Norepinephrine infusion during moderate-intensity exercise increases glucose production and uptake

Area of Science:

• Exercise Physiology
• Endocrinology
• Metabolic Regulation

Background:

• Intense exercise (>80% VO2max) elevates circulating norepinephrine (NE).
• The precise role of NE in modulating glucose metabolism during exercise remains unclear.
• Understanding NE's impact is crucial for optimizing exercise performance and metabolic health.

Purpose of the Study:

• To investigate the direct effect of norepinephrine infusion on glucose production and utilization during moderate-intensity exercise.
• To determine if elevated NE levels mimic or contribute to the metabolic responses seen during intense exercise.
• To examine the relationship between plasma NE concentration and glucose rate of appearance and disappearance.

Main Methods:

• Seven fit males performed 40 minutes of moderate-intensity cycle ergometer exercise (53% VO2max).
• Exercise was conducted under two conditions: control (CON) and with continuous norepinephrine (NE) infusion (0.1 µg/kg/min) during the last 10 minutes.
• Measurements included plasma NE, glucose rate of production (Ra), and glucose rate of disappearance (Rd).

Main Results:

• NE infusion significantly increased plasma NE levels (8-fold rest, 2-fold CON).
• Glucose Ra doubled in CON and rose further to 7.55 mg/kg/min with NE infusion (P=0.003).
• Glucose Rd and metabolic clearance rate were significantly higher with NE infusion compared to CON (P<0.02).

Conclusions:

• Norepinephrine infusion during moderate exercise increases glucose production and utilization in fit individuals.
• These findings support a potential role for elevated plasma NE in the augmented glucose metabolism observed during intense exercise.
• The metabolic effects of NE on glucose disposal during exercise may differ from its effects at rest.