Peinado, Ana B.

This study was performed to examine the role of the carotid bodies (CB) in glucoregulation during prolonged exercise in humans. Six healthy males (35 ± 5 yrs) completed two 120 minute bouts of cycling exercise (65% VO 2 max), during a dopamine infusion (D; 2 μg/kg/min) to acutely inactivate the CB, or a placebo, saline infusion (P). Arterial blood was drawn for glucose and counter‐regulatory hormones at baseline and during exercise (60–80: 60–80 minute mean; EE: end exercise). All variables at baseline were similar between conditions. Glucose concentration decreased throughout exercise and was similar between trials (60–80: 90 ± 7 vs. 98 ± 14; EE: 75 ± 12 vs. 80 ± 10 mg/dl; D vs. P respectively). However, when compared to baseline values, EE glucose had a greater decrease in 4 subjects during D, whereas 2 subjects had a greater attenuation during P. Glucagon was similar at 60–80 (108 ± 42 vs. 84 ± 40 pg/ml; D vs. P respectively), but was greater at EE in D than P (204 ± 104 vs. 136 ± 70 pg/ml). Cortisol (60–80: 13 ± 5 vs. 16 ± 4; EE: 22 ± 3 vs. 20 ± 7 μg/dl; D vs. P respectively) and growth hormone (60–80: 13 ± 3 vs. 12 ± 3; EE: 12 ± 4 vs. 10 ± 4 ng/ml; D vs. P respectively) concentrations were not different between conditions. Our preliminary results indicate that blood glucose during exercise with CB desensitization varies between subjects, and that the CB might contribute to blood glucose regulation during exercise. Funding: NIH R01DK090541

We tested the hypothesis that the carotid body chemoreceptors (CB) contribute to ventilatory control during steady‐state exercise. Six men completed two randomized bouts of cycling exercise at 65% VO 2 max for up to 2 hours during an IV infusion of dopamine (D; 2 µg/kg/min) to acutely inactivate the CB, or a saline infusion (S). Expired gases were analyzed at baseline, resting‐infusion, and during exercise (25%, 50%, 75% and 100% of total exercise time). A hypoxic ventilatory response (HVR) test was performed after exercise during the infusion condition. Subjects were classified as responders (RS; n=3) if their HVR was lower during D vs. S (1.03 ± 0.6 vs. 2.14 ± 0.4 L/min/%SaO 2 ). In RS, partial pressure of end‐tidal CO 2 had a greater delta from baseline at 75% (2.9 ± 2.1 vs. 1.1 ± 1.9 mmHg) and 100% (0.9 ± 3.4 vs. ‐0.3 ±3.3 mmHg) during D than S, and the increase in oxygen uptake at 100% was greater during D vs. S (34.7 ± 2.6 vs. 33.0 ± 2.6 mL/min/kg). In RS, there were no differences in the changes from baseline for ventilation (VE), VE/VCO 2 , respiratory rate, tidal volume, and respiratory exchange ratio between conditions. In the non‐responders group, there were no differences between D and S in any variables. When the data was pooled, HVR accounted for 37% of the variance in VE at 100%. Despite evidence that CB chemosensitivity was blunted, the CB appear to play a minor role in controlling ventilation during steady state exercise. Grant Funding Source : NIH R01DK090541

The carotid body chemoreceptors are activated during hypoglycemia and contribute to glucoregulation during prolonged exercise in dogs. Low-dose intravenous infusions of dopamine have been shown to blunt the activation of the carotid body chemoreceptors during hypoxia. Therefore, we tested the hypotheses that dopamine would blunt glucoregulatory responses and attenuate plasma glucose during prolonged aerobic exercise in healthy participants. Twelve healthy participants completed two randomized exercise sessions at 65% peak oxygen consumption for up to 120 min. Saline was infused during one exercise session, and dopamine (2 μg·kg−1·min−1) was infused during the other session. Arterial plasma glucose, growth hormone, glucagon, cortisol, norepinephrine, and epinephrine were measured every 10 min. Exercise duration during dopamine infusion was 107 ± 6 and 119 ± 0.8 min during saline infusion. Glucose area under the curve during exercise was lower during dopamine (9,821 ± 686 vs. 11,194 ± 395 arbitrary units; P = 0.016). The ratio of circulating growth hormone to glucose and the ratio of glucagon to glucose were greater during dopamine ( P = 0.045 and 0.037, respectively). These results indicate that the infusion of dopamine during aerobic exercise impairs glucoregulation. This suggests that the carotid body chemoreceptors contribute to glucoregulation during prolonged exercise in healthy exercise-trained humans.