Effects of branched chain amino acids on spontaneous growth hormone secretion in the baboon

Blood concentrations of the branched chain amino acids (BCAAs) are elevated during fasting in healthy subjects and are abnormally high both postprandially and during fasting in diabetic patients. Despite evidence that these amino acids influence brain metabolism and neurotransmitter synthesis, there is little information on the neuroendocrine effects of the BCAAs. This study provides evidence that elevation of postprandial blood levels of the BCAAs alters the ultradian rhythm of GH secretion observed in the baboon during daylight hours. To mimic the postprandial rise in the BCAAs that occurs in diabetic patients, we infused either saline or a mixture of valine, leucine, and isoleucine into six conscious male baboons from 1530-1900 h daily for 4 days during and after the normal feeding time. On the last day of the infusions, blood samples were collected at 20-min intervals from 0800-1500 h and at 30-min intervals from 1500-2000 h. The amino acid infusions increased postprandial blood concentrations of the BCAAs 2- to 5-fold over control levels and lowered the blood concentrations of tyrosine, phenylalanine, and lysine compared to concentrations observed during control infusions. A significant elevation in GH levels occurred in association with BCAA treatment in each animal between 0800 and 1100 h, 13 h after the previous day's infusion. Average +/- SE maximum GH levels observed between 0800 and 1100 h were 11.6 +/- 2.9 ng/ml under experimental conditions compared to a control value of 3.8 +/- 1.2 (P less than 0.02). Whether the increased GH levels represented the generation of a new peak or a phase shift in a nocturnal peak was not determined. Combined with evidence that spontaneous release of GH is neurally regulated in the baboon, this study suggests that changes in the blood levels of the BCAAs modulate neural mechanisms that regulate GH rhythmicity.