Influence of beta-agonist on plasma concentrations of growth hormone in broiler chickens on a low plane of nutrition

The effect of the chronic administration of a beta-agonist (L-640,033; donated by Merck, Sharp and Dohme, Research Laboratories, Rahway, NJ) on both the plasma concentration of growth hormone (GH) and the episodic pattern of GH secretion was examined. Administration of .25, 1.0, or 4.0 ppm beta-agonist in the diet for only 3 to 5 days did not affect the overall mean plasma concentration of GH. These treatments also did not influence the frequency of GH secretory pulses. However, the amplitude of the GH secretory pulses was reduced. In contrast, administration of 1.0 ppm beta-agonist for the 10 to 12-day period increased the mean plasma concentration of GH, the amplitude of the GH secretory pulses, the basal (between pulses) plasma concentration of GH, and the interpeak interval. No effect of in vivo GH secretion was found with .25 ppm beta-agonist treatment for 10 to 12 days. Chicks receiving 4.0 ppm beta-agonist for 10 to 12 days had GH secretory pulses with increased amplitude, but no other differences in GH secretory characteristics were observed.