Sodium-lithium countertransport and blood pressure: the Gubbio Population Study

A report on the Gubbio Study thirty-eight years after its inception

BACKGROUND

The Gubbio Population Study ("Gubbio Study") is a prospective epidemiological study carried out on the resident population of the city of Gubbio, Italy. The study's objectives are both of public health nature (the control and awareness of hypertension), and experimental (the role of electrolyte handling at the cellular membrane level and its relation to hypertension). Additional objectives were addressed during the 30+ year activity of the study, in particular the role of kidney dysfunction.

METHODS

Three active screenings ('Exams') were performed beginning 38 years ago; the first (Exam 1) in 1983-1986 (5376 individuals - response rate 92%) and two follow-up exams, were completed between 1989-92 (Exam 2) and 2001-2007 (Exam 3). Data collected include demographics, personal and family medical history, lifestyle (smoking, alcohol, diet and physical activity), education, type of work, anthropometry, blood pressure, pulse rate, blood biochemistry, urine biochemistry and special investigations on cellular electrolyte handling. Additional measurements were performed in selected sub-groups of participants. Data on hospitalizations, mortality and causes of death were collected after the completion of Exam 1.

RESULTS

The main results of the study, presented in this paper, identify new variables to consider in screening for cardiovascular risk factors, and show the impact that the focused and coordinated effort of a longitudinal program can have on a free-living population'.

CONCLUSIONS

The data are of relevance to Public Health and to experimental medicine alike, and vouch to the importance of the control of risk factors at the community level.

Cohort profile: The Gubbio Population Study

The Gubbio Study is a prospective epidemiological study on the population residing in the city of Gubbio, Italy. Original objectives of the study were the control of hypertension and the role of cellular electrolyte handling in hypertension. Other objectives were added during the 30-year activity of the study. The original target cohort consists of individuals aged ≥5 years residing within the medieval walls of the city. To complete family genealogies, individuals residing outside the city were also included. Three active screenings (exams) were conducted. A total of 5376 individuals (response rate 92%) participated in Exam 1 which was performed in 1983-86. Follow-up exams were completed between 1989-92 and 2001-2007. Data categories included demographics, personal and family medical history, lifestyle habits, education, type of work, anthropometry, blood pressure, pulse rate, blood biochemistry, urine biochemistry and special investigations on cellular electrolyte handling. Electrocardiogram, echocardiogram, 24-h ambulatory blood pressure and uroflowmetry were performed in selected subgroups defined by age and/or sex. Data about hospitalizations, mortality and causes of death were collected starting from completion of Exam 1. The study shared the data with other studies.

The role of HDL cholesterol in metabolic syndrome predicting cardiovascular events. The Gubbio population study

BACKGROUND AND AIMS

Metabolic syndrome (MS) has recently been claimed to be an important new risk factor for the occurrence of coronary heart disease (CHD) and cardiovascular disease (CVD) events, although it is simply a combination of known risk factors used in a dichotomized fashion. The aims of this analysis were to explore the predictive role of MS for CHD and CVD events in a population study, in comparison with using the same factors in a continuous fashion, with special emphasis on HDL cholesterol.

METHODS AND RESULTS

In the second examination of the Gubbio population study from central Italy, 2650 cardiovascular disease-free men and women, aged 35-74 years around 1990, were examined and followed-up for 12 years. The classic risk factors (sex, age, systolic blood pressure, serum cholesterol and smoking habits) were studied as predictors of CHD and CVD events, alone and with the contribution of other factors (HDL cholesterol, blood glucose, serum triglycerides and waist circumference) included in the so-called MS, based on several multivariate models. MS was also tested after adjustment for other risk factors. MS produced a predictive significant relative risk of 1.67 for CHD events and 1.82 for CVD events, but considering its single risk factors, the only ones contributing to prediction were HDL cholesterol and systolic blood pressure. Dedicated analyses showed that MS does not add anything to the power of prediction beyond the role of the single risk factors treated in a continuous fashion, while the best predictive power is obtained using classic risk factors (sex, age, smoking habits, total cholesterol, systolic blood pressure) with the addition of HDL cholesterol.

CONCLUSIONS

The predictive power of MS is bound only to the presence of HDL cholesterol and blood pressure and does not add anything to using the same risk factor treated in a continuous fashion.

Metabolic syndrome and left ventricular hypertrophy in a general population. Results from the Gubbio Study

Aims of this study were to investigate the prevalence of metabolic syndrome (MS), diagnosed according to the International Diabetes Federation (IDF) criteria and its relationship with echocardiographic parameters of cardiac structure and function. The study was performed in 707 subjects, age 45-54 years, of the Gubbio Population Study who underwent a comprehensive examination including measurement of body size, blood pressure (BP) and heart rate, 12-lead electrocardiogram, Doppler echocardiography, standardized blood and urine laboratory tests. One hundred and fifty-three subjects were found to have MS, which was more frequent among hypertensive patients than normotensive controls (36.2 vs 13.7%, P<0.001). Apart from visceral obesity present in all subjects by definition according to the IDF criteria, high levels of BP (>130/85 mm Hg) and triglycerides (>or=150 mg/dl) were the most frequently observed components of the syndrome, since their prevalence averaged 75% of those with the syndrome. Left ventricular mass (95.6+/-22 vs 86.4+/-22 g/m(2); P<0.001) and prevalence of left ventricular hypertrophy were increased in the subgroup with MS. Waist circumference, BP and blood glucose were the components of the syndrome with stronger impact on cardiac mass. An early impairment of the diastolic function was detected in this subgroup with a reduction of the early-to-late diastolic filling (0.91+/-0.17 vs 0.99+/-0.23, P<0.001). The results of the present study indicate that MS is frequent in middle-aged general population, particularly in subjects with arterial hypertension. The syndrome is associated to the increase in ventricular mass and the early impairment of diastolic function.

Arterial hypertension increases left ventricular mass: role of tight blood pressure control

In middle-age hypertensives from the Gubbio Population Study, we evaluated the relationship between blood pressure (BP) control over a long time and the prevalence of left ventricular hypertrophy (LVH). A population survey was performed in 1982-1985 and repeated in 1989-1992. During the second survey, subjects in the age range 40-60 years were invited to undergo an M-mode echocardiographic examination. A total of 487 subjects who participated in both surveys are included in the present analysis. Some of them (294) were normotensive (Group 1), 110 were hypertensive but had never taken antihypertensive drugs (Group 2), 47 hypertensives on drugs were in good BP control (Group 3) and 36 hypertensives on drugs had uncontrolled hypertension (Group 4). BP values at the 1989-1992 examination were, respectively, 122/77, 145/86, 124/78 and 153/91 mmHg, while 7 years earlier were 122/77, 133/84, 136/85 and 152/95 mmHg. Despite normal BP levels in Group 3, left ventricular mass index (LVMi, g/m(2.7)) was greater than in normotensives (42.4+/-10, 46.6+/-13, 47.0+/-10, 51.9+/-15 g/m(2.7)). Accordingly, the prevalence of LVH (LVMi >51 g/m(2.7)) was 18, 26.4, 36.7 and 50% in groups 1-4, respectively. The 193 hypertensives were, thereafter, divided according to BP control (ie <140/90 mmHg) on both surveys (1983-1985 and 1989-1992): 27 hypertensives with optimal BP levels on both visits also had a ventricular mass similar to normotensives and significantly lower than the other hypertensives (LVMi 44.6+/-11.6 vs 48.5+/-13.2, P<0.001). In conclusion, these findings indicate that hypertensive patients with BP values at levels similar to those in normotensives for a long period do not increase their left ventricular mass in comparison to subjects with normal BP levels.

Baseline Na–Li countertransport and risk of hypertension in children: a 10-year prospective study in Hanzhong children

Sodium-lithium countertransport (Na-Li CT) is associated with blood pressure (BP) and in many cross-sectional investigations and some longitudinal studies, essential hypertension has been proposed as a biochemical marker or predictor of hypertension risk in adults. The present study investigated prospectively whether baseline Na-Li CT rate was an index of increased risk of future development of hypertension in children. At baseline visit in 1987 of the Hanzhong Children Hypertension Study comprising 4000 school children aged 5-6 years old, 310 samples were randomly selected for measurement of baseline Na-Li CT rate; we made a 10-year follow-up of them in the same season in 1997. This cohort of children is the sample for analysis in the present report. Baseline Na-Li CT rate was positively correlated to systolic BP (SBP) both in baseline and follow-up (baseline, gamma=0.21, P<0.05; follow-up, gamma=0.32, P<0.01), and positively correlated to diastolic BP (DBP) (gamma=0.20, P<0.05) and body mass index (gamma=0.18, P<0.05) in follow-up examination. Longitudinal analysis of 10-year BP evolution, children in higher baseline Na-Li CT (ie, >260 micromoll RBC/h) had greater BP change than children in lower baseline Na-Li CT (ie, </=260 mumol/l RBC/h) (SBP, 15.8+/-12.9 vs 19.3+/-13.1, DBP 8.8+/-11.2 and 11.3+/-10.6, P<0.05). Multiple logistic regression analysis showed that children in the higher Na-Li CT (>260 mumol/l RBC/h) were associated with approximately 1.5 times greater risk of high BP) in comparison to placement in lower Na-Li CT (</=260 mumol/l RBC/h). Elevated baeline RBC Na-Li countertransport could be a risk predictor predisposing to the development of hypertension in children.

