Secretory Pattern of Growth Hormone, Insulin, and Related Metabolites in Growing Male Turkeys: Effects of Overnight Fasting and Refeeding

Abstract

The effect of an overnight fast on the secretory profile of growth hormone (GH), insulin, and related metabolites [glucose, nonesterified fatty acids (NEFA) and triglycerides (TG)] was determined in two separate experiments with 8- and 9-wk-old male turkeys. Toms were provided feed ad libitum or were fasted 20 h prior to sampling. Blood samples (.6 to .7 mL) were collected every 10 min for 8 h from the toms showing a positive weight gain between cannulation and the initiation of the experiment. Overall and baseline, GH levels were higher for the fasted birds versus the fed birds. The GH peaks for the fasted birds were of shorter duration than those for the fed birds, but were more frequent. The plasma NEFA levels of the fasted birds were higher than those of the fed birds. Plasma TG was lower for the fasted than the fed group. Insulin, which was secreted in a pulsatile fashion, was lower for the fasted versus the fed birds. Fasting produced no change in plasma glucose. A separate group of fasted males was refed after 4 h of sampling; the plasma levels of GH, insulin, and metabolites returned to those observed in birds given feed ad libitum within 30 min of refeeding. There appeared to be no relation between the pulsatile release of GH and the circulating levels of NEFA.