Globulins, steroid-binding

Sakai F, Cheix F, Clavel M, Colon J, Mayer M, Pommatau E, Saez S (1978) Increases in steroid binding globulins induced by tamoxifen in patients with carcinoma of the breast. J Endocrinol 76 219-226... 

The steroid hormones are hydrophobic, this property enabling them to readily cross the plasma membrane to bind their respective cytosolic receptors. However, transport of such hydrophobic hormones through the blood stream requires hormone-binding proteins such as the steroid-binding globulins and corticosteroid-binding globulins. 

W. Rosner The functions of cortico.steroid-binding globulin and sex hormone-binding globulin Recent advances. Endocrine Reviews 11, 80 (1990). 

Recent X-ray studies of enzymes for which steroids are primary substrates, steroid binding globulins, and fragments of steroid receptors with amino acids and nucleic acids are just beginning to provide additional insight into the nature of steroid receptor binding and macromolecular interactions, and the mechanism by which steroids exert their hormonal functions. 

Sex hormone-binding globulin /J steroid-binding globulin)... 

The testosterone in blood plasma is very largely bound to serum albumin and also, in many species, to a plasma sex steroid-binding globulin that is produced by the liver and is quite different from in-... 

Gonadal Steroids Are Transported by Sex Hormone-Binding Globulin... 

LOUKOVAARA M, CARSON M, PALOTIE A, ADLERCREUTZ H (1995) Regulation of sex hormone-binding globulin production by isoflavonoids and patterns of isoflavonoid conjugation in HepG2 cell cultures. Steroids. 60 656-61. 

MOUSAVi Y, ADLERCREUTZ H (1993) Genisteiu is an effective stimulator of sex hormone-binding globulin production in hepatocarcinoma hinnan hver cancer cells and suppresses proliferation of these cells in culture. Steroids. 58 301-4. 

H15. Hammond, G. L., Smith, C. L., and Underhill, D. A., Molecular studies of corticosteroid binding globulin structure, biosynthesis, and function. J. Steroid Biochem. Mol. Biol. 40, 755-767 (1991). 

Oral contraceptives have their most significant effect on endocrine parameters. Blood cortisol, thyroxine, protein-bound iodine, T3 uptake, and urinary free cortisol are elevated. Urinary 17,21-dihydroxy steroids, 17-ketosteroids, and estrogens are decreased. There is no effect on urinary catecholamines or VMA (Table 10) (LIO). The effect of thyroid functions tests is due to the administered hormone stimulating an increase in the production of thyroid-binding globulin which in turn binds 1-thyroxine. The lowering of free thyroxine stimulates the anterior pituitary to produce thyrotropin, which in turn stimulates the thyroid to produce more thyroxine. Since the additional thyroxine is bound to the extra protein, there is an equilibrium and the patient remains clinically euthyroid, but the protein-bound iodine and the thyroxine are elevated. 

Steroids reversibly bind with two proteins in the plasma corticosteroid-binding globulin, which is a specific a2-globulin and albumin, which has nonspecific activity and a weakly expressed affinity to steroids. 

Most steroid hormones exist in part as sulfate esters and may also become esterified with fatty acids.256 The fatty acid esters may have relatively long lives within tissues.256 A special sex hormone-binding globulin transports sex hormones in the blood and regulates their access to target cells.256a b... 

Thyroid hormones and most steroid hormones are associated with carrier proteins in the serum. The carrier proteins are called, appropriately, thyroxine-binding globulin, transcortin (for cortisol), and sex-steroid-binding protein. These proteins have a high affinity (Kd 10—9— 10 8 m) for their respective hormones. They buffer the concentration of free hormone and retard hormone degradation and excretion. The carrier proteins are distinguishable from the intracellular receptors for these hormones. 

Many studies have shown that lactation is not adversely affected by depot medroxyprogesterone acetate and that breast-milk production may even be increased (35). Because of the low binding affinity of medroxyprogesterone to sex hormone binding globulin, the concentration of steroids in the milk is close to that in the maternal plasma, unlike the 19-nortestosterone derivatives. 

Figure 17.5 Endocrine signaling pathway involving steroid hormone, sex hormone binding globulin (SHBG), and the SHBG receptor.

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