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 hypertension, and to investigate the effect of metformin and metoprolol, respectively.

DESIGN

A double-blind, triple cross-over, placebo-controlled study over a total period of 18 weeks. SETTING. A hypertension out-patient clinic and research laboratory at Sahlgrenska University Hospital.

SUBJECTS

Seventeen non-obese men with mild essential -hypertension and 17 weight-matched, healthy controls.

INTERVENTIONS

Metformin 850 mg b.i.d., metoprolol CR 100 mg once daily and placebo were given during 18 weeks. Each treatment period was 6 weeks. A euglycaemic clamp was performed and erythrocyte Na(+)-Li+ CT measured after each 6-week treatment period.

MAIN OUTCOME MEASURES

Insulin sensitivity, erythrocyte Na(+)-Li+ CT, their interrelation, and the effect of metformin and metoprolol CR on both variables, respectively.

RESULTS

The hypertensive men tended to have an elevated Na(+)-Li+ CT compared with the control subjects (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 exhibited 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 hypertensive subjects. In multiple regression analysis, Na(+)-Li+ CT showed a significant correlation to glucose disposal rate only. In the control subjects, there was no relation between glucose metabolism and Na(+)-Li+ CT. Neither metformin nor metoprolol influenced Na(+)-Li+ CT, glucose disposal rate or plasma insulin.

CONCLUSION

Erythrocyte Na(+)-Li+ CT seemed to be closely related to insulin-glucose metabolism in mild hypertension, but was not influenced by metformin or metoprolol.