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Red blood cell lithium-sodium countertransport in the tecumseh blood pressure study
A B Weder1, N J Schork, L Krause
1University of Michigan, Department of Internal Medicine, Ann Arbor 48109.
Insights
Elevated red blood cell lithium-sodium countertransport is linked to higher blood pressure and hypertension risk. This marker may identify a genetically predisposed subgroup for essential hypertension.
Area of Science:
- Cardiovascular Research
- Human Physiology
- Genetics
Background:
- Essential hypertension is multifactorial, necessitating subtype identification through reliable markers.
- Red blood cell lithium-sodium countertransport activity is a potential marker, showing increased levels in hypertensive individuals.
Purpose of the Study:
- To investigate the association between red blood cell lithium-sodium countertransport activity and distinct physiological characteristics in a population study.
- To determine if elevated countertransport identifies a specific subgroup predisposed to hypertension.
Main Methods:
- Classified 705 participants in the Tecumseh Blood Pressure Study based on red blood cell lithium-sodium countertransport levels (normal vs. high).
- Analyzed associations between countertransport activity and blood pressure, hypertension prevalence, hemodynamic parameters, and left ventricular mass.
Main Results:
- Subjects with high lithium-sodium countertransport exhibited higher average blood pressure and hypertension prevalence, with elevated pressure present since youth.
- The high countertransport group showed elevated vascular resistance and slightly depressed sympathetic nervous system activity.
- Increased countertransport was associated with significantly lower left ventricular mass index and rare left ventricular hypertrophy.
Conclusions:
- Red blood cell lithium-sodium countertransport activity is a useful marker for distinguishing subgroups within the population.
- Elevated maximal activity of this countertransport suggests a genetic predisposition to essential hypertension.
Abstract:
Human essential hypertension has more than one cause, but to dissect out subtypes, markers are required. The maximal activity of red blood cell lithium-sodium countertransport has been shown to be increased in hypertensive patients in case-control and population-based studies; in the latter, its distribution is a mixture of two overlapping but distinguishable subpopulations. In the present study, we classified 705 participants in the Tecumseh Blood Pressure Study as having either normal (mean, 0.234 mmol/l cells/hr; n = 614) or high (mean, 0.463 mmol/l cells/hr; n = 91) red blood cell lithium-sodium countertransport to determine if the red blood cell marker is associated with distinctive physiological characteristics. We found that subjects with elevated lithium-sodium countertransport have higher average blood pressure and a greater prevalence of hypertension than those with normal countertransport and that elevated blood pressure had been present since youth. Hemodynamically, the high countertransport group is characterized by elevated vascular resistance, whereas sympathetic nervous system activity appears to be slightly depressed. Subjects with increased lithium-sodium countertransport, compared with those with normal countertransport, have significantly lower average left ventricular mass index and only very infrequently demonstrate left ventricular hypertrophy. Our results support the usefulness of measurements of the maximal activity of red blood cell lithium-sodium countertransport as a way of distinguishing subgroups in the population. Our data are consistent with the idea that subjects with an elevated maximal activity for red blood cell lithium-sodium countertransport are a subset of the population with a genetic lesion that predisposes them to the development of essential hypertension.