Characterization of a [3H]methyltrienolone (R1881) binding protein in rat liver cytosol

The binding of radiolabelled methyltrienolone 17 beta-hydroxy-17 alpha-methyl-estra-4,9,11-trien-3-one (R1881) to adult male rat liver cytosol has been characterized in the presence of Na-molybdate to stabilize steroid-hormone receptors, and triamcinolone acetonide to block progestin receptors. Using sucrose density gradient analysis, male liver cytosol contains a [3H] R1881 macromolecular complex which sediments in the 8-9S region. 8S binding of R1881 to male rat serum, female liver cytosol or cytosol from a tfm rat cannot be demonstrated. Further metabolism of [3H] R1881 following 20h incubation with male rat liver cytosol was excluded: In the 8S region 97% of [3H] R1881 was recovered by thin layer chromatography. Characteristics of this [3H] R1881-8S binding protein include high affinity (Kd = 2.3 +/- 41 nM) and low binding capacity (18.8 +/- 3.3 fmol/mg cytosol protein), precipitability in 0-33% ammonium sulfate, and translocation to isolated nuclei following in vivo R1881 treatment. Whereas, the cytosol R1881-receptor is competed for by dihydrotestosterone, testosterone, and estradiol, [3H] estradiol binding in the 8S region is not competitive with androgens but does compete with diethylstilbestrol. The nuclear androgen binding site has a Kd = 2.8 nM for [3H] R1881, and is androgen specific (testosterone greater than 5 alpha-dihydrotestosterone greater than estradiol greater than progesterone greater than cyproterone acetate greater than diethylstilbestrol greater than dexamethasone greater than triamcinolone). Since a number of liver proteins including the drug and steroid metabolizing enzymes are, in part, influenced by the sex-hormone milieu, the presence of a specific androgen receptor in male rat liver may provide valuable insight into the regulation of these proteins.     

Up-regulation of androgen receptor binding in male rat fat pad adipose precursor cells exposed to testosterone: study in a whole cell assay system

Binding of androgens to adipocytes has previously been evaluated using cytosol fractions without taking into account nuclear binding, although the latter is suggested to be close to the physiological site of action. In the present study, performed in differentiated fat pad adipose precursor cells, we describe a simple, reliable and reproducible androgen binding assay in a system with intact cells. Tritiated and unlabeled methyltrienolone (R1881) were used to define specific and unspecific androgen binding. Triamcinolone acetonide was added to prevent the binding of R1881 to other types of receptors. Differentiated adipose precursor cells contain a homogeneous class of high affinity androgen binding sites, and binding is saturable and reversible. Binding apparently occurs at one site, with a Kd in the range of physiological androgen concentration (about 4 nM). Competition studies indicate that the receptor is specific for R1881, testosterone and dihydrotestosterone, which have approximately the same affinity, while progesterone, estradiol and dexamethasone show much lower affinity. Androgen binding was markedly enhanced after cellular exposure to R1881 and testosterone but not dihydrotestosterone, and this increase was dependent on protein synthesis, suggesting the formation of new receptors by these androgens. In conclusion, fully differentiated adipocytes contain a specific, high affinity receptor, the density of which is dependent on androgens.     

Binding of methyltrienolone to various androgen-dependent and androgen-responsive tissues in four animal species.

Comparative sucrose gradient studies of the in vitro binding of dihydrotestosterone (DHT) and of a synthetic androgen, methyltrienolone (R 1881), have been done with the cytosols of various tissues of the rat, mouse, cock and man. With rat prostate cytosol, the amount of R 1881 and DHT binding in the 8-9S region of the gradient was found to be comparable. Specific 8-9S peaks of R 1881 were also found in rat levator ani/bulbocavernosus and skeletal muscles and in the mouse kidney. Only 4-5S peaks could be demonstrated in the cock's comb while DHT under the same conditions showed both 8-9S and 4-5S binding. Binding of R 1881 to the cytosol of the hyperplastic prostate was polydispersed, and showed evidence of the presence of aggregates. Evidence was also found that R 1881 could bind to the progesterone receptor in rat uterus. Our study supports the theory that in a given species the androgen receptors are similar if not identical in all the tissues. The synthetic androgen R 1881 appears to be a useful tool for androgen receptor studies in various animal species provided that the tissue under study contains no progesterone receptor.     

