Sexual behavior in male rats treated with estrogen in combination with dihydrotestosterone

Male rats castrated at 30 days of age were treated with estradiol benzoate (dose range: 0.05–50 μg EB for 26 days) and dihydrotestosterone (1 mg DHT for 36 days) as adults. The combined EB and DHT treatments resulted in display of male sexual behavior which did not differ from the behavior shown by intact untreated males or castrated, testosterone propionate (1 mg TP for 26 days) treated males. EB alone or DHT alone were relatively ineffective in activating male behavior in castrated males.     

Sexual incentive motivation in male rats requires both androgens and estrogens

In Experiment 1 castrated male rats were implanted with a Silastic capsule containing either E or cholesterol (CHOL) 35 days after castration. They were then tested for sexual incentive motivation and copulatory behaviors every 5th day for 3 weeks. None of the treatments affected sexual incentive motivation. After the last test, all subjects were implanted with DHT-containing Silastic capsules, and tests continued for another 3 weeks. While E + DHT enhanced sexual incentive motivation and copulatory behavior, DHT alone failed to do so. In Experiment 2 the aromatase inhibitor fadrozole (F) was combined with testosterone (T). T restored all behaviors to the level seen in intact rats, and F significantly reduced these effects. In fact, T + F was not different from DHT. T and DHT restored the weight of the prostate and seminal vesicles to levels close to those of intact rats. In Experiment 3 a lower dose of E was employed. Also this dose of E failed to affect sexual incentive motivation while E + DHT restored it to the level of intact animals. Castration enhanced the serum concentrations of LH and FSH. E alone caused a marked reduction, and E + DHT brought both gonadotropins back to the level of intact animals. It was concluded that the doses of E and DHT employed in these experiments were within or close to the physiological range, and that such doses of E completely fail to enhance sexual incentive motivation in castrated animals. DHT has small or no effects. It appears that sexual incentive motivation and copulation require simultaneous stimulation of androgen and estrogen receptors.     

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.     

Homotypical sexual behavior in gonadectomized female and male rats treated with 5α-19-hydroxytestosterone: Comparison with related androgens

Ovariectomized female rats were treated in turn over several weeks with estradiol benzoate (EB), testosterone (T), 19-hydroxytestosterone (19HT), dihydrotestosterone (DHT) and 5α-19-hydroxytestosterone (5α19HT). EB was given as a single dose, the androgens were given over 3 days, and progesterone (P) was given 48 hr after the last injection. Each week, rats were tested for lordosis behavior 4–6 hr after P. High levels of receptivity were seen after EB + P, 19HT + P and T + P. Rats treated with DHT + P or 5α19HT + P were unreceptive. Four groups of castrated male rats were treated with T, 19HT, DHT and 5α19HT for 4 weeks starting from castration. In weekly sexual behavior tests, only T and 19HT maintained normal copulatory performance throughout the experiment. 19HT and 5α19HT had negligible effects on peripheral androgen target organs. The failure of 5α19HT to stimulate sexual behavior in rats of either sex supports the view that this steroid does not undergo central aromatization.     

Effects of chronically elevated intake of sweet solutions on sexual behavior of male rats

Three experiments were conducted on the sexual behavior of gonadally intact and castrated male Sabra rats. Half of the animals drank water during the course of the experiment and half were offered sweet solutions, the assumption being that sweet gustatory stimulation elevates the level of central endogenous opioid peptides in rats. The effects on sexual behavior of the following drugs were explored: the opiate receptor blocker naloxone (5 mg/kg, sc), the serotonin precursor 5-hydroxytryptophan (5-HTP) (20 mg/kg, sc), the serotonin antagonist methysergide (1 mg/kg, sc), and naloxone in combination with methysergide. Naloxone, whether administered alone or in combination with methysergide, impaired sexual performance in castrated male rats, and in gonadally intact rats maintained on sweet solutions. Methysergide elevated sexual behavior in all groups, whereas 5-HTP tended to suppress such behavior. The results support the hypothesis that endogenous opiates play a role in the expression of male sexual behavior in rats. While subtle in intact animals this role may become crucial following the disruption of sex hormone supply. Serotonergic influence on male sexual behavior is inhibitory.     

Synergistic actions of estrogen and androgen on the sexual behavior of the castrated male rabbit.

