PHYSICAL EXERCISE, ENDOGENOUS OPIATES AND FEEDING BEHAVIOR
Abstract
These experiments investigated the role of endogenous opiates (i.e., endorphins) in feeding behavior, especially that associated with swimming exercise. A radioimmunoassay was developed and validated for the measurement of beta-endorphin in blood plasma of rats. Plasma (beta)-EP-immunoreactivity ((beta)-EP-ir) was elevated 200-400% concomitant with feeding stimulated by darkness, 24-hr food deprivation (FD) and 2-deoxy-D-glucose (2-DG) administration. Feeding stimulated by insulin administration was associated with only a 32% increase in plasma (beta)-EP-ir. These data are consistent with the naloxone-sensitive (darkness, FD, 2-DG) and naloxone-resistant (insulin) nature of these feeding stimuli. Both day and night feeding following a strenuous swim for 1 hr produced biphasic feeding responses, with hyperphagia during the first 2 hr and a more prolonged hypophagia during subsequent periods. Post-exercise hyperphagia was accompanied by a 3-fold increase in (beta)-EP-ir, and the hyperphagia could be antagonized by naloxone. In support of the hypothesis that endorphins were depleted during the postexercise hypophagia, the 2-DG stimulus for feeding was significantly less effective, whereas the insulin stimulus was fully effective at 1.5 hr after exercise. However, plasma (beta)-EP-ir was not different between swimmers and controls during the hypophagic period. After one month of exercise training, trained rats weighed less and ate less during darkness and following a 2-DG stimulus than did control sedentary rats. Insulin-stimulated feeding was similar in both groups. These results are consistent with the hypothesized depletion of endorphin by chronic exercise. On the other hand, during the third month of exercise training these differences in feeding responses were no longer significant, and, contrary to the original hypothesis, naltrexone significantly reduced feeding during darkness only in the trained rats; also, plasma (beta)-EP-ir was elevated at night only in trained rats. The results are consistent with the hypothesis that increased feeding shortly after swimming is mediated by endogenous opiates, but are inconclusive on the question of endogenous opiate involvement in the hypophagia associated with acute and chronic exercise.
Degree
Ph.D.
Subject Area
Anatomy & physiology|Animals
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