GROWTH HORMONE

GROWTH HORMONE (GH)/SOMATOTROPIN

• Polypeptide.

• Synthesized & secreted by somatotropes.

• Subtype of acidophilic cells in adenohypophysis.

PHYSIOLOGICAL EFFECTS:

• Two major action –

– Stimulation of skeletal growth.

– Regulation of metabolism.

1. STIMULATION OF SKELETAL GROWTH:

• Mediated by “Somatomedins”/“Insulin-like Growth Factors” (IGF).

– Synthesized in liver.

• Somatomedin (IGF-1) stimulates proliferation of chondrocytes & osteocytes.

– Increases chondroitin sulfate deposition in cartilage.

– Increases ossification of newly formed cartilage.

CONDITIONS ASSOCIATED:

1. GH deficiency in early life –

• Causes dwarfism (reduced height).

• Yet, associated with Normal body proportion.

2. GH excess in early life –

• Leads to gigantism.

3. GH excess in adulthood –

• Results in Acromegaly.

2. REGULATION OF METABOLISM:

2a. On Protein metabolism:

• Predominantly anabolic effects on skeletal & cardiac muscle.

• By promoting amino acid transport into cells & Increasing protein synthesis.

2b. On Carbohydrate & Fat metabolism:

• Effects complicated by,

– Anti-insulin effect of GH.

– Insulin-like effects of somatomedins.

2c. Anti-insulin effects of GH – 

• Decreased peripheral glucose utilization.

• Increased gluconeogenesis.

• Hyperglycemia.

• Lipolysis.

Conditions associated:

• “Insulin-Resistant Diabetes mellitus” –

– Caused by GH excess, (mainly by anti-insulin effects of GH).

2d. Insulin-like effects of somatomedins/IGF – 

• Anti-lipolytic activity.

3. GH on kidneys:

• Promotes renal reabsorption of Ca²⁺, Na²⁺, K⁺& Cl^–. 

REGULATION:

• Regulated by hypothalamic GHRH.

• GH secreted in pulsatile fashion throughout life.

– Elevated secretion rate immediately after birth & at puberty.

– Large bursts of secretion at night during deep sleep onset.

FACTORS INFLUENCING GH SECRETION –

1. Stimuli increasing GH secretion –

• Hypoglycemia.

• Exercise.

• Fasting.

• Protein meals.

• Aminoacids (like arginine).

• Stress.

• Glucagon.

• Pyrogen.

• Lysin vasopressin.

• L-dopa & α-adrenergics.

• Estrogen & androgens.

• 2-deoxyglucose.

2. Stimuli decreasing GH secretion:

• REM sleep.

• Glucose.

• Somatostatin.

• Cortisol.

• FFA.

• GH itself decreases

• IGF- 1.

• Medroxyprogesterone.

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