FOOD-DEPRIVATION SUPPRESSES STRESS-INDUCED RISE IN CATABOLIC HORMONES WITH A CONCOMITANT TENDENCY TO POTENTIATE THE INCREMENT OF BLOOD-GLUCOSE

The organism of a food-deprived animal is directed toward minimizing energy expenditure and plasma levels of catabolic hormones and glucose are also reduced. Stress, on the other hand, is associated with enhancement of metabolic processes, elevated plasma catabolic hormones, and higher glucose levels. The question arises as to whether food deprivation may be able to attenuate the rise of plasma catabolic hormones seen in stress. For this purpose the variations in triiodothyronine (T3), thyroxine (T4), cortisol and glucose in blood plasma of sheep were monitored during 101 hr of food deprivation and 5 hr of stress. Stress was evoked by isolation of individual sheep from the flock. Blood was sampled by venipuncture once a day during 4 days preceding the isolation stress. On the day of isolation, blood was taken 4 times at 1.5- to 2-hr intervals. Food deprivation lowered the T3, T4 and glucose levels to 45.0, 59.5 and 78.0 percent of the basal level, respectively. Plasma cortisol level did not change over the fasting period in sheep not having visual contact with fed animals. Maintaining such a contact elevated cortisol level maximally by 139 percent over basal level. This indicates that the involvement of an emotional factor seems to be necessary for manifestation of stress. Isolation stress acting on fed and fasting sheep increased all measured hormones and glucose levels. However, in fed sheep, the maximal levels of T3, T4 and cortisol were 72.5, 48.4 and 50.0 percent higher than in corresponding isolated and food-deprived animals. Inversely, the maximal concentration of plasma glucose was about 16.6 percent higher in food-deprived than in fed animals. The mean Δ increase of hormones and glucose at 1, 3 and 5 hr of stress was lowered (T3, cortisol), equal to (T4), or higher (glucose) than in food-deprived animals. Increased frequency of venipuncture elevated the plasma T3 and glucose levels in nonisolated food-deprived sheep, despite a tendency to suppress plasma cortisol. However, unlike glucose, the elevated plasma T3 never achieved the basal level noted before the onset of food deprivation. This suggests that food-deprived animals possess a mechanism which suppresses the stress-induced rise of catabolic hormones, saving energy expenditure. In conclusion, the present experiment suggests that food deprivation attenuates a stress-induced increase in catabolic hormones like T3 and cortisol, and potentiates the increment of blood glucose during isolation, probably by a decreased utilization rate. © 1990.