Beta receptors in peripheral mononuclear cells increase acutely during exercise.

Five healthy adult well trained men (averaging 49 miles running per week) were exercised to exhaustion on a treadmill. Plasma epinephrine increased from 168 +/- 37 pg/ml prior to exercise to 633 +/- 155 pg/ml immediately after exercise (P less than 0.025) and plasma norepinephrine increased from 1608 +/- 345 to 8576 +/- 1662 pg/ml (P less than 0.025) in the two respective periods. Beta receptor density increased from 53 +/- 18 fmol/mg protein before exercise, to 223 +/- 63 fmol/mg (P less than 0.05) protein immediately after exercise, and then decreased to 83 +/- 27 fmol/mg protein 1 h later (P less than 0.05 compared to post-exercise). The mean Kd value prior to exercise of 1.5 +/- 0.2 X 10(-11) M was unchanged statistically throughout the study. Following correction for haemodilution, serum total and free T4 and T3 concentrations were also unchanged during exercise, although reverse T3 levels did increase from 39 +/- 4 to 45 +/- 0 ng/dl (P less than 0.05). These findings suggest that: 1) plasma epinephrine, norepinephrine and beta receptor density, but not Kd, increase acutely during exercise and 2) total and free T4 and T3, after correction for haemodilution, do not change during acute exercise. Our data indicate that acute exercise represents an unusual condition during which 'down regulation' is not observed, but, rather, there appear to be parallel alterations in beta receptor density and plasma catecholamine levels.