Inhibition of voluntary activity by growth hormone

During food deprivation and subsequent refeeding there are alterations in growth hormone (GH) secretion and wheel-running activity such that wheel running increases when GH secretion decreases and vice versa. To investigate if there might be a causal relationship between GH secretion and wheel running, the effect of GH administration on wheel running was studied. Female Sprague-Dawley rats were placed singly in activity-wheel cages shortly after weaning. Beginning at 70–75 days of age the rats received 14 daily control injections of saline followed by 14 daily injections of GH and a further 14 days of control injections. Wheel-running activity was inhibited during the period of growth hormone injections. Possible implications of this result are discussed.