Expression and Physiological Significance of Growth Hormone Receptors and Growth Hormone Binding Proteins in Rat and Man

Abstract

The molecular structure of the GH receptor has recently been characterized and the receptor identified as a member of a new receptor superfamily that includes the prolactin receptor and several cytokine receptors. No obvious signal transducing domain has been identified on any of these related receptors. One possible signalling mechanism involves receptor interaction with other membrane‐associated proteins that function as mediators of signal transduction. Whether such a mechanism is involved in signal transduction of the GH receptor is not known. Another common feature of these receptors is the presence of soluble forms such as the GHBP. The functions of these proteins in the circulation and at the level of the target cell remain to be resolved.

Effects of Cortisol and Growth Hormone on Lipolysis in Human Adipose Tissue1

“…lipolytic activity, with cortisol inhibiting and GH stimulating. In line with the fact that both glucocorticoid and GH receptors are expressed in human adipose tissue (28,29), the findings indicate that cortisol and GH act directly on adipose tissue to exert their physiological influences. Furthermore, the present results suggest that the lipolytic effect of GH is strengthened in the presence of cortisol.…”

Growth hormone, insulin‐like growth factors and bone remodelling

“…GH thus seems to exert both direct and indirect IGFmediated actions on human osteoblasts [14,15]. Increased proliferation is seen 2 h after addition of GH to osteoblast cultures [14], which suggests a direct effect mediated by GH binding to membrane receptors; and indeed membrane receptors on osteoblastic cells have been demonstrated [7,15]. In confluent cultures of human osteoblasts GH increases the synthesis of type I collagen, alkaline phosphatase, BGP [14].…”

“…Another common feature of these receptors is the presence of soluble forms such as the growth hormonebinding protein (GHBP) [7]. GHBPs are formed by alternate splicing in rodents, but in other species (man included) proteolytic cleavage of the membrane-bound GH receptor is thought to be the main mechanism [8].…”