Cellular sodium membrane transport and cardiovascular risk factors in non-insulin-dependent diabetes mellitus

Association have been described between cardiovascular risk factors and abnormalities of both sodium-lithium countertransport (SLC) and sodium-hydrogen ion exchange in subjects with insulin-dependent diabetes mellitus. The data in subjects with non-insulin-dependent diabetes mellitus (NIDDM) are few and more conflicting. This investigation examines erythrocyte SLC rates and platelet sodium-hydrogen ion-exchange kinetics and their relationship to cardiovascular risk factors in 45 nondiabetic and 35 NIDDM white men. The two groups did not differ significantly in erythrocyte SLC or platelet buffering capacity, sodium-hydrogen ion-exchange maximal rate (Vmax), or Km for extracellular sodium. Within the whole group, controlling for the presence of diabetes, SLC correlated weakly with triglyceride concentration (r = .23, P = .05), but not with urinary albumin excretion rate (AER), systolic or diastolic blood pressure, body mass index (BMI), or concentrations of glucose, insulin, or total or high-density lipoprotein (HDL) cholesterol. Platelet sodium-hydrogen exchange was not significantly related to any cardiovascular risk factor studied. In conclusion, (1)SLC activity was not increased in NIDDM subjects; (2) SLC rates correlated weakly with serum triglyceride concentrations; (3) platelet sodium-hydrogen exchange Vmax and K(m) for extracellular sodium and platelet buffering capacity did not differ between diabetic and nondiabetic groups; and (4) there was no significant relationship between platelet Na+/H(+)-exchange kinetics and any of the cardiovascular risk factors studied.

Diabetes, impaired glucose tolerance and cardiovascular disease risk factors in the Asian Indian Bhatia community living in Tanzania and in the United Kingdom

A population-based cross-sectional survey was carried out to study potential environmental risk factors contributing to diabetes and cardiovascular risk in the same homogeneous group in the United Kingdom and in Dar es Salaam, Tanzania. In Dar es Salaam, 222 members of the Bhatia community aged 15 years and over were studied. In the UK, 180 randomly selected subjects aged 15 years and over participated. Age, sex, and body mass index adjusted mean levels of fasting glucose (5.5 mmol l-1 vs 5.1 mmol l-1 (p < 0.001)) and 2 h glucose (6.8 mmol l-1 vs 6.0 mmol l-1 (p < 0.001)) were significantly higher in Tanzanian subjects than in UK subjects. Mean levels of serum triglycerides (1.5 mmol l-1 vs. 1.3 mmol l-1 (p < 0.05)) and systolic blood pressure (135 mmHg vs 127 mmHG (p < 0.05) were significantly higher in subjects in the UK. The age and sex adjusted prevalence of impaired glucose tolerance (28.4% vs 11.4% (p < 0.001)), newly diagnosed diabetes (8.6 % vs 1.5% (p < 0.01)), hypercholesterolaemia (9.9% vs 1.5% (p < 0.001)), and smoking (12.1% vs 3.9% (p < 0.01)) were significantly higher in subjects in Tanzania compared to subjects in the UK. The prevalence of known diabetes, hypertriglyceridaemia, hypertension, and obesity did not show significant differences between subjects in Tanzania and those in the UK. Within the same homogeneous community with the same likely genetic predisposition, there are substantial geographical differences in cardiovascular risk factors, the causes of which remain to be determined.

Association between left ventricular hypertrophy and erythrocyte sodium-lithium exchange in normotensive subjects with and without NIDDM

