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

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.

Effects of lithium on the human erythrocyte membrane and molecular models

The mechanism whereby lithium carbonate controls manic episodes and possibly influences affective disorders is not yet known. There is evidence, however, that lithium alters sodium transport and may interfere with ion exchange mechanisms and nerve conduction. For these reasons it was thought of interest to study its perturbing effects upon membrane structures. The effects of lithium carbonate (Li+) on the human erythrocyte membrane and molecular models have been investigated. The molecular models consisted in bilayers of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE), representing classes of phospholipids located in the outer and inner monolayers of the erythrocyte membrane, respectively. This report presents the following evidence that Li+ interacts with cell membranes: a) X-ray diffraction indicated that Li+ induced structural perturbation of the polar head group and of the hydrophobic acyl regions of DMPC and DMPE; b) experiments performed on DMPC large unilamellar vesicles (LUV) by fluorescence spectroscopy also showed that Li+ interacted with the lipid polar groups and hydrophobic acyl chains, and c) in scanning electron microscopy (SEM) studies on intact human erythrocytes the formation of echinocytes was observed, effect that might be due to the insertion of Li+ in the outer monolayer of the red cell membrane.

Lipid lowering: another method of reducing blood pressure?

Modern management of cardiovascular risk depends on assessment of cardiovascular risk factors. Hypertension and hyperlipidaemia are synergistic risk factors for cardiovascular events. Both show a degree of cross-correlation through sharing mechanisms of pathogenesis including insulin resistance and endothelial dysfunction. This article reviews the common pathways leading to dyslipidaemia and hypertension and the effects diet and lipid-lowering drug therapies have had on correcting blood pressure in patients with essential hypertension. Both statins and fibrates have shown a capability to lower blood pressure by up to 8/5 and 15/10 mmHg respectively, in some small-scale clinical trials and have effects on arterial wall structure and hence pulse wave velocity. This blood pressure action may account for some of the clinical effects of lipid-lowering drugs on cardiovascular risk. Thus, lipid lowering may provide an additional method of correcting hypertension in some high-risk patients. However, data from large-scale intervention trials are either absent or ambiguous. Definitive large-scale trials to investigate the antihypertensive effects of lipid-lowering drugs are required, although end point studies examining the interaction of lipid-lowering and antihypertensive drugs to determine optimum combinations are already under way.

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.

Sodium-lithium countertransport is increased in normoalbuminuric type 1 diabetes but is not related to other risk factors for microangiopathy

BACKGROUND

It has been reported that sodium-lithium countertransport (Na/Li CT) activity is increased in patients with diabetes mellitus and that this increased Na/Li CT activity is associated with the development of diabetic nephropathy. It is unclear however, whether Na/Li CT is related to other pathophysiological factors in diabetic patients. We studied kinetic parameters of Na/Li CT activity together with other putative risk factors for microangiopathy in normoalbuminuric type 1 diabetic patients and matched control subjects.

SUBJECTS AND METHODS

We measured maximum velocity (Vmax) and sodium affinity (Km) of Na/Li CT in 53 diabetic patients and 45 healthy controls. Endothelial function was assessed by monitoring forearm vascular response to intrabrachial infusion of acetylcholine. Blood samples were collected for measurement of HbA1c, glucose, insulin and lipids. Blood pressure was measured intra-arterially. Renal haemodynamics were measured by inulin/p-aminohippurate clearance. Urinary albumin was measured by enzyme-linked immunosorbent assay. Transcapillary escape of albumin (TERalb) was calculated by the disappearance curve of 125I-labelled albumin.

RESULTS

Vmax was increased in diabetic patients (779 +/- 36 micromol Li+ h-1 L-1 erythrocytes vs. 623 +/- 35 in controls, P < 0.01), whereas Km was decreased (64 +/- 16 mmol L-1 vs. 76 +/- 27 in controls, P = 0.03). The ratio of Vmax : Km was 12.4 +/- 0.6 in diabetic patients and 8.9 +/- 0.9 in controls (P < 0.001). When comparing diabetic patients in the lowest and highest quartile of Vmax or Km there were no differences in blood pressure, renal haemodynamics, urinary albumin excretion, TERalb, endothelial function, HbA1c, glucose, insulin, or lipid profile.

CONCLUSION

Na/Li CT is increased in uncomplicated type 1 diabetes and characterized by an increase in Vmax and a decrease in Km. The increase in Na/Li CT is not associated with changes in endothelial function, degree of metabolic control, blood pressure or renal haemodynamics.

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.