Monovalent and divalent ions in vascular tissue

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.

Ouabain-induced contraction of vascular smooth muscle in spontaneously hypertensive rats and the effect of hydralazine

The effect of ouabain (10(-3) M) on contractile responses of SHR (spontaneously hypertensive rat) and WKY (Wistar-Kyoto rat) aortas and mesenteric arteries was studied. Ouabain addition caused a rapid contraction of aortic strips with a steeper rate of rise and a larger maximal force development in strips from SHR than WKY. This difference in contractile response is known to occur in the prehypertensive period of SHR (4-week-old). Phentolamine (10(-6) M) pretreatment had no effect on the ouabain-induced contraction but partially suppressed it in both SHR and WKY aortas when diltiazem (10(-5) M) was also added. The difference in the ouabain-induced contractions of SHR and WKY aortas was more apparent in the residual contraction during suppression by diltiazem. The 45Ca uptake in the presence of ouabain was significantly larger in the early period of incubation in SHR aorta than in WKY aorta. The ouabain-induced contraction of hydralazine-treated SHR aorta from the prehypertensive period was very similar to that of non-treated WKY aorta. These results suggested that the abnormality of the ouabain-induced contraction in SHR arterial smooth muscle could have arisen from an increased Ca2+ movement due to Ca2+ leakage when ouabain inhibited the Na+-pump in the membrane. This abnormality seems to start during the prehypertensive period and continue in the hypertensive stage.

Altered erythrocyte and plasma sodium and potassium in hypertension, a facet of hyperinsulinemia

Red blood cell sodium and potassium, plasma potassium, glucose and insulin responses to oral glucose load, serum urate, and plasma triglycerides were determined in a stratified subsample (n = 89) of a representative population sample (n = 1211), comprising 30 nonobese normotensive subjects with normal glucose tolerance (reference group) and 59 subjects representing each of the seven possible combinations of abnormal glucose tolerance, obesity, and hypertension. Rate of cation imbalance (red blood cell sodium greater than or equal to 7.0 mEq/L, potassium less than 92.5 mEq/L, or plasma potassium greater than or equal to 4.5 mEq/L) was 88.1% in subjects with abnormal tolerance, obesity, or hypertension, as compared with 40.0% in the reference group (p less than 0.001). These subjects were also characterized by significantly greater rates of insulin response: 60- and 120-minute postload levels of 100 mU/L or more (88.1 vs 46.7%), plasma triglycerides of 80 mg/dl or more (89.8 vs 53.3%) and serum uric acid of 5.5 mg/dl or more (61.0 vs 26.7%; p less than 0.001 for all). The rate of cation imbalance was significantly associated with each of these three biochemical correlates: insulin response (p less than 0.01), triglycerides (p less than 0.001), and urate (p less than 0.001). In the total population sample, the rate of untreated hypertension increased from 18% to 35% to 55.3% (p less than 0.001), with an increase in the number of biochemical correlates of cation imbalance in combination with glucose intolerance and obesity.(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation of prostacyclin generation in cultured human vascular endothelial cells and the effects of human alpha-natriuretic polypeptide

Vascular endothelial cells have been known to possess not only a barrier function but also other biologically important functions maintaining vascular homeostasis. Among these, the generation of prostacyclin is one of the most conspicuous functions, and the modulation of its synthesis and liberation has been of interest with reference to the interaction with several vasoactive substances, including human atrial alpha-natriuretic polypeptide. This paper investigates the regulatory mechanism of prostacyclin generation using cultured human vascular endothelial cells as far as Ca2+ flux, (Na+ + K+)-ATPase activity, and Na+-Ca2+ exchange systems are concerned. Through these experimental studies the following results were obtained. Prostacyclin generation was triggered by an increase of Ca2+ influx, and an increase in intracellular Na+ also enhanced it, and this was accompanied by a decreased Ca2+ efflux arising from suppression of Na+-Ca2+ exchange systems. (Na+ + K+)-ATPase activity as well as prostacyclin generation was also enhanced by the increase of intracellular Na+. These results indicate a possible link between the mechanism which generates prostacyclin in the human vascular endothelial cells and the mobilization of electrolytes; however, in this aspect human atrial alpha-natriuretic polypeptide had no effect on the endothelial cells.

Hyperinsulinemia. A link between hypertension obesity and glucose intolerance

Hypertension and glucose intolerance, determined in a random population sample (n = 2,475), showed a highly significant (P less than 0.001) association from the mildest levels of both conditions, independent of the confounding effects of age, sex, obesity, and antihypertensive medications. Summary rate ratios for hypertension were 1.48 (1.18-1.87) in abnormal tolerance and 2.26 (1.69-2.84) in diabetes compared with normal tolerance. Altogether, 83.4% of the hypertensives were either glucose-intolerant or obese--both established insulin-resistant conditions. Fasting and post-load insulin levels in a representative subgroup (n = 1,241) were significantly elevated in hypertension independent of obesity, glucose intolerance, age, and antihypertensive medications. The mean increment in summed 1- and 2-h insulin levels (milliunits per liter) compared with nonobese normotensives with normal tolerance was 12 for hypertension alone, 47 for obesity alone, 52 for abnormal tolerance alone, and 124 when all three conditions were present. The prevalence of concentrations (milliequivalents per liter) of erythrocyte Na+ greater than or equal to 7.0, K+ less than 92.5, and plasma K+ greater than or equal to 4.5 in a subsample of 59 individuals with all combinations of abnormal tolerance obesity and hypertension was compared with those in 30 individuals free of these conditions. Altogether, 88.1% of the former vs. 40.0% of the latter group presented at least one of these three markers of internal cation imbalance (P less than 0.001). We conclude that insulin resistance and/or hyperinsulinemia (a) are present in the majority of hypertensives, (b) constitute a common pathophysiologic feature of obesity, glucose intolerance, and hypertension, possibly explaining their ubiquitous association, and (c) may be linked to the increased peripheral vascular resistance of hypertension, which is putatively related to elevated intracellular sodium concentration.

Blood pressure and nutrient intake in the United States

A data base of the National Center for Health Statistics, Health and Nutrition Examination Survey I (HANES I), was used to perform a computer-assisted, comprehensive analysis of the relation of 17 nutrients to the blood pressure profile of adult Americans. Subjects were 10,372 individuals, 18 to 74 years of age, who denied a history of hypertension and intentional modification of their diet. Significant decreases in the consumption of calcium, potassium, vitamin A, and vitamin C were identified as the nutritional factors that distinguished hypertensive from normotensive subjects. Lower calcium intake was the most consistent factor in hypertensive individuals. Across the population, higher intakes of calcium, potassium, and sodium were associated with lower mean systolic blood pressure and lower absolute risk of hypertension. Increments of dietary calcium were also negatively correlated with body mass. Even though these correlations cannot be accepted as proof of causation, they have implications for future studies of the association of nutritional factors and dietary patterns with hypertension in America.