Net influx and efflux of 22Na in erythrocytes from normotensive offspring of patients with essential hypertension

Venous volume in offspring of hypertensive patients

Twenty normotensive healthy male offspring of hypertensive patients were compared to 20 adequate controls regarding venous volume, the effect of ouabain on venous volume and signs of left ventricular hypertrophy. Among offspring there were slightly increased amplitudes in the orthogonal ECG as compared to controls but the differences were not statistically significant. Using a plethysmographic technique we found a significantly lower venous volume of the forearm in the offspring than in controls. There was, however, no effect of ouabain on the venous volume. The decreased venous distensibility among normotensive offspring might be an early manifestation of essential hypertension.

Blood pressure, cardiac output and systemic vascular resistance during rest, muscle work, cold pressure test and psychological stress. A study of male offspring from families with a history of essential hypertension for at least two generations

Haemodynamic changes in the early phases of hypertensive diseases have mainly been described in so-called borderline hypertensives. Their cardiac output (CO) has mostly been found to be elevated, but the peripheral vascular resistance (PRI) normal. In this study of the offspring (26 subjects) of hypertensive individuals, CO and intravascular pressures were measured during rest, muscular work, psychological stress and cold pressure test. For comparison, the same measurements were performed in a control group of healthy volunteers without known hypertension in their families. The offspring had higher blood pressure at rest than the controls throughout the study except during the cold pressure test and the highest dynamic work loads. Although there was no statistically significant difference between offspring and controls as regards PRI, the resistance was slightly higher in the group of offspring throughout the study. Arterial blood pCO2 in offspring was significantly lower at rest, during psychological stress and dynamic muscle work. Possible mechanisms behind this finding are considered.

Venous volume and blood flow in hand at rest and during psychological stress in male relatives to hypertensive patients

A total of 19 male relatives to hypertensive individuals were examined with regard to blood flow and venous volume in the hand at rest and during a psychological stress test. They were compared to 19 male controls without heredity for hypertension. There were no significant differences between the groups in hand blood flow or venous volume either at rest or during the test. The increase in vascular resistance during psychological stress was significantly higher in relatives than in controls. Possible mechanisms behind the differences in arterial vascular reactivity between the groups are discussed.

Plasma volume and plasma volume distribution at rest, during muscular work, cold pressure test and psychological stress in male offspring from families with heavy aggregation of hypertension

Total and central plasma volume was measured in 51 male offspring of hypertensive individuals belonging to families with a history of essential hypertension for at least two generations. They were compared to 38 age-matched individuals without known hypertension in their families for at least two generations. Central plasma volume was determined at rest and during muscle work, cold pressure test and psychological stress. The offspring had significantly lower total plasma volume than the controls. Central plasma volume was equal in offspring and controls. The quotient central/total plasma volume was thus higher in offspring than in controls, and the difference was statistically significant during psychological stress and dynamic muscle work. Possible reasons for the differences between offspring and controls are an increased transcapillary escape of plasma, an increased quotient intracellular/extracellular fluid and/or increased tone of the capacitance vessels.

Intraerythrocyte sodium content and transmembrane sodium flux in hypertensive patients treated with diuretics or beta-adrenoceptorblockers

Forty-seven male patients with essential hypertension were randomized to treatment with either a beta-adrenoceptorblocker (metoprolol), (n = 24), or a diuretic (hydrochlorothiazide), (n = 23). If their diastolic blood pressure was not lowered below 95 mm Hg by the maximum dose of either drug, hydralazine (15 patients) and in a few cases (6 patients) spironolactone was given. After five years of treatment all the patients were examined with respect to intraerythrocyte sodium (IeNa) and potassium (IeK), sodium influx and sodium efflux. Patients treated with the diuretic (D) tended to have a higher IeNa (9.8 +/- 0.4 mmol/l red cells) and sodium influx (0.044 +/- 0.002 mmol Na/l X min) compared with those taking the beta-adrenoceptorblocker (B) (8.9 +/- 0.3 mmol/l and 0.041 +/- 0.002 mmol Na/l X min), but neither of these differences was statistically significant. Sodium efflux, however, was significantly increased in D (0.073 +/- 0.003 mmol Na/l X min vs 0.061 +/- 0.003 mmol/l X min). No difference in IeK was noted between the two groups. Six patients taking spironolactone had a low IeNa (7.3 +/- 0.4 mmol/l), sodium influx (0.039 +/- 0.001 mmol Na/l X min) and sodium efflux (0.050 +/- 0.006 mmol Na/l X min).

