Effects of 1-sar-8-ala-angiotensin II on arterial pressure, renin and aldosterone in hypertension

1-Sar-8-ala-angiotensin II did not change intra-arterial pressure in 25 sodium replete hypertensive patients, whilst the pressure changes were closely related to the plasma renin level during sodium depletion (r = -0.87; n = 32). The study indicates that arterial pressure is not dependent on angiotensin II in sodium replete patients and in sodium deplete subjects with low PRC, while it is angiotensin dependent during sodium depletion in the others. Plasma renin is unaffected in sodium replete subjects, but increases during saralasin in sodium deplete conditions. Saralasin stimulates aldosterone secretion only in sodium replete patients.

Inhibition of superoxide dismutase induces collagen production in cardiac fibroblasts

BACKGROUND

The aim of this study was to determine whether inhibition of superoxide dismutase (SOD) with diethyldithiocarbamic acid (DETC) could affect the collagen production, the mRNA and protein expression of collagen types I and III, and fibronectin in control and angiotensin II (ANG II)-treated cardiac fibroblasts. Its effect was compared with the SOD mimetics tempol and EUK-8 and with polyethyleneglycol (PEG)-SOD.

METHODS

Cardiac fibroblasts were cultured to confluence, incubated in serum-free Dulbecco's modified Eagle's medium for 24 h, preincubated with(out) the tested inhibitors for 1 h and further incubated with(out) ANG II (1 micromol/l) for 24 h.

RESULTS

DETC dose-dependently inhibited the activity of CuZn-SOD in cardiac fibroblasts. Superoxide anion production was increased by DETC and decreased by tempol in control and ANG II-treated fibroblasts. DETC also reduced the intracellular generation of reactive oxygen species (ROS) (such as H2O2, hydroxyl radicals, hydroperoxides) in control and ANG II-treated fibroblasts, whereas tempol reduced the ROS production only in ANG II-treated fibroblasts. ANG II and DETC stimulated the collagen production and the collagen I and fibronectin content in fibroblasts. The SOD mimetics tempol and EUK-8 as well as PEG-SOD reduced the collagen production. ANG II and DETC stimulated the tissue inhibitor of metalloproteinase-1 (TIMP-1) and TIMP-2 levels, whereas tempol decreased the TIMP-2 content in control and ANG II-treated fibroblasts. Matrix metalloproteinase (MMP)-1 level was reduced by ANG II and DETC and increased by tempol.

CONCLUSION

These data suggest a vital role of SOD and the formed ROS in the accumulation of collagen in cardiac fibroblasts.

Intra-erythrocyte cation concentrations in relation to the C1797T beta-adducin polymorphism in a general population

Genetic variability in the ADD1 (Gly460Trp) and ADD2 (C1797T) subunits of the cytoskeleton protein adducin plays a role in the pathogenesis of hypertension, possibly via changes in intracellular cation concentrations. ADD2 1797CC homozygous men have decreased erythrocyte count and hematocrit. We investigated possible association between intra-erythrocyte cations and the adducin polymorphisms. In 259 subjects (mean age 47.7 years), we measured intra-erythrocyte Na(+) [iNa], K(+) [iK] and Mg(2+) [iMg], serum cations and adducin genotypes. Genotype frequencies (ADD1: GlyGly 61.5%, Trp 38.5%; ADD2: CC 80.4%, T 19.6%) complied with Hardy-Weinberg proportions. In men, ADD2 CC homozygotes (n=100) compared to T-carriers (n=23) had slightly lower iK (85.8 versus 87.5 mmol/l cells; P=0.107), higher iMg (1.92 versus 1.80 mmol/l cells; P=0.012), but similar iNa (6.86 versus 6.88 mmol/l cells; P=0.93). In men, iK, iMg and iNa did not differ according to ADD1 genotypes. In men, iK (R(2)=0.128) increased with age and serum Na(+), but decreased with serum total calcium and the daily intake of alcohol. iMg (R(2)=0.087) decreased with age, but increased with serum total calcium. After adjustment for these covariates (P<or=0.04 for all), findings in men for iK (CC versus T: 85.8 versus 87.3 mmol/l; P=0.14) and iMg (1.91 versus 1.82 mmol/l; P=0.03) remained consistent. In 136 women, none of the phenotype-genotype relations reached significance. Changes in intra-erythrocyte cations in ADD2 1797CC homozygous men might lead to osmotic fragility of erythrocytes, but to what extent they reflect systemic changes or are possibly involved in blood pressure regulation remains unknown.

Transforming growth factor-beta 1 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 Dulbecco's Modified Eagle's 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.

Transforming growth factor-beta 1-induced collagen production in cultures of cardiac fibroblasts is the result of the appearance of myofibroblasts

Transforming growth factor-beta 1 (TGF-beta 1), which appears in high concentrations in fibrotic cardiac tissue, is a potent inductor of tissue collagen deposition and of the differentiation of fibroblasts to myofibroblasts. It is accepted that TGF-beta 1 is a potent stimulator of collagen secretion by fibroblasts. The aim of the present study was to determine which type of cells, fibroblasts and/or myofibroblasts are stimulated, in terms of collagen production, by TGF-beta 1. Therefore, using cultures of second-passage rat cardiac fibroblasts, we investigated the dose- (0.003-15 ng/ml) and time-dependence (2-48 h) of the TGF-beta 1-induced effects on collagen production and on the appearance of myofibroblasts, as estimated by the presence of alpha-smooth muscle actin (alpha-SMA; a marker of myofibroblasts). The reversibility of the TGF-beta 1-stimulated effects was also studied. The dose- and time-dependent stimulation of collagen production was closely associated with the induction of alpha-SMA. TGF-beta 1 did not change the cell phenotype or increase collagen production in rat cardiac fibroblasts cultures after a long incubation (24-28 h) at low concentrations (< 1 ng/ml), or after a short incubation (2-4 h) at high concentrations (1-15 ng/ml). However, after a long incubation at high concentrations, TGF-beta 1 changed the cell phenotype and increased collagen production in these cultures through the differentiation of fibroblasts to myofibroblasts. A maximal increase of collagen production (two-fold, p < 0.001) was observed after incubation of fibroblasts with 15 ng/ml TGF-beta 1 for 48 h. Under these conditions, alpha-SMA was increased by 3.5-fold (p < 0.001) and second-passage cultures of fibroblasts and their offspring in the next passage consisted mainly of myofibroblasts. The stimulation of collagen by 15 ng/ml TGF-beta 1 for 48 h was irreversible. In fact, additional incubation of these second-passage TGF-beta 1-stimulated cultures without TGF-beta 1 for 2 days did not decrease the high activity of collagen production. Moreover, the third-passage offspring of these TGF-beta 1-stimulated fibroblasts cultured without TGF-beta 1 also showed a higher production of collagen compared with control fibroblasts. Furthermore, the increased collagen production in the third-passage fibroblast offspring of the second-passage TGF-beta 1-stimulated fibroblasts could not be further stimulated by TGF-beta 1. Thus, the activity of collagen production in TGF-beta 1-stimulated cultures and in their next passage offspring is not sensitive to TGF-beta 1. Our data suggest that TGF-beta 1-stimulated collagen production in cultures of adult rat cardiac ventricular fibroblasts cannot be explained by a direct stimulation of collagen production, either in fibroblasts or in myofibroblasts. Instead, TGF-beta 1 induces differentiation of fibroblasts to myofibroblasts, the latter having a higher activity for collagen production than the former.

Heritability of plasma renin activity and plasma concentration of angiotensinogen and angiotensin-converting enzyme

The purpose of the present investigation was to describe the relative impact of genes and environment on the variance of the plasma constituents of the renin angiotensin system. We ascertained 56 male and 80 female adult same-sex twin pairs from the Flemish population. Plasma renin activity (PRA), the concentration of angiotensinogen (AGT) and angiotensin-converting enzyme (ACE) were measured, and path analysis was applied, after transformation toward normality. For PRA and AGT significant heritability was only detected in the male subgroup, with heritability estimates of 66% and 90%, respectively. Angiotensin-converting enzyme concentration was determined by additive genes for 43% of its variance, by shared environmental influences for 42%, and by specific environmental influences for 15%. The high heritability found for AGT is compatible with the results of earlier studies linking the M235T polymorphism of the angiotensinogen gene to plasma AGT levels. For PRA, we are the first to show significant heritability. Our results regarding ACE confirm the findings in other populations.