A comparative study of the selectivity and efficiency of target tissue uptake of five tritium-labeled androgens in the rat

A comparative study of the tissue distribution of five tritium-labeled androgens was done in rats to determine the efficiency and selectivity of their uptake by target tissue. Testosterone (T), 5 alpha-dihydrotestosterone (DHT), 19-nortestosterone (nor-T), mibolerone (Mib) and methyltrienolone (R1881) all showed selective uptake by the ventral prostate in one-day castrated rats (250 g) that was 61-90% displaceable by co-injection of an excess of unlabeled steroid. The greatest uptake was with R1881 (0.69% injected dose per gram prostate tissue (%ID/g) at 1 h), and Mib (0.56% ID/g); the other three showed lower uptake (approx. 0.4% ID/g). The target tissue activity remained high for all compounds up to 4 h after injection, and at 2-4 h the prostate to blood ratio for Mib and R1881 exceeded 10 and 20, respectively. The uptake efficiency and selectivity of these five androgens appear to be related to their affinity for the androgen receptor and their resistance to metabolism. Mib and R1881 have substantial affinity for other steroid receptors, which might account for some of their prostate uptake. However, co-administration of triamcinolone acetonide, which has high affinity for progesterone and corticosteroid receptors but not for the androgen receptor, failed to block their uptake significantly, whereas co-administration of DHT, the most selective ligand for the androgen receptor, blocked their uptake as completely as the unlabeled tracer itself. The prostate uptake of Mib and R1881 in intact animals was significantly lower than in castrated animals, but treatment of the intact animals with diethylstilbestrol restored their uptake nearly to the level seen in castrated animals. These uptake patterns are consistent with earlier studies of in vivo androgen uptake and with known changes in androgen receptor content and occupancy as a result of castration or diethylstilbestrol treatment. They further suggest that high affinity androgens labeled with suitable radionuclides--particularly derivatives of mibolerone (Mib) or methyltrienolone (R1881)--may be effective receptor-based imaging agents for androgen target tissues and tumors, even when patients are already receiving hormonal therapy.     

Molecular and hormone-binding properties of a partially purified preparation of androgen receptors from the liver of male rats

Liver cytosol of mature male rats was found to contain androgen receptors (AR). These AR were purified 7--10-fold, and their molecular and hormone-binding properties were investigated. It was found that the AR molecules have a sedimentation coefficient of 9.3 +/- 0.15 and 4.7 +/- 0.11 S, Stokes radius of 6.5 +/- 0.25 and 3.2 +/- 0.08 nm, Mr of 263000 and 65700 Da and friction coefficient ratio of 1.55 and 1.22 for low and high ionic strength media, respectively. The values of rate constants of [3H]methyltrienolone (R1881) association with AR and for the dissociation of the complexes formed are equal to (0.66 +/- 0.29). .10(5) M-1 s-1 and to (0.68 +/- 0.08).10(-5) s-1, respectively, whereas those of equilibrium association constant--to (1.4 +/- 0.3).10(9) M-1 at 0-4 degrees C. It was shown that R1881, 5 alpha-dihydrotestosterone and testosterone strongly compete with 3H-R1881 for the binding with AR (as can be judged from the relative competitive activity of 35 nonlabeled hormonal agents); 19-nortestosterone and delta1-testosterone are more weak, whereas 5 alpha-androstandiols, some hydroxy derivatives of testosterone, cyproterone acetate, estradiol and progesterone are moderate competitors. Other natural testosterone, estradiol and progesterone metabolites as well as corticosteroids do not compete or weakly compete with 3H-R1881 for the binding to AR. It is concluded that the properties of AR are similar to those of classical type AR and that they can intermediate most of the direct effects of androgens on the liver.     

Purification and characterization of the androgen receptor from rat ventral prostate

The androgen receptor has been purified from rat ventral prostate cytosol by a combination of differential DNA-Sepharose 4B chromatography and testosterone 17 beta-hemisuccinyl-3,3'-diaminodipropylamine-Sepharose 4B affinity chromatography. Approximately 8 micrograms of protein was obtained from 38 g of rat ventral prostate, with a yield of 24%. The receptor was purified approximately 120 000-fold. Silver nitrate staining of a sodium dodecyl sulfate (NaDodSO4)-polyacrylamide gel revealed a major polypeptide band migrating at 86 000 daltons. Affinity labeling of a partially purified receptor preparation with either 17-hydroxy-17 alpha-[3H]methyl-4,9,11-estratrien-3-one or 17 beta-hydroxy-[1,2,4,5,6,7,16,17-3H8]-5 alpha-androstan-3-one 17-(2-bromoacetate) produced a major band of radioactivity migrating at 86 000 daltons on a NaDodSO4 gel. Under nondenaturing conditions, a Mr of 85 000 was determined by gel filtration (42 A) and sucrose gradient sedimentation analysis (4.5 S). The purified receptor had an isoelectric point of 6.3 [3H]-4,5 alpha-Dihydrotestosterone, bound to the purified receptor, was displaced with 4,5 alpha-dihydrotestosterone greater than testosterone much greater than progesterone greater than 5 alpha-androstane-3 alpha, 17 beta-diol greater than 17 beta-estradiol greater than cortisol. A number of physicochemical properties of the purified receptor were similar to those of the receptor in crude cytosol.     

