The interplay between sympathetic nervous system overactivity, blood pressure levels and non-alcoholic fatty liver disease in hypertensive patients

Objective: Non-alcoholic fatty liver disease (NAFLD) is the most important cause of chronic liver disease and a marker of increased cardiovascular risk. The purpose of this study was to investigate the interrelations between sympathetic nervous system (SNS) tone, as assessed by microneurography, blood pressure levels and NAFLD in hypertensive subjects. Design and method: 131 newly diagnosed untreated hypertensive patients (mean age 55±10 years, 63 males, office systolic/diastolic blood pressure 141±21/89±9 mmHg) without a history of cardiovascular disease were included in the study. NAFLD was diagnosed by liver ultrasound, and then patients were categorized into two groups according to the presence or absence of fatty liver. SNS over-activity levels were assessed by direct recording of muscle sympathetic nerve activity (MSNA), based on an established technique (microneurography). Results: Hypertensive subjects with NAFLD (n=79) compared to controls (n=52) were younger (53±10 vs. 57±9 years, respectively, p=0.01) and had higher body mass index (33±9 vs. 26±3 kg/m2, p<0.001). They also had statistically significant higher levels of office blood pressure (systolic/diastolic blood pressure 142±14.8 vs 140±14.6 mmHg, 90±10 vs 87±8 mmHg, respectively). Subjects with fatty liver had also higher levels of triglycerides (122±50 vs 104±43 mg/dl, p<0.04), while there was no statistically significant difference between the two groups in hemoglobin A1c, total cholesterol and glomerular filtration rate. Hypertensive subjects with NAFLD showed greater activation of the sympathetic nervous system, with increased levels of MSNA compared to the control group (45 ± 9.5 vs. 39 ± 7 bursts per minute, respectively, p<0.04). Also, according to the multiple logistic regression analysis, MSNA proved to be an independent determinant for the presence of NAFLD (OR 1.13, 95% CI 1.01-1.26, p=0.03). Conclusions: Higher stimulation of sympathetic nervous system, as reflected by MSNA, is significantly associated with the presence of NAFLD in hypertensive subjects, which is also related to higher office systolic blood pressure. These findings may partly explain the increased cardiovascular risk of hypertensive patients with NAFLD.