Effect of acute hyperglycemia on erythrocyte membrane ion transport in offspring of hypertensive parents

OBJECTIVE

Patients with essential hypertension exhibit several red blood cell (RBC) ion transport abnormalities, insulin resistance (IR) and increased risk of developing type 2 diabetes. The aims of this study were to assess RBC ion transport activities under basal conditions and to test the in vivo effect of acute hyperglycemia on RBC ion transport in the offspring of hypertensive parents (OHP) and healthy controls (C).

DESIGN AND METHODS

Activities of Na+-K+ pump, Na+-K+ cotransport, Na+-Li+ countertransport (SLC) and Na+, Rb+ and Li+ leaks were measured before and after a 5-h hyperglycemic (12 mmol/l) clamp (HGC) and compared to values found under euglycemic isovolumic conditions in OHP (n = 12) and C (n = 14). Insulin action was calculated as insulin sensitivity index (M/I) during HGC.

RESULTS

The offspring of hypertensive parents were characterized by lower M/I (0.07 +/- 0.03 versus 0.12 +/- 0.07 mg/kg per min per microU per ml; P < 0.05) and elevated SLC (0.080 +/- 0.004 versus 0.068 +/- 0.003 mmol/h per litre; P < 0.05), as well as by higher Li+ (0.106 +/- 0.004 versus 0.093 +/- 0.003 mmol/h per litre; P < 0.05) and Rb+ leaks (0.160 +/- 0.014 versus 0.120 +/- 0.007 mmol/h per litre; P < 0.05) compared to controls. Acute hyperglycemia did not cause significant changes in any investigated RBC ion transport parameters.

CONCLUSIONS

The offspring of hypertensive parents displayed higher insulin resistance, enhanced activity of SLC and formerly undocumented augmented Li+ and Rb+ leaks. Acute hyperglycemia did not modify any RBC ion transport activities in either offspring of hypertensive parents or controls.

Relation of urinary urea to blood pressure: interaction with urinary sodium

A previous study reported that urinary markers of protein intake are inversely related to blood pressure via unknown mechanisms. In man and rats, protein intake affects renal function and increases renal sodium excretion. The present study investigates the relation between markers of protein intake and blood pressure and the possible role of sodium in this relation. Blood pressure status, overnight urinary urea as index of protein intake, urinary and plasma sodium, and other variables were measured in a population sample of 3705 men and women, aged 25-74 years, without high plasma creatinine. Urinary urea was inversely related to blood pressure and hypertension: in multivariate analyses, 6.5 mmol/h higher urinary urea (about one s.d. in men and women) was related to 4.25 mm Hg lower systolic blood pressure (95% confidence interval = 1.34-8.49), and to 0.65 lower risk of hypertension (95% CI 0.34-0.87). An interaction was found between overnight urinary sodium and the relation of urinary urea to blood pressure: the relation was significant only in persons with overnight urinary sodium above the median. Urinary urea was significantly and inversely also related to plasma sodium. Data confirm an inverse relation to blood pressure of protein intake as measured by urinary urea. The possibility of sodium-related mechanisms is supported by the interaction of urinary sodium with the relation and by the inverse association of urinary urea with plasma sodium. The hypothesis is made that high protein intake could counteract sodium-dependent blood pressure rise via stimulation of renal sodium excretion.

Heart rate as a cardiovascular risk factor: do women differ from men?

Considerable progress has been made in our understanding of the role of high heart rate in determining cardiovascular morbidity and mortality. However, whether the association between fast heart rate and cardiovascular disease is equally strong in males and females is still a matter for debate. In most studies, the predictive value of tachycardia for all-cause mortality has been found to be weaker in women than in men, and in some studies no association between heart rate and cardiovascular mortality was observed. In particular, high heart rate appeared to be a weak predictor of death from coronary heart disease in the female gender. Multiple mechanisms by which sympathetic overactivity could cause hypertension and the metabolic syndrome of insulin resistance have been documented. Recent results obtained at the Ann Arbor laboratory from the analysis of four populations indicate that these mechanisms are operative mostly in males in whom tachycardia reflects a heightened sympathetic tone. In women, fast heart rate would merely represent the extreme of a normal distribution. However, tachycardia can also have a direct impact on the arterial wall, as demonstrated in laboratory studies, and can favour the occurrence of cardiac arrhythmias. The impact of these mechanisms may be similar in men and women and could explain why a high heart rate has been found to have a detrimental effect also in the female gender. Pharmacological reduction of high heart rate is an additional desirable goal of therapy in several clinical conditions such as hypertension, myocardial infarction and congestive heart failure. Although a greater effect is expected in men, cardiac slowing could counteract the detrimental haemodynamic effect of tachycardia also in women.

Impact of the Gubbio population study on community control of blood pressure and hypertension. Gubbio Study Research Group

BACKGROUND

Awareness and treatment of hypertension have markedly increased in the last 30 years in most parts of the world, but a satisfactory control of blood pressure is still infrequent

OBJECTIVES

To describe trends in community control of hypertension and blood pressure levels in the small town of Gubbio, Italy.

METHODS

Large samples of the populations (aged 30-79 years) were examined 6 years apart for measurement of blood pressure, other cardiovascular risk factors and knowledge, attitude and practice towards control of hypertension. Data were available from a total of 1125 men and 1445 women with two examinations and 1566 men and 1658 women with at least one examination. Two different definitions of hypertension were used (old definition: systolic blood pressure (SBP) > or = 160 mmHg or diastolic blood pressure (DBP) > or = 95 mmHg or use of antihypertensive drugs; recent definition: SBP > or = 140 mmHg or DBP > or =90 mmHg or use of anti-hypertensive drugs).

RESULTS

Awareness, treatment and control of hypertension increased from one survey to the other, whatever definition of hypertension was used. Control rose from 41 to 63% (old definition) and from 12 to 24% (recent definition). In a 6-year period, the average population SBP declined 2-8 mmHg and DBP declined 2-3 mmHg depending on type of analysis, against an expected rise of 9 mmHg for SBP and 2 mmHg for DBP. These trends are partly explained by a marked decline in alcohol consumption and by more common and intensive anti-hypertensive treatment, while change in body mass index, which showed a slight but systematic increase, cannot be considered as a contributor to this trend.

CONCLUSIONS

An epidemiological study has motivated a population group and its medical profession towards a better control of hypertension.

Pulse pressure and isolated systolic hypertension: association with microalbuminuria. The GUBBIO Study Collaborative Research Group

BACKGROUND

The long-term risk of end-stage renal disease is high in persons with isolated systolic hypertension, that is, those with an elevation of pulse pressure and not of diastolic pressure. Other data suggest that pulse pressure is a predictor of the hypertension-induced organ damage. Microalbuminuria is considered an early sign of glomerular damage caused by hypertension. The study shows the relationship of pulse pressure and isolated systolic hypertension to microalbuminuria in nondiabetic subjects.

METHODS

This is a cross sectional analysis for a population sample of 677 men and 890 women, aged 45 to 64 years, who were without diabetes mellitus and macroalbuminuria. Data collection included: overnight urinary albumin and creatinine excretion; fasting plasma glucose, cholesterol, and creatinine; creatinine clearance; and blood pressure, weight, height, medical history, and smoking habit. Pulse pressure was calculated as systolic minus diastolic pressure. Isolated systolic hypertension was defined as systolic pressure > or =140 mm Hg in persons not on antihypertensive drugs and with diastolic pressure <90 mm Hg. Microalbuminuria was defined as urinary albumin excretion > or =20 microg/min.

RESULTS

Pulse pressure and isolated systolic hypertension were significantly related to urinary albumin excretion and the prevalence of microalbuminuria in univariate and multivariate analyses. Controlling for gender and other variables, the risk of microalbuminuria was 1.71 with a 15 mm Hg higher pulse pressure (95% CI, 1.31 to 2.22) and 4.95 in the presence of isolated systolic hypertension (95% CI, 3.15 to 7.76).

