Cross-sectional and longitudinal relationship of sodium-lithium countertransport to insulin, obesity and blood pressure in healthy perimenopausal women.

The objectives of this study were to assess the possible role of insulin as a regulator of red blood cell sodium-lithium countertransport and to examine the relationship of countertransport activity to change over time in insulin, blood pressure, and other variables. At baseline, countertransport was measured, and at baseline and after 2-3 years of follow-up, blood pressure, body mass index (BMI), lipids, fasting and two-hour plasma insulin and glucose were measured in 144 white healthy, premenopausal women, age 42-50 years. At baseline, using high and low categories of fasting insulin, triglycerides and BMI, countertransport was independently related to fasting insulin (P = 0.017), and triglycerides (P = 0.001), but not to BMI by analysis of variance. In similar analyses with fasting insulin, BMI, and countertransport, diastolic blood pressure was independently related only to countertransport (P = 0.003). Among the 73 who remained premenopausal after 2-3 year follow-up, baseline countertransport was significantly correlated with increases in fasting and two-hour insulin (r = 0.37, 0.38, P = 0.003, respectively), and these relationships remained significant after adjustment for change in BMI. Among subjects with high baseline countertransport, systolic blood pressure increased 5.6 mmHg compared with -2.2 mmHg with low countertransport, P = 0.001 after adjusting for baseline and change in BMI, triglycerides, and fasting and two-hour insulin. The data are consistent with a role for insulin and lipids in the regulation of sodium transport which may, in turn, play a role in blood pressure regulation. A relatively short follow-up in this healthy population suggests a relationship of baseline countertransport to changes in insulin metabolism, and blood pressure.