| Summary: | Background/Aim: Smooth muscle function is explored by sublingual glyceryl trinitrate (GTN) administration in vascular function protocols, in order to compare with endothelium- dependent vasodilation of the brachial artery by flow-mediated dilation (FMD). The aim of this study is to evaluate the hemodynamic and autonomic effects of the two most often used GTN dosages.
Methods: In 80 essential hypertensive patients (HT) and 60 normotensive subjects (NT), we evaluated FMD of the brachial artery and endothelium-independent response to 25 and 400 mg of sublingual GTN by high-resolution ultrasound and automated image analysis. In a subgroup of 10 HT, muscle sympathetic nerve activity (MSNA) was also assessed by microneurography.
Results: NT showed significantly (p < 0.01) lower FMD (5.5±3.3%) as compared to healthy controls (6.9±2.2%). The response to GTN 25μg also tended to be lower (HT 7.2±3.3%; NT 7.9±2.9%; p = 0.06), whereas response to GTN 400μg was similar (HT 14.3±4.8%, NT 14.5±54.7%, p = ns). In the whole population, changes in blood pressure (BP) induced by GTN 400μg (systolic BP −3.2±7.7, diastolic BP −4.7±5.0 mmHg) were significantly higher (<0.001) compared to GTN 25μg (systolic BP −0.7±5.8, diastolic BP −0.7±4.4 mmHg). Changes in heart rate were also higher with GTN 400μg than with 25μg (+5.6±6.4 versus −0.2±5.4 bpm, p < 0.001). This behavior was similar in HT and NT subgroups. MSNA was significantly increased by GTN 400μg (31±7 to 41±6bursts/min, p < 0.001) but not by 25μg (33±9 to 37±11bursts/min, p = 0.19)
Conclusions: The administration of GTN at the dose of 25 μg allows exploring endothelium- independent vasodilation in FMD protocols, inducing only modest hemodynamic and sympathetic responses.
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