SPECIFIC GLUCOCORTICOID BINDING AT DIFFERENT LEVELS OF HUMAN MOTOR-ACTIVITY

We studied the number of glucocorticoid receptors and dissociation con stant in isolated human lymphocytes as well as blood concentrations of hormones produced by the hypothalamic-hypophyseal -adrenocortical sys tem in three experimental series: at normal (17 subjects), decreased ( 10 subjects, a 360-d head-down bed rest) and increased (8 subjects, ph ysical exercise on bicycle ergometer) levels of motor activity. In the first series we found that the number of glucocorticoid receptors and dissociation constant did not depend on the season, on the age of sub jects nor on cortisol concentrations in blood. In the second series we observed the following: at the end of the first month of bed rest the number of glucocorticoid receptors and receptor affinity significantl y increased; at the beginning of the third month of bed rest specific glucocorticoid binding significantly decreased and circadian rhythms o f adrenocorticotropin and cortisol in blood varied markedly; at the en d of the sixth month of bed rest the number of glucocorticoid receptor s returned to prebed rest levels and dissociation constant decreased. In the third series physical exercises that induced an activation of t he hypothalamic-hypophyseal-adrenocortical system (maximal physical ex ercises and prolonged submaximal exercises at 70% of maximal oxygen up take) led to a significant increase in the number of glucocorticoid re ceptors without changes of dissociation constant. These results indica te that both a decrease and an increase of human motor activity result ed in significant changes of specific glucocorticoid binding which wer e not influenced by changes of circulating hormone concentrations in b lood but by some other factors affected by physical activity.