17-11-2014, 02:53 AM
Hello-major breakthrough: 
(sorry geek humor)
Arrival and Entry of Steroid Hormones Into Target Tissue Cells
Steroid hormones are small, hydrophobic, and lipid-soluble molecules derived from cholesterol. They circulate in blood free or bound (95%) to plasma carrier proteins.56,57,58 Sex hormone-binding globulin (SHBG), also known as testosterone-estradiol-binding globulin (TeBG), and androgen-binding protein (ABP) are encoded by the same gene.59 ABP is produced by the Sertoli cells of the testis, and SHBG is produced by the liver and is present in the circulatory system.58 SHBG binds most gonadal steroids, and corticosteroid-binding globulin (CBG or transcortin) binds glucocorticoids and progesterone with different affinities. When circulating levels of steroid hormones exceed the binding capacity of their respective binding proteins, they can then bind nonspecifically and with low affinity to albumin, from which they can readily dissociate and enter target cells.60 The unbound and loosely albumin-bound steroids are believed to be the most biologically important fractions because the steroid is free to diffuse or be actively transported through the capillary wall and lipid plasma membrane bilayer. Extracellular binding proteins may modulate hormone response by regulating the amount of steroid available to the cell.60 The binding capacity of binding globulins is influenced by endocrine status and other factors.57
SHBG binds to a specific cell membrane receptor called sex hormone-binding globulin receptor (SHBG-R) and activates adenylyl cyclase, increasing intracellular cAMP.58 Binding of SHBG to SHBG-R also transfers SHBG into the cell as a consequence of receptor-mediated endocytosis.61 The interaction of SHBG with SHBG-R is inhibited when steroids are bound to SHBG, suggesting that SHBG is an allosteric protein.61 However, if unliganded SHBG is allowed to bind to its receptor on intact cells and an appropriate steroid hormone then is introduced, adenylate cyclase is activated and intracellular cAMP increases.62 After the steroid hormone is in the cytoplasm, it is not clear whether a transport protein is required for movement of the hydrophobic steroid molecule through the aqueous cytoplasm to the receptor, regardless of whether the receptor is cytoplasmic or nuclear in location. The currently accepted model is that the steroid hormone diffuses freel
(sorry geek humor)Arrival and Entry of Steroid Hormones Into Target Tissue Cells
Steroid hormones are small, hydrophobic, and lipid-soluble molecules derived from cholesterol. They circulate in blood free or bound (95%) to plasma carrier proteins.56,57,58 Sex hormone-binding globulin (SHBG), also known as testosterone-estradiol-binding globulin (TeBG), and androgen-binding protein (ABP) are encoded by the same gene.59 ABP is produced by the Sertoli cells of the testis, and SHBG is produced by the liver and is present in the circulatory system.58 SHBG binds most gonadal steroids, and corticosteroid-binding globulin (CBG or transcortin) binds glucocorticoids and progesterone with different affinities. When circulating levels of steroid hormones exceed the binding capacity of their respective binding proteins, they can then bind nonspecifically and with low affinity to albumin, from which they can readily dissociate and enter target cells.60 The unbound and loosely albumin-bound steroids are believed to be the most biologically important fractions because the steroid is free to diffuse or be actively transported through the capillary wall and lipid plasma membrane bilayer. Extracellular binding proteins may modulate hormone response by regulating the amount of steroid available to the cell.60 The binding capacity of binding globulins is influenced by endocrine status and other factors.57
SHBG binds to a specific cell membrane receptor called sex hormone-binding globulin receptor (SHBG-R) and activates adenylyl cyclase, increasing intracellular cAMP.58 Binding of SHBG to SHBG-R also transfers SHBG into the cell as a consequence of receptor-mediated endocytosis.61 The interaction of SHBG with SHBG-R is inhibited when steroids are bound to SHBG, suggesting that SHBG is an allosteric protein.61 However, if unliganded SHBG is allowed to bind to its receptor on intact cells and an appropriate steroid hormone then is introduced, adenylate cyclase is activated and intracellular cAMP increases.62 After the steroid hormone is in the cytoplasm, it is not clear whether a transport protein is required for movement of the hydrophobic steroid molecule through the aqueous cytoplasm to the receptor, regardless of whether the receptor is cytoplasmic or nuclear in location. The currently accepted model is that the steroid hormone diffuses freel