Free fatty acid inhibition of exercise-induced growth hormone secretion

In order to investigate the effect of plasma free fatty acids (FFA) elevations on growth hormone (GH) secretion in humans, paired physical exercise (ph.e.) tests were performed in nine untrained healthy volunteers of both sexes. Ph.e. tests were accomplished on a bicycle ergometer under a moderate work load (450 kpm/min x 40 min). On one of two test days, subjects were given 60 gr of a soy bean oil emulsion (Intralipid) 3 hr before, followed by two 50 mg heparin bolus injection, administered 10 min before and 15 min after the start of the exercise. Ph.e. in the control group induced a clear-cut elevation of GH levels which peaks at 40 min. On the other hand Intralipid plus heparin induced FFA elevation, completely block GH secretion elicited by exercise (p less than 0.05 at 20 and 40 min). There also seems to be a threshold level of FFA (3 mEq/l) above which GH suppression was complete. On the contrary, below this level GH blockade was rather inconsistent. FFA elevation has been able to block all the GH stimuli tested so far, and this data support a role of plasma FFA in GH regulation.