Reduced adrenocortical function and increased thyroid function in fasted and refed chickens

Abstract

The deprivation of food for 48 h markedly increased (P< 0·001) the corticosterone concentration in the plasma of 7- to 8-week-old chickens. When fasted birds were refed for 2 min or 5 s the corticosterone concentration fell to the level in fed birds within 30 min of refeeding. In fasted and refed birds the plasma corticosterone concentration remained lowered for at least 150 min after a 2-min period of refeeding, whereas in birds refed for 5 s the concentration had increased within 120 min to that in fasted birds. When fasted birds were refed 1, 5, 15 or 30 g diet the corticosterone level was again markedly reduced (P< 0·001) within 45 min of refeeding. The magnitude of this post-feeding decline was unrelated to the amount of food eaten, although its duration was; the level in birds refed 1, 5 or 15 g food increasing to that in fasted birds within 90, 135 and 225 min respectively. The corticosterone level in birds refed 30 g diet remained reduced for at least 225 min but increased to that in fasted birds 24 h after refeeding. The initial decline in the corticosterone concentration was unrelated to the consumption of food, since a similar reduction in the corticosterone level was observed in fasted birds which were given the sight of food but prevented from eating it by Perspex lids attached to the food troughs. This initial decline in the corticosterone level was not a result of stress, as it did not occur in fasted control birds. These results suggest that the adrenocortical changes in fasted and refed birds is initially mediated by a conditioned neural stimulus (reinforcement) and is maintained as a result of peripheral metabolic effects of ingested food. In fasted chickens the concentration of plasma tri-iodothyronine (T3) was greatly reduced (P<0·001) in comparison with fed birds. When fasted birds were refed for 2 min or with 5, 15 or 30 g diet, the level of plasma T3 was increased (P < 0·05) 90 min after refeeding although not to the level in birds which had free access to food. The magnitude and duration of this increase was related to the amount of food consumed and was not observed in birds refed for 5 s or with 1 g food or in fasted birds given sight of but not access to food.