EFFECTS OF FASTING AND GLUCOSE-LOAD ON FREE CORTISOL RESPONSES TO STRESS AND NICOTINE

The availability of energy appears to exert important regulatory funct ions in pituitary-adrenal stress responses. In two studies, the effect s of short-term fasting and subsequent glucose administration on the f ree cortisol response to psychological stress and nicotine consumption were investigated. Study 1: After fasting for 8-11 h, healthy young m en ingested either 100 g glucose (n = 13) or water (n = 12). One hour later they were exposed to a psychosocial stress task (Trier Social St ress Test). A third group also ingested 100 g glucose, but they were n ot exposed to any additional treatment (n = 10). Capillary blood gluco se levels were in the lower euglycemic range before and significantly elevated after the glucose load (64.9 +/- 9.8 vs. 162.5 +/- 43.5 mg/dL ; F = 149.04, P < 0.001). Although glucose load per se did not affect free cortisol levels, psychosocial stress induced a large cortisol res ponse in glucose-treated subjects. In contrast, fasted subjects who re ceived tap water did not respond to the Trier Social Stress Test with significant changes in cortisol levels (F = 6.27, P < 0.001). Both gro ups responded with a similar increase in heart rates (F = 33.53, P < 0 .001) with no statistically significant difference between glucose and water-treated subjects. Study 2: Twelve habitual smokers received 100 g glucose or tap water after fasting for at least 8 h on two separate sessions (cross-over, random sequence). Forty-five min after glucose/ water ingestion, they smoked two cigarettes with a nicotine content of 1.0 mg/cigarette. Subjects were euglycemic before smoking, with a sig nificant rise of glucose levels after consumption of 100 g glucose (64 .4 +/- 8.3 vs. 143.5 +/- 40.0 mg/dL; F = 40.25, P < 0.001). As in Exp 1, subjects showed a substantially larger free cortisol response to ni cotine under glucose load compared with water load (F = 4.91, P < 0.00 1). From these data we conclude that the free cortisol response to sti mulation is under significant control of centers responsible for monit oring energy availability. Low glucose levels appear to inhibit adreno cortical responsiveness in healthy subjects. In agreement with results from animal studies, the present results suggest that ready access to energy is a prerequisite for hypothalamus-pituitary-adrenal stress re sponses.