RESTORATION OF GROWTH-HORMONE SECRETION IN PROLONGED FOOD-DEPRIVED RATS DEPENDS ON THE LEVEL OF NUTRITIONAL INTAKE AND DIETARY-PROTEIN

Prolonged food deprivation inhibits GH secretion in rats. To learn more about the nutritional regulation of GH secretion, we observed whether the recovery of GH secretion from prolonged food deprivation depends on the level of nutritional intake or a specific macronutrient in the refeed meal. Adult male Wistar rats were deprived of food for 72 h. Serial blood specimens were withdrawn via an indwelling right atrial cannula every 10 min using an automatic blood-sampling device. In the 72-hour food-deprived rats, the amplitude of the GH pulse progressively decreased but the pulse frequency did not differ compared to that of the fed control rats. When adult male rats were fed 5, 1 0 or 40 kcal of mixed meal consisting of carbohydrate 60%, protein 25% and fat 15% after 72 h of food deprivation, both the pulse amplitude and the pulse frequency immediately increased compared to those of the fasted control rats. Following these changes, the pulsatility of GH secretion was restored to normal, while the pulse amplitude was recovered in a meal-size-dependent manner. The GH secretory pattern no longer differed from that of the fed control rats in the rats fed 40 kcal of mixed meal. In the second study, the 72-hour food-deprived rats were fed 10 or 40 kcal of a protein meal consisting only of casein powder or 40 kcal of a protein-deficient meal consisting of carbohydrate 85% and fat 15%. The GH secretory pattern was restored to normal among the food-deprived rats fed 40 kcal of a protein meal. Among the food-deprived rats fed 10 kcal of a protein meal, the pulse amplitude was significantly less compared to that of the rats fed 40 kcal of a protein meal or that of the fed control rats. When the 72-hour food-deprived rats were fed 40 kcal of a protein-deficient meal, the pulse amplitude was restored to that of the fed control rats, but the pulse frequency remained significantly increased compared to that of the fed control rats throughout the period of observation. We demonstrate that during the recovery from prolonged food deprivation, GH stimulation depends on the amount of food intake, and dietary protein is essential to restore the ultradian rhythmicity of episodic GH secretion.