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The purpose of this study was to evaluate the role of endogenous opiates in modulating physical performance during dynamic exercise in conscious man. The plasma concentration of fl-endorphin (BEP) and of adrenocorticotropic hormone (ACTH) along with muscle pain (McGuill Pain Questionnaire) were assessed in 17 trained, male runners before and after running the longest possible distance within 12 min (i.e., the Cooper test). Each runner participated twice in the test (double-blind cross-over design), with a 1-week interval-with or without an injection of the opiate antagonist naloxone (0.8 mg i.v.). The average (SEM) distance reached was 3,198 (45) m in the naloxone test and 3,240 (38) m in the placebo test. The BEP increased significantly during the tests by a factor of 4.1 on naloxone and by 2.8 on placebo (from the normal resting averages of 1.7 and 2.1 pmol/l, respectively). The ACTH also increased significantly by a factor of 2.0 on naloxone and 2.5 on placebo (from the normal resting averages of l 9.3 and 16.8 pmol/l, respectively). There were no significant differences between the naloxone and the placebo test with respect to the increments of BEP or ACTH by exercise. However, the perception of muscle pain was enhanced with naloxone. The increased perception of pain did not decrease the athletes ability to perform in terms of the distance run. We conclude that endogenous opiates are involved in the perception of pain associated with exhaustive exercise and may subserve psychological rather than physiological functions during exercise.

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The regional differences in secretory and absorptive responses to cholera toxin ( 0 and to infection by enterotoxigenic Eschericbia cob (ETEC), producing heat-stable enterotoxins, were studied in the porcine small intestine. Proximal, mid and distal small intestine from newly weaned piglets were used. Na' and C1fluxes and electrical parameters in CT-stimulated and ETEC-infected intestine were measured by the Ussing chamber technique. In addition, CT-induced fluid accumulation in ligated loops was measured. CT induced fluid accumulation, which was hghest in the proximal segment and decreased in the aboral direction of the small intestine. In addition, CT induced a net CI-secretion in the proximal and mid segments, while net Na+ absorption was reduced only in the proximal segment. The ETEC-infected intestine showed a net increase in C1-secretion in the proximal part and abolished the net Na' absorption in the distal segment. These results demonstrate segmental differences in the epithelial transport responses to enterotoxin from I4brio cholerae and to ETEC infection. This needs to be taken into consideration in relation to oral rehydration studies. U.S. ~opynght Clearance Center code Statement: 0931 -1 84X/98/4506-0369 $1 4.00/0