BACKGROUND: Although hormonal responses to exercise performed in fed state are 
well documented, far less in known about the effect of a single exercise bout, 
performed after overnight fasting, on cardio-respiratory responses and hormones 
secretion. It has been reported that recently discovered hormones as leptin and 
ghrelin may affect cardiovascular responses at rest. However, their effect on 
the cardiovascular responses to exercise is unknown.
AIMS: This study was designed to determine the effect of overnight fasting on 
cardio- respiratory responses during moderate incremental exercise. We have 
hypothesised that fasting / exercise induced changes in plasma leptin / ghrelin 
concentrations may influence cardiovascular response.
MATERIAL AND METHODS: Eight healthy non-smoking men (means +/- SE.: age 23.0 +/- 
0.5 years; body mass 71.9 +/- 1.5 kg; height 179.1 +/- 0.8 cm; BMI 22.42 +/- 
0.49 kg x m(-2) with VO2max of 3.71 +/- 0.10 l x min(-1)) volunteered for this 
study. The subjects performed twice an incremental exercise test, with the 
increase of power output by 30 W every 3 minutes. Tests were performed in a 
random order: once in the feed state--cycling until exhaustion and second, about 
one week later, after overnight fasting--cycling until reaching 150 W.
RESULTS: In the present study we have compared the results obtained during 
incremental exercise performed only up to 150 W (59 +/- 2 % of VO2max) both in 
fed and fasted state. Heart rate measured during exercise at each power output, 
performed in fasted state was by about 10 bt x min(-1) (p = 0.02) lower then in 
fed subjects. Respiratory quotient and plasma lactate concentration in fasted 
state were also significantly (p<0.001) lower than in the fed state. 
Pre-exercise plasma leptin and ghrelin concentrations were not significantly 
different in fed and fasted state. Exercise induced increase in hGH was not 
accompanied by a significant changes in the studied gut hormones such as 
ghrelin, leptin, and insulin, except for plasma gastrin concentration, which was 
significantly (p = 0.008) lower in fasting subjects at the power output of 150 
W. Plasma [IL-6] at rest before exercise performed in fasted state was 
significantly (p = 0.03) elevated in relation to the fed state. This was 
accompanied by significantly higher (p = 0.047) plasma noradrenaline 
concentration. Plasma IL-6 concentration at rest in fed subjects was negatively 
correlated with plasma ghrelin concentration (r = -0.73, p < 0.05) and 
positively correlated with plasma insulin concentration (r = 0.78, p < 0.05). 
Significant negative correlation (r = -0.90; p < 0.05) was found between plasma 
insulin and ghrelin concentration at rest in fed subjects.
CONCLUSIONS: We have concluded that plasma leptin and ghrelin concentrations 
have no significant effect on the fasting-induced attenuation of heart rate 
during exercise. We have postulated that this effect is caused by increased 
plasma norepinephrine concentration, leading to the increase in systemic 
vascular resistance and baroreceptor mediated vagal stimulation. Moreover we 
believe, that the fasting-induced significant increase in plasma IL-6 
concentration at rest, accompanied by higher plasma norepinephrine concentration 
and lower RQ, belongs to the physiological responses, maintaining energy 
homeostasis in the fasting state.