Paul Lijnen

Effect of endurance training on blood pressure at rest, during exercise and during 24 hours in sedentary men

The effect of 4 months of physical training on resting, exercise and 24-hour blood pressure (BP) was studied using a randomized crossover design in 26 healthy, sedentary men, with an average age of 39 +/- 10 (standard deviation) years. Peak oxygen uptake increased by 14% (p less than 0.001) and the physical working capacity at a heart rate of 130 beats/min by 25% (p less than 0.001). The heart rate was reduced by 7 beats/min at night (p less than 0.01) and by 6 beats/min during the day (p less than 0.001). Training-induced changes of BP varied according to measuring conditions. A decrease in BP at rest while sitting in the morning in the laboratory was significant for diastolic (-5 mm Hg, p less than 0.01) but not for systolic BP. During exercise, systolic BP was significantly lower after training, when measured at the same submaximal workloads. However, when workload was expressed as a percentage of peak oxygen uptake, systolic BP was not different before and after training. When measured during 24 hours, the training-induced change in BP was not significant at night either for systolic or diastolic BP. During the day the decrease in diastolic BP was significant (-5 mm Hg, p less than 0.001), but the change in systolic BP was not.

The relationship between blood pressure and sodium and potassium excretion during the day and at night.

Objective: The relationships between blood pressure and the urinary excretion rates of sodium and potassium during the day and at night were investigated. Methods: A total of 160 participants (135 normotensive subjects and 25 untreated patients with essential hypertension) were examined using ambulatory blood pressure monitoring and timed urine collections during waking and sleeping hours. Results: Blood pressure averaged 126/79 mmHg during waking hours and 107/62 mmHg during sleep. More sodium, potassium and aldosterone were excreted during the daytime, but the natriuretic substance kallikrein was excreted at a fixed rate throughout the 24 h. During waking hours there was poor correlation between blood pressure and urinary sodium and potassium excretion. By contrast, at night when the aldosterone: kallikrein ratio fell, the sodium and potassium excretion rates were positively correlated with blood pressure Conclusions: Pressure natriuresis, not apparent during waking hours, may be unmasked at night when the balance between sodium-retaining and sodium-losing mechanisms favours natriuresis. Thus, the relationship between blood pressure and 24-h sodium excretion, usually considered to show the influence of salt intake on blood pressure, may also reflect pressure-induced natriuresis, if urine is more completely collected at night than during the day, and in circumstances favouring sodium retention during the day and sodium loss during sleep

Body weight, sodium intake and blood pressure.

The aim of the present review is to examine the evidence that blood pressure may be reduced and hypertension prevented by decreasing body weight and sodium consumption. Cross-sectional and longitudinal population studies, and intervention studies in individual subjects, suggest that hypertension can be prevented by avoiding excessive weight. Children and adolescents should particularly avoid becoming overweight as this is strongly associated with hypertension in adult life. In contrast, the hypothesis that hypertension might be reduced by restricting sodium intake is less convincing. Moreover, the amount of sodium restriction needed to significantly reduce blood pressure might make it a less practical preventative measure in the struggle against hypertension than weight loss

Angiotensin II-stimulated collagen production in cardiac fibroblasts is mediated by reactive oxygen species

Objective The aim of the present study was to determine whether inhibition of reduced nicotinamide adenine dinucleotide (phosphate) [NAD(P)H] oxidase and of various superoxide generating systems could affect the collagen production, the mRNA and protein expression of collagen types I and III in control and angiotensin II-treated cardiac fibroblasts. Methods Cardiac fibroblasts from passage 2 from normal male adult rats were cultured to confluency and incubated in serum-free Dulbeccos modified Eagles medium for 24 h. The cells were then preincubated with(out) the tested inhibitors for 1 h and then further incubated with(out) angiotensin II (1 μmol/l) for 24 h. Collagen production was measured spectrophotometrically with picrosirius red as dye and with [3H]proline incorporation; collagen type I and III content by enzyme-linked immunosorbent assay and collagen type I and III mRNA expression by semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR). NAD(P)H-dependent superoxide anion production was assayed as superoxide dismutase-inhibitable cytochrome c reduction. Intracellular formation of reactive oxygen species was assessed with 2’,7’-dichlorofluorescein diacetate as fluorescent probe. Results Angiotensin II stimulated the collagen production, the collagen I and III content and mRNA expression in cardiac fibroblasts, and apocynin, a membrane NAD(P)H oxidase inhibitor, abolished this induction. Rotenone, allopurinol, indomethacin, nordihydroguiaretic acid, ketoconazole and nitro-L-arginine (inhibitors of mitochondrial NAD(P)H oxidase, xanthine oxidase, cyclooxygenase, lipoxygenase, cytochrome P450 oxygenase and nitric oxide synthase, respectively) did not affect the angiotensin II-induced collagen production. Angiotensin II increased the NAD(P)H-dependent superoxide anion production and the intracellular generation of reactive oxygen species in cardiac fibroblasts, and apocynin abrogated this rise. Conclusions Our data show that in adult rat cardiac fibroblasts the membrane-associated NAD(P)H oxidase complex is the predominant source of superoxide anion and reactive oxygen species generation in angiotensin II-stimulated adult cardiac fibroblasts. Inhibition of this NAD(P)H oxidase complex with apocynin completely blocked the angiotensin II-stimulated collagen production, and collagen I and III protein and mRNA expression.

