Metabolic Regulations of Human Growth Hormone Secretion

Abstract

Serial levels of Human Growth Hormone (HGH), glucose, and FFA were determined in various states of human subjects.
I. HGH secretion in normal subjects:
(1) After overnight fast and at bed rest during daytime, 9 subjects showed no significant change of HGH levels. In 8 hospital workers, with daily activity and meals, the elevation of HGH levels was observed 4 hours after breakfast. The HGH values at this time were widely distributed, but wider distribution was noted in younger (13-14) age group than other (over 15 and adults) group. This difference was more marked in males than females. (2) at night time, all 10 test subjects showed the elevation of HGH levels with the onset of sleep. HGH secretion appeared to be suppressed by the paradoxical sleep which was defined by brain wave. (3) In 5 subjects, blood was drawn at 40 minutes interval during 3 days fasting. Fluctuations and bursts of HGH levels were observed in all cases, and appeared to correlate with those of FFA.
II. Influence to the HGH secretion of experimental modifications of metabolic states in normal subjects
(1) In 28 subjects, insulin administration (0.1u./kg) caused marked increase of HGH levels. (2) Following 100 g glucose load in 21 subjects, HGH levels showed the secondary rise at 4 hours. (3) 25g of glucose infused intravenously for 20 minutes caused marked secondary rise, but the same amount of glucose infused for 3 minutes caused only slight rise. The results suggest that the changing of blood glucose level per se may not directly be correlated with the level of HGH. (4) L-arginine administration (20g) caused marked elevation of HGH levels in 5 cases. (5) Ingestion of 70g cheese in 6 subjects caused rise of HGH between 150 and 240 minutes. (6) Ingestion of 50g butter in 6 subjects caused no change of HGH levels. (7) For the purpose of decreasing FFA levels, intravenous administration of nicotinic acid (100 mg×2) was performed in 17 subjects. There was a temporary decrease of FFA, followed by a marked secondary rise. HGH levels showed marked increase in all subjects. Changing the manner of administration (100 mg×5) caused no essential difference on the rise of HGH levels. In 7 cases, with the combination of nicotinic acid and heparin injection, which inhibited the fall of FFA levels, the rise of HGH was clearly suppressed. The secondary rise of FFA was less than the cases of nicotinic acid injection alone. (8) Oral administration of 3.3 g of acetylsalicylic acid in 6 subjects also caused the rise of HGH levels. (9) Administration of heparin could not suppress the HGH rise caused by insulin or arginine administration. These results suggest that the decrease of FFA level is one of the stimulus for the secretion of HGH.
III. Clinical investigations :
(1) Patients with hypopituitarism caused no change of HGH levels following insulin (18 cases), arginine (6 cases), and nicotinic acid (6 cases) administrations. The marked decrease of the secondary rise of FFA following nicotinic acid or arginine administration in these patients was observed. These results suggest that the secreted HGH participate in inducing the secondary rise of FFA in these conditions. (2) Among 14 diabetic patients who had glucose infusion for 3 minutes, 9 patients showed marked rise of HGH levels. 4 out of 5 borderline cases showed marked rise. (3) In 6 obese patients, nicotinic acid administration caused no increase of HGH levels. The continuation of the secondary rise of FFA in these patients was less than the control normal subjects. These results of diabetes and obesity suggest some implication of the abnormality of HGH secretion in these states.