Testosterone radioactive

High concentrations of radioactivity were observed in body fat and livers of rats, mice, and squirrel monkeys given oral doses of 60 mg/kg " C-labeled chloroform (Brown et al. 1974a). The maximum levels of radioactivity in the blood appeared within 1 hour and were 3 pg equivalents chloroform/mL for mice and 10 pg equivalents chloroform/mL for monkeys, which represented -0.35 and 1%, respectively, of the total radioactivity. In monkeys, bile concentrations peaked within 6 hours. The distribution of radioactively labeled chloroform was studied in three strains of mice (Taylor et al. 1974). No strain-related differences were observed however, higher levels of radioactivity were found in the renal cortex of males and in the liver of females. The renal binding of radioactive metabolites may have been altered by variations in the testosterone levels as a result of hormonal pretreatment in females or castration in males. Sex-linked differences in chloroform distribution were not observed in rats or monkeys (Brown et al. 1974a). Chloroform accumulates in the adipose tissue of rats after oral exposure of intermediate duration (Pfaffenberger et al. 1980). 

Furthermore Tait and co-workers [322] pointed out the marked difference in the urinary and blood production rates of testosterone obtained in women after injection of radioactive testosterone. He concluded that steroids produced from dehydroepiandrosterone contribute little to the blood production rate of androstenedione and testosterone in normal subjects [403]. According to Tait [324], all the blood production rate of androstenedione in the female and testosterone in the male is due to the same secreted steroid, while the blood production rate of testosterone in the female and androstenedione in the male is due about one-half to the same secreted steroid and one-half to converted precursor. The normal male secretes a ratio of testosterone to androstenedione of about 10 1 and the normal female secretes a ratio of androstenedione to testosterone of about 25 1. 

Fig. 1. Separation of free and antibody-bound PH]testosterone on small columns (0.4 cm i.d. X 8 cm) of hydroxyapatite. [ H]Testosterone was incubated with antibody at 37° for 1 hr and applied to the column in 5 mM phosphate buffer. Radioactivity was eluted from the column by slowly increasing the concentration of eluting phosphate buffer. The concentration (C, in moles per liter) of the phosphate eluent was related to time (r, in minutes) by the equation C x 0.5 - 0.445e " . The flow rate was 0.1 ml/min, and 0.2 ml fractions were collected.

In the equilibrium dialysis/ultrafiltration method for determining free testosterone in blood, a sample is first equilibrated with radioactive testosterone. Free steroid is then separated from bound steroid by filtration through an anisotropic, hydrophilic ultrafiitration membrane. The driving force for ultrafiltration is provided by centrifugation at 1000 to 2000 xg. Filtrate containing free steroid collects in the filtrate cup, whereas protein-bound steroid remains above the filter. Radioactivity in the filtrate is a measure of... 

First, with a favorable partition coeflScient, 2-5 volumes of extractant secure such a good recovery with one extraction that the use of repetitive slightly smaller volumes gains only a marginal increase in recovery at very considerable expense of time and effort. As Peterson (P6, P6a) first pointed out, one extraction of an aqueous solution of cortisol with 5 volumes of dichloromethane should, and in fact does, secure a recovery of 98% of the cortisol in the aqueous sample. Because of a preference for an upper layer extractant, my own work has usually employed one extraction with 5-6 volumes of ethyl acetate-ether, 1 2 by volume, for this class of steroids. In their double-isotope method for plasma testosterone and 17-ketosteroids, Gandy and Peterson (Gla) used one extraction with 9 volumes of dichloromethane-ethyl acetate, 1 1 by volume. Calculation will quickly show that with a partition coeflBcient of 10 in favor of the extractant, two extractions with three volumes will secure a recovery of 99.8% as compared with 98.4% using one extraction with 6 volumes. While it can be shown that with a random error of performance of the extractions the double extraction procedure will reduce the overall error in the recovery value, this is trivial compared with the extra labor in the extraction of many samples. If an internal radioactive... 

Enzyme immunoassay (EIA) is emerging as possibly an effective alternative to RIA, avoiding the use of radioactive isotopes. A steroid-enzyme complex e.g. testosterone-glucoamylase ) competes with the free steroid for binding sites on... 

The mass balance approach was used to develop an in vivo animal model for skin penetration of topically applied dmgs in hairless rats (Simonsen et al., 2002). Two dmgs, C-sahcylic acid and C-butyl salicylate were topically applied for the assessment of the model. Rapid and differentiated percutaneous absorption of both compounds was indicated by urinary excretion data. Total mass balance on the applied radioactivity was performed, and 90% recovery was achieved. Carver and Riviere (1989) conducted an extensive mass balance study with " C-labeled xeno-biotics after topical and intravenous administration to pigs. These authors reported that dermal absorption of C-benzoic acid, caffeine, malathion, parathion, progesterone, and testosterone was 25.7, 11.8, 5.2, 6.7, 16.2, and 8.8%, respectively, following topical administration to pigs. 

Although cholesterol may serve as a precursor of steroid hormones, investigators still debate whether or not cholesterol is a required or the only intermediate. Other compounds formed from squalene may serve as precursors of steroid hormones. The slow transfer of radioactivity from cholesterol to testosterone in testes slices obtained from animals stimulated by chorionic hormones indicates that intermediates other than cholesterol participate in steroid hormone biosynthesis. Whereas chorionic hormones markedly stimulate the incorporation of acetate into cholesterol, the specific activity of testosterone is not markedly increased. 

Vingler, P., Filthuth, H., Bague, A., Pruche, F., and Kermici, M. (1993). Direct quantitative digital autoradiography of testosterone metabolites in the pilosebaceous unit an environmentally advantageous trace radioactive technology. Steroids 58 429-438. 

Testosterone sulfate does not seem to be hydrolyzed in the organism, but its direct metabolites have not been identified, as only 3.5% of the radioactivity was found in urine after radioactive testosterone sulfate administration. Unlike dehydroepiandrosterone sulfate, testosterone sulfate is not transformed by indirect metabolism into estrogens during pregnancy (Dray, 1963). 

Comparisons of in vitro and in vivo release data for radiolabeled testosterone from poly(caprolactone) capsules are presented in Figs. 19 and 20. Prior to implantation the capsules were conditioned in water for 19 days until the initial decline in release rate had leveled off. Amounts of drug released in vivo were determined by summing the radioactivity in urine and feces (3 or 4 day pools). After about two months the capsules were excised and drug release under in vitro conditions was followed for an additional month. 

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