Biomedical subjects

R Locher

Publications and source records attributed to R Locher.

At least 55 records · Page 3Linked to original sources

PubMed1989

Cortisol-stimulated phosphoinositide metabolism in vascular smooth muscle cells: a role for glucocorticoids in blood pressure control?

Physiological concentrations of cortisol (0.02-5.0 micrograms/ml) stimulate the phosphoinositide breakdown in cultured smooth muscle cells from rat aorta. After a 15-min stimulation of the cells with various concentrations of cortisol, the inositol-1,4,5-triphosphate concentrations showed a dose-dependent increase. This phenomenon was qualitatively similar but quantitatively more sensitive in smooth muscle cells from spontaneously hypertensive rats (SHR) than in vascular smooth muscle cells from normotensive animals. When the antihormone RU 486 was added before the vascular smooth muscle cells were stimulated with cortisol, the inositol-1,4,5-triphosphate production was reduced to 50%.

Animals↗

PubMed1988

Rapid activation of human platelets by low concentrations of low-density lipoprotein via phosphatidylinositol cycle.

The interaction of low-density lipoprotein (LDL) with the human platelet was investigated with regard to saturable high-affinity binding, shape change, cytosolic free Ca2+ concentration, phosphatidylinositol (PtdIns) turnover, and thromboxane B2 biosynthesis. The experiments show that LDL, at a concentration approximately 100 times lower than in plasma, causes platelet activation concomitantly with stimulation of the PtdIns cycle and thromboxane B2 formation, similarly to other activators of platelets. The effects of LDL were inhibited by high-density lipoprotein. The results suggest that activation of platelets by low concentrations of LDL may play a role in pathophysiological conditions and that platelet can serve as a model for studying the influence of LDL on various target cells.

Binding Sites↗

PubMed1988

Low density lipoprotein causes general cellular activation with increased phosphatidylinositol turnover and lipoprotein catabolism.

Low density lipoprotein (LDL), at concentrations high enough for receptor binding but not high enough to saturate the receptor, induces activation of phosphatidylinositol (PtdIns) turnover in a variety of cell types with various biological functions. Using both biochemical and electron microscopic studies, we have shown that blood platelets take up and degrade LDL in a manner reminiscent of phagocytic cell types. The activation of both PtdIns turnover and LDL metabolism is inhibited by high density lipoprotein. Thus, LDL at hormonal concentrations causes general cellular activation. Since all cell types studied responded to LDL with increased PtdIns turnover and uptake of LDL cholesterol, the PtdIns cycle may also be involved in the cellular regulation of LDL cholesterol metabolism.

Animals↗

PubMed1988

The phosphoinositide turnover of vascular smooth muscle cells is influenced by fish oil.

As the phosphoinositide cycle and high serum levels of low-density lipoprotein cholesterol may be involved in the pathogenesis of both hypertension and atherosclerosis, the effect of fish oil on low-density lipoprotein stimulation of phosphoinositide metabolism was studied in cultured rat vascular smooth muscle cells. Low-density lipoprotein-stimulated synthesis of inositol trisphosphate decreased to 5-48% of control values in vascular smooth muscle cells treated for 4 weeks with either fish oil or n-3 eicosapentaenoic acid (EPA), the active ingredient of fish oil. In addition, low-density lipoprotein-induced biosynthesis of thromboxane A2 was reduced by 50% in vascular smooth muscle cells precultured with either fish oil or EPA. Thus, our results may explain the mechanisms by which fish oil exerts its beneficial effects on both atherosclerosis and hypertension.

Animals↗

PubMed1988

Stimulation of the phosphoinositide signalling system as a possible mechanism for glucocorticoid action in blood pressure control.

