Leptin, an ob gene product of adipocytes, plays a key role in the control of 
food intake and energy expenditure but little is known about leptin response to 
strenuous exercise in fasted and fed subjects or before and after blood 
donation. This study was designed to determine the immediate effects of 
strenuous exercise in healthy volunteers under fasting or fed conditions and 
before and one day after blood donation (450 ml) on plasma levels of leptin and 
gut hormones [gastrin, cholecystokinin (CCK), pancreatic polypeptide (PP) and 
insulin], as well as on "stress" hormones (cortisol, catecholamines and growth 
hormone. Two groups (A and B) of healthy non-smoking male volunteers were 
studied. All subjects performed incremental exercise tests until exhaustion (up 
to maximal oxygen uptake--VO2max), followed by 2 h of rest session. Group A 
perfomed the tests on a treadmill, while group B on a cycloergometer. In group 
A, one exercise was performed under fasting conditions and the second following 
ingestion of a standard liquid meal. In group B, one exercise test was performed 
as a control test and the second 24 h after blood donation (450 ml). Blood 
samples were withdrawn 5 min before the start of the test, at the VO2max, and 2 
h after finishing the exercise. No significant change in plasma teptin were 
observed both immediately and 2 h after the exercise in fasted subjects, but 
after the meal the plasma leptin at VO2max and 2 h after the test was 
significantly higher, while after blood donation was significantly reduced. The 
postprandial rise in plasma leptin was accompanied by a marked increment in gut 
hormones; gastrin, CCK and PP and stress hormones such as norepinephrine, 
cortisol and GH. These hormonal changes could contribute to the postprandial 
rise in plasma leptin concentrations, while the fall of leptin after blood 
donation could be attributed to the inadequate response of stress hormones and 
autonomic nervous system to exhausting exercise. We conclude that strenuous 
physical exercise; 1) fails to affect plasma leptin level but when performed 
after meal but not after blood withdrawal it results in an increase and fall in 
plasma leptin, and 2) the release of gut hormones (gastrin, CCK and PP) and 
stress hormones (norepinephrine, cortisol, GH) increase immediately after 
exercise independently of feeding or blood donation and 3) following blood 
donation the strenuous exercise resulted in a marked reduction in the plasma 
leptin, cortisol and GH concentrations, possibly due to the impairment in the 
autonomic nervous control of these hormones.