Autologous down-regulation of androgen receptor messenger ribonucleic acid

Autoregulation of androgen receptor (AR) mRNA was investigated using Northern blot analysis with AR cDNA fragments as probes. The amount of AR mRNA increased 2- to 10-fold with androgen withdrawal and decreased below control levels after androgen stimulation in rat ventral prostate, coagulating gland, epididymis, seminal vesicle, kidney, and brain, and in a human prostate cancer cell line, LNCaP. In rat ventral prostate, AR mRNA increased 2- to 3-fold within 24 h after castration and remained elevated for 4 days. Treatment with testosterone propionate beginning 24 h after castration reduced ventral prostate AR mRNA 4-fold within 8 h of androgen replacement. Administration of estradiol 24 h after castration had no significant effect on prostatic AR mRNA. Androgens, including testosterone and the synthetic androgen methyltrienolone (R1881), or the antiandrogen cyproterone acetate down-regulated AR mRNA in vitro in LNCaP cells, whereas estradiol was without effect. Administration of testosterone propionate to rats with androgen insensitivity did not decrease AR mRNA. Down-regulation of AR mRNA by androgen is therefore a receptor-mediated process which occurs in vivo in rat tissues that differ in androgen responsiveness and in cultured human prostate cells.     

Binding of [3H] methyltrienolone (R 1881) in rat prostate and human benign prostatic hypertrophy (BPH).

Methyltrienolone (R 1881 - 17beta-hydroxy-17alpha-methyl-estra-4, 9, 11-trien-3-one) binding to rat ventral prostate cytosol has a specificity typical of an androgen receptor. In human benign prostatic hypertrophy (BPH) tissue, the specificity of [3H] R 1881 binding is different from that measured in rat prostate: progesterone and R 5020 (17, 21-dimethyl-19-nor-4, 9-pregnadiene-3, 20-dione) being more potent while 19-nortestosterone is less potent competitor. Moreover, the synthetic progestin [3H] R 5020 binds to BPH tissue with a similar specificity. These data suggest the presence of progestin binding components or of an atypical androgen receptor in human BPH cytosol.     

Characterization of androgen receptors after photoaffinity labelling with [3H]methyltrienolone (R1881)

The synthetic androgen 17 beta-hydroxy-17 alpha-[3H]methyl-4,9,11-estratrien-3-one (R1881) has been used as photoaffinity label to characterize androgen receptors in rat prostate, in a human transplantable prostatic adenocarcinoma (PC-82) and in calf uterus. Androgen receptors preparations were partially purified either via differential chromatography on 2',5'-ADP-Sepharose (rat prostate), via anion exchange fast protein liquid chromatography (rat prostate and PC-82) or via DNA-cellulose chromatography (calf uterus). Purification factors obtained with the three different methods were: 245, 75 and 40 respectively. Photolabelling of receptor preparations was performed via irradiation with a high pressure mercury lamp either before or after partial purification. Polyacrylamide gel electrophoresis under denaturing conditions showed that the DNA-binding form of the androgen receptor in calf uterus cytosol is a protein with a molecular mass of approx 95 kD. The covalent attachment of [3H]R1881 to the 95 kD protein could be completely suppressed by a 200-fold molar excess of dihydrotestosterone. In rat prostate cytosol an androgen receptor with a molecular mass of approx 50 kD could be photoaffinity labelled with R1881. A similar size was found for the androgen receptor in the human prostatic adenocarcinoma. Our results show that photoaffinity labelling of androgen receptors with [3H]R1881 as ligand can be applied for characterization of partial purified androgen receptor preparations.     