The determinants of left ventricular mass in normal control subjects and subjects with non-insulin-dependent diabetes (NIDDM) are ill-defined. We therefore recorded M-mode and pulsed Doppler echocardiograms and 24-h ambulatory blood pressure in 57 normotensive subjects, 34 with NIDDM and 23 matched non-diabetic control subjects. Measurements of erythrocyte sodium-lithium counter-transport, plasma angiotensin II, plasma and platelet catecholamines and fasting plasma insulin were also made. Six control subjects (26%) and 15 diabetic subjects (44%) had some degree of left ventricular hypertrophy. Subjects with left ventricular hypertrophy (n = 21) had an elevated mean rate of sodium-lithium countertransport (0.40 +/- 0.13 vs 0.31 +/- 0.09 mmol.l-1.h-1; p < 0.01), parallel differences being observed in both the diabetic and control groups. Twelve of the subjects with left ventricular hypertrophy (57%) had elevated rates of sodium-lithium counter-transport compared to only seven (19%) of those without (p < 0.05). There was no consistent difference between those with and without left ventricular hypertrophy in any other clinical or biochemical variable. Multivariate analysis, with the presence or absence of left ventricular hypertrophy as the dependent variable, demonstrated that the maximal rate of sodium-lithium countertransport was the only variable that independently contributed to left ventricular hypertrophy (partial r = 0.35; F1.55 = 7.74; p = 0.007). This study demonstrates for the first time an association between left ventricular hypertrophy and erythrocyte membrane cation transport that is independent of hypertension, is present in both diabetic and non-diabetic groups, and may represent a link between elevated rates of membrane sodium transport and cardiovascular risk.

The contribution of the sympathoadrenomedullary system to the etiology of essential hypertension: a study using plasma and platelet catecholamine concentrations

Platelets take up and store noradrenaline and adrenaline in proportion to plasma concentrations and may, therefore, provide an integrated index of sympathoadrenomedullary arousal. Plasma and platelet catecholamine concentrations were measured in 290 European and 155 Asian subjects, and were related to blood pressure, insulin levels, and social class. Plasma noradrenaline concentrations correlated with systolic and diastolic blood pressure in both ethnic groups (r = 0.20-0.30), and these levels were significantly elevated in hypertensive subjects (P < 0.003). In Europeans, but not in Asians, these relationships remained significant after adjusting for age and gender, and were independent of the relationship between insulin and blood pressure. There were much weaker relationships between platelet catecholamine concentrations and blood pressure, which were dependent on age and gender as covariates. In neither ethnic group was there any relationship of either plasma or platelet catecholamine concentrations with insulin concentrations, body mass index, or glucose intolerance. European subjects in manual occupations had significantly higher concentrations of plasma noradrenaline than those with nonmanual occupations. The findings suggest a significant role for the sympathetic nervous system in the determination of blood pressure, but do not provide evidence for a connection between hyperinsulinemia and sympathetic nervous system activity. The role of platelet catecholamines as an epidemiological marker of stress has not been supported.

Increased blood pressure variability during 24h blood pressure monitoring as an early sign of autonomic dysfunction in non-insulin-dependent diabetics

To evaluate the presence of early autonomic dysfunction in non-insulin-dependent diabetics we examined 24h control of blood pressure (1/4 hourly readings day and 1/2 hourly at night, using TM 2420) in 20 non-insulin-dependent diabetics, controlled only on diet or oral hypoglycaemics and 20 age/sex/BP matched non-diabetics selected from a random population survey. The two groups were aged 52 +/- 9 years and 53 +/- 8 years, respectively. Both groups included normotensives and mild hypertensives in equal numbers but none was on antihypertensive treatment. The groups were well matched for daytime systolic blood pressure (SBP; 132.2 +/- 11.4 vs. 131.2 +/- 10.3) and diastolic blood pressure (DBP; 82.1 +/- 8.3 vs. 81.1 +/- 7.0). The diabetics had a significantly greater heart rate (HR) both during the day (79.6 +/- 9.5 vs. 72.3 +/- 8.8: P = 0.015) and during sleep (67.7 +/- 6.8 vs. 62.5 +/- 8.9). There was increased BP variability in the diabetics during the day (standard deviation of SBP; 16.9 +/- 6.2 vs. 13.3 +/- 4.7: P < 0.05) but the difference for DBP variability was not significant. The day-night difference for SBP, DBP, HR and HR variability was the same in both groups. We conclude that in these patients there was evidence for an alteration in BP variability (which may reflect baroreflex insensitivity) at a stage where there was no alteration in day-night rhythms of BP or HR. The increased HR both at day and night may also reflect baroreflex dysfunction and/or sympathovagal imbalance.(ABSTRACT TRUNCATED AT 250 WORDS)