Daily injections of 2.5 mg dihydrotestosterone (DHT) for 30 days induced sexual behavior in 19% of piepuberally and 62% of postpuberally castrated New Zealand white male rabbits. Combined treatment of 2.5 mgm DHT plus 5 μgm of estradiol benzoate (EB) activated sexual behavior in 100 and 85% of prepuberally and postpuberally castrated rabbits respectively. Moreover, subjects (Ss) receiving DHT + EB displayed sexual activity in a significantly higher percentage of tests and presented a higher frequency of mounts and intromissions than those Ss receiving only DHT. The results demonstrate that estrogen synergizes with androgen (DHT) to stimulate sexual behavior in the male rabbit.     

An androgen-dependent pilosebaceous tumor spontaneously developed in the Japanese house musk shrew Suncus murinus

Following administration of [3H]testosterone to castrated male Japanese house musk shrews (Suncus murinus), radioactive metabolites were detected in sidegland nuclei and the major one of them was dihydrotestosterone (DHT). The androgen binding capacity of the cytoplasmic fraction of sideglands was measured in vitro by the use of [3H]R1881 as a ligand. The binding showed a high affinity for R1881 (Kd = 6.2 X 10(-10) M) and a low capacity (Bmax = 22 fmol/mg protein). Sucrose density gradient centrifugation brought about a peak of [3H]R1881 in the 7S region in low ionic strength buffer. Their characteristics as described above are consistent with those of other androgen target organs. A cutaneous pilosebaceous tumor, which spontaneously developed on the sidegland of old male S. murinus, was transplanted to nude athymic mice. It grew in males only and failed to grow in females and castrated males. A specific androgen binding was found in this tumor (Kd = 7.8 X 10(-10) M, Bmax = 100 fmol/mg protein). Therefore, this transplantable pilosebaceous tumor is androgen-dependent and can be utilized as a new suitable model in the study of the mechanism of androgen on tumor development.     

Dihydrotestosterone activates male mating behavior in castrated King—Holtzman rats

Having previously found that King-Holtzman rats respond behaviorally to dihydrotestosterone (DHT), this strain was used to compare the effectiveness of DHT and dihydrotestosterone propionate (DHTP) in maintaining and reinstating copulatory behavior. The 5α-reduced androgens were capable of stimulating mating behavior in these castrated male rats. DHT and DHTP were equally effective in maintaining ejaculatory behavior, whereas DHT was slightly more potent behaviorally than DHTP in restoring mating responses. It was found that as little as 200 μg hormone/day restored ejaculatory behavior in 78% of the DHT-treated and 50% of the DHTP-treated rats. In both the maintenance and restoration paradigms, the mating performance of the DHT(P) treated males declined over time. The present data suggest that the conversion of androgen to estrogen may not be critical for the activation of male mating behavior.     

A single injection of 17β-estradiol facilitates sexual behavior in castrated male mice

Sexual behavior was assessed in castrated adult CD-1 male mice given exogenous steroids under various treatment regimens. Castrated mice maintained on 20 μg testosterone (T) daily for 1 week, but given 250 μg testosterone propionate (TP) on the day of testing showed higher levels of copulatory activity than intact mice or the males receiving an additional dose of 20 μg T on the test day, although plasma testosterone levels were not different at the time of behavioral testing. Castrated males given 50, 125, or 250 μg TP for 1 week including the day of testing showed higher levels of sexual behavior than males receiving the same doses of TP only once, on the test day. A single injection of 17β-estradiol (E₂) completely restored the male copulatory pattern, including ejaculation, in castrated mice under every condition examined. Testosterone and dihydrotestosterone (DHT) were less effective than E₂, as was the combination of E₂ and DHT. The relative efficacy of a single dose of T, DHT, and E₂ plus DHT was dependent upon factors such as the delay between steroid administration and testing, as well as whether or not the castrated mice received androgen replacement prior to testing. Estradiol benzoate (E₂B) was not capable of restoring sexual behavior in castrated mice in this study. The comparison of results obtained with TP, T, E₂, and E₂B suggests that an appreciable, but not necessarily sustained, elevation of E₂ levels in the brain may be critical in the facilitation of male copulatory behavior in mice.     

