Haemorheological, platelet and endothelial factors in essential hypertension

The role of exercise in the reversal of IGF-1 deficiencies in microvascular rarefaction and hypertension

Hypertension has been linked with peripheral and central reductions in vascular density, and with devastating effects on brain function. However, the underlying mechanisms in the relationship between blood pressure and cognitive impairment have yet to be fully elucidated. Here, we review compelling evidence from two lines of inquiry: one that links microvascular rarefaction with insulin-like growth factor 1 (IGF-1) deficiencies, and another which posits that vascular dysfunction precedes hypertension. Based on the findings from experimental and clinical studies, we propose that these lines of evidence converge, and suggest that age-related declines in IGF-1 concentrations precede microvascular rarefaction, initiate an increase in vascular resistance, and therefore are causally linked to onset of hypertension. Physical exercise provides a relevant model for supporting our premise, given the well-established effects of exercise in attenuating vascular dysfunction, hypertension, IGF-1 deficiency, and cognitive decline. We highlight here the role of exercise-induced increases in blood flow in improving vascular integrity and enhancing angiogenesis via the actions of IGF-1, resulting in reversal of rarefaction and hypertension, and enhancement of cerebral blood flow and cognition.

Haemostatic factors, lipoproteins and long-term mortality in a multi-ethnic population of Gujarati, African-Caribbean and European origin

OBJECTIVES

To examine the relations between haemostatic factors and lipoproteins with mortality in British Europeans, African-Caribbeans (AfC) and Gujarati Indians.

METHODS

A prospective cohort study of 331 subjects (40-79 years), followed-up over 26 years for mortality. Apolipoprotein-A1 (Apo-A1), apolipoprotein-B (Apo-B), factor VII coagulant activity (FVIIc), fibrinogen and von Willebrand Factor (vWF) were measured at baseline in 118 Europeans, 100 AfC and 113 Gujaratis. Aortic pulse wave velocity (aPWV) was measured in 174 participants.

RESULTS

147 (44.4%) subjects died during a median of 24 years follow-up with 69 cardiovascular deaths. Women at baseline had higher, and AfC males the lowest FVIIc and Apo-A1 levels. Baseline age-sex and ethnicity adjusted FVIIc levels were higher in those who died (131.0 vs. 117.4%; P = 0.048). In similarly adjusted partial correlations, Apo-A1 was inversely related to arterial stiffness (ρ = -0.23, P = 0.04). Over the 26 years follow-up, participants below the median (i.e. with lower concentration) of FVIIc, Fibrinogen, Apo-B and vWF had better survival rates than those with higher concentrations; those with higher concentrations of Apo-A1 had better survival. In Cox multivariable regression analyses including sex, ethnicity and aPWV, independently increased risk of all-cause mortality came only from SBP (per 5 mmHg); P = 0.011), age (per year); P < 0.0001 and FVIIc at 7% (per 10-unit; HR 1.07 (1.02, 1.12); P = 0.008. Separately, Apo-A1 (HR 0.12 (0.02, 0.75; P = 0.029) was independently associated with a very significant 88% reduction in all-cause mortality.

CONCLUSIONS

Despite a relatively small sample size, long-term follow-up suggests an independent effect of the prothrombotic state (via FVIIc) and apo-A1 (a constituent of HDL) on mortality.

How a Damaged Blood Vessel Wall Contibutes to Thrombosis and Hypertenasion

In order to maintain an anticoagulant nature, the healthy endothelium secretes factors such as tissue plasminogen activator, ADPase, and expresses membrane thrombomodulin. However, when damaged, it releases increased amounts of pro-coagulants such as von Willebrand factor. Similarly, the healthy endothelium uses nitric oxide, prostacyclin and other molecules to help maintain normal blood pressure, and these molecules also inhibit platelet activity. But a dysfunctional endothelium fails to produce these vasodilators so that vasospasm and hypertension can result. Thus the (damaged/dysfunctional) endothelium can contribute to Virchow's triad by failing to maintain an anticoagulant surface and in failing to correctly regulate blood pressure, factors that are likely to promote thrombosis and hypertension.

