Decreased erythrocyte cholesterol/phospholipid ratio in untreated patients with essential hypertension

Increased membrane ratios of metabolite to precursor fatty acid in essential hypertension

Desaturase enzymes are responsible for the conversion of essential fatty acids to the longer-chain eicosanoid precursors. These enzymes require zinc as an essential cofactor, and the following ratios-C20:4/C18:2, C20:5/C18:3, and C22:6/C20:5-are considered indexes of their activity. We analyzed these parameters in plasma and erythrocyte membranes of 105 essential hypertensive patients, 20 white coat hypertensive patients, and 100 age-matched normotensive control subjects. Dietary analysis excluded significant quantitative and qualitative differences in fatty acid dietary intake between essential hypertensive patients and normotensive control subjects. Zinc levels and C20:4/C18:2, C20:5/C18:3, and C22:6/ C20:5 ratios were significantly higher in essential hypertensive patients than control subjects, whereas white coat hypertensive patients showed intermediate values for all these parameters. These data provide evidence for an alteration in fatty acid metabolism of essential hypertensive patients, consistent with increased activity of desaturase enzymes. The consequent greater bioavailability of eicosanoid precursors, and in particular of arachidonic acid, could affect several vascular functions and have a bearing on the pathogenesis or complications of hypertension.

The rate of transbilayer movement of erythrocyte membrane cholesterol is correlated with sodium-lithium countertransport

Hypertension is associated with some abnormalities in cell membrane structure, including an impaired distribution of cholesterol into the monolayers of erythrocyte membrane. Transbilayer movement of membrane cholesterol modulates the formation of these structural cholesterol domains. We tested whether the rate of cholesterol movement may influence on the erythrocyte Na(+)-Li+ countertransport, that is a marker of human essential hypertension. In single regression analysis, the half-time for the decrease in specific radioactivity of cholestenone (inverse of membrane cholesterol transbilayer movement) was negatively related to the erythrocyte cation flux mediated by Na(+)-Li+ countertransport (r = -0.8983, P < 0.0001 for control subjects; r = -0.8191, P < 0.005 for normocholesterolaemic hypertensive patients; r = -0.7664, P < 0.005 for hypercholesterolaemic hypertensive patients). These data suggest that changes in the transbilayer movement of membrane cholesterol interfere with the main cation transport system which is implicated in the pathophysiology of essential hypertension. This also provides a new link between kinetic cholesterol pools and cell membrane functions.

Disturbed energy balance in skeletal muscle of patients with untreated primary hypertension

OBJECTIVE

It has been shown that the distribution of Na+ and Ca2+ in various cells is abnormal in patients with untreated primary hypertension, indicating an altered membrane permeability in these cells. This would activate certain ion pumps and thereby enhance ATP turnover. We investigated possible alterations in energy economy of skeletal muscle tissue.

DESIGN

Skeletal muscle energetics were studied in vitro and in vivo in patients with untreated primary hypertension. Phosphocreatine (PCr), energy charge (EC) and total adenylate values were assessed.

SETTING

The study was performed at the outpatient clinic of a general hospital and at a university clinical chemistry department and at a specialized bioenergetic laboratory.

SUBJECTS

Altogether, 17 patients with untreated primary hypertension were examined together with matched, healthy and normotensive controls with normal body-mass index.

MAIN OUTCOME MEASURES

Skeletal muscle biopsies were obtained from 10 patients and 10 controls for analysis of high energy phosphate compounds. Another seven patients were enrolled for in vivo NMR spectroscopy.

RESULTS

We found a decrease of 30% (P < 0.01) of PCr content in the patients, whilst EC and total adenylates were unchanged. Nuclear magnetic resonance spectroscopy showed an abnormal decrease of PCr during exercise followed by a markedly slower regeneration of PCr during post-exercise recovery parallelled by a slower recovery of pH. This phenomenon was mirrored by a more pronounced decrease of ATP/Pi in patients during exercise and a slower recovery of ATP/Pi.

CONCLUSION

The data are compatible with an increased ATP turnover in skeletal muscle cells of patients with untreated primary hypertension although ATP was favoured and kept at a normal resting level at the expense of the PCr store.

Direct effect of insulin on 45calcium uptake in human erythrocytes

OBJECTIVE

High blood pressure is prevalent in obesity and non-insulin dependent diabetes mellitus; both conditions, with insulin resistance and essential hypertension, have been associated with increasing intra-erythrocytic levels of calcium ions. We tested the hypothesis of whether insulin itself might be responsible for the abnormal red cell cytosolic free calcium.

DESIGN

The ionic effects of insulin were studied on the kinetics of 45calcium uptake in vitro in normal human erythrocytes.

SETTING

The study was performed in the outpatient clinic of a central hospital.

SUBJECTS

Sixteen healthy, normotensive individuals with normal body mass index were recruited for the study.

MAIN OUTCOME MEASURES

Blood from eight individuals was used for time-dependent studies of 45calcium uptake in erythrocytes and blood from another eight individuals was used for dose-dependent studies of insulin effect.

RESULTS

The rate of 45calcium influx in red blood cells has two components, a fast component (0-10 min), which measures the initial rate of 45calcium influx, and a slow component (10-60 min) probably reflecting a relatively large backflux of calcium (calcium efflux), which accordingly determines an apparent low rate of 45calcium influx between 10-60 min. The uptake was linear with time between 10-120 min regardless of insulin being present or not. Insulin at a concentration of 120 mU L-1 significantly decreased the 45calcium uptake in a time-dependent fashion between 10-120 min. The uptake was 508 (+/- 59) at 60 min in the presence of insulin vs. a control value of 529 (+/- 59) pmol mL red blood cells-1 (P < 0.001). The corresponding figures at 120 min were 742 (+/- 109) and 767 (+/- 127), respectively (P = 0.02). Inconsistent results were obtained on 45calcium uptake at 60 min by varying insulin concentrations from 40-640 mU L-1 and a dual effect of insulin on 45calcium uptake could not be excluded, one at a fairly low concentration of insulin (40-120 mU L-1) and another at a high concentration (160-640 mU L-1).

CONCLUSION

The data indicate a direct role of insulin in the transport process of calcium into normal human erythrocytes.