Cortisol stimulates the phosphoinositide signalling system in smooth muscle cells of the rat aorta. After stimulation of the cells with cortisol, epinephrine or both compounds, inositol-1,4,5-trisphosphate concentrations were analysed by standardized ion-exchange chromatography procedure. A 15-min stimulation with physiological concentrations of cortisol (0.02-5.0 microgram/ml) led to a dose-dependent increase of the inositol trisphosphate concentrations (up to 500%) and also to a translocation of the calcium- and lipid-dependent protein kinase C activity from the cytosolic to the membranous compartment. Incubation of smooth muscle cells with epinephrine (10(-9) to -5 mol/l) did not lead to an increase in the inositol trisphosphate concentrations. However, after pre-incubation with an average dose of cortisol (0.2 microgram/ml) the inositol trisphosphate response was potentiated by 10(-7) mol/l epinephrine. Our results suggest that stimulation of the phosphoinositide system is a still unknown mechanism of glucocorticoid action in smooth muscle cells, which could influence intracellular free calcium and thus vascular reactivity and blood pressure.

Animals↗

PubMed1986

Effect of atrial natriuretic polypeptide on angiotensin II-induced increase of cytosolic free calcium in cultured smooth muscle cells.

We investigated the effects of angiotensin II (ANG II) and synthetic atrial natriuretic polypeptide (ANP) on cytosolic free calcium concentration [( Ca2+]i) of cultured rat vascular smooth muscle cells. Incubation with ANP alone showed little or no change in [Ca2+]i, whereas ANG II alone increased [Ca2+]i in a dose-dependent manner up to 164%, compared with basal levels of 253 +/- 17 nmol/l (mean +/- s.e.m.). Simultaneous addition of 10 nmol/l ANG II and varying concentrations of ANP produced a reduction in the ANG II-induced increase in [Ca2+]i. These data suggest that the vasorelaxant effect of ANP is at least partly mediated by changes in [Ca2+]i.

Angiotensin II↗

PubMed1986

Enalapril as a first-step agent in essential hypertension: a comparative study with atenolol.

The aim of the present double-blind crossover study was to compare the antihypertensive efficacy and tolerability of enalapril and atenolol in 48 patients with mild to moderate essential hypertension. After a 2-week wash-out period, treatment was started with either enalapril 20 mg or atenolol 50 mg daily. In patients with a diastolic blood pressure value of more than 90 mmHg after 2 weeks of therapy, doses were doubled. After 4 weeks of therapy, cases were classified as responders (diastolic blood pressure less than or equal to 95 mmHg) or non-responders (diastolic blood pressure greater than 95 mmHg) and after a 2-week wash-out phase switched over to the alternative drug for another 4-week therapy period. Both substances significantly lowered mean systolic and diastolic blood pressure to a comparable degree. After 2 weeks, 57% of patients under enalapril and 59% under atenolol shared a satisfactory response, which did not change at the higher dose levels. After 4 weeks of therapy the incidence of side effects was slightly, but insignificantly, higher on atenolol than on enalapril. Thus, our results show that both agents seem equally qualified as first-step drugs in the treatment of mild to moderate essential hypertension.

Adult↗

PubMed1985

Stereospecific modulation of the calcium channel in human erythrocytes by cholesterol and its oxidized derivatives.

To study the effect of cholesterol and its pathophysiologically important oxidized derivatives (OSC) on the calcium entry channel, the human red blood cell was used as a model system. The calcium ejecting adenosinetriphosphatase (ATPase) was inhibited by vanadate. The cells were loaded with OSC at concentrations between 1.25 X 10(-5) and 25 X 10(-5) mol/l. 22-Hydroxycholesterol, cholestan-3 beta,5 alpha,6 beta-triol, 5 alpha-cholestan-3 beta-ol,3 beta,5 alpha-dihydroxycholestan-6-one and 3 beta-hydroxy-5 alpha-cholestan-7-one stimulated 45Ca2+ influx by up to almost 90%, whereas 25-hydroxycholesterol, 7 beta-hydroxycholesterol, 20 alpha-hydroxycholesterol and 7-oxocholesterol inhibited influx by up to 75%. Both stimulation and inhibition were dependent on the amount of OSC incorporated into the membrane. More than 90% of the total modification of calcium influx by OSC was accounted for by an influence on the nitrendipine-inhibitable part of influx. Enrichment of cholesterol in the membrane greatly stimulated, and cholesterol depletion inhibited, Ca2+ influx. These results demonstrate that cholesterol and its oxidized derivatives are able to modulate the calcium channel in human red blood cells in a highly stereospecific manner.

Calcium↗

PubMed1985

High density lipoproteins--modulators of the calcium channel?