CONCLUSIONS

In nondiabetic, middle-aged adults, pulse pressure and isolated systolic hypertension are directly related to microalbuminuria, independent of diastolic pressure and other correlates.

Abnormalities in insulin sensitivity, vascular resistance and erythrocyte cation transport are independent genetic traits in familial hypertension

Several isolated abnormalities have been noted in normotensive members of hypertensive families, including exaggerated forearm vascular resistance (FVR), decreased insulin sensitivity and elevated sodium-lithium (Na/Li) countertransport. No family study has investigated the aforementioned abnormalities concurrently within the same hypertensive families. It is therefore unknown whether these disturbances reflect single or different genetic traits. Thus, we studied cardiovascular reactivity of the forearm vasculature, cellular sodium transport mechanisms and insulin sensitivity concomitantly in normotensive (n = 24) and borderline hypertensive (n = 16) members of hypertensive families, compared with normotensive members (n = 24) of normotensive families. At least one abnormality was noted in 27 (67%) out the 40 subjects with a positive family history of hypertension. Na/Li-countertransport was increased in 15 (37%), FVR was increased in 14 (35%) and insulin sensitivity was decreased in 9 (22%) subjects with familial hypertension. The concomitant occurrence of at least 2 out of the 3 abnormalities mentioned was noted in 9 (22%) out of the 40 subjects with family history of hypertension. Decreased insulin sensitivity, increased basal FVR and increased Na/Li countertransport were concurrently observed in two (5%) subjects. This investigation documents the frequent occurrence of abnormalities such as decreased insulin sensitivity, increased basal FVR and Na/Li-countertransport in subjects with family history of hypertension. The concomitant occurrence of at least two of the mentioned abnormalities being observed in less than one-quarter of the subjects with family history of essential hypertension, it is assumed that insulin sensitivity, basal FVR and Na/Li-countertransport reflect more than one genetic trait predisposing to hypertension.

Prospective analysis of traits related to 6-year change in sodium-lithium countertransport. Gubbio Population Study Research Group

Sodium-lithium countertransport (Na-Li CT) activity in red blood cells relates cross-sectionally and longitudinally to blood pressure and hypertension. Lifestyle and metabolic factors relate cross-sectionally to this sodium transporter. The aim of this study was to conduct a prospective analysis of 6-year Na-Li CT change and of traits related to Na-Li CT change. In 2183 participants in the Gubbio Population Study (972 men and 1211 women; baseline ages, 18 to 74 years), the following data collected at baseline and 6-year follow-up were analyzed: Na-Li CT; gender; age; body mass index (BMI); blood pressure; antihypertensive treatment; alcohol intake; smoking habits; urinary sodium-to-potassium ratio; and plasma cholesterol, glucose, uric acid, sodium, potassium, and triglycerides (measured only at follow-up). Six-year changes were defined as follow-up minus baseline values. Na-Li CT was higher at follow-up than at baseline in both genders (P<0.001). Baseline Na-Li CT; baseline and change values of BMI; and change values of alcohol intake, plasma potassium, and plasma glucose related to Na-Li CT change significantly and independently with control for other variables. Follow-up plasma triglyceride levels also related independently to Na-Li CT change. Coefficients were positive for BMI, alcohol intake, and plasma glucose and triglyceride levels and were negative for baseline Na-Li CT and plasma potassium levels. Baseline and change values of other variables did not relate significantly to Na-Li CT change. In conclusion, in prospective analyses, BMI, alcohol intake, plasma glucose, and lipids were directly related to Na-Li CT change; baseline Na-Li CT and plasma potassium levels were inversely related. The data support the concept that lifestyle and related metabolic factors influence Na-Li CT.

G proteins and hypertension: an alternative candidate gene approach

Hypertension affects approximately 20 to 30% of individuals in industrialized countries, and is commonly believed to develop on the basis of both genetic and environmental factors. The identification of genes susceptible to the most frequent form of hypertension, commonly referred to as "essential" hypertension, is hampered by the fact that blood pressure is a poorly defined phenotype that is modulated by multiple factors, such as gender, race, body mass etc., and that the definition of hypertension depends on a rather arbitrarily chosen cut-off value. Hence, more progress has been made in the identification of genes responsible for rare autosomal dominant forms of hypertension, such as Liddle's disease. This review focuses on an experimental approach that attempts to define candidate genes for essential hypertension using immortalized cells from well characterized normotensive and hypertensive subjects. From the presently available results, one attractive speculation is that an increased intracellular signal transduction caused by an enhanced reactivity of Gj-type G proteins represents a genetically fixed trait that renders affected individuals susceptible to essential hypertension.

Insulin, sodium-lithium countertransport, and microalbuminuria in hypertensive patients

Both microalbuminuria (>0.290 nmol/min [20 microg/min]) and high sodium-lithium countertransport (SLC) in diabetic or hypertensive humans are predictive of overt nephropathy and more aggressive cardiovascular complications, perhaps induced by insulin resistance. To analyze the relationships between microalbuminuria, SLC, microalbuminuria, and insulin in essential hypertension, we studied 90 hypertensive white patients, 25 of whom had microalbuminuria and 32 of whom were healthy. When urine sampling was completed for albuminuria determination, SLC was measured; all patients then underwent standard (75 g) oral glucose load to measure basal (0 minutes) and 2-hour glucose and insulin serum levels. Glucose-insulin ratio was used as insulin sensitivity index (ISI). In both hypertensive patients with normal microalbuminuria and those with pathological microalbuminuria, plasma insulin at 120 minutes was significantly higher than in control subjects. When the patients with pathological microalbuminuria were divided into thirds on the basis of their microalbuminuria, in the lower third, we found statistically significant less fasting insulin and higher basal ISI. SLC was higher in hypertensives than normotensives and, among hypertensives, higher in the subgroup with elevated microalbuminuria. In hypertensives, we found a weak but significant correlation between SLC and microalbuminuria, independent of insulin or ISI. The prevalence of high value of SLC (> or =0.383 mmol x L-1 x h-1) was significantly lower in hypertensives with normal rather than abnormal urinary albumin excretion. Our results indicate that in nondiabetic hypertensive whites, higher microalbuminuria is accompanied by signs of insulin resistance; moreover, a link exists between SLC and microalbuminuria, both predictive of aggressive complications of hypertension.

Pathophysiology and treatment implications of hypertension in the African-American population

Regardless of the etiology, hypertension remains a major public health problem in African-Americans and is associated with significant morbidity and mortality. Additional data on the pathophysiology of this disease in this population are needed, as are data on the best therapies to decrease the high complication rate. Because many of the large studies on hypertension have included few African-Americans, recruitment of this ethnic group into clinical trials should be promoted. Further studies into the genetic factors in the pathophysiology of racial differences in hypertension may shed more light on this complex issue.

Baseline sodium-lithium countertransport and 6-year incidence of hypertension. The Gubbio Population Study

BACKGROUND

Sodium-lithium countertransport (Na-Li CT) activity is high in persons with hypertension. This study investigated whether high Na-Li CT relates to development of hypertension.

METHODS AND RESULTS

At the baseline visit of the Gubbio Population Study, 4210 people of the 5376 surveyed were 18 to 74 years old; of these, 1599 were hypertensive (systolic pressure > or = 140 mm Hg, or diastolic pressure > or = 90 mm Hg, or on antihypertensive drug therapy). Of the 2611 nonhypertensives, 302 did not have Na-Li CT measured and 580 did not participate in 6-year follow-up. This analysis, therefore, deals with data collected on 1729 men 18 to 74 years old and women 18 to 74 years old who at baseline were nonhypertensive and had Na-Li CT measurement. Compared with individuals who were nonhypertensive at baseline and follow-up, individuals with incident hypertension at follow-up (systolic pressure > or = 140 mm Hg, or diastolic pressure > or = 90 mm Hg, or on antihypertensive drug therapy) had higher baseline values of Na-Li CT, blood pressure, age, body mass index, plasma cholesterol, and alcohol intake (P < .05). Baseline Na-Li CT was positively associated (P < .05) with development of hypertension in quartile analysis, with highest incidence of hypertension among men and women with Na-Li CT in the highest quartile (for men, > or = 376 and for women, > or = 311 mumol Li-L red blood cells-1.h-1). In univariate logistic regression, incidence of hypertension was related to baseline value of Na-Li CT, blood pressure, age, body mass index, plasma cholesterol, and alcohol intake (P < .05). In multiple logistic regression analysis, individuals with baseline Na-Li CT higher by 127 mumol (pooled SD for men and women) had 1.23 times greater risk of incident hypertension with control for sex and baseline age, body mass index, systolic pressure, and other confounders (P < .001).