Histochemical localization of estrogen and progesterone receptors: evaluation of a method

A histochemical method for the detection of estrogen (ER) and progesterone (PR) receptors in human endometrium, using estrogen and progesterone derivatives linked to fluorochrome-labeled bovine serum albumin (E2-BSA-fluorescein isothiocyanate (FITC) and progesterone-BSA-tetramethylrhodamine isothiocyanate (TMRITC], has been evaluated. The fluorochrome-labeled steroids were bound to the cytoplasm--preferably in glandular epithelial cells but to a lesser extent also to stromal cells. The steroid specificity of the observed binding was studied by preincubating the sections with a series of unlabled steroids and nonsteroidal, hormonally active compounds (estradiol-17 beta, diethylstilbestrol, tamoxifen, 5 alpha-dihydrotestosterone and R 1881 for ER and ORG 2058, R 5020, dexamethasone, cortisol and 5 alpha-dihydrotestosterone for PR). The inhibition studies indicated that E2-BSA-FITC and progesterone-BSA-TMRITC bind to ER and PR in human endometrium with a reasonable degree of specificity. The method was reproducible and various procedural steps were tested, showing satisfactory technical stability. The method is applicable to small tissue samples, and is a valuable complement to quantitative biochemical receptor assays, as it localizes the receptors in tissue slices.     

Effect of 16 beta-ethyl-17 beta-hydroxy-4-estren-3-one (TSAA-291) on the binding of promegestone (R5020) and methyltrienolone (R1881) to hyperplastic and neoplastic human prostate

The effect of a synthetic steroidal compound TSAA-291 (16 beta-ethyl-17 beta-hydroxy-4-estren-3-one) on the binding of methyltrienolone (R1881) and promegestone (R5020) to hyperplastic and neoplastic human prostate was investigated. TSAA-291 inhibits both androgen and progestogen binding to hyperplastic and neoplastic human prostate. Glycerol density gradient analysis revealed that the inhibition of promegestone (R5020) binding by TSAA-291 was significantly greater than that of methyltrienolone (R1881) in both hyperplastic and neoplastic human prostate. The nature of the inhibition was competitive as determined by Scatchard analysis and double reciprocal plots. Comparison of the Ki values for the inhibition by TSAA-291 of R1881 binding (3.2 X 10(-7) M) and of R5020 binding (2.0 X 10(-8) M) suggests that TSAA-291 binds to progesterone receptor with a greater affinity than to androgen receptor. Our results suggest that the effectiveness of the drug in the treatment of benign hyperplasia might be due not only to its anti-androgenic properties but also due to its ability to inhibit progesterone receptor.     

Metabolism of estradiol and estrone in organ cultures of dorsolateral and ventral prostate of untreated and sex hormone-implanted rats.

Since dorsolateral but not ventral prostate undergoes estrogen-induced dysplasia in the androgen-supported Noble rat in 16 weeks, we studied estrogen metabolism by these tissues from untreated and sex hormone-implanted animals. We incubated 8.5 nM [6,7-3H]-labeled estradiol (E2) and estrone (E1) for 21 hours in serum-free, prostate-lobe cultures and 8.5 nM [2-3H]E2 with explants from untreated rats and animals treated with testosterone, 5 alpha-dihydrotestosterone, or E2 plus testosterone. Untreated rat ventral prostate metabolized 3.7 times as much E2 to E1 as dorsolateral prostate, whereas the latter tissue converted 2.5 times as much E1 to E2 as the former. After dorsolateral prostate culture with 8.5 nM [6,7-3H]-labeled E2 or E1, 0.6 M KCl-extracted, Sephadex G25-excluded nuclear protein bound preponderantly E2, whereas the counterpart nuclear protein fraction from ventral prostate explants incubated with E2 bound substrate and E1 almost equally. The combination sex hormone treatment decreased E2 metabolism and increased its uptake by the dysplastic dorsolateral prostate. Implantation of 5 alpha-dihydrotestosterone, but not of testosterone, also decreased E2 metabolism to E1 by dorsolateral prostate cultures. Treatments with E2 plus testosterone and with 5 alpha-dihydrotestosterone changed E2 uptake/E1 retention in dorsolateral prostate explants from 2.4 to 7.4 and 8.5, respectively. C-2 tritium release marking the 2,3-catechol estrogen pathway was greater for ventral than dorsolateral prostate, but was unaffected by the sex hormone treatments.(ABSTRACT TRUNCATED AT 250 WORDS)     

Androgen binding in peripheral tissues of fetal rhesus macaques: effects of androgen metabolism in liver

