Physical exercise and normobaric hypoxia: independent modulators of peripheral cholecystokinin metabolism in man

The purpose ofthe present investigation was to determine the independent effects ofhypoxia and physical exercise on peripheral cholecystokinin (CCK)metabolism in humans. Thirty-two physically active men wererandomly assigned in a double-blind manner to either a normoxic (N;n = 14) or hypoxic (H; n = 18) group.During the acute study, subjects in the H group only participated in two tests, separated by 48 h, which involved a cycling test to exhaustion in normobaric normoxia and normobaric hypoxia (inspired O₂ fraction = 0.21 and 0.16, respectively). In theintermittent study, N and H groups cycle-trained for 4 wk at the samerelative exercise intensity in both normoxia and hypoxia. Acutenormoxic exercise consistently raised plasma CCK during both studies by 290-723%, which correlated with increases in the plasma ratio offree tryptophan to branched chain amino acids (r = 0.58-0.71, P < 0.05). In contrast, acute hypoxicexercise decreased CCK by 7.0 ± 5.5 pmol/l, which correlated withthe decrease in arterial oxygen saturation (r = 0.56, P < 0.05). In the intermittent study, plasma CCKresponse at rest and after normoxic exercise was not altered afterphysical training, despite a slight decrease in adiposity. We concludethat peripheral CCK metabolism 1) is more sensitive to acutechanges than chronic changes in energy expenditure and 2) ispotentially associated with acute changes in tissue PO₂ and metabolic precursors of cerebralserotoninergic activity.