CONCLUSIONS

Na-Li CT is a predictor of hypertension risk in adults.

Effect of dietary versus pharmacological correction of hypertriglyceridemia on red blood cell membrane sodium/lithium countertransport activity

An elevated red blood cell Na/Li countertransport (Na/Li CT) is often associated with high blood pressure and metabolic abnormalities. Recent studies suggested that a reduction in serum TG levels is associated with a decrease in Na/Li CT activity. However, it is still unclear if this phenomenon could be originated from systemic metabolic alterations or from modifications of the membrane dynamic properties. Aim of the present study was to investigate whether dietary or pharmacological TG lowering therapy might have a different effect on Na/Li CT activity and related metabolic parameters. Twenty normotensive hyper-TG patients were recruited from the Lipid outpatient Clinic: they had a baseline Na/Li CT activity significantly higher compared with age- and BMI-matched normolipidemic controls (386+/-33 vs 274+/-39 umol/l RBC/h, p<0.05). The patients were randomly prescribed one of the following two-months treatment: Group 1)-triglyceride lowering diet; Group 2)-lipid lowering drug (Gemfibrozil 600 mg b.i.d.). Na/Li CT and metabolic and anthropometric variables were measured at baseline and after 1 and 2 months of treatment. At the end of intervention, there was in both groups a significant and comparable fall in plasma triglyceride (group 1: -2.61+/-0.73 mmol/l p<0.01; group 2: -4.29+/-1.20 mmol/l p<0.01). In the diet-treated group there were, in addition small but significant reductions in body weight (-3.7+/-0.8 kg p<0.01), fasting glucose (-0.36+/-0.14 mmol/l p<0.05) and insulin levels (-2.1+/-0.5 mU/l, p<0.01), while no such changes were observed in the fibrate treated patients. Na/Li CT activity was significantly and comparably reduced at the end of treatment in both groups (group 1: -97+/-28 umol/l cell/h, p<0.01; group 2: -89+/-30 umol/l cell/h, p<0.01). In conclusion, these results indicate that the decrease in Na/Li CT associated with both dietary and drug treatment of hypertriglyceridemia is to be traced to a direct effect of plasma TG concentration on this transport system (probably as a result of modification in the membrane lipid environment) rather than to changes in plasma insulin levels or insulin resistance.

Genetic polymorphisms and erythrocyte sodium-lithium countertransport in essential hypertension

Erythrocyte sodium-lithium countertransport (SLC) activity is elevated in essential arterial hypertension. With the growing attention to the genetic substrate of disturbed biochemical tests associated with essential arterial hypertension, we were particularly interested in the involvement of key genes for the regulation of SLC, possibly related to the pathophysiology of essential arterial hypertension. Consequently, the aim of the present study was to investigate SLC and its determining factors in essential hypertension. The influence of haptoglobin (Hp)-polymorphism, insertion/deletion polymorphism of angiotensin converting enzyme (ACE-I/D) and MNS blood group system on the regulation of SLC was studied. SLC activity was studied in a cross-sectional case-control study including 90 Caucasians: 60 patients with essential arterial hypertension who had been treated for at least 1 year and 30 normotensive controls. In essential hypertension, the SLC activity is significantly higher (P = 0.00005) than in controls. In normotensive patients, no differences in SLC are observed for the different polymorphisms studied. However, in the hypertensive group, SLC activity is higher (P = 0.003) in Hp 2-1 phenotype and independent of ACE-I/D genotyping and MNS blood group polymorphism. Multifactor analysis of variance in essential hypertension reveals significant (P = 0.001) differences in SLC activity for the presence or absence of Hp 2-1 phenotype and for body weight (P = 0.0003). Multivariate regression analysis shows the same parameters to be independent determining factors of SLC in essential arterial hypertension. No relation is found between SLC activity and target organ damage which includes coronary artery disease, peripheral arterial occlusive disease, left ventricular hypertrophy and cerebrovascular accident. We conclude that erythrocyte SLC activity is elevated despite pressure-lowering therapy. In essential arterial hypertension, individuals of Hp 2-1 phenotype show higher SLC activity than patients of other Hp-types, suggesting genetic heterogeneity of essential arterial hypertension. The presence or absence of Hp 2-1 phenotype is an independent determining factor of SLC activity whereas body weight codetermines SLC activity in essential hypertension.

Metabolic manifestations of low-dose diuretics

Hypertension has been defined and treated as a disease of abnormal systolic and diastolic blood pressure. Recent data have, however, demonstrated that effective blood-pressure control has not resulted in the expected decrease in coronary artery disease. These findings are probably a result of hypertension being a complex inherited syndrome of cardiovascular risk factors, all of which are genetically linked and all of which contribute to the development of cardiovascular disease in these patients. Included in the hypertension syndrome are abnormalities of lipid profile, insulin resistance, changes in renal function, left ventricular hypertrophy and reduced arterial compliance. In many patients, high blood pressure is a late manifestation of this disease process. Since all cardiovascular risk factors contribute to heart disease in these patients, they should all be considered in the management of this disease process. Diuretics and beta blockers, when used at high doses, negatively impact lipid metabolism and insulin sensitivity, while angiotensin converting enzyme (ACE) inhibitors and calcium antagonists tend to have a neutral effect on these metabolic risk factors. These findings have resulted in decreased use of diuretics and beta blockers in favor of newer agents such as ACE inhibitors and calcium antagonists. However, recent data have demonstrated that when used at low doses (6.25 or 12.5 mg of hydrochlorothiazide), diuretics lack significant metabolic side effects while bringing about significant reductions in blood pressure. Thus, at these doses, hydrochlorothiazide is a useful drug in the treatment of hypertension, both as monotherapy and in combination therapy.

Sodium-lithium countertransport and blood pressure change over time: the Gubbio study

Sodium-lithium countertransport activity in red blood cells relates to blood pressure (BP) and the prevalence of hypertension. This study investigated in adults the relation of sodium-lithium (Na-Li) countertransport to BP change from baseline to 6-year follow-up. In the Gubbio Population Study, 4210 men and women were 18 to 74 years old at baseline (1983-1986), and 3766 had a valid baseline Na-Li countertransport measurement; of these, 2729 were reexamined at 6 years of follow-up (1989-1992) and made up the study cohort. At baseline, data collection included age, height, weight, BP, pulse rate, drug treatment, alcohol intake, ratio of sodium to potassium in spot urine, plasma cholesterol, and Na-Li countertransport in red blood cells. At 6-year follow-up, data for age, BP, and drug treatment were collected as at baseline. From baseline, average BP declined for people on antihypertensive medication at follow-up and for those with baseline BP greater than or equal to 140/90 mm Hg (systolic/diastolic) and did not change or increased for the remaining participants. In quartile and correlation analyses controlled for sex, baseline BP, and antihypertensive treatment, BP change related significantly and directly to baseline Na-Li countertransport. In multiple linear regression analyses done for the entire cohort with control for other confounders, the regression coefficient of baseline Na-Li countertransport to BP change over time was positive and borderline significant. The Na-Li countertransport coefficient was positive and significant when analyses were done with the use of a categorical value of baseline Na-Li countertransport (quartile 4 and quartiles 1 through 3 combined). In both models, the Na-Li countertransport coefficient was the strongest for people with baseline BP greater than or equal to 120/80 mm Hg or for people with baseline age of 45 years or older. In conclusion, Na-Li countertransport significantly relates to BP change over time in adults.