Évaluation des effets prosexuels des extraits de Bridelia ferruginea chez le rat mâle naïf

The stem barks and the leaves from Bridelia ferruginea (BF, Euphorbiaceae), a medicinal plant, are used in traditional medicine for the treatment of several ailments including male impotency. The present study was aimed at investigating the effects of the dried stem bark of BF on the sexual behaviour of normal and castrated sexually inexperienced male Wistar rats. Animals were orally administered with 100 mg/kg of either the aqueous or the ethanol extracts of BF whilst the neutral control group received in the same way 10 ml/kg of distilled water. The positive control group was treated with a subcutaneous injection of testosterone propionate (20 mg/kg/day/3days) prior to the experiment. The sexual behaviour of all rats was monitored on days 0, 1 and 7 by measuring frequencies of penile erection, mount, intromission and ejaculation. In a separate group of normal sexually inexperienced rats, the pro-sexual effects induced by a single dose of the aqueous extract (100 mg/kg) were measured after pre-treatment with either haloperidol (10 mg/kg), atropine (10 mg/kg) or L-omega-nitro-arginine methyl ester (Lω-NAME, 10 mg/kg). Results obtained showed a significant influence of the duration of treatment on the frequencies of penile erection, mount and intromission of both normal and castrated rats. An increase in all sexual performance parameters was observed when compared to respective controls. The intromission frequency of normal animals was significantly increased (P < 0.05–0.01) on day 1 of treatment and the effect was more expressed in rats receiving the aqueous extract. In castrated animals, a statistical increase was noticed on day 7 for rats treated with testosterone. The sexual effects induced by the aqueous extract of BF were completely abolished after pre-treatment of rats with atropine or haloperidol while pre-administration of Lω-NAME did not produce any significant effects. Flavonoids and sterols revealed in the aqueous and ethanolic extracts from the barks of BF may account for the enhancement of sexual activity in naive rats which could be expressed through dopaminergic and/or cholinergic receptor(s). Results of this work also give value to the traditional use of the plant for the improvement of male sexual behaviour.     

Inhibition of testosterone-induced sexual behavior in the castrated male rat by aromatase blockers

The effect of some aromatase inhibitors (aminoglutethimide, 1,4,6-androstatrien-3, 17-dione, and 4-hydroxy-androstenedione) on testosterone propionate (TP)-induced copulatory behavior was tested in sexually inexperienced castrated male rats. A single injection of 6 mg of TP induced mounting in 48% and ejaculatory pattern in 19% of the rats within 120 hr. Treatment with the aromatase inhibitors (injections every 12 hr for 108 hr) suppressed ejaculation in all but one rat and significantly reduced the number of rats mounting and intromitting. Concurrent administration of estradiol benzoate (EB, 1 or 3 μg every 12 hr) prevented the inhibitory effect of aromatase blockers. No inhibitory effect of the aromatization blockers was observed in rats in which sexual behavior was induced by dihydrotestosterone (1 mg/day) and EB (2.5 μg/day) for 20 days. The results support the concept that aromatization is an essential step for the induction of male sexual behavior by androgen in the rat.     

Sexual responses of the male rat medial preoptic area and medial amygdala to estrogen II: site specific effects of selective estrogenic drugs

In the medial preoptic area (MPO) and medial amygdala (MEA), estradiol (E(2)) aromatized from testosterone (T) may act via either estrogen receptor (ER) α or ERβ to mediate mating in male rats. We tested the hypothesis that, in the MPO, ERα exclusively mediates sexual responses to E(2) by monitoring mating in four groups of castrated male rats administered dihydrotestosterone (DHT) subcutaneously and MPO implants delivering either: cholesterol, E(2), propyl pyrazole triol (PPT, ERα-agonist) or diarylpropionitrile (DPN, ER β-agonist); a fifth group of intact males served as DPN toxicity control, receiving DPN MPO implants. In a follow-up study, either 1-methyl-4-phenyl pyridinium (MPP, ERα-antagonist) or blank MPO cannulae were implanted in castrated male rats receiving T subcutaneously, whereas intact MPP toxicity controls received MPP MEA implants. PPT or E(2) MPO implants maintained mating, but cholesterol or DPN MPO implants did not. Moreover, MPP MPO implants interfered with T reinstatement of mating suggesting that, in the MPO, ERα is necessary and sufficient for mating in androgen-maintained male rats and ERβ is not sufficient. Because it is unknown which ER subtype(s) mediate sexual responses of the MEA to E(2), we examined mating following MEA implants of cholesterol, E(2), PPT or DPN in four groups of castrated male rats administered DHT subcutaneously. E(2) MEA implants maintained mounting but mating was significantly decreased in groups receiving PPT, DPN or cholesterol MEA implants suggesting that, unlike the MPO where ERα alone is essential, sexual responses of the MEA to E(2) require simultaneous interactions among multiple ER subtypes.     

Testicular 3 alpha-hydroxysteroid oxidoreductase activity in the developing male rat.