It has recently been shown that human red blood cells possess a voltage-independent calcium channel which can be influenced by in vitro modification of the membraneous cholesterol content. To determine whether there is also a link between plasma lipids and the calcium influx through this channel under in vivo conditions, the calcium influx was measured in red blood cells from 51 male donors (aged 41 +/- 5 years). The influx through the channel was defined as the nitrendipine (15 mumol/l)-inhibitable part of 45Ca2+ influx. The Ca(2+)-ejecting ATPase was inhibited by vanadate. The results demonstrate a strong inverse relationship (r = -0.81; P < 0.001) between the plasma concentration of high density lipoproteins (HDL) and 45Ca2+ influx. No significant correlation was found between 45Ca2+ influx and triglycerides, low density lipoproteins (LDL), very low density lipoproteins (VLDL), total plasma cholesterol or extracellular electrolytes (K+, Na+, Ca2+, Mg2+). The results indicate that HDL are involved in the modulation of the calcium channel and provide a link between the cellular cholesterol turnover and the calcium influx in the pathogenesis of atherosclerosis and hypertension.

Adult↗

PubMed1984

The cholesterol content of the human erythrocyte influences calcium influx through the channel.

In order to study the influence of the cholesterol content on the calcium entry channel, the human red blood cell was used as a model system. The cholesterol to lecithin ratio (C/L ratio) of the membrane was modified experimentally by incubating the cells (15h, 25 degrees) with liposomes of defined C/L ratios. Subsequently, net 45Calcium-influx into the cell was measured by inhibiting the Ca-ejecting ATPase with vanadate. Additionally, the use of nitrendipine, a potent calcium channel inhibitor, during incubation allowed the determination of Ca-influx through the calcium channel. A positive correlation between the 45Ca++-influx and the molar C/L ratio of the membrane was found over a wide C/L range. A molar C/L ratio of 1.4 in the membrane increased calcium influx by 150 % compared to controls (molar C/L ratio = 0.8, calcium influx rate = 100 %), while a molar C/L ratio at less than 0.75 decreased calcium influx by 50 %. We conclude, that the cholesterol content of the membrane greatly influences the calcium channel and thus plays a pivotal role for the availability of calcium as a second messenger. These findings may provide a link between high plasma cholesterol and the development of atherosclerosis as well as enhanced platelet aggregability.

Calcium↗

PubMed1984

Angiotensin II binding to human mononuclear cells: receptor or free fluid endocytosis?

It has recently been claimed that there are angiotensin II (ANG II) receptors on human mononuclear cells and on platelets and this has been used for investigating the regulation of the renin-angiotensin system in hypertension. We here show the following. Binding kinetics of 125I-labelled ANG II and [3H]ANG II to mononuclear cells were slow (maximum at 90 min) and the same as for [3H]-inulin. As with [3H]inulin there was no binding at 4 degrees C. Release from the cells was slow and incomplete (about 30% after 15 min, 60% after 60 min). Binding was not saturable over a range from 10(-12) to 10(-6) mol of ANG II/l, about 8% of offered peptide being bound at all concentrations. Various inhibitors of free fluid endocytosis exhibited the same inhibition pattern of ANG II binding to mononuclear cells. Therefore uptake of ANG II into mononuclear cells displayed all the features of free fluid endocytosis. ANG II was degraded by carboxypeptidase A. When this degradation was prevented by D-phenylalanine, no binding occurred. In platelet preparations contaminated by 0.3-5% of mononuclear cells, 125I-labelled ANG II was degraded as well. Free fluid endocytosis of the degradation product strongly depended on the percentage of contaminating mononuclear cells. We conclude that there are no ANG II receptors on human mononuclear cells and that their presence on human platelets is doubtful.

Angiotensin II↗

PubMed1984

Human red blood cells--an ideal model system for the action of calcium agonists and antagonists.

