Ingredient Related Studies
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Nutr Neurosci. 2003 Oct;6(5):269-75.
Effects of an oral mixture containing glycine, glutamine and niacin on memory, GH and IGF-I secretion in middle-aged and elderly subjects.
Author(s): Arwert LI, Deijen JB, Drent ML.
Aging is associated with declining activity of the growth hormone-insulin-like growth factor-I (GH-IGF-I) axis and with a decrease in cognitive function. The stimulatory effect of an orally administered nutritional supplement, mainly containing glycine, glutamine and niacin on the GH-IGF-I axis and on mood and cognition was investigated. Forty-two healthy subjects (14 men and 28 women, aged 40-76 years) were enrolled in a randomised, double blind, placebo-controlled trial. They received 5 g of a nutritional supplement or placebo, twice daily orally for a period of 3 weeks. At baseline and after 3 weeks, blood was collected for measurement of serum GH and IGF-I levels and mood and cognitive function were tested. The nutritional supplement ingestion for 3 weeks was found to increase serum GH levels with 70% relatively to placebo, whereas circulating IGF-I levels did not change. Mean GH (+/- SD) increased in this group from 3.23 (+/- 4.78) to 4.67 mU/l (+/- 5.27) (p = 0.03). GH increase was not associated with improvement in mood or memory. Correlation analyses, however, revealed that individual increases in IGF-I, but not GH, were associated with improved memory and vigour. It is concluded that an oral mixture of glycine, glutamine and niacin can enhance GH secretion in healthy middle-aged and elderly subjects.
Source: Department of Endocrinology, VU University Medical Center, de Boelelaan 1117, 1081 HVAmsterdam, The Netherlands.
Study documenting effects of alpha-GPC on GH response to GHRH in young and elderly subjects: http://www.ncbi.nlm.nih.gov/pubmed?term=alpha-glycerylphosphorylcholine%20AND%20growth%20hormone
Horm Metab Res. 1992 Mar;24(3):119-21.
alpha-Glycerylphosphorylcholine administration increases the GH responses to GHRH of young and elderly subjects.
Author(s): Ceda GP, Ceresini G, Denti L, Marzani G, Piovani E, Banchini A, Tarditi E, Valenti G.
Growth hormone (GH) secretion is decreased during aging in humans and in rodents. This decrease may be due to increased hypothalamic somatostatin release, which is inhibited by cholinergic agonists, or to decreased secretion of GHRH. Alpha-glyceryl-phosphorylcholine (alpha-GFC) is a putative acetylcholine precursor used in the treatment of cognitive disorders in the elderly. In order to learn what effect alpha-GFC had on GH secretion, GH-release hormone (GHRH) was given to young and old human volunteers, with or without the addition of alpha-GFC. GH secretion was greater in the younger subjects than in the old individuals, and both groups had a greater GH response to the GHRH+alpha-GFC than to GHRH alone. The potentiating effect of alpha-GFC on GH secretion was more pronounced in the elderly subjects. These findings confirm the observation that aged individuals respond less well to GHRH than younger subjects, and provides further evidence that increased cholinergic tone enhances GH release.
Source: Chair of Gerontology and Geriatrics, University of Parma, Italy.
Full paper of study showing effects of glutamine on GH release: http://www.ajcn.org/content/61/5/1058.long
Link to abstract: http://www.ncbi.nlm.nih.gov/pubmed/7733028
Am J Clin Nutr. 1995 May;61(5):1058-61.
Increased plasma bicarbonate and growth hormone after an oral glutamine load.
Author(s): Welbourne TC.
An oral glutamine load was administered to nine healthy subjects to determine the effect on plasma glutamine, bicarbonate, and circulating growth hormone concentrations. Two grams glutamine were dissolved in a cola drink and ingested over a 20-min period 45 min after a light breakfast. Forearm venous blood samples were obtained at zero time and at 30-min intervals for 90 min and compared with time controls obtained 1 wk earlier. Eight of nine subjects responded to the oral glutamine load with an increase in plasma glutamine at 30 and 60 min before returning to the control value at 90 min. Ninety minutes after the glutamine administration load both plasma bicarbonate concentration and circulating plasma growth hormone concentration were elevated. These findings demonstrate that a surprisingly small oral glutamine load is capable of elevating alkaline reserves as well as plasma growth hormone.
Source: Department of Physiology, Louisiana State University College of Medicine, Shreveport 71130, USA.
Study documenting effects of L-dopa on GH (and how co-administration of glucose affects this): http://www.ncbi.nlm.nih.gov/pubmed/1158029
Diabetes. 1975 Jul;24(7):633-6.
Effect of glucose on the growth hormone response to L-dopa in normal and diabetic subjects.
Author(s):Ajlouni K, Martinson DR, Hagen TC.
The effect of hyperglycemia on the growth hormone response to oral L-dopa (500 mg.) was assessed in eight normal and eight insulin-dependent diabetic subjects. A peak growth hormone response of 21.0 +/- 4.0 ng./ml. (mean +/- S.E.M.), significantly above baseline (p less than 0.01), was achieved in the normal group following oral L-dopa. Glucose concentrations did not change and were approximately 80 mg./100 ml. throughout. Administration of 100 gm. oral glucose with the L-dopa, or thirty minutes thereafter, totally suppressed the growth hormone response in all eight and six of the subjects, respectively. A peak growth hormone response of 20.0 “/- 1.7 ng./ml. (mean +/- S.E.M.), significantly above baseline (p less than 0.001), was obtained in eight nonobese, insulin-dependent diabetics, in spite of prevailing hyperglycemia (mean plasma glucose 243-258 mg./100 ml.) throughout the test. Endogenous hyperglycemia was achieved in these patients by lessening the usual strict adherence to plasma glucose control for the purpose of the study. These results suggest an abnormality in the hypothalamus or pituitary of diabetic subjects allowing growth hormone responsiveness in spite of hyperglycemia.
Important Notice: Secretagogue is for use by healthy individuals. Individuals with diabetes should consult their physician before beginning this or any nutritional regimen.