Correlations of Na+-Li+ exchange activity with Na+ and Li+ binding and phospholipid composition in erythrocyte membranes of white hypertensive and normotensive individuals: a nuclear magnetic resonance investigation

Enhanced Na+-Li+ exchange activity has been reported in red blood cells (RBCs) of white patients with essential hypertension compared with RBCs of normotensive individuals. To understand the factors responsible for this finding, we applied novel and conventional spectroscopic and kinetic methods to blood samples from 10 hypertensive and 10 normotensive individuals. We measured the kinetic parameters (V std, V max, and K m) for RBC Na+-Li+ exchange by atomic absorption spectrophotometry and used 23Na and 7Li nuclear magnetic resonance relaxation methods to measure Na+ and Li+ binding to RBC membranes as well as 31P nuclear magnetic resonance spectroscopy to measure membrane phospholipid compositions. We found significant differences between the two groups for the affinity of Na+ for the RBC membrane (0.202 +/- 0.054 mmol/L-1 for hypertensive patients versus 0.296 +/- 0.071 mmol/L-1 for normotensive subjects, P<.005). The kinetic parameters of RBC Na+-Li+ exchange (V std, V max, and K m) were 0.32 +/- 0.09 and 0.66 +/- 0.17 mmol Li+/L cell.h and 160 +/- 62 mmol/L, respectively, for hypertensive patients versus 0.21 +/- 0.06 and 0.32 +/- 0.14 mmol Li+/L cell.h and 86 +/- 69 mmol/L for normotensive subjects (P<.05). The fractions of phosphatidylserine and phosphatidylethanolamine were 0.153 +/- 0.009 and 0.294 +/- 0.016 for hypertensive patients versus 0.138 +/- 0.013 and 0.325 +/- 0.018 for normotensive subjects (P<.05). The Na+ binding constants were negatively correlated with the Km values for both the hypertensive (r=-.61, P=.01) and normotensive (r=-.43, P=.04) groups. Changes in lipid-protein interactions in the RBC membranes of hypertensive patients appear to be responsible for weaker Na+ binding to the membrane and for the faster rates of RBC Na+-Li+ exchange.

Sodium-lithium countertransport has low affinity for sodium in hyperinsulinemic hypertensive subjects

We recently reported that incubation of red blood cells with insulin markedly decreases the affinity for external Na+ and increases the maximal transport rate (Vmax) of Na(+)-Li+ countertransport. The association of hypertension with insulin resistance and its compensatory hyperinsulinemia led us to investigate the relationship between insulin levels in vivo and the Na+ activation kinetics of this antiporter. We studied normotensive (n = 28) and hypertensive (n = 25) subjects after they had fasted overnight and determined their plasma glucose and insulin concentrations. Insulin levels were higher in the hypertensive subjects (11.7 +/- 1.5 microU/mL, mean +/- SEM) than in the normotensive subjects (8.2 +/- 1.2 microU/mL), but glucose levels were similar and within normal limits. Antiporter activity was measured as sodium-stimulated Li+ efflux by a new procedure that uses isosmotic conditions to raise external Na+ to 280 mmol/L. In normotensive subjects, Vmax was reached between 50 and 100 mmol/L Na+, whereas in most hypertensive subjects, Na+ concentrations higher than 150 mmol/L were needed. This different kinetic behavior was because the Na+ concentration for half-maximal activation (Km) was twofold higher in hypertensive subjects (58.9 +/- 5.3 mmol/L) than in normotensive subjects (29.8 +/- 2.6 mmol/L, P < .001). Hypertensive subjects with fasting insulin levels greater than 10 microU/mL (n = 12) had a higher Km for Na+ than subjects with insulin levels less than 10 microU/mL (n = 13) (73.4 +/- 8.7 versus 45.6 +/- 3.9 mmol/L, respectively, P < .01) and similar Vmax (0.57 +/- 0.05 versus 0.41 +/- 0.05 mmol.L-1.h-1).(ABSTRACT TRUNCATED AT 250 WORDS)

Red blood cell sodium and potassium concentration and blood pressure. The Gubbio Population Study

The relations of red blood cell sodium (RBC Na) and potassium (RBC K) concentrations to blood pressure and prevalence of hypertension were assessed for 1805 men and women, aged 25 to 74 years, who participated in the baseline examination of the Gubbio Population Study in north central Italy. In men, in univariate analyses, RBC Na concentration was not significantly related to systolic or diastolic blood pressure, while RBC K concentration was significantly and inversely related to blood pressure. In women RBC Na values correlated significantly and directly with systolic and diastolic pressure, but RBC K concentration was not significantly related to blood pressure. Results of the multivariate analyses indicated in men a significant independent and inverse relationship of RBC K concentration with hypertension and blood pressure, and in women a significant positive association of RBC Na concentration with hypertension. RBC Na did not relate independently to either systolic or diastolic blood pressure in men or women. Age-specific analyses suggested that the relationships between RBC K level and blood pressure in men and the relationship between RBC Na level and hypertension in women were stronger in older (age 55 to 74 years) compared to younger participants (25 to 54 years). These findings indicate that the associations of RBC Na and K concentrations and hypertension may be sex and age specific. The nature of these gender- and age-specific associations remains to be clarified. Prospective data are also needed for further clarification of the relation of intracellular Na metabolism to the etiology of hypertension.

Urinary sodium to potassium ratio and urinary stone disease. The Gubbio Population Study Research Group

The relation was investigated of urinary sodium to potassium ratio in first morning voided urine (spot urine) to urinary stone disease in 3,625 men and women aged 25 to 74 years participating in the baseline examination of the Gubbio Population Study. History of urinary stone disease (excretion of stone, and/or radiographic or ultrasonic evidence of urinary stone, and/or operation for urinary stone removal) was reported by 127 individuals (3.50%). Prevalence of urinary stone disease was lower in women than in men (2.59 and 4.58%, P < 0.001) and positively related to age (P < 0.001). Compared to nonstone formers, stone formers (N = 127) had higher urinary sodium to potassium ratio (P < 0.01), with similar plasma potassium and sodium concentration. In both sexes, urinary stone disease was positively related (P < 0.001) to sodium to potassium ratio: quartile analysis of this ratio showed that prevalence of stone formers in quartile 4 compared to quartile 1 was 3.33 times higher in women (P < 0.005, 95% confidence interval 1.36/8.60) and 2.71 times higher in men (P < 0.004, 95% confidence interval 1.35/5.93). In multiple logistic regression, urinary stone disease was significantly related to age, sex, and urinary sodium to potassium ratio (P < 0.01), controlled for other possible confounders, with or without exclusion of stone formers with plasma creatinine > 1.20 mg/dl. In an alternative model, with urinary sodium to potassium ratio not included, urinary stone disease was positively related to urinary sodium to creatinine ratio (P < 0.001) and weakly (P = 0.079) related inversely to urinary potassium to creatinine ratio.(ABSTRACT TRUNCATED AT 250 WORDS)

Hyperlipidemia in the hypertensive patient

Hypertension is known to be strongly associated with multiple metabolic abnormalities. A recent population survey carried out in Italy (the Gubbio study) involving 5,376 individuals showed that, up to the age of 64 years, hypertensive men were more markedly overweight (body mass index > or = 30) than normotensive men, whereas in women the prevalence of obesity was higher in hypertensive women at all ages. The prevalence of marked hypercholesterolemia (> or = 250 mg/dL) was uniformly higher in hypertensive compared with normotensive men except in the oldest age group; it was also higher in hypertensive women in the age 45-74 years group. Postabsorptive hyperglycemia and hyperuricemia were also more prevalent in hypertensive men and women, especially in the older age groups. Furthermore, the Tecumseh Blood Pressure Study indicated that not only patients with "sustained" hypertension but also those with so-called "white-coat" hypertension are, as a group, overweight and have elevated levels of cholesterol, insulin, and triglycerides and decreased levels of high-density lipoprotein. The multiple metabolic abnormalities clustered in hypertensives are important in relation to prognosis and therapy. The most recent World Health Organization/International Society of Hypertension guidelines for management of mild hypertension give considerable attention to the global assessment of cardiovascular risk in patients with hypertension and stress that, among individuals with mild hypertension, the risk of serious cardiovascular disease is also determined by a variety of risk factors other than blood pressure. The higher the absolute risk, the greater is the absolute benefit brought about by lowering blood pressure and correcting other risk factors, such as dyslipidemia.

