Growth hormone release in chickens after oral administration of thyrotropin releasing hormone

Thyrotropin releasing hormone (TRH) was administered directly into the crops of male broiler chickens. Significant increases in plasma growth hormone (GH) levels were attained within 30 min after administration of saline solutions containing from 10 to 200 micrograms of TRH. Growth hormone levels remained elevated for 120 min when TRH solutions were introduced into crops of ad libitum-fed birds but for a shorter period in fasted birds. Repeated introduction of 200 micrograms of TRH at 30-min intervals failed to sustain elevated plasma GH levels. Introduction of 50 or 200 micrograms of TRH into the crop in a corn meal vehicle caused a marked elevation in plasma GH levels within 30 min. Levels remained significantly elevated up to 90 min after the introduction of the higher dose, but by 120 min posttreatment GH levels were not significantly different than controls. Thyrotropin releasing hormone that had been stored in solution for 24 or 48 hr was nearly as effective in releasing GH as was a freshly prepared solution.