Influence of cholesterol lowering on plasma membrane lipids and cationic transport systems

Background In order to determine whether alterations in membrane lipids affect transmembrane cationic transport systems in erythrocytes and platelets, cationic fluxes and intracellular cationic concentrations were measured in hypercholesterolaemic patients before and during administration of an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase. Methods After a 1-month run-in placebo period on a lipid-lowering diet the patients were treated, in a double-blind manner, with either placebo (n=25) or pravastatin (n=25) for 6 months. Placebo or pravastatin (10 mg during the first month, 20 mg during the second month and 40 mg during the remaining 4 months) was administered once a day in the evening. Results Compared with the placebo group, the erythrocyte and platelet membrane cholesterol content was reduced in the patients treated with pravastatin. The intra-erythrocyte and intraplatelet Na+ concentration was reduced during pravastatin administration, whereas the activity of the erythrocyte and platelet Na+-K+ pump was increased. However, the intra-erythrocyte and intraplatelet K+, Mg2+ and cytosolic Ca2+ concentrations, and water content, as well as the activities of the erythrocyte Na+-Li+ countertransporter and Na+, K+ cotransporter, and Na+ and K+ leakage, were not changed during pravastatin treatment. Conclusions The present data show that cholesterol lowering in hypercholesterolaemic patients may result in a significant decrease in erythrocyte and platelet membrane cholesterol content. These changes in membrane cholesterol are accompanied by an increase in activity of the Na+-K+ pump and a decrease in intra-erythrocyte and intraplatelet Na* concentrations.

Beta-blockers: once or three times a day?

In a double-blind, crossover trial 16 hypertensive patients were treated, in random order, with placebo, metoprolol 300 mg in a single daily dose, or metoprolol 300 mg/day in three doses. Both therapeutic regimens produced detectable plasma metoprolol concentrations and appreciable beta-blockade, estimated from exercise tachycardia, throughout the day. Fluctuations throughout the day in plasma drug concentrations and degree of beta-blockade were insignificant on the thrice-daily regimen, but they varied considerably on the single-dose regimen. Both therapeutic regimens also significantly lowered blood pressure throughout the day. Although the thrice-daily regimen again tended to produce a stronger and less fluctuating hypotensive action, the differences in hypotensive effect between the two regimens were not statistically significant. A single-dose of 300 mg of metoprolol can therefore be recommended if the only aim is to reduce blood pressure but not if a steady degree of beta-blockade is needed.

Urinary Cadmium and Lead Concentrations and Their Relation To Blood-pressure in a Population With Low Exposure

The 24 hour urinary excretion of cadmium (U-Cd) and lead (U-Pb), and the excretion of beta-2- microglobulins and retinol binding protein concentration in spot urines, were determined in a random 4% sample of the population of a small Belgian town. Blood pressure and body weight were measured on two separate occasions. U-Cd averaged 2.4 nmol/24 h in 46 youths, increased with age, and was significantly higher in 57 adult men as compared with 59 women (9.3 v 7.2 nmol/24 h; p less than 0.01). U-Pb averaged 28 nmol/24 h in youths and similarly increased with age: adult men excreted more lead than women (64 v 40.0 nmol/24 h; p less than 0.001). Among men, manual workers excreted more cadmium (12.6 v 7.5 nmol/24 h; p less than 0.05) but a similar amount of lead (62 v 61 nmol/24 h) compared with office workers. After adjusting for sex and age, U-Cd and U-Pb were not related to body weight and cigarette consumption. In simple regression analysis, U-Cd was positively correlated with both systolic (r = +0.30; p less than 0.05) and diastolic (r = +0.38; p less than 0.01) blood pressure in women. After adjusting for other contributing variables, however, a weak but negative relation became apparent between systolic pressure and U-Cd in women (t = -2.21; p = 0.033) and between diastolic pressure and U-Cd in men (t = -2.04; p = 0.047). In women urinary beta-2-microglobulin was related to diastolic pressure (r-0.44; p<0.01) and after adjusting for age to both systolic (t=2.75; p=0.009) and diastolic (t=-3.07; p=0.004) pressure. In none of the sex-age groups did U-Pb and retinol binding protein contribute to the blood pressure variability.