In vitro assay of collagen gel contraction by cardiac fibroblasts in serum-free conditions

The aim of the present study was to investigate whether collagen gel contraction can be induced by cardiac fibroblasts in serum-free conditions. Cardiac fibroblasts (from normal male adult rats) from passage 2 were cultured to confluency and added to a hydrated collagen gel in Dulbecco's Modified Eagle's Medium with or without fetal bovine serum for 1, 2, 3 or 7 days. Control gels containing adult rat cardiac fibroblasts showed a significant amount of contraction after 2 days of incubation in a serum-free medium, causing a contraction to 47% of the area at the start of the incubation. Increasing the percent of fetal bovine serum induced further stimulation of the collagen gel contraction by cardiac fibroblasts. Optimal conditions for collagen gel contraction by adult fibroblasts were obtained with 100,000 cells incubated for 1 (up to 3) days. The presence of insulin-transferrin-selenium in the medium caused a more pronounced stimulation of the collagen gel contraction by cardiac fibroblasts, while sodium azide inhibited this contraction.

A randomised, placebo-controlled, double-blind, crossover study of losartan and enalapril in patients with essential hypertension

The primary objective of this randomised, placebo- controlled, double-blind, crossover study, was to evaluate and compare the longer term effects of the angiotensin II type 1 receptor antagonist losartan and the converting enzyme inhibitor enalapril on 24-h ambulatory blood pressure (BP). After a 4-week placebo run-in period, nine patients with essential hypertension entered the double-blind phase of the study, which consisted of three 6-week periods during which patients were treated with placebo, enalapril 20 mg o.d. or losartan 50 mg o.d. Losartan and enalapril, taken between 07.00 and 08.00, reduced ambulatory BP throughout the 24-h period. Average night time BP was reduced from 133/85 mm Hg on placebo to 124/78 mm Hg on enalapril and to 126/77 mm Hg on losartan. Daytime BP averaged 157/101 mm Hg on placebo, and was significantly lower during enalapril (142/91 mm Hg) than during losartan treatment (147/95 mm Hg). Clinic BP, measured 2 to 4 hours after drug intake, was reduced to the same extent by both drugs. The losartan-induced BP changes were significantly related to those obtained with enalapril (0.63 < r < 0.93). Ambulatory BP monitoring was repeated after 4 weeks of combined therapy in six patients. The BP lowering effect of the combination was not significantly better than that achieved with enalapril alone. In conclusion, losartan 50 mg o.d. and enalapril 20 mg o.d. lower BP to approximately the same extent, except for a more pronounced effect of enalapril on daytime ambulatory BP. The current study does not provide convincing evidence that addition of losartan to enalapril in the doses used further reduces BP.

Induction of cardiac fibrosis by aldosterone

An intracardiac aldosterone system which responds to short- and long-term physiological stimuli has been described. This cardiac generated aldosterone has possibly autocrine or paracrine actions. Normal cardiac tissue contains mineralocorticoid receptors (MR) and cardiac high affinity MR are localized in cardiac myocytes and endothelial cells. Data concerning the presence of MR in cardiac fibroblasts are, however, controversial. MR are not specific for aldosterone but they also bind glucocorticoids. Cardiac fibroblasts however contain the enzyme 11beta-hydroxy-steroid dehydrogenase II which converts these glucocorticoids to inactive metabolites. Discordant findings on the in vitro effect of aldosterone on the collagen synthesis in cardiac fibroblasts are reported and can at least partly attributed to the presence of various fibroblasts phenotypes. During chronic aldosterone infusion in uninephrectomized rats on a high-salt diet, a marked accumulation of interstitial and to a lesser extent perivascular collagen occurs in the heart in both ventricles. This cardiac fibrosis in this aldosteronism model is prevented by spironolactone. This effect of aldosterone is crucially dependent on the salt status of the rat. Indeed, rats on a restricted salt intake infused with aldosterone had no cardiac fibrosis above control levels. During the continuous infusion of aldosterone in the rat the appearance of fibrosis was delayed and starts 4 weeks after the beginning of the infusion which argues against a direct effect of aldosterone. The mechanism of aldosterone-salt induced cardiac fibrosis possibly involves angiotensin II acting through upregulated AT1 receptors and the cardiac AT1 receptor is the target for aldosterone. An accumulation of collagen in the heart has also been found in patients with adrenal adenomas and during chronic activation of the renin-angiotensin-aldosterone system such as in surgically induced unilateral renal ischemia, unilateral renal artery banding or renovascular hypertension. Spironolactone prevents aortic collagen accumulation in spontaneously hypertensive rats. In patients with stable chronic heart failure spironolactone treatment in addition to diuretics and angiotensin-converting enzyme (ACE) inhibition reduced circulating levels of procollagen type III N-terminal aminopeptide. Also, in the Randomized Aldactone Evaluation Study spironolactone coadministered with conventional therapy of ACE inhibitors, loop diuretics and digitalis in patients with symptomatic heart failure defined as NYHA classes III-IV reduces total mortality by 30%.

Reconstitution of the human 5-HT(1D) receptor-G-protein coupling: evidence for constitutive activity and multiple receptor conformations

The 5-hydroxytryptamine (5-HT) 1D/1B receptors have gained particular interest as potential targets for treatment of migraine and depression. G-protein coupling and other intrinsic properties of the human 5-HT(1D) receptor were studied using a baculovirus-based expression system in Sf9 cells. Coexpression of the human 5-HT(1D) receptor with Galpha(i1), alpha(i2), alpha(i3), or Galpha(o)-proteins and Gbeta(1)gamma(2)-subunits reconstituted a Gpp(NH)p-sensitive, high affinity binding of [(3)H]5-HT to this receptor, whereas the Galpha(q)beta(1)gamma(2) heterotrimer was ineffective in this respect. Competition of [(3)H]5-HT binding by various compounds confirmed that coexpression of the human 5-HT(1D) receptor with Galpha(i/o)beta(1)gamma(2) reconstitutes the receptor in a high affinity agonist binding state, having the same pharmacological profile as the receptor expressed in mammalian cells. Binding of the antagonist ocaperidone to the human 5-HT(1D) receptor in coupled or noncoupled state was analyzed. This compound competed with [(3)H]5-HT binding more potently on the human 5-HT(1D) receptor in the noncoupled state, showing its inverse agonistic character. Ocaperidone acted as a competitive inhibitor of [(3)H]5-HT binding when tested with the coupled receptor form but not so when tested with the noncoupled receptor preparation. Finally, [(35)S]GTPgammaS binding experiments using the inverse agonist ocaperidone revealed a high level of constitutive activity of the human 5-HT(1D) receptor. Taken together, the reconstitution of the human 5-HT(1D) receptor-G-protein coupling using baculovirus-infected Sf9 cells made possible the assessment of coupling specificity and the detection of different binding states of the receptor induced by G-protein coupling or ligand binding.

Human 5-hydroxytryptamine(5A) receptors activate coexpressed G(i) and G(o) proteins in Spodoptera frugiperda 9 cells

The ability of the human 5-hydroxytryptamine serotonin type 5A (h5-ht(5A)) receptor to couple to G proteins from distinct families was investigated through the simultaneous infection of Spodoptera frugiperda 9 insect cells with recombinant baculoviruses encoding the various proteins. Expression of G proteins was demonstrated in immunoblots. Receptor-G protein coupling was monitored by high-affinity agonist binding and agonist-induced stimulation of [(35)S]guanosine-5'-O-(3-thio) triphosphate binding to membranes. Receptors expressed alone displayed low-affinity agonist binding, and endogenous G proteins were only poorly stimulated on the addition of 5-hydroxytryptamine. When receptors were coexpressed with mammalian G(i)/G(o) proteins (Galpha(i) or Galpha(o) plus Gbeta(1)gamma(2)), the coupled phenotype was achieved: agonists bound with high affinity in a guanosine-5'-(beta, gamma-imido)triphosphate-sensitive manner and stimulated [(35)S]guanosine-5'-O-(3-thio)triphosphate binding to high levels. These effects were not observed on coexpression with G(z)/G(s)/G(q/11/16) or G(12/13). Various ligands were evaluated for their agonistic, antagonistic, or inverse agonistic behavior in both receptor binding and activation assays. Although G(o) displayed different receptor coupling characteristics than G(i) proteins, no clear coupling preference was evident. Coexpression of receptors and Galpha(i) subunits without Gbeta(1)gamma(2) produced increases in both agonist affinity and maximum G protein activation that were smaller than those in the presence of Gbeta(1)gamma(2), suggesting that Gbeta(1)gamma(2) coexpression improves receptor-G protein coupling. Similarly, coexpression of receptors with Gbeta(1)gamma(2) alone resulted in an improved interaction with endogenous G proteins. Our results demonstrate that h5-ht(5A) receptors expressed in Spodoptera frugiperda 9 cells selectively and functionally couple to coexpressed mammalian G(i) and G(o) proteins.