Normotensive young men with family histories of hypertension gain weight and decrease their intraerythrocyte sodium content during a 5-year follow-up

Young normotensive men matched for age and body mass index with (n = 16) and without (n = 13) family histories of hypertension were investigated at baseline and after 5 years of follow-up with respect to blood pressure, body weight and intracellular sodium content. Subjects with positive family histories of hypertension increased significantly in body weight (from 81.9 +/- 11.5 kg to 89.5 +/- 11.4 kg, P less than 0.001) compared to subjects with negative family histories of hypertension (from 79.9 +/- 10.8 kg to 80.7 +/- 12.2 kg, NS). Their blood pressure did not differ initially (137 +/- 12/75 +/- 11 mmHg vs. 135 +/- 8/72 +/- 9 mmHg), but was reduced in subjects without family histories of hypertension (to 125 +/- 3/68 +/- 13 mmHg) in the follow-up examination. At follow-up, body mass index showed a positive correlation with blood pressure among subjects with positive family histories of hypertension (r = 0.77, P less than 0.001). At baseline, subjects with hypertensive fathers had significantly higher intraerythrocyte sodium levels than subjects with normotensive parents. At re-examination 5 years later, this difference was no longer present. We conclude that normotensive subjects with positive family histories of hypertension are predisposed to gain weight rather than to show an increase in blood pressure at this age. Normalization of intracellular sodium content, as found in the present study, could be a consequence of this weight gain and the ensuing metabolic adaption.

'Sodium sensitivity' in man

Increased cell membrane permeability to sodium is proposed as the initial event leading to high blood pressure in susceptible subjects when sodium intake is increased. All cells, including circulating cells, would be affected, but a key role for endothelial cells in the pathophysiology of the diastolic blood pressure elevation is proposed. Involvement of capillary endothelium could increase capillary permeability to proteins, and thereby would contribute to the altered fluid distribution on the high sodium diet which has been observed. If movement of fluid into the interstitium raised interstitial fluid pressure, venous capacitance would fall and right atrial pressure would rise. Several mechanisms would cause vascular smooth muscle tone to increase. Altered fluid distribution correlates with the rise in diastolic blood pressure from reduced sodium to high sodium diet, but arteriolar constriction would reduce capillary flow so altered fluid distribution occurs first. Arteriolar constriction could serve as a negative feedback to the raised atrial filling pressure by reducing raised capillary flow, which would decrease both altered fluid distribution and interstitial fluid pressure rise. Consequently, diastolic blood pressure would be chronically raised in 'sodium sensitive' subjects taking increased amounts of sodium in the diet. The relationship of the findings to "essential" hypertension and to premorbid cardiovascular sequelae, and the key role of capillary endothelium in the development of "essential" hypertension is discussed.

Erythrocyte cation transport is sex-related and is modified by oral contraceptives

Cation transport across the erythrocyte membrane was studied in normotensive male and female subjects, 20 to 45 years of age. Inward sodium-potassium cotransport was found to be significantly greater in men than in women who were not taking oral contraceptives. Intracellular potassium concentration was lower in men than in women, and was inversely correlated with cotransport. Women who were using oestrogen-progestogen oral contraceptives had higher cotransport than those who were not. It is concluded that a difference in cotransport exists between Caucasian men and women, which is not evident if women are taking oral contraceptives, and which could invalidate comparisons of cation transport between subject groups that are not sex-matched.

