Effects of fasting on growth hormone secretion in the male baboon

The effects of prolonged fasting on the quantity and pattern of spontaneous GH secretion in 5 adolescent male baboons were investigated. Serum GH concentrations were measured in blood samples taken at 20-min intervals over 12 daytime hours after an overnight fast (control period) and during 84-96 h of fasting. Rhythmic GH secretion, with a mean (+/- SE) period of 5.4 +/- 0.2 h occurred in 4 of the 5 animals in 11 control experiments, and GH peaks occurred randomly in the fifth animal. In response to prolonged fasting, the percent half-amplitude of daytime GH peaks decreased from control values of 144 +/- 12% to 105 +/- 17%. The period of the GH rhythm in 4 animals decreased during fasting, but the change was not statistically significant, and the episodic pattern of GH release in animal 5 was apparently unaffected by fasting. After 84 h of fasting, the mean and integrated concentrations of GH released over 12 daytime hours in the 5 animals were not significantly different from control values. In summary, despite a reduction in GH peak amplitude, the quantity and rhythm of GH secretion were maintained in baboons fasted for 84 h. The observed decrease in GH maxima may play a role in the metabolic adaptation to fasting in the baboon.