Effect of protease inhibitors on angiotensin-converting enzyme activity in human T-lymphocytes

The purpose of these investigations was to determine whether the aminopeptidase B and leucine aminopeptidase inhibitor bestatin, the chymase inhibitor chymostatin, the calpain inhibitor E-64, and the neutral serine protease inhibitor leupeptin affect the angiotensin converting enzyme (ACE) activity in T-lymphocytes. ACE activity in homogenates of T-lymphocytes or in intact T-lymphocytes in suspension was measured by determining fluorimetrically histidyl-leucine, formed from the conversion of hippuryl-histidyl-leucine, coupled with ophtaldialdehyde. The effect of various concentrations (10(-9) to 10(-3) mol/L) of the angiotensin-converting enzyme inhibitors lisinopril and captopril and of the various protease inhibitors on ACE activity was studied. Lisinopril and captopril reduced the ACE activity in homogenates of T-lymphocytes in a concentration-dependent manner. Lisinopril exhibited a more pronounced inhibition of ACE in T-lymphocytes than did captopril. Chymostatin and E-64 had no effect on the ACE activity in T-lymphocytes, whereas leupeptin inhibited its activity in a dose-dependent fashion. Bestatin, on the contrary, increased the ACE activity in homogenates of T-lymphocytes as well as in intact T-lymphocytes in proportion to the concentration. Our data showed that the ACE activity in T-lymphocytes was stimulated by bestatin and inhibited by leupeptin, whereas chymostatin and E-64 did not affect the ACE activity in T-lymphocytes.

Inhibition of proliferation of human peripheral blood mononuclear cells by calcium antagonists. Role of interleukin-2

To evaluate the role of interleukin-2 (IL-2) in the inhibition of the proliferation of human peripheral blood mononuclear cells (PBMC) by calcium channel blockade, the effect of nifedipine, which blocks the L-type calcium channel on the proliferation, the IL-2 expression and the IL-2 production in human PBMC, was compared with the effect of mibefradil, which blocks both L- and T-type calcium channels with a more selective blockade of T-type channels. The rate of [3H]-thymidine incorporation into control and concanavalin A-induced PBMC in the presence or absence of the calcium channel blockers nifedipine or mibefradil (1, 10 or 50 microM) was assayed in the cells cultured for 3 days. The cellular cytotoxicity and the cell number in growing cultures was also determined in nifedipine- or mibefradil-treated control or stimulated cells. Restoration of the proliferative response in nifedipine- or mibefradil-treated cells was investigated by addition of exogenous IL-2. IL-2 receptor expression in the cells was monitored using antiactivated T-cell antigen (Tac) antibody, and the IL-2 production in the cell supernatants of the cultures was determined by an enzyme amplified sensitive immunoassay. Nifedipine and mibefradil concentration-dependently reduced the cell number and [3H]-thymidine incorporation or the do novo DNA synthesis in control and concanavalin A-stimulated human PBMC. The proliferative response of nifedipine- or mibefradil-treated cells was restored by addition of exogenous IL-2. The normal expression of IL-2 receptors was preserved while the IL-2 production was blocked in the presence of nifedipine or mibefradil.

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

OBJECTIVES

To compare the effects of a highly beta1-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 subjects 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 beta-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.

Modification of intracellular calcium and plasma renin by dietary calcium in men

A double blind, placebo-controlled, parallel study was conducted on the effect of a high daily oral calcium supplementation of 1 g elemental calcium, given twice daily for 16 weeks in normal male subjects, on plasma renin, aldosterone, kallikrein, cGMP, cAMP, and calciotropic hormones, intracellular calcium concentrations, and plasma total and ionized calcium. After a 1-month run-in period on a limited use of dairy products, the subjects (n = 32) were allocated to a placebo or a calcium group. Placebo or 1 g elemental calcium was administered twice daily in the morning and evening for 16 weeks. All subjects were investigated at baseline and after 1, 2, 4, 8, and 16 weeks of placebo or calcium administration. A decreased intraerythrocyte and intraplatelet Ca2+ concentration was observed in the calcium-treated subjects. Compared with the placebo group, an increase in the plasma renin activity (PRA) in the calcium group was observed after 4, 8, and 16 weeks of oral calcium administration. However, plasma aldosterone and urinary excretion of aldosterone, kallikrein, cGMP, and cAMP were not changed during calcium administration. Oral calcium supplementation in these men was also accompanied by a reduction in the plasma concentration of intact parathyroid hormone and 1,25-dihydroxyvitamin D3, and an increase in 24-h urinary calcium excretion, but no change in the plasma total Ca2+ concentration, serum ionized Ca2+ level, and plasma phosphate or 25-hydroxyvitamin D3. Our data show that the increase in PRA observed in men during oral calcium supplementation is accompanied by a reduction in the intracellular free and total Ca2+ concentration in platelets and erythrocytes and by a decrease in the plasma concentration of intact parathormone and 1,25-dihydroxyvitamin D3.

Antagonism of the renin-angiotensin system, hypertrophy and gene expression in cardiac myocytes

In response to humoral and mechanical stimuli, the myocardium adapts to increased work load through hypertrophy of individual muscle cells. Myocardial hypertrophy is characterized by an increase in cell size in the absence of cell division and is accompanied by changes in gene expression. Angiotensin II (Ang II), the effector peptide of the renin-angiotensin system (RAS), regulates volume and electrolyte homeostasis and is involved in cardiac and vascular growth in rats. In this review, the role of RAS in myocyte protein synthesis (myocyte hypertrophy) and in induction of gene expression will be discussed in rat cardiomyocytes in culture. Traditional RAS can be considered as a system in which circulating Ang II is delivered to target tissues or cells. However, a local RAS has also been described in cardiac cells and evidence has been accumulated for autocrine and/or paracrine pathways by which biological actions of Ang II can be mediated. These actions of Ang II are primarily mediated through Ang II receptors subtype I (AT1-R). When evaluating the effects of Ang II in situ, both changes in circulating levels and local production have to be taken into account. Contrasting results have been found concerning the in vitro effect of Ang II on the protein synthesis in cardiac myocytes and can be at least partly be attributed to methodological problems such as assay of de novo protein synthesis and isolation and separation procedure of cardiac myocytes. The Ang II-induced hypertrophic effect also depends on the existence of nonmyocytes in a cardiocyte culture. In rat cardiocytes, AngII also causes induction of many immediately-early genes (c-fos, c-jun, jun-B, Egr-1 and c-myc) and induces also late markers of cardiac hypertrophy (skeletal alpha-actin and atrial natriuretic peptide expression) and growth factors (TGF-beta 1 gene expression). In vivo AngII via AT1-R, causes not only ventricular hypertrophy but also a shift to the fetal phenotype of the myocardium. Angiotensin-converting enzyme inhibitors and AngII receptor antagonists of the subtype I not only induce the regression but also prevent the development of cardiac hypertrophy in experimental rat models.

