4. Discussion
Hyperglycemia
HYPERGLYCEMIA, HYPERGLYCEMIA, DISEASE
Hyperglycemia attenuates HRV by reducing parasympathetic tone and/or increasing sympathetic nervous system activity [We confirm that in healthy young participants, an OGC reduces HRV, as evidenced by the reduction in SDNN, RMSSD, LF, HF, and TP (The OGC is also a metabolic perturbation that causes an increase in REE and a shift in substrate oxidation. In the fasted state, fat is the primary substrate utilized. In the postprandial state, increased plasma glucose and insulin are cues for metabolism to shift from fat to carbohydrate oxidation. In response to a meal challenge or insulin stimulation, REE and RER are positively associated with sympathetic activity [A major limitation of our study is our inability to directly link improved NO bioavailability to the preservation of HRV during the OGC. Several studies have documented the importance of NO to autonomic function in health and disease [In conclusion, we show that the autonomic system is susceptible to a hyperglycemic episode. Furthermore, using a rigorous study design, we show the efficacy of a naturally rich source of amino acids, L-citrulline, and L-arginine, to preserve HRV during a hyperglycemic episode. These findings build on our previous work that shows WMJ supplementation protects vascular function during hyperglycemia. NO bioavailability is potentially a link between these two integrated physiological systems, but more work is required to develop a mechanistic understanding of this relationship. 