Association Between Factor VII Polymorphisms and Blood Pressure

The purpose this study was to determine whether Arg353Gln and −323Del/Ins polymorphisms of factor VII (FVII) are related to blood pressure levels and hypertension. Subjects were drawn from the Stanislas Cohort, a longitudinal, familial French cohort examined twice since 1994. The “blood pressure study” included 1342 subjects free of medication use that could affect blood pressure. The “hypertension study” included 645 normotensive and 77 hypertensive adult subjects. Association with hypertension was also studied in 547 hypertensives enrolled in a clinical trial and in 624 normotensives drawn from the Stanislas Cohort. In the “blood pressure study,” parents with the 353Gln or −323Ins allele had lower blood pressures than did noncarriers at each examination, independent of covariates (0.01≤ P ≤0.05, except for diastolic blood pressure [DBP] at baseline, where P =0.103). Similarly significant relations were observed in their offspring ( P ≤0.05, except for systolic blood pressure [SBP] at 5 years, where P =0.186). In a representative subgroup of 267 individuals, the −323Del/Ins polymorphism was significantly associated with plasma FVII levels in both parents and offspring ( P <0.001). FVII levels in plasma were significantly correlated with SBP and DBP in parents but not in offspring. After inclusion of both FVII levels and the −223Del/Ins in the same model in parents, only FVII levels remained significantly associated with SBP and DBP. The “hypertension study” revealed that the 353Gln and −323Ins alleles were related to decreased risk (odds ratio [OR]=0.554, 95% confidence interval [CI], 0.362 to 0.848, and OR=0.475, 95% CI, 0.299 to 0.755, respectively). These results suggest that the FVII gene may be a susceptibility locus for hypertension.

Capillary rarefaction and abnormal cardiovascular reactivity in hypertension

OBJECTIVE

To determine the effects of capillary rarefaction on cardiovascular reactivity and microcirculatory functioning in essential hypertension.

DESIGN

Hypertension is associated with abnormal cardiovascular reactivity and increased vasoconstriction. Capillary rarefaction amplifies these abnormalities, which modify microcirculatory hemodynamics. Hence this study of the hemorheological pattern and the veno-arteriolar reflex in hypertensive patients and normotensive control subjects.

METHODS

Sixty-one men with never-treated essential hypertension and capillary rarefaction (< 80 capillaries per field) and 20 age-matched and sex-matched controls underwent a strenuous cycle ergometer test to monitor, during exercise and recovery, the blood pressure profile and the hemorheological pattern: blood viscosity at low shear, hematocrit and leukocyte counts, soluble P-selectin levels, and red and white blood cell filterability rates. The veno-arteriolar reflex was determined by laser-Doppler flowmetry before exercise and at recovery.RESULTS Hypertensive men with < or = 72 capillaries per field had an abnormal hemorheological profile before exercise. The physiological response to exercise was observed only in the controls and in hypertensives with > or = 73 capillaries per field. Abnormal responses to exercise worsened as capillaries were more rarefied. At recovery, hemorheological parameters in hypertensives with 65-72 capillaries per field returned to baseline, remaining significantly (P < 0.05) different to control values. Variations in the hemorheological pattern in hypertensives with < 64 capillary per field persisted at recovery. The veno-arteriolar reflex followed the same pattern.

CONCLUSION

A reduced microvascular network may contribute to abnormal cardiovascular reactivity and to exercise-induced rheological abnormalities in hypertension.

[Hypertensive heart disease and microangiopathy]

Cardiac alterations in patients with arterial hypertension comprise the manifestation of stenosis in epicardial arteries, disease of coronary resistive vessels, prothrombotic changes and endothelial dysfunction, pronounced perivascular and interstitial fibrosis, left ventricular hypertrophy, dilatation of the left atrium, increased sympathetic drive and degeneration of aortic valve. These alterations leads to the major clinical manifestations of hypertensive heart disease, that are symptoms of reduced coronary conductance, left ventricular hypertrophy, diastolic and systolic dysfunction with or without left ventricular enlargement and arrhythmia. Different non-invasive and invase procedures are available for screening and follow up of patients with hypertensive heart disease. The primary therapeutic target is, apart from lowering blood pressure, to reverse cardiac manifestations of arterial hypertension using specific therapeutic algorithms.

Management of the hypertensive patient with coronary insufficiency but without atherosclerosis

Arterial hypertension is a major risk factor for the clinical syndrome of angina pectoris, in which the ECG is abnormal but the coronary arteries are normal. Structural and functional abnormalities in coronary circulation as well as extravascular factors (eg, left-ventricular hypertrophy, fibrosis with diastolic dysfunction) compromise the adequate ratio of coronary blood flow to oxygen demand causing angina, dyspnea, and major cardiac events. Recent studies stress the importance to functional disturbances of coronary microvasculature leading to profound morphologic changes associated with impaired coronary conductance. In patients without epicardial coronary stenosis hypertensive microvascular disease can be qualitatively assessed by noninvasive diagnostic approaches based on new Doppler echocardiography techniques and may also be monitored by widely available stress tests. For ultimate quantitative assessment, invasive procedures are still required. Beyond guidelines to control blood pressure in hypertensive individuals, restoration of functional and structural integrity of the coronary microvasculature represents the ultimate therapeutic goal in hypertensive patients with coronary insufficiency and without angiographic evidence of atherosclerosis. Concomitant factors reducing coronary conductance such as left-ventricular hypertrophy and diastolic dysfunction should be reversed in parallel. Currently, therapeutic intervention in the renin-aldosterone-angiotensin-II-system using ACE inhibitors, angiotensin receptor blockers, and low doses of aldosterone antagonists represent the most promising strategy to achieve these goals. Using the knowledge of these recent results we should refine the overall management of our hypertensive patients with coronary insufficiency but without atherosclerosis.