Renin-angiotensin system, hypertrophy and gene expression in cardiac myocytes

In response to humoral and mechanical stimuli, the myocardium adapts to increased work load through hypertrophy of individual muscle cells. Myocardial hypertrophy is characterized by an increase in cell size in the absence of cell division and is accompanied by changes in gene expression. Angiotensin II (ANG II), the effector peptide of the renin-angiotensin system (RAS), regulates volume and electrolyte homeostasis and is involved in cardiac and vascular growth in rats. In this review, the role of RAS on the myocyte protein synthesis (myocyte hypertrophy) and on the induction of gene expression will be discussed in rat cardiomyocytes in culture. The traditional RAS can be considered as a system in which circulating ANG II is delivered to target tissues or cells. However, a local RAS has also been described in cardiac cells and evidence has been accumulated for autocrine and/or paracrine pathways by which biological actions of ANG II can be mediated. These actions of ANG II are primarily mediated through ANG II receptors of the subtype I (AT1-R). When evaluating the effects of ANG II in situ, both changes in circulating levels and local production have to be taken into account. Discrepant findings on the in vitro effect of ANG II on the protein synthesis in cardiac myocytes are described and can be at least partly be attributed to methodological problems such as assay of the de novo protein synthesis, isolation and the separation procedure of cardiac myocytes. The ANG II-induced hypertrophic effect also depends on the existence of non-myocytes in a cardiocyte culture. In rat cardiocytes ANG II also causes induction of many immediately-early genes (c-fos, c-jun, jun-B, Egr-1 and c-myc) and induces also late markers of cardiac hypertrophy (skeletal alpha-actin and atrial natriuretic peptide expression) and growth factors (TGF-beta1 gene expression). In vivo ANG II via AT1-R, causes not only ventricular hypertrophy, independently of blood pressure, but also a shift to the fetal phenotype of the myocardium. Angiotensin-converting enzyme inhibitors and ANG II receptor antagonists of the subtype I not only induce the regression, but also prevent the development of cardiac hypertrophy in experimental rat models.

Proliferation of human peripheral blood mononuclear cells during calcium entry blockade. Role of protein kinase C

To evaluate the role of protein kinase C (PKC) and intracellular calcium and particularly Ca(2+)-uptake in the initiation of lymphocyte mitogenesis, the proliferation of human peripheral blood mononuclear cells (PBMC) was investigated during calcium entry blockade with nifedipine (an L-type calcium channel blocker) and mibefradil (an L- and T-type calcium channel blocker with a higher selectivity for T-type channels). The rate of [3H]-thymidine, [3H]-uridine and [3H]-leucine incorporation into control and concanavalin A-stimulated PBMC cultured for 3 days in the presence or absence of the calcium channel blockers nifedipine or mibefradil (1, 10 or 50 microM) is assayed. Nifedipine and mibefradil concentration-dependently reduced cell number and [3H]-thymidine incorporation or de novo DNA synthesis in control and concanavalin A-stimulated PBMC, as well as de novo RNA and protein synthesis. The proliferative response of nifedipine- or mibefradil-treated cells was restored by addition of phorbol-12-myristate-13-acetate (PMA), an exogenous PKC activator. Our data show that PBMC treated with the Ca2+ channel blockers nifedipine or mibefradil are still capable of proliferating in response to PMA. However, in PKC-depleted cells, the proliferative response of PBMC was suppressed.

Antagonism of the renin-angiotensin-aldosterone system and collagen metabolism in cardiac fibroblasts

The renin-angiotensin-aldosterone system has emerged as a potential candidate for the accumulation of collagen in cardiac fibroblasts. The traditional renin-angiotensin-aldosterone system can be considered a system in which circulating angiotensin II or aldosterone is delivered to target tissue or cells. However, an independent local renin-angiotensin system has also been described in cardiac cells and evidence has been accumulated for autocrine and/or paracrine pathways by which biological actions of angiotensin II can be mediated. These actions of angiotensin II are primarily mediated through angiotensin II receptors of the subtype I (AT1). When evaluating the effects of angiotensin II in situ, changes in circulating levels and local production both have to be taken into account. Functional angiotensin II receptors have been documented in cardiac fibroblasts although the presence of aldosterone receptors in cardiac fibroblasts is obscure, and the expression of mRNA for mineralocorticoid receptors in cardiac fibroblasts has been described. In vitro, angiotensin II increased cardiac fibroblast-mediated collagen synthesis and mRNA levels of collagen type I, type III, pro-alpha 1 (I) collagen, pro-alpha 1 (III) collagen and fibronectin, and inhibited matrix metalloproteinase I activity. The ability of angiotensin II to induce collagen synthesis and expression of collagen in cardiac fibroblasts may be mediated by an increase in transforming growth factor-beta 1 in an autocrine/paracrine fashion. The angiotensin II-stimulated secretion and expression of collagen was completely abolished by AT1 receptor antagonism, but not affected by AT2 receptor antagonism. The discordant findings that have been reported concerning the in vitro effect of aldosterone on collagen synthesis in cardiac fibroblasts can at least partly be attributed to differences in methodology such as the use of the total population or a sub-population of cardiac fibroblasts. In vivo, chronic infusion of angiotensin II or aldosterone increased the collagen volume fraction in the ventricles. Angiotensin-converting enzyme (ACE) inhibition and AT1 receptor antagonism, but not AT2 receptor antagonism, reduced collagen deposition in the myocardium in spontaneously hypertensive rats. The cardioprotective mechanism of action of ACE inhibitors can be attributed to local blockade of the formation of angiotensin II, to the degradation of bradykinin or to the release of nitric oxide and/or eicosanoids. Angiotensin-converting enzyme inhibitors also reduced collagen deposition in rat myocardium following myocardial infarction suggesting that collagen deposition may in part result from mechanisms other than through AT1 receptors. However, further research is necessary to unravel the various mechanisms involved in the action of angiotensin-converting enzyme inhibitors or of AT1 receptor antagonists on collagen deposition in the myocardium.

Mibefradil-induced inhibition of proliferation of human peripheral blood mononuclear cells

To evaluate the role of intracellular calcium and particularly Ca2+-uptake in the initiation of lymphocyte mitogenesis, the effect of mibefradil, which blocks both L- and T-type calcium channels with a more selective blockade of T-type channels, on the proliferation of human peripheral blood mononuclear cells (PBMCs) is compared with the effect of nifedipine, which blocks only the L-type calcium channel. The rate of [3H]thymidine incorporation into control and concanavalin A-stimulated PBMCs in the presence or absence of the calcium channel blockers mibefradil or nifedipine (1, 10, or 50 microM), and of the intracellular calcium antagonist 3,4,5-trimethoxybenzoic acid 8-(diethylamino) octyl ester (TMB-8; 1, 10, 25, or 50 microM) was assayed in the cells cultured for 3 days. The cellular cytotoxicity and the cell number in growing cultures also was determined in mibefradil- or nifedipine-treated control or stimulated cells. Restoration of the proliferative response in mibefradil- or nifedipine-treated cells was investigated by addition of exogenous interleukin-2. Interleukin-2-receptor expression in the cells was monitored by using anti-activated T-cell antigen (Tac) antibody, and the interleukin-2 production in the cell supernatants of the cultures was determined by an enzyme-amplified sensitive immunoassay. Mibefradil and nifedipine concentration-dependently reduced the cell number and the [3H]thymidine incorporation or the de novo DNA synthesis in control and concanavalin A-stimulated human PBMCs. Mibefradil exhibited a more pronounced inhibition of the proliferation of human PBMCs than did nifedipine. The inhibitory effect of mibefradil or nifedipine on DNA synthesis was dependent on the timing of treatment with the drugs. The inhibitory effect of mibefradil or nifedipine on the lymphoproliferative response was nearly abolished if the drugs were added 20 h after cell stimulation. A markedly reduced inhibitory effect was found when mibefradil or nifedipine was added 1-7 h after cell stimulation. However, regardless of time of addition, TMB-8 caused a persistent inhibition of the proliferation of human PBMCs. The inhibitory effect of mibefradil or nifedipine on the proliferation of human PBMCs is nearly abolished by addition of the calcium channel activator Bay K 8644. The proliferative response of mibefradil- or nifedipine-treated cells is restored by addition of exogenous interleukin-2. The normal expression of interleukin-2 receptors was preserved, whereas the interleukin-2 production was blocked in the presence of mibefradil or nifedipine. Our data show that mibefradil has a more pronounced inhibitory effect on the proliferation of human PBMCs than nifedipine and that this inhibitory effect on DNA synthesis is dependent on the timing of treatment with both drugs.