Increased erythrocyte sodium efflux during overfeeding without evidence of mediation by circulating catecholamines or thyroid hormone

Ten slightly obese middle-aged men were instructed to increase their energy intake 25% during a period of 1 week, which was preceded by a control period of seven days. Body weight increased by 0.67 kg (SD 0.60) indicating good compliance with the regimen. Transmembrane sodium fluxes were determined with the use of 22Na. The pre-diet erythrocyte sodium content was 9.7 mmol/L (SD 0.8) decreasing to 8.9 mmol/L (SD 1.1) (P less than 0.05) during overfeeding. The Na-efflux rate constant increased from 0.40 h-1 to 0.54 h-1 (P less than 0.05). Urinary excretion of catecholamines and concentrations of catecholamines and insulin in plasma and of thyroxine, triiodothyronine, and reverse T3 in serum did not change. Thus, overfeeding seems to enhance the total Na efflux in erythrocytes from slightly obese men. There were no measurable changes in thyroid hormone or catecholamine levels leaving the regulatory mechanisms unexplained.

High-resolution 23Na-NMR studies of human erythrocytes: use of aqueous shift reagents

Aqueous shift reagents were used to clearly distinguish intra-and extracellular 23Na-nuclear magnetic resonance (NMR) signals in samples consisting of whole blood or suspensions of washed human erythrocytes (both fresh and outdated). The lanthanide chelates Dy(PPP)2(7-) and Tm( TTHA )3- were used to shift the extracellular signals upfield, and Dy( TTHA )3- and Tm(PPP)2(7-) were similarly used to shift extracellular resonances downfield. The absolute intensities of the signals were used along with the measured hematocrit to simultaneously determine the intra- and extracellular Na+ concentrations. The results were generally within 5% of the values determined by more time-consuming centrifugation-flame emission photometry measurements on the same samples. Thus the 23Na-NMR signals from both intra- and extracellular cations suffer no NMR invisibility within experimental error. The lower level of intracellular Na+ in fresh erythrocytes (less than 12 mM) is easily distinguished from the higher level (approximately 30 mM) in erythrocytes that have been stored (in the cold) outside the body for some weeks.

Influence of carboxyhemoglobin, gamma-glutamyl-transferase, body weight, and heart rate on blood pressure in middle-aged men

Carboxyhemoglobin (COHb%) and gamma-glutamyl-transferase (GGT) are indicators of tobacco and alcohol consumption; similarly, body weight broadly reflects dietary habits. Relationships between COHb%, GGT, relative body weight, heart rate and blood pressure were studied in 242 48-year-old men attending a general health screening program in Malmö, Sweden. All were without treatment for high blood pressure. Positive correlations were found between blood pressure and body weight, GGT, and pulse, and a reciprocal correlation between blood pressure and COHb%. Use of objective markers for known or suspected risk factors, such as alcohol consumption, smoking, or overweight, were studied to elucidate their usefulness for further prospective studies.

Erythrocyte Na+, K+ cotransport and blood pressure in identical twins

The erythrocyte Na+, K+ cotransport system was studied in ten pairs of identical twins. Cation fluxes were remarkably similar in each pair of twins, which supports the concept of a genetic determinant for the cotransport system. There was, however, no apparent correlation between cotransport values and the family history of hypertension.

Whole body measurements of sodium turnover in offspring of patients with sustained essential hypertension

The elimination rate (percent per day) of injected 22Na using a whole body measurement technique was significantly lower (5.8 +/- 1.5) in normotensive or borderline hypertensive offspring of essential hypertensive patients than in 15 age- and sex-matched, normotensive controls (7.3 +/- 1.0). There were no significant differences in exchangeable sodium, whole body potassium or in the urinary excretion of sodium, potassium and creatinine. The basis for the difference in turnover rate during week 1 is probably an alteration in the cellular handling of sodium (i.e. increased intracellular sodium) in the still normotensive offspring of patients with essential hypertension. The long-term (more than 100 days) whole body retention of 22Na was found to be only 0.1% of that injected, which justifies the use of this method on larger population groups.