EFFECT OF PARENTERAL ADMINISTRATION OF SELECTED NUTRIENTS AND CENTRAL INJECTION OF GAMMA-GLOBULIN FROM ANTISERUM TO NEUROPEPTIDE-Y ON GROWTH-HORMONE SECRETORY PATTERN IN FOOD-DEPRIVED RATS

Serial changes in growth hormone (GH) secretory pattern during 72 h food deprivation and in response to refeeding after 72 h food deprivation were observed in adult male Wistar rats. In addition, the effects of intravenous administration of glucose, fatty acids or amino acids and central injection of gamma-globulin from antiserum to human neuropeptide Y(NPY) on the GH secretory pattern were examined in 72 h food-deprived rats. Rats were provided with chronic indwelling right atrial cannula and serial blood specimens were withdrawn via the cannula every 10 min using an automatic blood-sampling device. The GH secretory pattern was analyzed using a Pulsar computer program. In fed rats, episodic GH secretion with an amplitude exceeding 350 ng/ml occurred at 170-min intervals and intervening trough GH levels were less than 10 ng/ml. During the 72 h food deprivation, the amplitude of pulsatile GH secretion decreased progressively without altering the pulse frequency. When 72 h food-deprived rats were refed lab chow, the pulse frequency and the pulse amplitude increased rapidly and lasted for 6-8 h. Normal pulsatile GH secretion resumed by 10-12 h after refeeding following the 72 h food deprivation. To identify the specific nutrient (i.e. glucose, fatty acids or amino acids) serving as the signal causing restoration of the central drive to GH secretion, glucose solution (2 or 6 kcal), lipid emulsion (2 or 6 kcal) or amino acid solution (2 kcal) was administered intravenously to the 72 h food-deprived rats. Although normal pulsatile GH secretion was not restored by the administration of any one nutrient, intravenous injection of the amino acid solution was followed by a rapid increase in both the pulse frequency and the pulse amplitude. Injection of a glucose solution prevented the progressive decrease of pulse amplitude without altering the pulse frequency, while injection of a high (6 kcal) but not a low dose (2 kcal) of the lipid emulsion suppressed GH secretion in food-deprived rats. Central administration of gamma-globulin from the antiserum to NPY, a peptide implicated in the regulation of feeding behavior and GH secretion, increased the amplitude and frequency of GH pulses in 72 h food-deprived rats, but normal pulsatile GH secretion was not restored. These findings suggest that amino acids either directly or indirectly reactivate GH secretion in food-deprived rats, and that NPY participates by exerting an inhibitory influence on GH secretion in food-deprived rats.