ENERGY SUBSTRATES, HORMONE RESPONSES AND GLUCOCORTICOID BINDING IN LYMPHOCYTES DURING INTENSE PHYSICAL EXERCISE IN HUMANS FOLLOWING PHOSPHOCREATINE ADMINISTRATION

Eight healthy untrained male volunteers pedalled a cycle ergometer acc ording to two exercise protocols: the first involved step-wise increas ing physical exercise to maximal (MPE); the second involved prolonged (35 min) submaximal physical exercise (PPE) at 70% of the individual's maximal oxygen uptake. Each volunteer performed these exercise twice, following either an intravenous injection of phosphocreatine (PCr) or a placebo of an isotonic NaCl solution. Anaerobic threshold (AT) was determined from the point of departure of the ventilatory response fro m linearity and from the sudden increase in venous blood lactate conce ntrations during MPE. After exercise following placebo administration we observed increases in concentrations of blood substrates, plasma ad renocorticotropin (ACTH), growth hormone and cortisol and in the numbe r of glucocorticoid receptors in lymphocytes without changes in the di ssociation constant. Intravenous administration of PCr (starting 1 day before exercise) led to an increase in the total workload (on average by 5.8%) and in AT (on average by 6.8%) during MPE and to a better to lerance of exercise during PPE. Following PCr administration we observ ed lower blood lactate concentrations and different patterns of some e nzyme activities, less pronounced changes in plasma ACTH and cortisol concentrations and in glucocorticoid binding in lymphocytes, but no ch anges in plasma growth hormone concentrations compared to the placebo. The results showed that intense physical exercise led not only to inc reases in blood hormone concentrations but also to an increase in the density of glucocorticoid receptors in lymphocytes. Intravenous PCr in jection led to smaller changes in ACTH and cortisol concentrations as well as to a lower activation of glucocorticoid binding in lymphocytes .