Bioassayable growth hormone release in rats in response to a single bout of treadmill exercise

Plasma growth hormone (GH) measured by immunoassay and by tibial bioassay increases in humans in response to exercise. In rats, however, IGH does not change in response to exercise. The objective of this study was to determine the BGH response to an acute exercise bout in rats. The rats ran on a treadmill at a rate of 27 m/min for 15 min, after which plasma and pituitary hormones, including IGH and BGH, and plasma metabolites were measured. Plasma and pituitary IGH were unchanged from control groups after the acute exercise bout, whereas plasma BGH was increased by 300 percent and pituitary BGH was decreased by 50 percent. Plasma thyroxine and corticosterone levels were significantly increased after a single exercise bout, but plasma testosterone, 3,5,3'- triiodothyronine, glucose, lactate, and triglyceride concentrations were unchanged. Given previous results from in situ nerve stimulation studies, these in vivo results are consistent with the rapid BGH response during exercise being induced by the activation of muscle afferents. (Author)