Cytosolic calcium and lymphoproliferative response during calcium antagonism in men

OBJECTIVE

A double-blind, placebo-controlled parallel study was conducted on the effect of mibefradil, both an L- and T-type Ca2+-channel blocker with a more selective blockade of T-type channels, administered once daily for 1 week to normal male subjects, on blood pressure, intracellular cationic concentrations, sodium-proton exchange rate and 3H-thymidine incorporation in peripheral blood mononuclear cells (PBMC).

METHODS

After a 1-week run-in period on placebo, the subjects (n = 40) were allocated to a placebo or a mibefradil group. Placebo or 50 mg mibefradil was administered once daily in the morning for 1 week. All subjects were investigated at baseline and after 1 week of placebo or mibefradil administration. Standing or recumbent blood pressure and heart rate of subjects in the mibefradil group was decreased (P < 0.05 or less) compared with that of subjects in the placebo group.

RESULTS

Decreased (P < 0.001) intracellular free Ca2+ concentration and reduced (P < 0.001) 3H-thymidine incorporation in the PBMC were observed in the mibefradil-treated subjects. The intracellular sodium, potassium or magnesium concentration as well as the sodium-proton exchange rate were not changed during mibefradil administration.

CONCLUSION

The blood pressure lowering action of mibefradil in men is accompanied by a decrease in intracellular free Ca2+ concentration. Mibefradil also reduced the 3H-thymidine incorporation or de novo DNA synthesis in PBMC by modulating the calcium homeostasis.

Proliferation of human peripheral blood mononuclear cells during calcium channel blockade

To evaluate the role of intracellular calcium and particularly Ca2+ uptake in the initiation of lymphocyte mitogenesis, the effect of mibefradil--which blocks both L- and T-type calcium channels with a more selective blockade of T-type channels--on the proliferation of human peripheral blood mononuclear cells (PBMC) is compared with the effect of nifedipine, which blocks only the L-type calcium channel. The rate of 3H-thymidine, 3H-uridine, and 3H-leucine incorporation into control and concanavalin A-stimulated PBMC in the presence or absence of the calcium channel blockers mibefradil or nifedipine (1, 10, or 50 micromol/L), and of the intracellular calcium antagonist TMB-8 or the calmodulin antagonist W-7 (1, 10, 25, or 50 micromol/L) was assayed in cells cultured for 3 days. The cellular cytotoxicity and the cell number in growing cultures was also determined in mibefradil- or nifedipine-treated control or stimulated cells. Mibefradil and nifedipine reduced the cell number and the 3H-thymidine, 3H-uridine, or 3H-leucine incorporation or the de novo DNA, RNA, or protein synthesis in control and concanavalin A-stimulated human PBMC in a concentration-dependent manner. Mibefradil exhibited a more pronounced inhibition than nifedipine. The inhibitory effect of mibefradil or nifedipine on DNA synthesis was dependent upon the timing of treatment with the drugs. The inhibitory effect of mibefradil or nifedipine on the lymphoproliferative response was nearly abolished if the drugs were added 20 h after cell stimulation. A markedly reduced inhibitory effect was found when mibefradil or nifedipine were added 1 to 7 h after cell stimulation. However, regardless of time of addition, TMB-8 and W-7 caused a persistent inhibition of the proliferation of human PBMC. Our data show that mibefradil had a more pronounced inhibitory effect on the proliferation of human PBMC than nifedipine and that this inhibitory effect on de novo DNA synthesis was dependent upon the timing of treatment with both drugs. Mibefradil and nifedipine also reduce RNA and protein synthesis in human PBMC. Therefore, administration of these calcium channel blockers to inhibit cellular proliferation might be most beneficial at anatomic sites where cellular proliferation is not already an active process, while being ineffective in the presence of ongoing active proliferation, as suggested by some prospective studies.

Human erythrocytes contain Ca2+, calmodulin-dependent cyclic nucleotide phosphodiesterase which is involved in the hydrolysis of cGMP

To determine whether phosphodiesterase (PDE) is involved in the degradation of cGMP in human erythrocytes, we studied the cell cGMP content in the presence of different PDE inhibitors: zaprinast and dipyridamole, specific inhibitors of cGMP-binding, cGMP-specific PDE (cG-BPDE); vinpocetine, a specific inhibitor of Ca2+, calmodulin-dependent phosphodiesterase (CaM-PDE); an unspecific inhibitor, 3-isobutyl-1-methylxanthine (IBMX). IBMX, zaprinast, and dipyridamole at 30 microM did not affect the intracellular cGMP content. However, vinpocetine at this concentration increased the cGMP content by 102 +/- 14% (p < 0.05). The effect of vinpocetine was dose-dependent, reached the maximal level after 1 min of incubation and flattened at the same level. Ca2+ (10 microM) in the presence of the Ca(2+)-ionophore, A23187 (5 microM), decreased the cGMP content (-23% +/- 4; p < 0.05), which can be explained by the CaM-PDE activation. The Ca(2+)-induced decrease in cGMP was completely inhibited by the CaM antagonist, W-7 (100 microM). These data suggest that erythrocytes contain Ca2+, CaM-PDE.

Activation by calcium of erythrocyte Na+/H+ exchange in men

OBJECTIVE

To determine whether protein kinase C is necessary for the calcium activation of the Na+/H+ exchange in human erythrocytes by studying activation by calcium of erythrocyte Na+/H+ exchange in control cells, in protein kinase C-depleted cells after downregulation of protein kinase C with phorbol-12-myristate-13-acetate and in cells that had been treated beforehand with phorbol-12-myristate-13-acetate with and without the calpain inhibitor E-64d.

METHODS

Erythrocyte Na+/H+ exchange was measured by determining the initial rates of the influx of Na+ into Na+-depleted, acid loaded cells. The effects of various concentrations (0-1 mmol/l) of CaCl2 and the effects of 1 mmol/l CaCl2 on activation of the intracellular pH and on the external Na+ activation of Na+/H+ exchange were studied. The effects of 1 mmol/l CaCl2 on Na+/H+ exchange in control cells and cells that had been incubated beforehand with and without 1 micromol/l phorbol-12-myristate-13-acetate and with E-64d and 1 micromol/l phorbol-12-myristate-13-acetate for 1, 2, 3 and 24 h were also investigated.

RESULTS

Addition of Ca2+ to a concentration in the range 0-1 mmol/l in the presence of calcimycin resulted in stimulation of Na+/H+ exchange: 1 mmol/l CaCl2 increased (P< 0.001) the erythrocyte Na+/H+ exchange by 74%. Calcium increased the maximum rate for activations by intracellular pH and by external Na+ of Na+/H+ exchange, whereas it did not affect the Michaelis-Menten constants for activation by intracellular H+ and external Na+. However, calcium did not activate the Na+/H+ exchange in protein kinase C downregulated erythrocytes and administration of the calpain inhibitor E-64d could not prevent this inactivation.

CONCLUSION

Our data indicate that protein kinase C is necessary for the activation by calcium of the erythrocyte Na+/H+ exchange.

Protein kinase C induced changes in erythrocyte Na+/H+ exchange and cytosolic free calcium in humans

To investigate the interrelationship between erythrocyte Na+/H+ exchange rate and free cytosolic Ca2+ concentration, the effect of the (non)selective protein kinase C inhibitors staurosporine, Ro 31-8220 and CGP 41251 (1 micromol/L) and of the protein kinase C activator phorbol-12-myristate-13-acetate (PMA, 1 micromol/L) was studied in vitro on these variables. PKC depleted erythrocytes were obtained after 24 h PMA down-regulation of the cells and intracellular Ca2+ clamping was obtained using quin-2 AM and fluo-3 AM. PMA increased (P < .05) the erythrocyte Na+/H+ exchange activity and this rise was accompanied by an increase in the free cytosolic Ca2+ concentration. When staurosporine and Ro 31-8220 were added to erythrocytes in suspension, a decrease in free cytosolic Ca2+ concentration was also found, whereas no significant change was observed after CGP 41251 administration. The Na+/H+ exchange rate was decreased in the 24 h PMA down-regulated erythrocytes as well as in Ca2+-clamped cells. Addition of Ca2+ in a concentration range of 0 to 1 mmol/L in the presence of calcimycin resulted (P < .001) in a stimulation of Na+/H+ exchange by 74%. Calcium increased the Vmax for cellular pHi or external Na+ activation of Na+/H+ exchange, whereas it did not affect the Km for H+(i) or external Na+ activation. However, in PKC down-regulated cells, calcium did not activate the Na+/H+ exchange in erythrocytes and the calpain inhibitor E-64d did not prevent this inactivation. Our data show a concomitant increase in free cytosolic Ca2+ concentration and Na+/H+-exchange rate upon protein kinase C activation and a corresponding decrease in both variables upon PKC inhibition, indicating a Ca2+ requirement for protein kinase C activation of Na+/H+ exchange.

