Sodium-lithium countertransport and platelet cytosolic free calcium concentration in relation to peripheral insulin sensitivity in postmenopausal women

1. Peripheral glucose disposal (assessed by the euglycaemic-hyperinsulinaemic clamp technique), Na⁺-Li⁺ countertransport in erythrocytes and the cytosolic free Ca²⁺ concentration in platelets were determined in 41 women with impaired glucose tolerance and in 38 women with normal glucose tolerance. The groups were matched for body mass index (range 18–44 kg/m²) and diastolic blood pressure (range 58–109 mmHg).

2. Na⁺-Li⁺ countertransport was correlated significantly with body mass index, basal plasma insulin concentration and basal plasma glucose concentration, and was inversely correlated with peripheral glucose disposal rate. Stepwise regression analysis showed that Na⁺-Li⁺ countertransport was positively correlated with basal plasma insulin concentration (r² = 8.7%).

3. Systolic blood pressure was correlated with fasting plasma insulin concentration (model r² = 25%) and with Na⁺-Li+ countertransport (model r² = 34%) in the group with impaired glucose tolerance. In the group with normal glucose tolerance there were no correlations between blood pressure and Na⁺-Li⁺ countertransport.

4. No correlation was found between platelet cytosolic free Ca²⁺ concentration and any of the variables measured.

5. It is concluded that Na⁺-Li⁺ countertransport is correlated with the degree of peripheral insulin sensitivity and with the plasma insulin concentration. Platelet cytosolic free Ca²⁺ concentration was not correlated with any of these variables, and there was no relationship between Na⁺-Li⁺ countertransport and the platelet cytosolic free Ca²⁺ concentration.