To characterize the pharmacological properties of the slow calcium channel of human red blood cells, we studied the action of various calcium antagonists and two agonists on the 45Ca2+-influx. The Ca2+-ejecting ATPase was inhibited by vanadate. All dihydropyridine derivatives tested showed their inhibiting or stimulating effect on the channel at concentrations attainable in vivo (nitrendipine:Ki = 2.5; Bayer K 6244:Ki 5 microM; nicardipine:Ki = 15 microM, Ks = 0.5 microM; Ciba 28 392:Ki = 20, Ks = 0.3 microM; Ki = inhibition constant, Ks = stimulation constant). Of special interest was the biphasic behaviour (stimulation and inhibition) of the calcium antagonist nicardipine and the agonist Ciba 28 392. The maximum inhibition by the phenylalkylamine derivative verapamil was obtained at much higher concentrations (250 microM; Ki = 100). These data suggest that the calcium channel of human red blood cells has pharmacological properties very similar to the channel in heart and smooth muscle cells with respect to dihydropyridine action. Therefore, human red blood cells are an ideal model to study the action of calcium agonists and antagonists.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMed1984

Cholesterol and its oxidized derivatives modulate the calcium channel in human red blood cells.

The human red blood cell was used as a model system in order to study the effect of cholesterol and its medically important oxidized derivatives (OSC = oxidized sterol compounds) on the calcium entry channel. The calcium-ejecting adenosine triphosphatase (ATPase) was inhibited by vanadate and the influx of 45Ca2-into the cells measured. The cells were loaded with OSC at concentrations between 0.075 and 1.5 micrograms OSC/10(7) cells. Two classes of OSC could be distinguished: one stimulating Ca2+ influx dose-dependently by almost 100% at maximum concentrations, the other inhibiting it dose-dependently by up to 80%. The calcium channel blocker nitrendipine inhibited influx by 70% at 15 microM. More than 90% of the total stimulation or inhibition was accounted for by an influence on the nitrendipine-inhibitable part of influx, i.e. the calcium channel. Cholesterol (incorporated using liposomes) had a stimulatory (+288%), cholesterol depletion an inhibitory effect on calcium influx (-18%). These results demonstrate that cholesterol and its oxidized derivatives modulate the calcium channel in a highly stereospecific manner and provide new insights into the mechanism of action and the atherogenic effect of these compounds.

Calcium↗

PubMed1983

Production, characterization and clinical application of antisera to cortisol.

In the present paper the production of highly specific and sensitive antisera to cortisol is described. The antisera were generated in rabbits using both cortisol-3-monooxime and cortisol-3,20-dioxime derivatives. Bovine thyroglobulin was used as a carrier protein. Antibody characteristics were determined by radioimmunoassay procedure. Antibody titers observed after immunization with the monooxime conjugate were significantly higher (p less than 0.001) than those obtained with the dioxime conjugate. In addition, cross reactivity for various naturally occurring steroids was markedly lower and sensitivity was increased as compared to dioxime antisera (15 vs. 40-60 pg/tube). Accuracy and precision were calculated for the monooxime antiserum used in a RIA system for clinical application. A close correlation (r = 0,9802) was found between plasma cortisol values measured by radioimmunoassay and the competitive protein binding method. The concentrations obtained by the protein binding method were slightly but significantly higher than those measured by radioimmunoassay indicating higher specificity of the antibody used (p less than 0.005).

Aldosterone↗

PubMed1983

Altered calcium and sodium metabolism in red blood cells of hypertensive man: assessment by ion-selective electrodes.

Free intracellular calcium [Ca2+]i, sodium [Na+]i and potassium [K+]i were assessed in freeze-thawed human red blood cells (RBC) by ion-selective electrodes. After metabolic depletion by 30 mM 2-desoxy-glucose, [Ca2+]i increased faster and to significantly higher values in RBC from 16 patients with mild to moderate essential hypertension (mean diastolic blood pressure 111 +/- 10 mmHg) than in the RBC of 24 normotensives. The rate of [Ca2+]i increase was 7.0 +/- 3.6 versus 3.7 +/- 4.0 mumol/h/l cells (P less than 0.01) for the first 24 h and 8.1 +/- 4.8 versus 6.4 +/- 3.5 mumol/h/l cells for the following 24 h. [Na+]i before and after 24 h incubation was significantly higher in hypertensives, whereas basal [Ca2+]i and [K+]i before and after incubation were the same in both groups. After Ca loading by ionophore A 23187, the maximum rate of [Ca2+]i extrusion was not significantly lower in intact RBC from hypertensives than in those from normotensives (59.5 +/- 7.8 versus 87.9 +/- 18.1 mumol/min/l cells). These results indicate disturbances in RBC Ca metabolism similar to those observed earlier for Na and K. If generalized, the defect could lead to raised [Ca2+]i in smooth muscle and sympathetic nerve tissue, thus causing increased vascular tone and probably catecholamine release with subsequent arterial hypertension.

