Direct and indirect effects of growth hormone.

GROWTH HORMONE:

The hormone responsible for general somatic growth. It accounts for 4% to 10% of the wet weight of the anterior pituitary in human adult (5 to 10 mg per gland). it is a polypeptide synthesized by somatotrophs of the pars distalis. It is derived from prohormone in pituitary cells but is rapidly converted to GH by proteolysis. Growth hormone exerts its effects both directly and indirectly.

• GH regulates growth indirectly through hepatic IGF-I then affects growth through its action on skeletal tissues and many other connective tissue and organs. Several hormones (e.g., prolactin, placental lactogen, insulin) may also exert part of their growth promoting activity through effects on hepatic IGF production. The structures of human placental lactogen (hpL) and prolactin (PRL) are similar to that of GH, IGF levels remains normal in hypophysectomies pregnant rats even in the absence of PRL and GH, these levels decline promptly postpartum. Thus other GH related factors may be important in IGF production during particular physiological states such as pregnancy.
• Growth hormone has a direct action on number of target cells in addition to its action on hepatic IGF production. These GH actions have been described in diabetogenic in nature. For example GH stimulates lipolysis which provides substrate for glucose formation and thus has a sparing effect on direct glucose utilization.