Absence of clinically overt atherosclerotic vascular disease and adverse changes in cardiovascular risk factors in 70 patients with insulinoma

Hyperinsulinemia has been assumed to contribute to the pathogenesis of atherosclerosis. To assess the reliability of such claim we planned a retrospective study on a cohort of patients with pancreatic insulin producing neoplasm. A correlation was sought between fasting insulin plasma levels and the metabolic profile emerging from those parameters known to be cardiovascular risk factors, i.e. plasma triglycerides and cholesterol, insulin resistance, hypertension. Special attention was paid to the duration of disease, because the time exposure to hyperinsulinemia could play an important role in developing cardiovascular disease. Seventy patients, 41 females and 29 males, aged 44.9 +/- 1.96 yr (range 15-80), with surgically proved insulinoma were included in the study. Chronic exposure to hyperinsulinemia was documented through the measurement of insulin plasma levels either in the fasting state or post-prandially, resulting in 44.7 +/- 3.28 and 149.9 +/- 12.22 microU/ml, respectively. Fasting glycemia in average was 45.3 +/- 1.34 mg/dl. Plasma triglycerides and cholesterol concentrations were 136.3 +/- 7.93 and 195.8 +/- 5.18 mg/dl, respectively, their distribution overlapping that anticipated for the general population. No correlation arose between the degree of hyperinsulinemia and the lipidic profile. Preoperative blood pressure was 136.9 +/- 2.87 mmHg, systolic and 81.9 +/- 1.32 mmHg, diastolic. Hypertension was present in 5 (7.1%) out of 70 patients and persisted after tumor removal. A condition of insulin resistance (M = 4.06 +/- 0.4 mg/kg min vs 7.41 +/- 0.21) was documented through the euglycemic hyperinsulinemic clamp technique in 20 patients and showed a positive and significant correlation with fasting insulinemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Sodium-lithium countertransport activity is decreased after weight loss in healthy obese men

Maximal red blood cell (RBC) sodium-lithium countertransport activity has been consistently related to essential hypertension and may be a marker for risk of developing hypertension. Although there is strong evidence for genetic control of sodium-lithium countertransport, increasing evidence suggests that obesity and insulin-glucose metabolism are related to countertransport activity. This study was performed to determine whether countertransport activity decreases with weight loss in healthy obese adults. Forty-five healthy, white, obese adults were studied at baseline and after 6 months of behavioral dietary intervention. Weight loss was 11.5 kg (25.4 lb) in 24 men and 8.1 kg (17.8 lb) in 21 women. Sodium-lithium countertransport activity decreased 55.0 mumol Li/L RBC/h in men (P < .001, paired t test) and 14.6 mumol Li/L RBC/h in women (NS). Change in countertransport activity was correlated with change in body mass index (BMI) in men (r = .52, P < .01) and women (r = .27, NS) and was also strongly correlated with change in fasting glucose levels in both men and women (r = .50 and r = .56, respectively; P < .01) and with change in fasting insulin levels in men (r = .42, P = .04). Change in countertransport activity was not significantly related to change in physical exercise or serum lipid levels. There was a large decrease in systolic blood pressure in men (10.0 mm Hg, P < .001) and a smaller decrease in women (4.1 mm Hg, P < .05). These changes were significantly correlated with change in weight, but not with change in countertransport or baseline countertransport activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Sodium-lithium countertransport and triglycerides in diabetic nephropathy

Elevated erythrocyte sodium-lithium countertransport (SLC) activity is an intermediate phenotype of essential hypertension among Caucasians, and is controversially associated with nephropathy in Type 1 (insulin-dependent) diabetes. Hypertriglyceridemia is a frequent concomitant of elevated SLC in the general population, and may be found in diabetic nephropathy. The present study was designed to investigate the influence of kidney disease, serum triglycerides and blood pressure on the interindividual variability of SLC in Type 1 diabetes. SLC and fasting major serum lipids were studied in 35 Type 1 diabetic patients with persistently elevated urinary albumin excretion and in a group of patients matched for age, sex and duration of diabetes, but with normoalbuminuria. SLC was elevated in patients with clinical nephropathy (N = 10; median: 420 mumol.1RBC-1.hr-1) and in patients with microalbuminuria (N = 25; median: 405 mumol.1RBC-1.hr-1) compared with normoalbuminuric patients (median: 296 mumol.1RBC-1.hr-1; P < 0.01 vs. both groups). Hypertriglyceridemia and hypercholesterolemia were found only among patients with macroalbuminuria. Analysis of covariance indicated that the association of elevated SLC with kidney disease (P < 0.006 in all models) was largely independent of serum triglycerides, but also of total cholesterol, insulin dose and measures of glycemic control. Only diastolic blood pressure was positively associated with SLC (P < 0.02) independently from nephropathy (P < 0.005) also after restricting analysis to the normoalbuminuric patients. Kidney disease and raised blood pressure remain major concomitants of elevated SLC in Type 1 diabetics.

Sodium-lithium countertransport activity in red blood cells of patients with IgA nephropathy

In this paper we report some results of our studies on patients with immunoglobulin (Ig)A nephropathy regarding (1) the familiar aggregation of erythrocyte sodium-lithium (Na,Li) countertransport; (2) the association of Na,Li countertransport with the presence of arterial hypertension and lipid abnormalities; (3) the correlation between Na,Li countertransport activity and renal functional reserve; and (4) the preliminary results of a longitudinal study. In 13 families of patients with IgA nephropathy, selected because both parents were available, we found a significant correlation between midparent and offspring Na,Li countertransport activity (Spearman's rank correlation = 0.65; P = 0.023), but no husband-wife relationship. In 49 patients, the activity of Na,Li countertransport was significantly higher in erythrocytes from 20 hypertensive patients than from either 29 normotensive patients or from 36 healthy age- and sex-matched normal subjects. Hyperlipidemic patients had an erythrocyte Na,Li countertransport activity significantly higher than normolipidemic patients and controls. In 17 patients a significant inverse correlation was found between the peak variation of creatinine clearance over baseline value after an oral protein load and the erythrocyte Na,Li countertransport activity (Spearman r = 0.54; P = 0.03). In a longitudinal study of 36 patients followed from 12 to 36 months, those showing a progression toward renal failure had an erythrocyte Na,Li countertransport activity higher than median value. The results of our studies show that in patients with IgA nephropathy a high erythrocyte Na,Li countertransport rate, genetically determined, is associated with the presence of arterial hypertension and lipid abnormalities, and perhaps with a less favorable disease outcome.

Sodium-lithium countertransport and probability of hypertension in Caucasians 47 to 89 years old

The objectives of the present study were to determine whether sodium-lithium countertransport contributes to predicting the probability of having hypertension and to determine whether it does so after other predictor traits have been considered. We used logistic regression to model the relation between sodium-lithium countertransport and the probability of having hypertension, estimated by the prevalence of hypertension among 172 men and 252 women, aged 47-89 years, from the Caucasian population of Rochester, Minn. When sodium-lithium countertransport was the only predictor trait considered, it made a statistically significant contribution to prediction both in men (model chi(2)1df = 20.50, p < 0.001) and in women (model chi(2)1df = 16.69, p < 0.001). For each standard deviation increase in sodium-lithium counter-transport, the expected odds of having hypertension increased 2.25 times in men (95% confidence interval [CI], 1.44-3.51) and 1.77 times in women (95% CI, 1.32-2.37). When sodium-lithium countertransport was not considered, the other traits identified as predictors were age, body mass index, and plasma apolipoprotein CII and CII squared; plasma apolipoprotein AI was an additional predictor in women but not in men. When sodium-lithium countertransport was added to models that included the other predictors, it improved prediction both in men (increase in model chi(2)1df = 12.29, p < 0.001) and in women (increase in model chi(2)1df = 4.86, p < 0.027). Based on these complete models, when the other predictors remained at their mean values, each standard deviation increase in sodium-lithium countertransport increased the expected odds of having hypertension 2.06 times in men (95% CI, 1.31-3.22) and 1.48 times in women (95% CI, 1.04-2.21). These results establish that sodium-lithium countertransport provides information that is helpful in predicting the probability of having hypertension and is not reflected in other identified predictor traits.

Plasma lipids affect maximum velocity not sodium affinity of human sodium-lithium countertransport: distinction from essential hypertension

Inheritance is a major determinant of increased sodium-lithium countertransport (SLC) activity in hypertension. However, hyperlipidaemia can also cause increased SLC activity in some individuals and it is difficult to distinguish this effect from the effect of hypertension. Erythrocyte SLC activity and its kinetic determinants sodium affinity (km) and maximum velocity (Vmax) were measured in 25 hyperlipidaemic patients and 15 normal controls (NC). Increased SLC activity (0.31 +/- SEM 0.03 mmol Li/(h x 1 cells) vs. NC 0.20 +/- 0.01, P < 0.01) in the hyperlipidaemic patients was associated with increased Vmax (0.59 +/- 0.07 vs. NC 0.41 +/- 0.03, P < 0.01) but normal km (median 120 range [40-324] mmol l-1 vs. 140 [108-260]. Lipid-lowering therapy resulted in decreased SLC activity secondary to a fall in Vmax. Km remained constant despite the changes in lipids and Vmax. The mechanism of increased SLC activity in hyperlipidaemia is different from that in essential hypertension where increased sodium affinity is found. Measurement of the kinetic characteristics of SLC may discriminate between the independent influences of hypertension and hyperlipidaemia on the sodium-lithium countertransporter.

