The Staub Traugott phenomenon. III. Effects of starvation

Improved tolerance with closely spaced successive glucose loads is known as the Straub-Traugott effect. Results of previous studies from this laboratory suggest that this phenomenon is not dependent upon changes in circulating growth hormone or insulin, but may depend on nutrient induction of essential glycogenic and glycolytic enzymes. To test this thesis, three, hourly spaced, intravenous glucose tolerance tests were administered to obese subjects before and at the conclusion of a prolonged fast. While a clear Straub-Traugott effect was shown in the fed state, this effect was conspicuously absent after long-term caloric deprivation. Compared to the findings before fasting, insulin levels after prolonged caloric deficit were similar during the initial intravenous glucose challenge but failed to elicit incremental insulin rise with successive glucose loads, in keeping with earlier suggestions that distinct mechanisms mediate the insulin-initiating and potentiating actions of glucose. After starvation there was greater suppression of plasma free fatty acids and immunoreactive glucagon levels. Initial intravenous glucose tolerance after fasting was either frankly improved or unchanged in all but one of the subjects studied. Absence of the Staub-Traugott effect after fasting, however, would appear to reflect a failure of nutrient induction of improved glucose metabolism as alterations in glucoregulatory hormones and free fatty acids do not consistently explain the presence or absence of this phenomenon in the different metabolic states so far studied.