Influence of sex hormone binding globulin and serum albumin on the conversion of androstenedione to testosterone by human erythrocytes

Sex hormone-binding globulin and male sexual development

The masculinization of the brain, reproductive tract and many other structures is critically dependent on the testicular hormone, testosterone (T). In many species, T circulates bound with high affinity to sex hormone-binding globulin (SHBG). This protein has a wide phylogenetic distribution and SHBG or SHBG-like proteins are produced by the liver, testes, placenta, brain and other tissues. SHBG activity is detectable during gestation and its expression is both stage- and tissue-dependent. Although SHBG binds circulating androgens, it is argued that the trapping of steroids in the circulation is not the principal function of this protein. The specific binding and uptake of SHBG by various tissues has been observed and suggests that SHBG may directly affect the delivery of androgen signals to target tissues. Effects of SHBG on androgen metabolism, tissue retention, cellular targeting, and action are reviewed. Evidence to date indicates that SHBG is able to enhance or inhibit the uptake of androgens in a cell- and tissue-specific manner. Future work will be necessary to demonstrate whether such actions of SHBG are important for normal male reproductive development.

Conversion of 11-ketoandrostenedione to 11-ketotestosterone by blood cells of six fish species

Blood cells from Baltic salmon, Salmo salar, three-spined stickleback, Gasterosteus aculeatus, eel pout, Zoarces viviparus, crucian carp, Carassius carassius, African catfish, Clarias gariepinus, and reedfish, Calamoichthys calabaricus, were incubated with tritiated 11 beta-hydroxyandrostenedione (OHA) or 11-ketoandrostenedione (OA). In all fish there was conversion of OA to 11-ketotestosterone (OT), indicating that 17 beta-hydroxysteroid dehydrogenase activity was present in the blood cells. On the other hand, OHA was not converted to 11 beta-hydroxytestosterone in any fish. The addition of serum to the incubates largely prevented the OA-OT conversion by salmon blood cells.

In vitro metabolism of steroid hormones in the liver and in blood cells of male rainbow trout (Salmo gairdneri Richardson)

Male rainbow trout show high plasma androgen levels beginning with the period of full spermatogenesis until the end of spermiation. The difficulties in explaining the steroid levels in regard to the concomitant changes of the plasma GTH concentrations prompted investigations into whether the steroid demand may be met in part by extragonadal steroid metabolism. The results of in vitro experiments with liver tissue fit into the concept of an interrenal-liver-gonad axis of androgen production, since increased amounts of C-19 steroids were detected in the media after incubation of hepatic tissue with cortisol. 17 beta-Hydroxysteroid dehydrogenase and hydroxysteroid glucuronyltransferase activities were shown to be associated with blood cells of mature males. The fact that unidentified products from incubations with 17 beta-estradiol, testosterone, and 17 alpha-hydroxyprogesterone were also found suggests that other steroid metabolizing enzymes are also associated with blood cells. The possibility is discussed that, assuming the blood cell activities are relevant in vivo, a production of potent androgens or the formation of water soluble steroid derivatives could proceed in the blood (e.g., 11-ketoandrostenedione----11-ketotestosterone; testosterone----testosterone glucuronide), possibly affecting the organism's steroid balance.

Administration of constant low doses of androgens to steers by silastic implant. Suppression of gonadotropins and peripheral conversion of androgens

Yearling Hereford calves approximately 300 kg in weight were castrated and assigned to one of six treatment groups receiving subcutaneous implants (3 implants, 0.5 cm diameter by 10 cm length, 10% steroid by weight) of either androstenedione (D); testosterone (T); 5 alpha-androstane-3 beta, 17 beta-diol (3 beta-diol); dihydrotestosterone (DHT); androsterone (A); or control (no steroid). Blood samples were obtained at half-hour intervals for eight hours one day prior to, and one week after, castration. The castration-induced elevation in FSH secretion was suppressed or modified by the DHT, T, and 3 beta-diol implants. LH levels were not significantly suppressed. The T implants elevated serum T concentrations; DHT implants elevated serum 5 alpha-androstane-3 alpha, 17 beta-diol (3 alpha-diol) and 3 beta-diol, but not DHT concentrations; 3 beta-diol implants elevated serum 3 beta-diol concentrations. The effects of D and A implants upon serum androgen concentrations were not statistically significant, although observations in vitro suggested an adequate release rate. These data imply that T and DHT, or metabolites of DHT, suppress FSH secretion and suggest that extensive peripheral androgen metabolism occurs.

Immunohistochemical detection of the sex steroid-binding plasma protein in human mammary carcinoma cells

A sex steroid-binding plasma protein-like antigen has been detected in human mammary carcinoma cells. A monospecific antiserum was used, and this protein was located mainly on the cytoplasmic membranes. These results are in agreement with a recent hypothesis according to which steroid hormones could be carried into cells by specific binding plasma proteins.

Peripheral aromatization as a risk factor for breast and endometrial cancer in postmenopausal women: a review

In menopause, estrogens are produced almost exclusively through peripheral aromatization of androgens, especially androstenedione. Obesity increases the production rate of estrogens by means of the same mechanism. In postmenopause, plasma levels of SHBG diminish significantly. Obesity even further decreases the levels of SHBG, thus increasing "free" E2 available to target tissues. The increase in circulating estrogenic activity in menopause, whether as a result of obesity or of ingestion of estrogens, implies a risk factor for endometrial and breast cancer not only because of the permissive and stimulating effects of estrogens but also due to the special circumstance that they may act on target tissues in the almost absolute absence of the "protecting effect" of progesterone. The modifications performed by obesity on the values of SHBG and circulating estrogens are reversible, since they tend to normalize with weight loss.

Immunochemical characterization and quantitation of human sex steroid binding plasma protein

The interest in the measurement of human sex steroid binding plasma protein (h-SBP) is now increasing since it allows the estimation of the free fraction of circulating hormones in plasma. Up to this date, this protein could only be determined by measuring the total binding capacity of serum for dihydrotestosterone (DHT). The purpose of the present work was to purify the protein, to prepare a rabbit monospecific antiserum and to develop an immunoelectrophoretic assay of h-SBP. The immunological assay is specific, accurate and sensitive. A good correlation with the radioligand assay was found. The h-SBP levels obtained by immunoelectrophoretic assay of different serum samples were 5.3 +/- 1.4 (SEM) mg/L in normal men and 13.4 +/- 2.6 (SEM) mg/L in normal women.