In rhesus monkeys sexual differentiation of the brain and reproductive tract (RT) is androgen-dependent. Presumably these effects are mediated through the androgen receptor (AR). The AR has not been characterized in fetal tissues such as liver, kidney, heart, spinal cord and RT in this species. We characterized AR binding using [3H]R1881 as the ligand in cytosols from tissues obtained on days 100-138 of gestation. Scatchard analyses revealed a single, saturable, high affinity AR in liver, kidney, heart, spinal cord and RT. The apparent dissociation constant (Kd) ranged from 0.52 to 0.85 nM with no significant tissue differences. The number of AR (Bmax; fmol/mg protein) differed significantly (P less than 0.01) between tissues (liver greater than RT much greater than kidney greater than or equal to heart greater than or equal to spinal cord). Radioinert testosterone (T) and 5 alpha-dihydrotestosterone (DHT) but not androstenedione, progesterone, estradiol-17 beta, estrone or cortisol in a 50-fold molar excess inhibited [3H]R1881 binding to the AR in spinal cord, heart, kidney and RT. However, in liver only DHT competed significantly (P less than 0.01) for binding. This difference in binding of DHT vs T in the liver was further investigated by incubating liver and kidney cytosols with [3H]DHT and [3H]T at 4 degrees C. We identified the metabolic products by mobility on Sephadex LH-20 columns and reverse isotope dilution. Liver cytosols metabolized [3H]DHT to 5 alpha-androstane- 3 alpha,17 beta-diol (5 alpha-diol) and [3H]T to 5 beta-androstane-3 alpha, 17 beta-diol (5 beta-diol) at 4 degrees C. In contrast, kidney cytosols metabolized [3H]DHT while [3H]T remained unchanged. Further studies indicated that a 50-fold molar excess of 5 alpha-diol inhibited the binding of [3H]R1881 in liver cytosols by about 50% whereas the same molar concentration of 5 beta-diol had no effect. These data demonstrate the presence of AR in peripheral tissues of fetal rhesus monkeys and suggest that androgens through their receptors may affect development of these tissues. Liver cytosols are capable of metabolizing T and DHT at 4 degrees C at conditions similar to those used for measuring cytosolic AR. However, T and DHT are metabolized differently, generating different isomers which have different affinities for hepatic AR.     

Quantification of cytosolic steroid receptors in secretory and non-secretory epithelial cells of the canine prostate

Radiolabelled methyltrienolone, dihydrotestosterone and estradiol were used as ligands to identify and quantify androgen and estrogen receptors in freshly dispersed cells from the canine prostate. Soluble extracts (cytosols) were obtained from secretory and non-secretory epithelial cells separated on the basis of their density in Percoll gradients. For both cell types, as well as for the whole prostate, Scatchard plot analyses were linear and showed a single class of high affinity binding sites: Kd values of 3.6 +/- 2.2 X 10(-9) M and 3.0 +/- 1.2 X 10(-10) M were measured for the androgen and estrogen receptors, respectively. The number of binding sites for the cytosolic androgen receptor, expressed per mg of protein or per mg of DNA, was 2.4- to 6.7-fold higher in the non-secretory cells compared to the secretory cells. However, these two cell types contained a similar number of specific sites for the estrogens. The specificities of the androgen and estrogen receptors were shown to be identical for the two cell types: the binding of [3H]R1881 was strongly inhibited by unlabelled R1881, 5 alpha-androstane-3 alpha, 17 beta-diol and dihydrotestosterone, while 5 alpha-androstane-3 beta, 17 beta-diol, estradiol and estrone did not displace bound R1881. The addition of triamcinolone acetonide did not alter the binding of R1881 in extracts of either cell type or in the whole prostate. The binding of [3H]estradiol to the estrogen receptor was highly specific since a strong displacement was only observed with estradiol (83%).     

Partial characterization of the androgen receptor of the newborn rat gubernaculum

Androgen receptors were measured by sucrose density gradient techniques in low-salt and high-salt extracts of gubernaculum, urogenital sinus, and bladder from 3- to 5-day-old male rats. Specific 5 alpha-[3H] dihydrotestosterone binding was present in both the low-salt and high-salt extracts of gubernacular tissue. The total amount of receptor in gubernaculum was approximately one-fifth the total amount of androgen binding measured in the urogenital sinus (119 fmol/g tissue in gubernaculum vs. 562 fmol/g tissue in urogenital sinus). No androgen receptor was detected in bladder. A 10-fold excess of nonradioactive 5 alpha-dihydrotestosterone competed well for 5 mM 5 alpha-[3H]-dihydrotestosterone binding, whereas 10-fold molar excesses of testosterone, estradiol, and progesterone were ineffective. These results suggest that the gubernaculum may be a target tissue for androgens.     