Effect of narcotic agents and of bleeding on systemic and renal haemodynamics in healthy and CCl4-treated cirrhotic rats

1. The haemodynamic effects of different narcotic agents have been tested in healthy rats and in rats with cirrhosis. 2. Pentobarbital suppresses the sympathetic nervous system. Susceptibility to ketamine is unpredictable, leading to both insufficient pain relief and narcosis related mortality. The combination diazepam-fluanisone induces profound hypotension. After insertion of catheters, awake, freely moving rats are stable and not distressed. This allows repeated measurements after manipulation. Moreover, procedure-related mortality is low and rats have a better stress response. 3. In the awake animal, arterial pressure is 126 +/- 10 for healthy animals, and 111 +/- 16 and 102 +/- 10 mmHg for cirrhotic animals without and with ascites, respectively (P = 0.018). The respective values for portal pressure are 6.9 +/- 1.4, 11.6 +/- 2.5 and 16.2 +/- 2.9 mmHg (P = 0.0001). After a bleeding, arterial pressure is better preserved than portal pressure in the three groups (P < 0.0001). Plasma volume in cirrhotic rats exceeds that of healthy rats. Plasma renin activity, aldosterone and catecholamines do not differ between the groups studied. In cirrhotic rats with and without ascites, glomerular filtration rate tends to be higher (P = 0.12), renal plasma flow is elevated (P = 0.001) and filtration fraction is lower (P = 0.002) than in healthy rats. 4. In conclusion, haemodynamic experiments in the cirrhotic rat should be performed in the awake rat. Arterial hypotension, impaired filtration fraction, enlarged plasma volume and portal hypertension are present in cirrhosis before the development of ascites. This can as well be explained by splanchnic pooling of blood, as by peripheral vasodilatation. The decrease in portal pressure with preserved arterial pressure after a bleeding protects cirrhotic rats from ongoing variceal bleeding.

In vitro proliferative response of human peripheral blood mononuclear cells to concanavalin A

The proliferation response of human peripheral blood mononuclear cells (PBMC) to concanavalin A (con A) was tested in a medium with or without addition of fetal calf serum (FCS) or a serum substitute. The time profile of the proliferative response of PBMC to con A was different in cells cultured in a medium supplemented with or without FCS. This different pattern occurred for the con A-induced DNA-synthesis as well as for the RNA- or protein-synthesis. The peak proliferation rate and the stimulation index of proliferation of human PBMC to con A was also higher when the cells were cultured in a medium with 10% FCS compared to cells cultured in a FCS-free medium. Substitution of the fetal calf serum by a serum substitute even induced a profound inhibition of the de novo synthesis of DNA in human PBMC. The results indicate that a lymphocyte proliferation response to con A can still be obtained in a culture medium where no FCS was added, although a weaker stimulation occurred in comparison to a culture medium with FCS. However, addition of a serum substitute caused a marked inhibition of the lymphocyte proliferation rate.

Cytosolic calcium changes induced by angiotensin II in human peripheral blood mononuclear cells are mediated via angiotensin II subtype 1 receptors

OBJECTIVE

To determine the effects of angiotensin II (AII) (1-8) on cytosolic free calcium concentrations in the absence and in the presence of the selective angiotensin subtype 1 (AT1) receptor antagonist losartan and of the selective angiotensin subtype 2-receptor antagonist P-186 in human peripheral blood mononuclear cells (PBMC). We also assessed the effect of the AII analogues AII (2-8), AII (3-8) and AII (4-8) on the cytosolic free-calcium concentration in human PBMC.

METHODS

The cytosolic free-calcium concentration was assayed in human peripheral blood mononuclear cells by measuring the fluorescence of fura-2 entrapped by these cells.

RESULTS

Administration of AII caused a concentration-dependent increase in the cytosolic free-calcium concentration in human peripheral blood mononuclear cells with a half-maximal increase at 5 x 10(-8) mol/l. Also administration of the heptapeptide AII (2-8) increased the intracellular free-calcium concentration in human PBMC, whereas AII (3-8) and AII (4-8) had no effect. The AII (1-8)-induced rise in cytosolic free-calcium concentration was blocked completely by losartan but not by P-186.

CONCLUSION

Our data demonstrate that the effects of AII on the cytosolic free-calcium concentration in human PBMC are AT1 receptor-mediated since they were abolished by the specific AII AT1 receptor antagonist losartan but not by the specific angiotensin subtype 2 receptor antagonist P-186.

Effect of angiotensin-converting enzyme inhibition on Na+/H(+)-exchange and Ca(2+)-efflux in human erythrocytes

The effect of the angiotensin-converting enzyme inhibitor, captopril, on Na+/H(+)-exchange activity and on Ca(2+)-ATPase mediated Ca(2+)-efflux was investigated in red blood cell membranes of patients with essential hypertension. The erythrocyte Na+/H(+)-exchange rate was measured as the difference in H(+)-efflux rate when measured in the presence or absence of Na+. The erythrocyte Ca(2+)-transport mediated by Ca(2+)-ATPase was assayed as the erythrocyte Ca(2+)-efflux rate. Our data show that captopril, in vitro and in vivo, inhibits the Ca(2+)-ATPase mediated Ca(2+)-efflux rate in human erythrocytes, while in vivo it stimulates the erythrocytes Na+/H(+)-exchange rate.

Salt and blood pressure in community-based intervention trials

This article reviews community-based salt intervention trials. In the Belgian Salt Intervention Trial, a controlled 5-y intervention in two Belgian towns resulted in a reduction in urinary sodium of 17 mmol/24 h (P < 0.001) in adult (aged > or = 20 y) women in the intervention town, which differed from the concurrent trend (an increase of 8 mmol/24 h) in the control town (P = 0.01). However, both systolic (-7.5 compared with -7.9 mm Hg) and diastolic (-2.3 compared with -3.0 mm Hg) pressures declined to the same extent in women of the two towns. In adult men in the intervention town, decreases were observed in urinary sodium (-12 mmol/24 h) and in systolic (-5.6 mm Hg) and diastolic (-2.4 mm Hg) blood pressures, but these trends were the same in the control town (-12 mmol/24 h, -4.9 mm Hg, and 0.2 mm Hg, respectively). The Belgian study and the four other community-based salt intervention trials reviewed show that, in general, salt intake in the long-run cannot be restricted below 5 g/24 h. More moderate salt restriction may constitute a more realistic goal, but its influence on blood pressure in the community at large is probably trivial.

Regulation of human erythrocyte Na+/H+ exchange by soluble and particulate guanylate cyclase

Guanylate cyclase activity in human erythrocytes is investigated by evaluating the intracellular guanosine 3',5'-cyclic monophosphate (cGMP) content in the presence of various agents that exert specific effects on soluble or particulate guanylate cyclase. The increase in the intraerythrocyte cGMP content by the soluble guanylate cyclase activators nitroprusside and NaNO2 suggests the presence of this enzyme in human erythrocytes. The effects of four different atrial natriuretic peptide (ANP) fragments on the intraerythrocyte cGMP content is also studied. ANP II and ANP III increase the intraerythrocyte cGMP content, whereas ANP I and des-Ser5,des-Ser6-ANP III are ineffective. Thus our data show that human erythrocytes possess particulate guanylate cyclase together with the soluble enzyme. The ANP fragments ANP II and ANP III also activate the erythrocyte Na+/H+ exchange. Nitroprusside, M & B 22948 (an inhibitor of cGMP phosphodiesterase), and the cGMP analogues dibutyryl cGMP and 8-bromoguanosine 3',5'-cyclic monophosphate also increase the erythrocyte Na+/H+ exchange rate. The latter data also suggest that the erythrocyte Na+/H+ exchange is regulated by cGMP.

