Enkephalins, catecholamines, and psychological mood alterations

FARRELL, P. A., A. B. GUSTAFSON, W. P. MORGAN, and C. B. PERT. Enkephalins, catecholamines, and psychological mood alterations: effects of prolonged exercise. Med. Sci. Sports Exerc., Vol. 19, No. 4, pp. 347–353, 1987. Seven healthy trained men were studied to determine if running at various relative intensities [percent maximal oxygen consumption (V̇O2max)] alters peripheral venous levels of leucine enkephalin-like material. Enkephalins were measured using a radio-receptor assay (Leu-Enk RRA). Subjects ran for 80 min at 40 and 60% V̇O2max and for 40 min at 80% V̇O2max. Each session was separated by at least 1 wk. Heart rate, blood pressure, lactic acid, and rectal temperature responses increased in an intensity-dependent manner. Epinephrine increased from resting values of 38.2 ± 6.8 pg·ml-1, mean ± SE to 75.0 ± 13.3 pg·ml-1 during the 40% V̇O2max run, from 60.2 ± 15 to 186 ± 45 pg·ml-1 during the 60% run, and from 33.4 ± 7.6 to 311 ± 52 pg·ml-1 at the 40th min of the highest workload (80% V̇O2max). These increases were significant (P < 0.05). Plasma Leu-Enk RRA was between 3.8 and 6.2 pmol · ml-1 prior to each run and did not change significantly as a result of exercise. Levels of Leu-Enk RRA also did not change during 30 min of supine recovery. Perception of effort increased (P < 0.05) with increases in exercise intensity, and effort sense was unrelated to plasma Leu-Enk RRA. Psychological tension decreased significantly (P < 0.05) following exercise at 60 and 80% of V̇O2max, but the decrease following the 40% run was not significant (P > 0.05). Reduced tension following exercise was not related to Leu-Enk RRA. These findings suggest that leucine enkephalin-like peptides and catecholamines do not increase concomitantly in response to exercise in trained individuals. Also, psychological alterations occur during exercise which are unrelated to circulating Leu-Enk RRA.