Testosterone binding protein

Hemopexin (binds heme) Retinol-binding protein (binds retinol) Sex hormone-binding globulin (binds testosterone, estradiol) Thyroid-binding globulin (binds T4, T3) Transferrin (transport iron)... 

Sertoli cells, in the seminiferous tubule wall, are known to be important in spermatogenesis, in part through their synthesis of an androgen-binding protein (ABP). ABP, when secreted into the lumen of the seminiferous tubules, selectively binds testosterone of Leydig cell origin and serves as a hormone reservoir and transport protein for the androgen. 

FSH, for example, increases the expression of a polypeptide known as androgen-binding protein (ABP). ABP helps concentrate testosterone within the seminiferous tubules and helps transport testosterone to the epididymis.39 FSH may also affect Leydig cell function indirectly by increasing the production of other chemical messengers from the Sertoli cells that enhance differentiation and function of Leydig cells.146 147... 

Fig. 2. Specificity determined by availability of steroid. A. Even though glucocorticoid ( i>) and progesterone (2) receptors are present, in the absence of plasma progesterone, only glucocorticoid (G) effects are seen. B. Both oestradiol (E) and testosterone (T) may be present in the plasma but E is not available to the hypothalamic cell due to sequestration by neonatal oestradiol binding protein ([ ]). Therefore maternal oestrogen will not affect the cell whereas, in male foetuses, testosterone can be aro-matised to oestradiol within the cell.

D9. Dechaud, H., Lejeune, H., Garoscio-Cholet, M., Mallein, R., andPugeat, M., Radioimmunoassay of testosterone not bound to sex-steroid-binding protein in plasma. Clin Chem. 35, 1609-1614 (1989). 

The liver synthesizes two enzymes involved in intra-plasmic lipid metabolism hepatic triglyceride lipase (HTL) and lecithin-cholesterol-acyltransferase (LCAT). The liver is further involved in the modification of circulatory lipoproteins as the site of synthesis for cholesterol-ester transfer protein (CETP). Free fatty acids are in general potentially toxic to the liver cell. Therefore they are immobilized by being bound to the intrinsic hepatic fatty acid-binding protein (hFABP) in the cytosol. The activity of this protein is stimulated by oestrogens and inhibited by testosterone. Peripheral lipoprotein lipase (LPL), which is required for the regulation of lipid metabolism, is synthesized in the endothelial cells (mainly in the fatty tissue and musculature). 

The measurement of steroid hormones in a free state distinct from a protein-bound state may be advantageous under certain situations. When alterations in the binding proteins that carry the bulk of steroids in the circulation occur, the interpretation of the total circulating concentration of that particular steroid may be significantly influenced. In addition, it is the free hormone that binds to the steroid receptor and elicits the biochemical effect thus knowledge of the free hormone concentration is desirable in a number of clinical situations. The concept of measuring free hormones has been in the literature for a number of years with the documented clinical utility of urinary free cortisol. Other applications include the measurement of free and weakly bound testosterone in the clinical work-up of the patient presenting with hirsutism. ... 

One important group of nutrients, rarely included in the Western diet, is the essential fatty acids. These compounds are precursors to prostaglandins, which inhibit testosterone binding in the prostate. They also act as anti-inflammatory agents and restrain protein synthesis and cell growth in the prostate. The omega-3 marine lipids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) have been shown to inhibit the growth of prostatic tumors. Flax seed, a rich source of essential fatty acids, has been shown to inhibit cancer metastasis in studies done with mice. 

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