Effect of strength training on blood pressure measured in various conditions in sedentary men

To examine the effect of long term strength training on heart rate and blood pressure, measured in different conditions, and on their variability, thirty healthy, previously sedentary men were randomized into a training and a control group. The strength training program consisted of 48 training sessions on a multigym apparatus at a frequency of 3 sessions each week, involving leg press, bench press, leg curl, shoulder press, leg extension and sit ups. The control group was asked not to change their sedentary lifestyle. In the subjects of the training group the load could be increased significantly for all exercises (p < 0.01). Heart rate and blood pressure were measured at rest in the supine and sitting position, during 24 hours with a non-invasive ambulatory device and during an exercise test on a cycloergometer. Repeated measures analysis of variance did not show an effect of strength training on heart rate or on blood pressure. In addition, power spectral analysis of the RR interval (ECG) and of the beat-to-beat blood pressure in the supine subject revealed similar total, low frequency and high frequency power before and after training, indicating that the neural control of both heart rate and blood pressure was not affected by a 16-week program of strength training.

The effect of long-term treatment with spironolactone on variceal pressure in patients with portal hypertension without ascites

The effect of spironolactone on esophageal variceal pressure (VP) in patients without ascites was investigated. VP was assessed using a noninvasive endoscopic gauge. Spironolactone was administered during a 6-week period at a dosage of 100 mg/d. This treatment decreased VP from 16.8 +/- 1.9 (SD) to 14.1 +/- 2.7 mm Hg (P < .001) in a group of 12 patients and from 18.6 +/- 2.1 to 13.7 +/- 4.1 mm Hg (P < .01) in another group of 8 patients who still had high VP despite chronic intake of propranolol. In both groups, placebo administration to 12 and 8 comparable patients did not significantly alter VP. Spironolactone induced a significant reduction of plasma volume (42.1 +/- 5.5 to 36.1 +/- 6.6 mL/kg body weight, P < .01) and of the concentration of alpha-atrial natriuretic peptide (alpha-ANP) (39.8 +/- 22 to 27.7 +/- 20 pg/mL, P < .01); in addition, a pronounced increase in plasma renin activity (PRA) (1.1 +/- 0.9 to 7.5 +/- 3.4 ng/mL/h, P < .001) was induced by the treatment. No significant changes in systemic hemodynamics were observed during the studies. Severe side effects were not observed except for a high incidence (55%) of painful gynecomasty in the male patients. In conclusion, chronic spironolactone administration effectively lowers VP, even in patients under chronic propranolol therapy. The combination of propranolol and spironolactone deserves further study as a prophylactic therapy of variceal hemorrhage, but development of gynecomasty might be a problem. Finally, we confirmed the reproducibility of VP measurements with the noninvasive gauge in chronic conditions.

Blood pressure and cationic transport systems during combined calcium channel blocker and calcium administration in males

A double-blind, placebo-controlled parallel study was conducted on the effects of a high daily oral supplementation of 1 g elemental calcium, given twice daily for 16 weeks, followed by additional administration of 2 mg b.i.d. lacidipine or placebo for 8 weeks, on blood pressure, intracellular cationic concentrations and transport systems, plasma total calcium, ionized calcium and calciotropic hormones in normal male subjects. No significant difference in the effect of lacidipine vs. placebo on standing or recumbent systolic or diastolic blood pressure or heart rate was found between calcium- and placebo-treated subjects. The difference in lacidipine effect on erythrocyte Mg2+ concentration and platelet membrane cholesterol content between the placebo and calcium groups was statistically significant. There was no additional effect between groups of lacidipine on erythrocyte and platelet intracellular Ca2+, Na+ and K+ concentrations or transport systems and on plasma Ca2+ levels and calciotropic hormones. Combined calcium and lacidipine administrations in normal male subjects did not induce antihypertensive effects different from those induced by either agent alone.

Cell membrane cation transport systems during aldosterone antagonism

We conducted a double-blind, placebo-controlled parallel study of the effect of the aldosterone antagonist spironolactone, administered once daily for 1 week to normal male subjects, on blood pressure, intracellular cationic concentrations, and transmembrane cation transport systems and plasma or urinary variables. After a 1-week run-in period on placebo, the subjects (n = 40) were allocated to a placebo or a spironolactone group. Placebo or 100 mg spironolactone was administered once daily in the morning for 1 week. All subjects were investigated at baseline and after 1 week of placebo or spironolactone administration. Standing systolic blood pressure of subjects in the spironolactone group was decreased (p < 0.001) as compared with that of subjects in the placebo group, but standing diastolic blood pressure did not change. Decreased intraerythrocyte and intraplatelet Na+ and free Ca2+ concentration and decreased activity of the platelet Na(+)-pump activity were observed in the spironolactone-treated subjects. The intraerythrocyte and intraplatelet K+ and Mg2+ concentrations, as well as the activities of the erythrocyte Na+, Li(+)-countertransporter and Na+, K(+)-cotransporter, and Na+ and K+ leakage, were not changed during spironolactone administration. The blood pressure-lowering action of spironolactone in men in the standing position is accompanied by a decrease in cytosolic free platelet Ca2+ concentration, by a reduction in intraplatelet and intraerythrocyte Na+ concentration, and in the platelet Na+ pump activity.

Influence of cholesterol-lowering on plasma membrane lipids and function

In order to determine whether alterations in membrane or plasma lipids affect transmembrane cationic transport systems in erythrocytes and platelets, cationic fluxes and intracellular concentrations, membrane lipids, plasma lipids, lipoproteins and apolipoproteins were measured in hypercholesterolemic patients before and during administration of a HMG-CoA reductase inhibitor. After a 1-month placebo run-in period, the patients were treated double-blind either with placebo (n = 25) or with pravastatin (n = 25) for 6 months. Placebo or pravastatin 10 mg during the 1st month, 20 mg during the 2nd month and 40 mg during the additional 4 months was administered once daily in the evening. Blood was collected in the morning after an overnight fast for assay of membrane and plasma lipids and of cationic fluxes and concentrations, at the end of the placebo run-in period and after 1, 2, 3 and 6 months of pravastatin therapy. Compared to the placebo group the plasma concentration of total cholesterol and phospholipids, free cholesterol and cholesterol esters, and plasma LDL-cholesterol and LDL-phospholipids were decreased during 6 months of pravastatin therapy. No changes in plasma VLDL-, HDL-, HDL2- or HDL3-cholesterol, phospholipids or triglycerides were observed in the pravastatin-treated patients. A decrease in the plasma level of apolipoprotein B and of LDL-apo B, but not of VLDL-apo B, was observed during pravastatin therapy; the plasma apolipoprotein AI and AII levels, as well as HDL2- and HDL3-apo AI and apo AII levels, however, remained unchanged. Plasma lipoprotein Lp(a) did not change during pravastatin therapy, while the plasma lecithin cholesterol acyltransferase activity (LCAT) increased. Compared to the placebo group the erythrocyte and platelet membrane cholesterol content was reduced in the pravastatin-treated patients. The intraerythrocyte and intraplatelet Na+ concentration was reduced during pravastatin administration, while the erythrocyte and platelet Na+/K+ pump activity was increased. However, the intraerythrocyte and intraplatelet K+, Mg2+, cytosolic Ca2+ concentration and water content as well as the erythrocyte Na+/Li+ countertransport and Na+/K+ cotransport activity and the Na+ and K+ leak were not changed during pravastatin treatment. Our data show that cholesterol lowering in hypercholesterolemic patients may result in a significant decrease in erythrocyte and platelet membrane cholesterol content. These changes in plasma membrane cholesterol are accompanied by an increase in the Na+ pump activity and a decrease in intracellular Na+ concentration. Whether these changes in membrane lipids and function observed during cholesterol lowering also occur in other cells remains to be further elucidated.

