Veterinary Physiology-III

METABOLIC EFFECTS OF GROWTH HORMONE

• As a protein anabolic hormone GH enhances almost all facets of amino acid metabolism including uptake, while at the same time reducing the break down of proteins. This includes transport through the cell membrane to the interior of the cells and increased protein synthesis in all cells of the body more specifically the muscle cells. It stimulates extracellular collagen deposition
• Stimulates the formation of RNA by increasing the tran­scription process in the nucleus.
• By enhancing the ribosomal machinery, produces greater number of protein molecules.
• As a potent protein sparer, it causes decreased catabo­lism of protein and amino acids for energy. Protein content of the body is increased by GH.
• It stimulates lipolysis and mobilizes large quantities of free fatty acids from the adipose tissue. It enhances the conversion of fatty acids to acetyl Co‑ A, which is used for energy. Excessive amount of STH at times causes greater amounts of fat mobilization resulting in excess acetyl Co‑A which is converted to acetoacetate, b ‑OH butyric acid and acetone leading to ketonemia which is called as ketogenic effect of GH. It reduces lipid synthesis and leads to leaner animal. GH decreases body fat content and promotes lean body mass.
• GH causes decreased utilization of glucose for energy (possibly duo to utilization of fat for energy) and enhanced glyco­gen deposition. It diminishes uptake of glucose by the cells for energy by the muscle and adipose cells, thus increases blood glu­cose concentration which is known as diabetogenic effect of GH.
• GH shows positive nitrogen balance and phosphorus balance. It decreases urinary excretion of Na⁺ and K⁺ by increasing the uptake of these ions by the growing tissues.
• In the cow lactation can be induced with STH more easily and with greater regularity than with lactogenic hormone (prolactin). This is due to galactopoietic effect of STH
• In summery, STH favours economical use of proteins and car­bohydrates, encouraging the body to retain these building blocks for tissue growth and development.
• Injection of growth hormone increases milk yield by 10-25%, lactose, protein and fat contents of milk. Endogenous plasma concentrations of GH are high in high yielding than low yielding animals.GH partitions nutrients for milk yield and increases fatty acid mobilisation. Exogenous GH increases nitrogen retention and improves carcass quality with improved muscle growth; helps in lean meat production with less adipose tissue in cattle, pigs, sheep.