Chronic sympathetic attenuation and energy metabolism in autonomic failure

Impaired metabolic flexibility to fasting is associated with increased ad libitum energy intake in healthy adults

OBJECTIVE

We investigated how changes in 24-h respiratory exchange ratio (RER) and substrate oxidation during fasting versus an energy balance condition influence subsequent ad libitum food intake.

METHODS

Forty-four healthy, weight-stable volunteers (30 male and 14 female; mean [SD], age 39.3 [11.0] years; BMI 31.7 [8.3] kg/m2) underwent 24-h energy expenditure measurements in a respiratory chamber during energy balance (50% carbohydrate, 30% fat, and 20% protein) and 24-h fasting. Immediately after each chamber stay, participants were allowed 24-h ad libitum food intake from computerized vending machines.

RESULTS

Twenty-four-hour RER decreased by 9.4% (95% CI: -10.4% to -8.5%; p < 0.0001) during fasting compared to energy balance, reflecting a decrease in carbohydrate oxidation (mean [SD], -2.6 [0.8] MJ/day; p < 0.0001) and an increase in lipid oxidation (2.3 [0.9] MJ/day; p < 0.0001). Changes in 24-h RER and carbohydrate oxidation in response to fasting were correlated with the subsequent energy intake such that smaller decreases in fasting 24-h RER and carbohydrate oxidation, but not lipid oxidation, were associated with greater energy intake after fasting (r = 0.31, p = 0.04; r = 0.40, p = 0.007; and r = -0.27, p = 0.07, respectively).

CONCLUSIONS

Impaired metabolic flexibility to fasting, reflected by an inability to transition away from carbohydrate oxidation, is linked with increased energy intake.

Residual sympathetic tone is associated with reduced insulin sensitivity in patients with autonomic failure

PURPOSE

Parkinson disease, an α-synucleinopathy, is associated with reduced insulin sensitivity, impaired glucose tolerance, and diabetes mellitus. Importantly, these metabolic alterations have been shown to contribute to disease progression. The purpose of this study was to determine if reduced insulin sensitivity is also present in other α-synucleinopathies associated with autonomic failure.

METHODS

We studied 19 patients with multiple system atrophy and 26 patients with pure autonomic failure. For comparison, we studied 8 healthy controls matched for body mass index. Insulin sensitivity and beta cell function were calculated using fasting glucose and insulin levels according to the homeostatic model assessment 2. A multiple linear regression model was performed to determine factors that predict insulin sensitivity in autonomic failure.

RESULTS

There was a significant difference in insulin sensitivity among groups (P = 0.048). This difference was due to lower insulin sensitivity in multiple system atrophy patients: 64% [interquartile range (IQR), 43 to 117] compared to healthy controls 139% (IQR, 83 to 212), P = 0.032. The main factor that contributed to the reduced insulin sensitivity was the presence of supine hypertension and residual sympathetic tone.

CONCLUSIONS

Multiple system atrophy patients have reduced insulin sensitivity that is associated with residual sympathetic activation and supine hypertension. These patients may therefore be at high risk for development of impaired glucose tolerance and diabetes mellitus.