Public health implications of environmental exposure to cadmium and lead: an overview of epidemiological studies in Belgium. Working Groups

The CadmiBel Study was a cross-sectional population study that investigated the health effects of environmental exposure to cadmium and lead. The 2327 participants constituted a random sample of the population of four Belgian districts, chosen in order to provide a wide range of environmental exposure to cadmium. After adjustment for confounding factors, such as smoking and occupational exposure, the urinary cadmium excretion, a measure of lifetime exposure, was nearly 30% higher in the polluted areas. The CadmiBel Study produced evidence inconsistent with the hypothesis that environmental exposure to cadmium and lead would lead to an increase in blood pressure and to a higher prevalence of hypertension and other cardiovascular diseases. On the other hand, the serum alkaline phosphatase activity and the urinary excretion of calcium were significantly and positively correlated with urinary cadmium in both sexes. These findings suggested that the homeostasis of calcium was gradually affected as cadmium accumulated in the body. Furthermore, several markers of renal tubular dysfunction (urinary excretion of retinol-binding-protein, N-acetyl-beta-glucosaminidase, beta 2-microglobulin and amino acids) were significantly and positively associated with urinary cadmium. Across 10 small areas of which six were polluted with cadmium, an inverse association existed between the creatinine clearance and several indexes of environmental exposure to cadmium (cadmium concentration in the soil, cadmium content of locally grown vegetables, the inhabitants' 24 h urinary cadmium excretion). In the CadmiBel Study, the creatinine clearance was also inversely correlated with the concentrations of lead and zinc protoporphyrin in the blood. Thus, environmental exposure to cadmium and lead was associated with alterations in renal function. The significance in terms of morbidity and mortality of the functional disturbances observed in the CadmiBel Study, and the possible strategies to prevent the transfer of cadmium from the environment to man are under investigation in the prospective PheeCad Study in which half of the Cadmibel participants have been enrolled (participation rate 80%).

Cholesterol modulation of transmembrane cation transport systems in human erythrocytes

The aim of this study was to investigate whether in vitro cholesterol enrichment of human erythrocytes affects transmembrane cation transport systems by changes induced in the membrane microviscosity of these cells. Human erythrocytes in suspension were incubated with cholesterol-lecithin dispersions to obtain an enrichment of their membrane cholesterol. The ouabain-sensitive Na+ efflux, the Na+, Li+(-)countertransport activity, the Na+, K+(-)cotransport activity, the basal transmembrane leakage of Na+ and K+, and the enzymatic activity of ATPases were determined in these cholesterol-rich cells and compared with control cells. Membrane core and surface microviscosity was also measured in the control and cholesterol-enriched cells, using the fluorescent probes, 1,6-diphenyl-1,3,5-hexatriene (DPH) and trimethylammonium (TMA)-DPH, respectively. The cholesterol content of the erythrocytes incubated in the presence of cholesterol-rich dispersions increased gradually over time. A 47% increase membrane cholesterol content was obtained after 16 h of incubation, while no change in the erythrocyte phospholipid content was found. High membrane cholesterol in the human erythrocyte phospholipid content was found. High membrane cholesterol in the human erythrocyte, obtained by in vitro enrichment of the cells with cholesterol-lecithin dispersion, inhibited in intact cell suspensions the ouabain-sensitive Na+ efflux, an estimate of the Na+(-)pump activity, and in isolated erythrocyte membranes the enzymatic activity of Na+, K+(-)ATPase, and Mg2+(-)ATPase. The dissociation constant for internal sodium and the maximal rate of ouabain-sensitive Na+ efflux is decreased in cholesterol-rich erythrocytes compared to control cells. The elevated erythrocyte membrane cholesterol content was also accompanied by a decrease in the Na+,K+(-)cotransport activity, the Na+, Li+(-)countertransport activity, and the transmembrane basal leakage of Na+ and K+. Microviscosity, measured in the erythrocyte membrane core with the fluorescence probe DPH, was increased in the cholesterol-rich cells compared to the control cells. However, the membrane surface microviscosity, measured with the probe TMA-DPH, was not different between the control cell and the cholesterol-rich cells. The present data show that enrichment of the human erythrocyte membrane with cholesterol results in an increase of membrane core microviscosity, resulting in an inhibition of transmembrane cation transport systems in erythrocytes in suspensions and of erythrocyte membrane Na+,K+(-)ATPase, Ca2+(-)ATPase, and Mg2+(-)ATPase.

Effect of oral calcium supplementation on intracellular calcium and plasma renin in men

A double-blind, placebo-controlled parallel study was conducted on the effect of a high daily oral calcium supplementation of 1 g elemental calcium, given twice daily for 16 weeks in normal male subjects, on plasma renin, aldosterone, kallikrein, cGMP, cAMP and calciotropic hormones, intracellular calcium concentrations and plasma total and ionized calcium. After a 1-month run-in period on a limited use of dairy products, the subjects (n = 32) were allocated to a placebo or a calcium group. Placebo or 1 g elemental calcium was administered twice daily in the morning and evening for 16 weeks. All subjects were investigated at baseline and after 1, 2, 4, 8 and 16 weeks of placebo or calcium administration. A decreased intraerythrocyte and intraplatelet Ca2+ concentration was observed in the calcium-treated subjects. Compared with the placebo group, an increase in the plasma renin activity (PRA) in the calcium group was observed after 4, 8 and 16 weeks of oral calcium administration. However, plasma aldosterone and urinary excretion of aldosterone, kallikrein, cGMP and cAMP were not changed during calcium administration. Oral calcium supplementation in these men was also accompanied by a reduction in the plasma concentration of intact parathyroid hormone and 1,25-dihydroxyvitamin D3, an increase in 24-h urinary calcium excretion but no change in the plasma total Ca2+ concentration, serum ionized Ca2+ level and plasma phosphate or 25-hydroxyvitamin D3. Lacidipine tended to increase PRA in the placebo-treated subjects and to decrease it in the calcium-treated subjects: this difference in lacidipine effect between the placebo and calcium group was significant (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Dietary calcium, blood pressure and cell membrane cation transport systems in males

OBJECTIVE

A double-blind, placebo-controlled parallel-group study was conducted on the effect of a high level of daily oral calcium supplementation (1 g elemental calcium given twice a day for 16 weeks) in normal male subjects on blood pressure, intracellular cationic concentrations and transmembrane cation transport systems, plasma total and ionized calcium, and calciotropic hormones.

METHODS

After a 1-month run-in period with a limited intake of dairy products, the 32 subjects were allocated to a placebo or a calcium group. Placebo or 1 g elemental calcium was administered twice a day, in the morning and evening, for 16 weeks. All subjects were investigated at baseline and after 1, 2, 4, 8 and 16 weeks of placebo or calcium administration.

RESULTS

Compared with the placebo group, standing systolic blood pressure was decreased in the calcium group, whereas the standing diastolic blood pressure tended to decrease. The changes in supine systolic and diastolic blood pressure did not differ between the placebo and calcium groups. Decreased intra-erythrocyte and intraplatelet sodium and calcium concentrations, an increased activity of platelet and erythrocyte sodium-pump activity and a reduced membrane cholesterol content were observed in the calcium-treated subjects. Erythrocyte membrane surface and core microviscosity, however, did not change during calcium supplementation. Oral calcium supplementation in these men was accompanied by a reduction in the plasma concentrations of intact parathormone and 1,25-dihydroxyvitamin D3, and an increase in 24 h urinary calcium excretion, but no change in the plasma total calcium concentration, serum ionized calcium level, or plasma phosphate or 25-hydroxyvitamin D3. The intra-erythrocyte and intraplatelet potassium and magnesium concentrations as well as the activities of the erythrocyte Na,Li-countertransporter and Na,K-cotransporter, and sodium and potassium leakage did not change during calcium administration.

CONCLUSIONS

The lowering of standing blood pressure seen in men with a high calcium intake is accompanied by a decrease in cytosolic free platelet calcium and total erythrocyte calcium, by a reduction in intraplatelet and intra-erythrocyte sodium concentration and erythrocyte membrane cholesterol and by an increase in the activity of the erythrocyte and platelet sodium-pump.