Hematocrit, blood pressure, and hypertension. The Gubbio Population Study

Baseline data from the Gubbio Population Study in north central Italy were used to investigate the relation of hematocrit to blood pressure and hypertension among 2,809 men and women aged 25-74 years. Independent of gender, age, and other confounders, the hypertensive group had a higher hematocrit than the nonhypertensive group (p less than 0.001). In comparison with the untreated hypertensive group, the hypertensive group being treated with diuretics or with other drugs only had similar mean hematocrit levels despite significantly lower blood pressures. Hematocrit was positively correlated with systolic pressure (r = 0.085, p less than 0.01 and r = 0.264, p less than 0.001 for men and women, respectively) and diastolic pressure (r = 0.214, p less than 0.001 and r = 0.266, p less than 0.001). In both sexes, whether or not the treated hypertensive group was included, age-adjusted prevalence of hypertension and average blood pressure were higher for persons in higher quintiles of hematocrit (p less than 0.001). The association of hematocrit with blood pressure and hypertension was significant and independent of several confounders. The regression coefficient of blood pressure on hematocrit ranged between 0.410 and 0.620 mm Hg per unit of hematocrit for systolic pressure and between 0.371 and 0.581 for diastolic pressure, depending on gender and whether the treated hypertensive group was included in multiple regression analysis. Based on exponentiation of the multiple logistic coefficient, prevalence of hypertension was at least two times greater for persons whose hematocrit levels were higher by 10 units.

Erythrocyte sodium-lithium countertransport and blood pressure in identical twin pairs discordant for insulin dependent diabetes

OBJECTIVE

To investigate whether insulin dependent diabetes is responsible for the abnormal behaviour of the carrier in sodium-lithium countertransport and whether the diabetic state is associated with rise in blood pressure.

DESIGN

Case-control study.

SETTING

London teaching hospital.

SUBJECTS

44 twin pairs discordant for insulin dependent diabetes living in United Kingdom and 44 healthy control subjects matched for age, sex, and body mass index. None of the twin pairs or the controls had evidence of microalbuminuria.

MAIN OUTCOME MEASURES

Sodium-lithium countertransport activity in erythrocytes and arterial blood pressure.

RESULTS

The mean (95% confidence interval) sodium-lithium countertransport activity (mmol Li per litre of red blood cells per h) of the diabetic twins (0.291 (0.244 to 0.338)) was similar to that of their non-diabetic cotwins (0.247 (0.204 to 0.290)); both values were significantly higher than that of the controls (0.187 (0.157 to 0.216); p < 0.05). In addition, systolic blood pressure was higher in those twins with diabetes (127 (122 to 133) mm Hg) than in the non-diabetic cotwins (122 (117 to 127) mm Hg; p < 0.01). There were no significant differences in mean diastolic blood pressure between any of the groups studied.

CONCLUSIONS

The raised erythrocyte sodium-lithium countertransport activity in the diabetic twins compared with the controls seems to be inherited rather than a consequence of overt diabetes. The higher systolic blood pressure in diabetic twins than non-diabetic cotwins indicates that insulin dependent diabetes does exert a small influence on systolic blood pressure.

New insights and approaches to reduce end-organ damage in the treatment of hypertension: subsets of hypertension approach

Antihypertensive therapy should be directed toward reduction of all end-organ damage including congestive heart failure, left ventricular hypertrophy, coronary heart disease, myocardial infarction, cerebrovascular accident, and chronic renal failure. The Subsets of hypertension approach is based on pathophysiology, hemodynamics, risk factor reduction for end-organ damage, concomitant diseases and problems, demographics, adverse effects on quality of life, compliance, and total health care costs. This approach provides a more individualized and logical treatment of the hypertensive syndrome and addresses the metabolic and structural abnormalities that are present.

Is increased erythrocyte sodium-lithium countertransport a useful marker for diabetic nephropathy?

Genetic predisposition to essential hypertension has been proposed as a risk factor for the development of diabetic nephropathy in type 1 (insulin-dependent) diabetes mellitus. An increased sodium-lithium countertransport activity (NaLiCT) has been suggested as a genetic marker for essential hypertension. We therefore evaluated NaLiCT in diabetic patients with (N = 39) or without (N = 23) diabetic nephropathy (DNP), patients with non-diabetic renal diseases (N = 42) and in healthy controls (N = 24). The NaLiCT was elevated in both diabetic patient groups compared to healthy controls (median 244; range 134 to 390 mumol.liter cells-1.hr-1), but was not different in patients with DNP (median 314; range 162 to 676), without DNP (median 325; range 189 to 627) and patients with non-diabetic renal disease (median 300; range 142 to 655). The genetic predisposition to DNP is illustrated by the fact that diabetic sibs of probands with DNP showed a higher occurrence of DNP than diabetic sibs of patients without DNP. We analyzed whether familial DNP clustered with an increased NaLiCT. The NaLiCT in sibs concordant for the presence of DNP (N = 10; median 307; range 217 to 428 mumol.liter cells-1.hr-1) was not significantly different from that in sibs concordant for absence of DNP (N = 15; median 279; range 189 to 442). We conclude that erythrocyte sodium-lithium countertransport activity cannot be used as a marker to identify patients at risk for the development of diabetic nephropathy.

Renal abnormalities in normotensive insulin-dependent diabetic offspring of hypertensive parents

To assess the effects of genetic predisposition of essential hypertension on early renal function in recent insulin-dependent diabetics, we studied inulin, para-aminohippuric, sodium, and lithium clearances in 69 unselected diabetics with (n = 20) and without (n = 49) a family history of essential hypertension. Despite similar metabolic control, glomerular filtration rate and mean arterial pressure were significantly higher in diabetics with than in those without a family history of hypertension. However, no difference was found between the two groups regarding renal vascular resistance, sodium excretion, or fractional proximal and distal sodium reabsorption. Renal responses to acute captopril (75 mg) administration were evaluated in 27 patients (six with family history of hypertension). Captopril decreased filtration fraction and mean arterial pressure similarly in both groups, whereas glomerular filtration rate and renal vascular resistance decreased more dramatically in diabetics with family history of hypertension. These findings indirectly suggest an abnormal response to angiotensin of vascular tone in recent diabetics with familial predisposition to hypertension. Renal response to acute nicardipine (2.5 mg i.v.) administration was analyzed in 24 patients (five with family history of hypertension). In both groups, nicardipine similarly decreased mean arterial pressure and renal vascular resistance and induced a marked natriuretic effect due to a predominant reduction in proximal reabsorption of sodium. However, the increase in sodium excretion was twofold to threefold more pronounced in diabetics with a family history of hypertension. Whether these early renal abnormalities may contribute to the risk of diabetic nephropathy, as suggested by retrospective studies, remains to be determined.

The Gubbio data. Epidemiology and pathophysiology. Gubbio Study Research Group

The relation between the maximal velocity of red blood cell sodium-lithium countertransport and blood pressure/hypertension has been studied in 2,748 men and women aged 25-74 years who participated in the 1983-85 baseline examination of the Gubbio Population Study, an epidemiologic investigation performed in a hill town of north central Italy. Men had a higher sodium-lithium countertransport velocity than women at all ages, and, in both sexes, a higher velocity was observed at successive ages. Hypertensives of both sexes had a higher sodium-lithium countertransport velocity than normotensive individuals, the difference remaining significant after control for age, body mass index and plasma uric acid concentration. Individuals with high sodium-lithium countertransport velocity had significantly greater prevalence of hypertension in both sexes. The data show the existence of a cross-sectional association between sodium-lithium countertransport velocity and hypertension in general population. Prospective study of the Gubbio population is now in progress to investigate the relation between baseline sodium-lithium countertransport velocity, its change over the years and the incidence of hypertension.

Sodium-lithium countertransport and body fat distribution

The relationship between erythrocyte sodium-lithium countertransport (Na-Li CT) and body fat distribution is analyzed in a sample (n = 101) of normotensive and untreated hypertensive men participating in an epidemiological study of coronary heart disease risk factors. Na-Li CT is significantly and positively associated with both subscapular skinfold and waist to hip ratio, but not with triceps skinfold. The univariate correlation between Na-Li CT and blood pressure is diminished when adjusted for body mass index and waist to hip ratio. These findings support the existence of an association between Na-Li CT and central body fat distribution and suggest that the metabolic abnormalities associated with centrally distributed body fat could explain, at least in part, the association between Na-Li CT and blood pressure. The maximal velocity of the sodium-lithium countertransport (Na-Li CT) in erythrocytes has been reported to be directly associated with blood pressure and hypertension in numerous reports from both clinical and epidemiological studies. In most of these studies, indices of weight and/or adiposity (body mass index, in particular) have been shown to be among the most important correlates of Na-Li CT. Adiposity is an important determinant of blood pressure, and there is evidence suggesting that the patterning of the fat cells in the body is linked to a number of metabolic disturbances that could lead to hypertension and an increase in other CHD risk factors. The present report analyses the relationship between Na-Li CT and body fat distribution in a sample of normotensive and untreated hypertensive men participating in an epidemiological study.

