Endocrine responses to the oral ingestion of a physiological dose of essential amino acids in humans

Abstract

The response of insulin, human growth hormone (hGH), cortisol, leptin and ghrelin, in addition to various metabolic parameters, was measured at 10 minute intervals following the oral ingestion of a standardised physiological dose of essential amino acids (AA). Twenty-eight healthy male, fasted volunteers (aged 18-40 yrs, BMI 18.0-24.5 kg/m(2)) took part in the study; 13 volunteers in the AA group, nine subjects in an iso-caloric control group, and a further six subjects served as fasting controls. Twenty minutes after ingestion, insulin reached peak concentrations that were up to 500% higher than basal values (P<0.0001). The AA group and iso-caloric control group showed a similar insulin response. AA ingestion led to an increase in hGH secretion with maximum concentrations being 2100+/-1013% higher than the basal values (P<0.0001). In contrast, no changes in hGH concentrations were observed in the iso-caloric controls; in the fasting controls only a slight increase in hGH was found towards the end of the fasting period. While cortisol decreased significantly (P<0.01) during the study in the AA group, neither control group showed a significant change in this parameter. Changes in leptin levels remained insignificant in all three groups, whereas ghrelin showed a different profile in each of the three groups, i.e. a continuous rise towards the end of the study period (P<0.001) in the AA group, a less significant effect for the fasting group, and no effect at all in the iso-caloric control group. There was no significant correlation between the concentrations or the area under curve of the hormones measured in any of the groups. The endocrine data provided in this study indicate that a single bolus of essential AA in fasted individuals is associated with both anabolic and catabolic hormonal responses.