Testosterone-estradiol binding

Distribution - Testosterone in plasma is approximately 98% bound to a specific testosterone-estradiol binding globulin. There are considerable variations in the reported half-life of testosterone, ranging from 10 to 100 minutes. The half-life of testosterone cypionate IM is approximately 8 days for oral fluoxymesterone, it is approximately 9.2 hours and for methyltestosterone it is 2.5 to 3 hours. 

Corticosteroid-binding globulin (also called transcortin). Testosterone-estradiol-binding globulin. 

TeBP Testosterone-estradiol-binding globulin Maximal velocity... 

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

Internal standard Isotope labeled analyte with optimized binding assessment, and verified standard curve IS peak area within 50 % of each analyte 13C6-Estradiol, 16a-Hydroxyestra-diol-rf2, Testosterone-, 13C,-Etheylnylestradiol IS peak area within 50 % of each analyte Testosterone-, Estradiol-rf3 Estron-d4, Estradiol-d3... 

In vivo studies in animals suggest that endosulfan may disrupt normal reproductive hormone levels in male animals, but that it is not an endocrine disrupter in females. Persistent depressed testicular testosterone was seen in male rats after intermediate duration oral exposures to endosulfan. In ovariectomized female rats, orally administered endosulfan did not induce normal development of female reproductive tissues, and in female mice and immature female rats, acute parenteral exposure to endosulfan did not affect several endocrine-related end points. In vitro studies have evaluated endosulfan for estrogen receptor (ER) and cytosolic protein binding affinity, ER-mediated reporter gene expression, estrogenic induction of cell proliferation, and alteration of relative abundance of active estradiol metabolites. Overall, in vitro evidence in favor of endosulfan estrogenicity indicates relatively weak potency compared to 17[3-estradiol. Apparently contradictory results were reported in different... 

Estrogens are bound to SHBG and progestins to CBG. SHBG binds estradiol about five times less avidly than it binds testosterone or DHT, while progesterone and cortisol have little affinity for this protein (Table 42-8). In contrast, progesterone and cortisol bind with nearly equal affinity to CBG, which in turn has little avidity for estradiol and even less for testosterone, DHT, or estrone. 

Testosterone and dihydrotestosterone bind to the intracellular androgen receptor, initiating a series of events similar to those described above for estradiol and progesterone, leading to growth, differentiation, and synthesis of a variety of enzymes and other functional proteins. 

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