Adenosine Triphosphate↗

PubMed1983

Interactions between 8-L-arginine vasopressin and prostaglandin E2 in human mononuclear phagocytes.

The effect of 8-L-arginine vasopressin (AVP) on biosynthesis of prostaglandins in human mononuclear phagocytes was examined. AVP, oxytocin, and deamino-(8-D-arginine) vasopressin (dDAVP) affected prostaglandin biosynthesis in a rank order that parallels their pressor but not antidiuretic activity (AVP greater than oxytocin greater than dDAVP). Radioimmunoassay, incorporation studies using [14C]arachidonic acid and radiometric thin-layer chromatography, revealed prostaglandin E2 (PGE2) to be the only prostaglandin synthesized by the mononuclear phagocytes. While high concentrations of PGE2 elevated cytoplasmic levels of cyclic AMP by five- to sevenfold above basal values, low concentrations of PGE2 that are released by the cells in the presence of AVP failed to increase cyclic AMP content in the cells. However, PGE2 at concentrations that do not alter cyclic AMP levels markedly interferes with the activity of AVP. This effect is, however, very time dependent. Addition of PGE2 to the cells 30 min before AVP, was followed by a period of unresponsiveness to the hormone that lasts at least 30 min. Pretreatment of the cells with indomethacin enhanced the AVP-mediated accumulation of intracellular cyclic AMP level. PGE2 did not modify [3H]AVP binding, indicating that its inhibitory effect on the activity of the peptide is not due to downregulation of vasopressin receptors.

Arginine Vasopressin↗

PubMed1981

Receptor dysfunctions in human disease.

The characterization of binding parameters of hormones and drugs to specific receptors at various human cell types have introduced an interesting approach for the evaluation of pathogenic mechanisms involved in endocrine and metabolic disorders. The dysregulation of cellular receptors in those disease include changes in receptor number, changes in binding affinity and production of antibodies against receptor molecules. It can be concluded from these observations that altered receptor physiology may be of important value for abnormalities in cellular recognition and control mechanisms which can be observed in neoplastic, inflammatory, immune and developmental diseases.

Adenylyl Cyclases↗

PubMed1981

125I-8-L-arginine vasopressin binding to human mononuclear phagocytes.

The binding of vasopressin to human circulating blood cells was examined. Direct binding studies with preparations of single cell types indicated that the mononuclear phagocyte system is almost entirely responsible for binding of the hormone. Binding of 125I-8-L-arginine vasopressin (AVP) (40 pM) in the presence of excess unlabeled hormone was saturable (2.8 +/- 0.4 fmol/2 x 10(6) cells per ml), was linear with cell number, was dependent upon the concentration of the radioligand used, and was reversible. Binding equilibrium was achieved in 30--40 min at 22 degrees C. Scatchard analysis of binding at this time showed an apparent dissociation constant of 25 +/- 0.21 pM, providing an estimate of 640 +/- 80 sites/cell. Pretreatment of the cells with cytochalasin B, an agent that can block phagocytosis, did not modify radioligand binding, which indicates that 125I-AVP uptake by the cells is due to binding and not to endocytosis. Specificity of vasopressin-sensitive sites on mononuclear phagocytes was demonstrated with a series of vasopressin analogues with various degrees of antidiuretic potency, and with peptide hormones that bind to specific receptors on circulating blood cells but that lack antidiuretic activity. AVP (40 pM) elevated the intracellular level of cyclic AMP from 137 +/- 8.6 to 350 +/- 20.5 pmol/mg cell protein. The binding affinities of the various analogues were correlated with their ability to stimulate intracellular cyclic AMP synthesis (Lys8-vasopressin less than deamino(8-D-Arg)-vasopressin less than oxytocin).

Arginine Vasopressin↗