Catecholamine Response is Attenuated During Moderate Intensity Exercise in Response to the “Lactate Clamp”.

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0149 Plasma catecholamines are known to respond to feedforward and feedback mechanisms. Norepinephrine (NE) and epinephrine (E) rise in response to stresses, such as exercise, that compromise blood glucose homeostasis. Both NE and E have been correlated with blood pH, blood lactate, and ATP demand as assessed by relative exercise intensity. PURPOSE: To assess the hypothesis that the lactate anion (La-) is involved in feedback control of catecholamine release plasma concentrations of norepinephrine and epinephrine were determined at rest and during exercise at 55% of VO2peak with (LC) and without (CON) exogenous lactate infusion. METHODS: Six apparently healthy recreationally active young men were recruited to participate in this study (26 ± 2 yr, 82 ± 2 kg, 50.7 ± 2.1 ml·kg−1·min−1 VO2peak). Participants were studied on 5 occasions. Exercise intensities were 65% of VO2peak for the first trial, and 55% of VO2peak for all remaining trials. The blood lactate profile of the first (65%) trial was matched during the subsequent LC trials, target [lactate] > 4 mM. Participants were studied after an overnight fast; exogenous lactate was infused in a forearm vein; blood was sampled from an arterialized hand vein during 90 min of rest and 90 min of exercise, and catecholamines were determined using HPLC with electrochemical detection. RESULTS: Plasma concentrations of NE and E increased from rest (NE: 241 ± 98 pg/ml, E: 63 ± 25 pg/ml) to exercise (NE: 1498 ± 611 pg/ml, E: 207 ± 187 pg/ml; P <0.05). There was also a condition effect during exercise with NE and E lower during the LC trial (NE: LC = 1211 ± 494 pg/ml, CON = 1785 ± 728 pg/ml, E: LC = 145 ± 59 pg/ml CON = 269 ± 109, P <0.05). As reported previously, LC did not affect endogenous lactate Ra, but raised total [La-], Ra and Rd to levels seen in the 65% trial. Neither glucose, insulin (I), or glucagon (G) concentrations or the I/G were affected, but RER was decreased, and blood pH raised by LC. CONCLUSIONS: NE and E responses were attenuated during moderate intensity (55% of VO2peak) exercise with the exogenous lactate infusion. Results indicate an effect of lactate or an associate parameter of acid-base balance on regulation of catecholamine secretion during physical activity. Supported by NIH grant: AR-42906