Effect of bisoprolol and atenolol on endurance exercise capacity in healthy men

Objectives To compare the effects of a highly β1-selective adrenoceptor antagonist bisoprolol with those of atenolol and placebo on endurance exercise capacity in young, healthy male volunteers. Design Twelve subjects randomly received oral placebo, atenolol (100 mg/day) or bisoprolol (10 mg/day) for 3 weeks, following a double-blind cross-over design. Methods At the end of each period, the subects performed an endurance exercise test on the bicycle ergometer at 70% of maximal aerobic power. Cardiac output was measured by means of an automated CO2-rebreathing method. Venous blood was sampled before, during and after exercise. Results Exercise duration was not significantly different between the two drugs tested. Total exercise duration was significantly reduced by bisoprolol (−19.4 ± 6.7%, P < 0.01) (mean ± SEM) and by atenolol (−29.8 ± 6.6%, P < 0.001), compared with placebo. Atenolol and bisoprolol were equally effective in lowering resting plasma renin activity, heart rate and systolic blood pressure. Resting and exercise stroke volume were significantly increased by both drugs, so that cardiac output was not significantly affected. Both drugs induced significant decreases in plasma-free fatty acid concentrations during recovery and blunted the exercise-induced increase. There were no significant relationships between the reduction of exercise duration and the haemodynamic changes or the degree of impairment of the exercise-induced increase in free fatty acid release resulting from β-blockade. Conclusions It is concluded that both drugs affect endurance exercise capacity in young, normotensive men, with a tendency to a smaller reduction during bisoprolol treatment. Haemodynamic variables are unlikely to be involved in the reduction of endurance exercise capacity. The role of the reduced availability of plasma free fatty acids remains unclear.

Transforming growth factor-beta1 promotes contraction of collagen gel by cardiac fibroblasts through their differentiation into myofibroblasts

Myofibroblasts and transforming growth factor-beta 1 (TGF-beta 1) are key elements of cardiac tissue fibrosis development. The aim of this study was to determine whether the ability of TGF-beta 1 to affect the contractile activity of cardiac fibroblasts depends on their differentiation into myofibroblasts. Cardiac fibroblasts (from male adult Wistar rats) from passage 2 were therefore cultured to confluency and incubated on a hydrated collagen gel, both with and without TGF-beta 1 (0, 20, 40, 100, 200, 400 or 600 pmol/l), for 1, 2 and 3 days in a Dulbeccos Modified Eagles Medium (DMEM) without fetal bovine serum (FBS). Growing cultures of cardiac fibroblasts were obtained by incubating second-passage fibroblasts in DMEM with 10% FBS with or without TGF-beta 1 (0 to 600 pmol/l) for 6 days. These fibroblasts were then further incubated on the collagen gel for 1, 2 and 3 days in DMEM without FBS. TGF-beta 1 dose-dependently increased the contraction of collagen gel mediated by cardiac fibroblasts, either added directly to the gel or after growing of the cardiac fibroblasts in the presence of TGF-beta 1 for 6 days, reaching a maximal effect at 100 pmol/l TGF-beta 1. In both culturing conditions, TGF-beta 1 also stimulated the [3H]-thymidine incorporation and the total protein content in the cardiac fibroblasts in the collagen gel lattice. TGF-beta 1 dose-dependently induced an increase in alpha-smooth muscle actin, a marker of myofibroblasts, in both culturing conditions. The TGF-beta 1-induced reduction of area of the collagen gel was negatively correlated to the TGF-beta 1-evoked appearance of alpha-smooth muscle actin in the collagen gel matrix. TGF-beta 1 increased the contractile activity of adult rat cardiac fibroblasts and their ability to differentiate into myofibroblasts. Because contractile activity was correlated with differentiation, the influence of TGF-beta 1 on cardiac fibroblast-induced collagen gel contraction may depend on the promotion of myofibroblast differentiation.

Radioimmunoassay of angiotensin II in unextracted plasma

Abstract A reliable, direct radioimmunoassay of plasma angiotensin II (PAII) is described. No cross-reactivity of human renin, sheep renin substrate, saralasin acetate and angiotensin I with the anti-angiotensin II antiserum was found. However, des- 1 Asp-angiotensin II has a stronger binding affinity for the antiserum than angiotensin II. A significant correlation was found between PAII determined in plasma samples without and with extraction on a Dowex 50W-X 2 resin. The combination of EDTA and o-phenanthroline has been found to be a very efficient angiotensinase inhibitor in plasma and is of equal potency as EDTA and diisopropylfluorophosphate in inhibiting the angiotensinase and converting enzyme activity. A significant correlation was found between PAII measurements performed in plasma samples in the presence of both inhibitor solutions. The intra-assay variations were checked by multiple analysis of a plasma pool and the inter-assay variations by measuring the angiotensin II concentration in different plasma samples on two occasions. The mean PAII in 10 healthy, male subjects on an ad libitum diet was 25.1 ± 13.5 (S.D.) pg/ml (range: 10.1 to 51.4). PAII correlated also better with plasma renin activity (active renin) than with plasma renin concentrations, measured after acidification of plasma (total renin).