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

The purpose of the present investigation was to determine the independent e ffects of hypoxia and physical exercise on peripheral cholecystokinin (CCK) metabolism in humans. Thirty-two physically active men were randomly assig ned 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 parti cipated in two tests, separated by 48 h, which involved a cycling test to e xhaustion in normobaric normoxia and normobaric hypoxia (inspired O-2 fract ion = 0.21 and 0.16, respectively). In the intermittent study, N and H grou ps cycle-trained for 4 wk at the same relative exercise intensity in both n ormoxia and hypoxia. Acute normoxic exercise consistently raised plasma CCK during bath studies by 290-723%, which correlated with increases in the pl asma ratio of free tryptophan to branched chain amino acids (r = 0.58-0.71, P < 0.05). In contrast, acute hypoxic exercise decreased CCK by 7.0 +/- 5. 5 pmol/l, which correlated with the decrease in arterial oxygen saturation (r = 0.56, P < 0.05). In the intermittent study, plasma CCK response at res t and after normoxic exercise was not altered after physical training, desp ite a slight decrease in adiposity. We conclude that peripheral CCK metabol ism 1) is more sensitive to acute changes than chronic changes in energy ex penditure and 2) is potentially associated with acute changes in tissue PO2 and metabolic precursors of cerebral serotoninergic activity.