Veterinary Physiology-III

SOMATOTROPIN (STH)

• Somatotropin or growth hormone (GH) is a complex protein having 191 amino acids and S‑S bridges.
• The STH is species specific and most domestic animals respond best to homologous STH and least to heterologous STH.
• STH is structurally related to prolactin and chorionic somatomammotropin of the same species.

Control of STH output

• The control of STH output is achieved by a balance between the growth hormone releasing hormone (GHRH) and somatostatin.
• A sharp drop in blood glucose and fatty acids levels is the primary cause of GHRH release from the hypothalamus and it results in two to ten fold increases in STH secretion.

Stimuli that increases the GH secretion

• Deficiency of energy - hypoglycaemia, exercise, fasting, insulin
• Increase in circulating levels of certain amino acids - protein meal, arginine vasopressin
• Glucagon (mechanism not known)
• Stress (trauma, surgery) pyrogen
• Sleep
• Ghrelin, a 28 amino acid polypeptide hormone secreted from hypothalamus (also from stomach) stimulates GH release

Stimuli that decreases the GH secretion

• Increase in glucose, cortisol, free fatty acids, GH
• Obesity results in reduced GH release
• GIH
• STH appears to be released at a rather similar rate through out the life of the animal.
• Although skeletal growth cease after puberty, STH has a biological role throughout life as an anabolic agent as well as synergistic role by enhancing the actions of ACTH, TSH, LH, and FSH on their target organs.
• Females are more responsive to GH stimuli than males.