Increased sodium-lithium countertransport activity in red cells of IgA nephropathy patients

The aim of this work was to analyze Na,Li countertransport activity in the erythrocytes from patients with IgA nephropathy, in relationship with their blood pressure status and lipid profile. Forty-nine patients (32 males, 17 females) with biopsy-proven IgA nephropathy and without significant impairment of renal function (serum creatinine less than or equal to 1.4 mg/dl) and 36 normal subjects (21 males, 15 females) were evaluated. Twenty-nine patients with IgA nephropathy were normotensive and 20 hypertensive (diastolic pressure greater than or equal to 95 mm Hg or treated by antihypertensive drugs). Na,Li countertransport was significantly higher in red cells from hypertensive than from normotensive patients (P = 0.002) and normal subjects (P = 0.0001), (values respectively 309 +/- 17; 241 +/- 12 and 211 +/- 11 mumol/liter RBC/hr); normotensive patients with IgA nephropathy did not differ from controls regarding the Na,Li countertransport rate. A multiple stepwise logistic regression analysis with blood pressure status as the dependent variable and Na,Li countertransport activity, age, serum creatinine, proteinuria, cholesterol, triglycerides, plasma potassium and time from onset as independent variables, indicated an independent significant association for Na,Li countertransport (P = 0.002) proteinuria (P = 0.006), plasma potassium (P = 0.006) and age (P = 0.029). Other tested variables were not independently related to blood pressure status. Hyperlipidemic patients (plasma total cholesterol concentration greater than 200 mg/dl and/or plasma triglycerides greater than 172 mg/dl) had an erythrocyte Na,Li countertransport activity significantly higher than normolipidemic (P = 0.005) and controls (P = 0.001) (values respectively 295 +/- 14; 226 +/- 12 and 211 +/- 11 mumol/liter RBC/hr).(ABSTRACT TRUNCATED AT 250 WORDS)

Correlates of sodium-lithium countertransport. Findings from the Gubbio Epidemiological Study. The Gubbio Collaborative Study Group

BACKGROUND

Numerous reports have presented evidence for a positive association between the maximal velocity of the sodium-lithium countertransport (Na-Li CT) in erythrocytes and hypertension. The nature of this association remains to be clarified.

METHODS AND RESULTS

This report presents correlates of Na-Li CT in a population sample of 3,591 people aged 5-74 years. Males had higher mean age-specific levels of Na-Li CT than females except for the 5-14-year age stratum. In adults aged 25-74, for both men (n = 1,044) and women (n = 1,192), body mass index, plasma uric acid and glucose, alcohol consumption, and red blood cell mean corpuscular volume were positively related to countertransport in multivariate analyses; plasma high-density lipoprotein (HDL) cholesterol and plasma potassium were inversely related. Plasma non-HDL cholesterol was independently and directly related to Na-Li CT in women, and plasma sodium was inversely associated with Na-Li CT in men. These relations prevailed for men when persons with hypertension were excluded from the analyses and prevailed in part for women. When stepwise regression analyses were done for all men and women combined (n = 2,236), sex ceased to be significantly related to countertransport with plasma uric acid and alcohol intake in the model. In adults of either sex, no independent association was detected between Na-Li CT and age, heart rate, or the ratios of sodium to potassium or of sodium to creatinine in overnight untimed urine.

CONCLUSIONS

In both sexes, Na-Li CT is significantly and independently associated with a number of metabolic variables (plasma uric acid, plasma glucose, body mass index, plasma potassium, and life-style habits [e.g., alcohol intake]). Further research is needed to elucidate the meaning of the significant associations between Na-Li CT and the foregoing variables (all of them also related to blood pressure).

Exercise-loaded blood pressure and Li-Na countertransport system in the erythrocyte membrane as predictors of mild essential hypertension prognosis

1. The blood pressure response to exercise loading, Na concentration in the erythrocyte and Li-Na countertransport (Li-Na CT) system in the erythrocyte membrane in 40 male volunteers and 98 patients with mild essential hypertension were investigated. Subjects were divided into a juvenile group (less than 36 years) and a middle-aged (greater than 36 years and less than 65 years) group. Exercise-loaded blood pressure in patients with mild essential hypertension was followed up for more than 5 years. 2. Systolic blood pressure (SBP) at 6 min during exercise loading was significantly higher in the mild hypertension group compared with the control group. 3. Patients with high SBP at exercise loading in the mild hypertension group transferred more often to the moderate hypertension group within 5 years. 4. No difference in the haemodynamic parameter at rest was noted in the transferred group for moderate hypertension and the non-transferred group. 5. A higher blood pressure response to noradrenaline was noted in the transferred group compared with the non-transferred group of the juvenile group. 6. High Na concentration in the erythrocyte and acceleration of the Li-Na CT system in the erythrocyte membrane were noted in the mild hypertension group compared with the volunteer group. 7. A correlation between SBP at exercise loading and Li-Na CT system in the erythrocyte membrane was noted. This correlation was strongly noted in subjects less than 50 years old. 8. From these results it was concluded that SBP at exercise loading and Li-Na CT system in the erythrocyte membrane are useful as indicators for the prognosis of mild essential hypertension.

Sodium-lithium countertransport and hypertension in Rochester, Minnesota

The objectives of the present study were to determine whether increased sodium-lithium countertransport is associated with essential hypertension in the general Caucasian population and to determine whether this association is independent of the effects of gender, age, body size, and plasma lipids. We studied 543 men and 589 women from the population of Rochester, Minnesota. Mean sodium-lithium countertransport was higher in hypertensive than in normotensive subjects in men (370 +/- 147 [mean +/- SD] versus 315 +/- 110 mumol/l red blood cells [RBC]/hr, p less than 0.001) and in women (339 +/- 114 versus 269 +/- 92 mumol/l RBC/hr, p less than 0.001). Interindividual differences in plasma triglycerides, body mass index (wt/[ht]2), and plasma total cholesterol explained 13.0% of sodium-lithium countertransport variation in men (p less than 0.001) and 20.2% in women (p less than 0.001). Age did not predict additional sodium-lithium countertransport variation in either gender. Slopes of the regressions of sodium-lithium countertransport on plasma triglycerides, body mass index, and plasma total cholesterol did not differ between diagnostic groups in men (p = 0.31) or in women (p = 0.29). After adjustment to remove sodium-lithium countertransport variation attributable to these covariates, mean sodium-lithium countertransport remained significantly higher in hypertensive than in normotensive subjects in men (354 +/- 139 versus 319 +/- 104 mumol/l RBC/hr, p less than 0.01) and in women (311 +/- 103 versus 278 +/- 83 mumol/l RBC/hr, p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Serum insulin, insulin sensitivity, and erythrocyte sodium metabolism in normotensive and essential hypertensive subjects with and without overweight

Increased insulin circulating levels and perturbations of intracellular sodium metabolism have been reported in essential hypertensive patients, leading to postulate their involvement in the pathophysiology of the disease. In-vitro studies have shown that insulin modulates the activity of some transmembrane sodium transporters. The aim of this investigation was to assess in subjects with essential hypertension and/or overweight, the levels of fasting serum insulin, the activity of sodium transporters and their possible relationships. In 18 lean normotensive, 12 overweight normotensive, 18 untreated lean essential hypertensive, and 16 untreated overweight essential hypertensive subjects, we measured the fasting levels of blood glucose and serum insulin, and calculated the glucose/insulin ratio as an index of sensitivity to insulin. In addition, in the red blood cells of these subjects, we evaluated the maximal rate of ouabain-sensitive Na/K pump, furosemide-sensitive outward Na/K cotransport, Nai/Lio countertransport, and the constant rate of passive permeability to Na. When compared to lean normotensive, overweight normotensive, lean hypertensive, and overweight hypertensive subjects exhibited significantly higher fasting insulin levels, with lower glucose/insulin ratio. No significant difference was found in the activity of Na/K pump, Na/K cotransport, and passive permeability to Na. The Nai/Lio exchange was significantly increased in both hypertensive groups. Mean blood pressure correlated positively and independently with body mass index and fasting insulinemia, and inversely with the glucose/insulin ratio. No relationships were found between blood pressure, fasting insulin levels or glucose/insulin ratio and the activity of sodium transport systems. We conclude that hyperinsulinemia and insulin resistance are associated with essential hypertension independently of overweight. These data lend support to the hypothesis that insulin is involved, concurrently with other factors, in the pathogenesis of essential hypertension in both lean and obese subjects.