 mg and propranolol 80 mg. A preliminary study was done to compare cigarette smoking and sham smoking to evaluate the time-course of the haemodynamic effects of cigarette smoking. The second experiment was then carried out in the same six volunteers, according to a double-blind randomized placebo-controlled crossover design, to evaluate the possible effect of pre-treatment with beta-adrenoceptor blockers on blood pressure, heart rate and forearm haemodynamics (forearm blood flow, brachial artery diameter and brachio-radial pulse-wave velocity) measured at baseline, during smoking and every five minutes up to 1 h afterwards. No major difference from placebo in blood pressure or forearm haemodynamics was found and pre-treatment with beta-blockers did not prevent the acute vascular effects of cigarette smoking.

Mechanical factors in large artery disease and antihypertensive drugs

Hypertension may induce early alterations in large arteries by 2 mechanical stresses: one related to intravascular pressure, the other to blood flow dynamics. Distending pressure force acts in a circumferential direction, inducing decreased arterial distensibility. Arterial distensibility can be evaluated in humans by measurement of arterial compliance and pulse-wave velocity. It is well established that in chronic hypertension age and elevated pressure act together to increase arterial rigidity. Blood flow dynamics induce frictional forces in the endothelial surfaces of arteries. These forces, expressed by shear stress, are proportional to the viscosity of the blood and to the velocity gradient at the arterial wall. Measurement of blood viscosity and evaluation of velocity profile in the brachial arteries of hypertensive subjects have shown a reduction in wall shear rate and stress despite the elevation in blood viscosity. Several studies have shown that drug therapy that successfully reduces blood pressure does not necessarily improve arterial compliance. In contrast, few data are available on the effects of antihypertensive medication on arterial wall shear in humans. Arterial compliance and wall shear stress are 2 main therapeutic targets of potential importance in the physiopharmacologic approach to the effects of hypertension on atherogenesis.

Relevance of intrinsic sympathomimetic activity for beta blockers

Intrinsic sympathomimetic activity (ISA) characterizes a group of beta blockers that are able to stimulate beta-adrenergic receptors (agonist effect) and to oppose the stimulating effects of catecholamines (antagonist effect) in a competitive way. Partial agonists are ligands that elicit a submaximal response when bound to beta receptors at maximal occupancy. In the isolated rat atrium, acebutolol produces a maximal stimulatory effect that is only 17 +/- 8% of the maximal effect induced by the full beta agonist isoproterenol. The presence of ISA results in less resting bradycardia and less of a reduction in cardiac output than is observed with beta blockers without ISA. In the long term, partial beta agonists may produce arterial vasodilation and increase arterial compliance, possibly leading to additional beneficial effects in the treatment of hypertension. beta blockers with ISA do not have adverse effects on plasma lipoproteins during long-term treatment; in addition, the presence of ISA could counteract the up-regulation of beta adrenoceptors often observed with beta blockers without ISA. Finally, the presence of ISA has been a conflicting issue for the use of such beta blockers in secondary prevention after myocardial infarction. However, the impressive results of the Acebutolol Prevention of Secondary Infarction trial in high-risk patients after myocardial infarction show that acebutolol, a beta blocker with moderate partial agonist activity, can be effective in decreasing the postinfarction mortality rate. By exhibiting a strikingly different hemodynamic profile from that of beta blockers without ISA, the partial beta agonists form an intriguing pharmacologic class of drugs for which prospective clinical trials should be extensively pursued.

Nicardipine monotherapy in ambulatory elderly patients with hypertension

The antihypertensive effect of nicardipine was evaluated in 89 ambulatory elderly patients with hypertension through a multicenter trial enrolling patients over the age of 65 years. After a baseline period during which they received placebo, subjects were randomized by an unbalanced assignment to a double-blind comparison of nicardipine (n = 57) and placebo (n = 32). The initial dose of nicardipine was 20 mg every 8 hours, which was then increased to 30 mg if needed. Blood pressure and heart rate were measured 1 and 8 hours after doses at each visit with subjects in both the supine and standing positions. Seventy-six per cent of patients who received nicardipine and 55% who received placebo responded (p less than 0.05). During standing, blood pressure did not decrease significantly from supine levels in either group, but a small, transient increase in heart rate occurred with nicardipine. Adverse reactions (apart from failure to respond) occurred in 8% of those who received nicardipine and 3% who received placebo. Three patients were withdrawn: two for symptoms, nausea, or flushing and one for transient and asymptomatic abnormalities on ECG. Nicardipine is effective and safe as monotherapy in elderly patients with hypertension, causing greater reduction in systolic than in diastolic pressure, but without orthostatic hypotension.