RELATIONSHIP BETWEEN SODIUM-LITHIUM COUNTERTRANSPORT AND INSULIN SENSITIVITY IN MILD HYPERTENSION

Objectives. To study the relationship between insulin sensitivity and sodium-lithium countertransport (Na+-Li+ CT) in mild, essential hypert ension, and to investigate the effect of metformin and metoprolol, res pectively. Design. A double-blind, triple cross-over, placebo-controll ed study over a total period of 18 weeks. Setting. A hypertension out- patient clinic and research laboratory at Sahlgrenska University Hospi tal. Subjects, Seventeen non-obese men with mild essential hypertensio n and 17 weight-matched, healthy controls. Interventions. Metformin 85 0 mg b.i.d., metoprolol CR 100 mg once daily and placebo were given du ring 18 weeks. Each treatment period was 6 weeks. A euglycaemic clamp was performed and erythrocyte Na+-Li+ CT measured after each 6-week tr eatment period. Main outcome measures. Insulin sensitivity, erythrocyt e Na+-Li+ CT, their interrelation, and the effect of metformin and met oprolol CR on both variables, respectively. Results. The hypertensive men tended to have an elevated Na+-Li+ CT compared with the control su bjects (0.34 +/- 0.03 versus 0.26 +/- 0.02 mmol L(-1) h(-1), P < 0.1). Glucose disposal rate was similar, but plasma insulin levels higher ( P < 0.05) among the hypertensives than the controls. Na+-Li+ CT exhibi ted a positive relationship to BMI (r = 0.53, P = 0.03) and a negative correlation to glucose disposal rate (r = -0.66, P = 0.008) in the hy pertensive subjects. In multiple regression analysis, Na+-Li+ CT showe d a significant correlation to glucose disposal rate only. In the cont rol subjects, there was no relation between glucose metabolism and Na-Li+ CT. Neither metformin nor metoprolol influenced Na+-Li+ CT, gluco se disposal rate or plasma insulin. Conclusion. Erythrocyte Na+-Li+ CT seemed to be closely related to insulin-glucose metabolism in mild hy pertension, but was not influenced by metformin or metoprolol.