Plasma beta endorphin immunoreactivity: Effects of sustained hyperglycemia with and without prior exercise

Abstract

Seven healthy untrained men were studied to determine if sustained hyperglycemia is a stimulus to enhanced plasma levels of beta endorphin (β-EP) and if so whether prior exercise affects that enhancement. After an overnight fast hyperglycemia glucose clamps were performed on 3 separate days: after prior rest, 2 h after exercise, and 48 h after exercise. Subjects exercised on a bicycle ergometer for 1 h at 150 W (64% VO 2 max). Plasma glucose concentration was elevated in 4 continuous sequential stages to 7, 11, 20 and 35 mM with each stage lasting 90 min. Plasma glucose concentrations did not differ for each subject across the three clamps. β-EP immunoreactivity was measured in arterialized venous blood samples using a specific and sensitive radioimmunoassay. Resting β-EP at basal glucose concentrations was 3.8±0.7 fmol·ml −1 (mean ± se) and prior exercise either 2h (3.2± 0.5 fmol·ml −1) or 48 h (4.3± 0.7 fmol·ml −1) before a clamp study did not effect these levels, (p > 0.05). At no time during the 3 hyperglycemic clamps did plasma levels of β-EP differ significantly from resting values. At the highest level of hyperglycemia (35 mM) β-EP was 3.1±0.2, 4.9±0.6 and 4.8±0.7 fmol·ml −1 in the resting, 2h and 48 h post exercise clamp studies respectively. The significance of these data is that this lack of a response is in distinct contrast to elevations of this peptide found during hypoglycemic states. We conclude that sustained hyperglycemia is not a stimulus to enhanced secretion of β-EP into plasma and this lack of a response is not effected by prior exercise.