- Kinetic and thermodynamic properties of red cell lithium (Li) efflux were examined in patients with essential hypertension; the maximal rate of Li efflux as affected by temperature was measured at the range of 12 degrees to 42 degrees C. Fifty-two patients with essential hypertension and 22 normotensives were studied. The mean Li efflux, both into sodium (Na) medium and Li-Na countertransport, was higher in hypertensive than in normotensive persons, but the distinction between the two groups was limited by extended scatter and overlap. The distinction could be markedly improved by determining the effect of temperature on Li efflux. While all the normotensives exhibited Arrhenius plots of Li efflux with a change in slope ("break") around 30 degrees C, the corresponding "break" for most (75%) of the hypertensives was about 20 degrees C. Consideration of both the rate and the temperature dependence of Li efflux further improved the differentiation of hypertensive patients. Analysis of normotensive offspring of hypertensives and of patients with secondary hypertension indicates that the temperature dependence of Li efflux may serve as a genetic marker for essential hypertension.