MCF-7; a human breast cancer cell line with estrogen, androgen, progesterone, and glucocorticoid receptors.

We have identified receptors for glucocorticoids, progestins, and androgens in a human breast tumor cell line (MCF-7) known to have estrogen receptor. Sucrose density gradients show that MCF-7 cytosol contains approximately 100 fm/mg protein estradiol (E2-3H) receptor, more than 300 fm/mg protein progesterone receptor (measured with R5020-3H), about 40 fm/mg protein 5alpha-dihydrotestosterone (5alpha-DHT-3H) receptor, and 800 fm/mg glucocorticoid receptor (measured with dexamethasone-3H). Dissociation constants obtained by Scatchard analyses were approximately 0.6 x 10(-10)M (E2), 1 x 10(-9)M (R5020), 2.8 x 10(-10)M (5alpha-DHT) and 8 x 10(-9)M (dexamethasone). No cross competition was found for estrogen receptor, but progestins competed for androgen and glucocorticoid binding. The androgen, but not the glucocorticoid, partially competed for R5020 binding to progesterone receptor. This first demonstration of 4 classes of steroid receptors in human breast cancer means that MCF-7 may be an excellent in vitro model for studying the mechanism of tumor response to endocrine therapy as well as the complex relationships between binding and biological actions of these hormones.     

Inhibition of growth and induction of apoptosis by androgens of a variant of LNCaP cell line

Here are described the effects of androgens, and other molecules known to bind to androgen receptors (AR), on MOP cells established from the human prostate cancer cell line LNCaP. MOP cells contained AR: 100 000 binding sites/cell, K_D for 5 dihydrotestosterone (DHT) 0.5 nM, size 110 kDa. The AR gene has the same repetition polymorphism in exon 1 and the T876A mutation in exon 8 as LNCaP. The proliferation of MOP cells in culture was repressed by the synthetic androgen 17β-hydroxy-17-methyl-estra-4,9,11-trien-3-one (R 1881), the antiandrogen cyproterone acetate (CYPA), estradiol (E2), progesterone and the synthetic progestin promegestone: 17,21 dimethyl-19 nor-4,9 pregnandiene-3,20 dione (R 5020). The number of cells recovered after 7 days decreased to ≈40% of controls. ED₇₀s ranged between 50 pM for R 1881 to 50 nM for E2 and CYPA. Treatment with R 1881 decreased [³H]thymidine incorporation into DNA and increased dramatically the doubling time. R 1881, CYPA and E2 blocked the cell cycle between G1 and S phases and they induced apototosis as demonstrated by the increase of blebs on the plasma membrane, nuclear fragmentation, TdT-mediated dUTP nick end-labeling (TUNEL)-positive cells and internucleosomal DNA breaks. In athymic nude mice, testosterone enanthate prevented the growth of MOP tumors and, when tumors did develop, brought about regression. However, the tumors did not regress completely and finally escaped treatment. In conclusion, a variant of the LNCaP cell line has been established. With these cells it was possible to confirm that androgens paradoxically repress the growth of some prostate cancer cells both in culture and in vivo. In addition it is demonstrated in culture but not in vivo, for the first time to the authors’ knowledge, that a synthetic androgen is able to induce apoptosis of cells established from human prostate carcinoma.     

A comparison of the effects of methyltrienolone (R 1881) and 5 alpha-dihydrotestosterone on sexual behavior of castrated male rats.

The synthetic steroid methyltrienolone (R 1881) binds specifically with high affinity to intracellular androgen receptors and is not metabolized to androstanediol. Administration of R 1881 (1 mg/day) to castrated male rats facilitated intromission in significantly more animals than did 5α-dihydrotestosterone (DHT) (1 mg/day); however, the percentage of animals ejaculating and the pattern of behavior displayed were equivalent in the two groups. Combined administration of estradiol benzoate (EB) (2 μg/day) plus either R 1881 or DHT further facilitated males' sexual performance to levels previously seen in castrated male rats of the same strain when given testosterone propionate (TP). The results suggest that conversion of DHT to 3α- or 3β-androstanediol neither detracts from nor contributes to its ability to activate sexual behavior in the male rat.