The inhibiting effect of atropine on growth hormone release during exercise

The effects of atropine upon changes in the circulating levels of growth hormone (GH), cortisol, lactate, glucose, and free fatty acids (FFA) were studied during exercise using both constant and progressively increasing work loads. At low work loads, atropine had no effect upon the changes in either cortisol or lactate levels, but the normal exercise-induced rise in GH was abolished or markedly reduced. At higher work loads, especially when prolonged, the usual rises in cortisol and lactate were enhanced by atropine, but the rise in GH was diminished and delayed. In no circumstances were the changes in FFA or glucose significantly affected by atropine. We regard the effect of atropine upon changes in cortisol and lactate responses as secondary to its cardiovascular effect, but suggest that the inhibition of Gh release may be evidence of a cholinergic mechanism in the control of Gh release during exercise.