Impact of insulin sensitivity treatment with pioglitazone on endothelial function in non-diabetic patients with arterial hypertension

Objective: The thiazolidindione (TDZ) pioglitazone reduces insulin resistance and blood pressure in non-diabetic patients with arterial hypertension as previously reported [Fullert et al. 2002]. The question is still not answered whether it is a direct effect on the endothelial wall or it is related with improvement of insulin sensitivity. The present investigation is the first placebo controlled study which examines the effect of TDZ induced changes of insulin sensitivity (SI) on endothelial function and blood pressure in in non-diabetic patients with high blood pressure. Material and methods: Insulin sensitivity indices (SI indices) were obtained by analyzing fasting glucose and insulin concentration with homeostasis model assessment (HOMA), the glucose and insulin profiles after 75 g dextrose oral glucose tolerance tests (OGTT, Matsuda-Index) and euglycemic hyperinsulinemic clamp (m-value) in a double-blind placebo-controlled study in 60 patients with arterial hypertension before and after 4 months treatment with Pioglitazone 45 mg (PI045). Flow-mediated dilatation of brachial artery (FMD) after reperfusion was used to determine endothelial function. Blood pressure in the morning of every visit (casual blood pressure, RRc) and 24-h ambulatory blood pressure (24RR) were measured. Results: Antihypertensive treatments were equally distributed in the placebo and PIO45 group. All SI indices were closely related to with alanine-aminotransferase activities (ALAT): HOMAr = 0.1041, p < 0.05, Matsuda-Index r = 0.4242, p < 0.01, M value r = 0.1944, p < 0.01. There were no relationships of SI indices with FMD, RRc and 24RR in the study population with treated arterial hypertension. FMD was closely related to the nocturnal systolic and diastolic 24hRR (systolic r = 0.0943, p < 0.05, diastolic r = 0.0947, p < 0.05). SI indices improved after 4-month therapy with PI045 when compared with controls: HOMA 65% (p < 0.01), Matsuda-Index 60% (p < 0.01) and M value 17.7% (p = 0.008). FMD did not change after PIO45. Casual diastolic blood pressure (p = 0.016) and systolic blood pressure were lower (p = 0.053) under PIO45. No significant changes of 24-h blood pressure were found after treatment with TDZ. Conclusion: 4-month treatment with PIO45 improves SI, liver function and lowers casual blood pressure (RRc. No effects on 24-h ambulatory blood pressure and on endothelial function after PIO45 therapy were observed. The higher insulin sensitivity was not related to lower blood pressure. Thus, PI045 appears to have a direct effect on the arterial system which cannot be explained by changes of endothelial function or improved SI in non-diabetic patients with treated high blood pressure.