Serum dihydrotestosterone

By reducing serum levels of dihydrotestosterone, which is linked to the development of prostate cancer, it has been... 

Sub-type inhibition of the 5a-reductase enzyme Percent of inhibition of serum dihydrotestosterone level Percent of patients with reduction in serum dihyrotestosterone Time to peak onset of reduction in serum dihydrotestosterone level Percent inhibition of intraprostatic d i hy d rotestosterone Half-life... 

Rasmussen, L. E., Buss, C. O., Hess, D. L., and Schmidt, M. J. (1984). Testosterone and dihydrotestosterone concentrations in elephant serum and temporal gland secretions. Biology ofReproduction 30,352-362. 

D. The enzyme 5a-reductase catalyzes the formation of dihydrotestosterone from testosterone. In normal accessory sex gland tissues, such as the prostate, most of the direct androgen effect is due to dihydrotestosterone rather than testosterone. Thus when 5a-reductase is lacking, serum levels of testosterone may be normal or even slightly elevated with a hypotrophied prostate gland. 

B. Finasteride is a 5a-reductase inhibitor, which essentially makes dihydrotestosterone unavailable to the prostate but does not reduce serum testosterone levels. The decreased prostatic levels of dihydrotestosterone frequently result in a size regression of the prostate, while the relatively normal testosterone levels minimize a depressed libido. Flutamide and spironolactone exhibit antiandrogen effects by competing for the androgen receptor ketoconazole inhibits testosterone synthesis and stanozolol is an oral anabolic androgen preparation. 

Mechanism of Action An androgen hormone inhibitor that inhibits 5-alpha reductase, an intracellular enzyme that converts testosterone into dihydrotestosterone (DHT) in the prostate gland, resulting in a decreased serum DHT level. Therapeutic Effect Reduces size of the prostate gland. 

Cimetidine inhibits binding of dihydrotestosterone to androgen receptors, inhibits metabolism of estradiol, and increases serum prolactin levels. When used long-term or in high doses, it may cause gynecomastia or impotence in men and galactorrhea in women. These effects are specific to cimetidine and do not occur with the other H2 antagonists. 

A number of reproductive effects, including decreased fertility, damage to the gonads, and alterations in hormone levels, have been observed in male and female animals orally exposed to 2,3,7,8-TCDD. In male rats, a dose- and time-dependent reduction of serum testosterone and dihydrotestosterone levels was observed after acute oral exposure to 2,3,7,8-TCDD (Mebus et al. 1987 Moore et al. 1985, 1991). Furthermore, male rats had decreased weight of seminal vesicles following oral exposure to... 

In rats and rabbits orally administered 2.5,5, or 10 mg/ kg of the same tribulus extract daily for 8 weeks, an increase in dihydrotestosterone was observed in rabbits at the 5 and 10 mg/kg doses. In castrated rats orally administered 5.5 mg/kg of the tribulus extract daily for 8 weeks, an increase in serum testosterone levels was observed (Gauthaman and Ganesan 2008). 

Bovine serum albumin 3-(0-Carboxymethyl)-oximino-5a-dihydro-testosterone-bovine serum albumin conjugate 7-(0-Carboxymethyl)-oximino-5Q -dihydrotestosterone-bovine serum albumin conjugate... 

Carboxymethyl)-oximino-5o -dihydrotestosterone-bovine serum albumin conjugate Carcinoembryonic antigen... 

In this condition there is an impaired abihty to produce dihydrotestosterone (DHT), causing an increased serum ratio of testosterone DHT (Fig. 43.1). Because DHT is four times as potent as testosterone, genetic males with 5-ARD usually present as neonates with ambiguous genitalia and gender assignment is a major issue. 

Dutasteride is an analogue of testosterone, and it is a competitive, selective inhibitor of both reproductive (type 2) and skin and hepatic (type 1) 5a-reductase. This results in inhibition of the conversion of testosterone to dihydrotestosterone (DHT) and markedly suppresses serum DHT levels. 

RA and its isomers inhibit prostate epithelial cell growth [54]. Inhibition of RA metabolism raises plasma RA and inhibits relapse in the rat Dunning prostate cancer model [55]. RA decreases the concentrations of dihydrotestosterone, 3a-adiol and androsterone in serum, seems to cause a metabolic deviation away from the 5a-reductase path in liver [56], and causes a three-fold decrease in androgen receptor binding capacity [57]. Conversely, androgens affect the actions of retinoids by decreasing the mRNA of RARa approximately five-fold in prostate epithelia and 15 to 20-fold in seminal vesicles, while increasing it two-fold in kidney [58]. 

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