Primary aldosteronism (PA) is associated with an increased risk of impaired glucose tolerance or type 2 diabetes mellitus. Previous studies have reported that impaired insulin secretion and insulin sensitivity in PA may lead to impaired glucose tolerance. However, the relationship between PA and glucose tolerance, and the factor associated with these glucose metabolism abnormalities is not well understood. In particular, few studies have analyzed the association between aldosterone excess and insulin sensitivity or resistance after the adjustment for other clinical variables. In this study, we analyzed the associations between multiple clinical variables observed in PA and the indices of insulin sensitivity and resistance, using the result of 75 g oral glucose tolerance test (OGTT). This was a retrospective observational study that analyzed the data of 646 patients with PA who underwent adrenal venous sampling and 75 g OGTT. The insulinogenic index and Matsuda index, indices of insulin secretion and sensitivity, respectively, were calculated from the results of a 75 g OGTT. Correlations between these indices and the multiple clinical variables were analyzed. In addition, we performed multiple regression analyses to identify the independent explanatory variables of these indices. Insulinogenic index had positive correlations with the body mass index (BMI), alanine aminotransferase (ALT) level, triglyceride (TGL) level, and potassium level, and negative correlations with both age and plasma aldosterone concentration (PAC). In a multiple regression analysis, both the age (β = -0.231, p < 0.001) and potassium level (β = 0.175, p = 0.002) were selected as the independent explanatory factors. The Matsuda index had positive correlations with the PAC and cortisol level after a 1 mg dexamethasone suppression test (DST), and negative correlations with BMI, ALT level, TGL level, plasma renin activity (PRA), and potassium level. In a multiple regression analysis, BMI (β = -0.216, p < 0.001), ALT level (β = -0.290, p < 0.001), TGL level (β = -0.225, p < 0.001), the cortisol level after 1 mg DST (β = 0.124, p = 0.009), and PRA (β = -0.119, p = 0.019) were selected as the independent explanatory factors. In PA patients, older age and decreased potassium levels were associated with impaired insulin secretion. An increase in the variables associated with metabolic abnormalities such as BMI, ALT, and TGL were associated with decreased insulin sensitivity. In addition, we found that decreased PRA was associated with increased insulin sensitivity.
