Description

The human Somatotropic Hormone (GH, Growth Hormone) is a polypeptide composed of one hundred and ninety-one amino acids and with a molecular weight of about 21,500 daltons. The anterior pituitary contains between five and ten milligrams of GH, which is synthesized and accumulated in the somatotropic cells. GH production is influenced by both age and sex, and is estimated to be 0.4 – 1.0 mg/day in adult men, with higher values ​​in adolescents and women. Serum GH concentrations vary during the day, generally from 0.5 to 3.0 g/liter in adult men, depending on production, higher in adolescents and in women. GH is metabolized in the liver and has a plasma life of between seventeen and forty-five minutes. Regulation of GH secretion GH secretion by the pituitary gland is pulsatile and is regulated by a feedback mechanism in which two hormones are involved, one with excitatory action, GH-Releasing Hormone (GHRH), and the other inhibitory action, Somatostatin (SRIF). The response of the pituitary to GHRH is influenced by numerous factors and may decrease with age. GH is excreted in response to numerous physiological and pharmacological stimuli that act on specific areas of the brain through pathways controlled by serotonergic, dopaminergic, adrenergic, and cholinergic neurons. The stimuli integrate with each other and can act synergistically or competitively, but ultimately they are all included in the final common pathway made up of GHRH and SRIF. There are sexual differences in the secreting capacity of GH: these are correlated to estrogen levels.During the day there are small episodes of GH secretion, the largest of which take place between 60 and 90 minutes after the onset of sleep, which corresponds to the phase of deep sleep (slow waves on the EEG). Nocturnal GH secretion may be increased in athletes due to increased physical activity. Physical and psychological stress can increase GH secretion. Although the exact mechanism and its control center are not known with certainty, it is possible that they act through the increase in the central secretion of catecholamines. GH secretion is stimulated by hypoglycemia and inhibited by hyperglycemia. Insulin hypoglycemia is considered a test to assess pituitary function and involves an increase in GH in 85% of normal subjects. Glucocorticoids stimulate GH at physiological concentrations, while hypercortisolism inhibits the response to stimuli. Also amino acids (especially ARGININE) stimulate GH They are effective when taken orally or injected intravenously.