27 Endocrine Control of Growth

27.1 Somatotropic hormone (STH)

Somatostatin is a peptide inhibiting the release of STH as well as the release of insulin and other hormones affecting growth. It is possible to increase the growth rate of lambs by auto-immunization against somatostatin. The carcasses of treated lambs are heavier than normal but have normal ratios of muscle to fat to bone. However,  the initial experiments on the enhancement of growth by immunization against somatostatin were conducted on unimproved breeds of sheep and the enhancement of growth in improved breeds is far less impressive.

27.2 Insulin-like growth factor (IGF)

Another name change!  Back in the days of "growth hormone", it was added to cultered muscle cells in anticipation of a surge of extra mitotic activity.  But nothing happened.  "Growth hormone" was then tried on many other types of tissue, and one did respond - liver. The exciting next experiment was - what would happen when "growth hormone" was added to a culture of both types of tissue (muscle + liver). Yes, both types of tissue now had a surge of mitotic activity in response to the added hormone. What happens? The liver responds to the "growth hormone" by producing another hormone, and this other hormone is the one actually stimulating mitosis in both types of tissue. At first, this new hormone was called somatomedin. But then somatomedin was found to be like a very potent form of insulin, so the name was changed to insulin-like growth factor (IGF).

Sulphation factor

IGF-1 and IGF-2

Insulin-like properties

The effects of IGFs are widespread: they stimulate
(1) the transport of glucose,
(2) the uptake and incorporation of amino acids in muscle, and
(3) collagen synthesis .

27.3  Control of protein synthesis in myofibres

  27.4 Cortisol and animal stress

Further information

Structure and Development of Meat Animals and Poultry.  Pages 476-483.