In the testes, 17β-hydroxy-5α-androstan-3-one (dihydrotestosterone, DHT) is converted to 5α-androstane-3α,17β-diol (3α-diol) by the enzyme 3α-hydroxysteroid oxidoreductase (3α-HSO). This steroid has been shown to possess biological activity in the male rat. The secretion of 3α-diol is much greater in the prepubertal animal than in the adult. This study is designed to quantitate the activity of 3α-HSO in the cytosol fraction of testes from male rats throughout sexual development. Following homogenizatlon of whole testes, the 105,000 × g supernatant or cytosol fraction was incubated with ³H DHT and varying concentrations of unlabelled DHT in the presence of 0.25μm NADPH. The incubation was carried out at 34°C for 10 min at a pH of 7.4. The K_m of 3α-HSO in testicular cytosol was calculated to be 1.25μM. The specific activity of testicular cytosol 3α-HSO, expressed as pmoles of 3α-diol converted from DHT per min per mg testicular cytosol protein, was high in young rats from 10 to 22 days of age, and was followed by a decline between day 22 and 37, with activity remaining low throughout adulthood. Total testicular cytosol activity of 3α-HSO, expressed as nmoles of 3α-diol converted from DHT per min per pair of testes, gradually increased from day 10 to day 60 and remained high in the adult rat. In the post-pubertal period, a possible lack of available substrate, DHT, or possible endogenous testicular regulatory mechanisms acting on 3α-HSO activity might account for the actual decrease in 3α-diol concentration in the blood and testes of mature rats.     

Effects of estrone, estradiol and estriol combined with dihydrotestosterone on mounting and lordosis behavior in castrated male rats

Prepuberally castrated male rats were injected with estrone (1 or 5 μg), estradiol (1 or 5 μg) or estriol (1, 5, or 25 μg) either alone or in combination with dihydrotestosterone, (0.5 mg). Each of these steroids, when given alone, had no or only weak stimulatory effects on male sexual behavior. When combined with dihydrotestosterone all estrogens stimulated full copulatory behavior, the order of potency being estradiol, estrone, and estriol. Lordosis behavior in response to male mounting or manual stimulation was facilitated by all estrogens. All estrogens caused a slight weight increase of the seminal vesicles, ventral prostate and glans penis.     

Lordosis behavior in castrated male rats treated with estradiol benzoate or testosterone propionate in combination with an estrogen antagonist, MER-25, and in intact male rats

Lordosis behavior could be elicited by manual stimulation in castrated male rats after treatment with estradiol benzoate (15 μg for 10 days) or testosterone propionate (1 or 3 mg for 10 days). The effect was antagonized by treatment with the estrogen antagonist MER-25 (10mg for 10 days). Prolonged treatment with testosterone propionate (1 mg for 26 days) resulted in display of male (nine of ten rats) as well as female (seven of ten rats) sexual behavior. Eleven of 32 intact male rats (age 120 days) and 22 of 37 other intact males (age 75 days) displayed lordosis in response to manual stimulation without hormonal treatment. Seven intact males which showed lordosis without hormone treatment were injected with MER-25 (10 mg/day × 10 days) and lordosis was abolished in six cases. The results suggest that estrogen is involved in the regulation of lordosis behavior in TP-treated and intact male rats.     

A single injection of 17 beta-estradiol facilitates sexual behavior in castrated male mice

Sexual behavior was assessed in castrated adult CD-1 male mice given exogenous steroids under various treatment regimens. Castrated mice maintained on 20 μg testosterone (T) daily for 1 week, but given 250 μg testosterone propionate (TP) on the day of testing showed higher levels of copulatory activity than intact mice or the males receiving an additional dose of 20 μg T on the test day, although plasma testosterone levels were not different at the time of behavioral testing. Castrated males given 50, 125, or 250 μg TP for 1 week including the day of testing showed higher levels of sexual behavior than males receiving the same doses of TP only once, on the test day. A single injection of 17β-estradiol (E₂) completely restored the male copulatory pattern, including ejaculation, in castrated mice under every condition examined. Testosterone and dihydrotestosterone (DHT) were less effective than E₂, as was the combination of E₂ and DHT. The relative efficacy of a single dose of T, DHT, and E₂ plus DHT was dependent upon factors such as the delay between steroid administration and testing, as well as whether or not the castrated mice received androgen replacement prior to testing. Estradiol benzoate (E₂B) was not capable of restoring sexual behavior in castrated mice in this study. The comparison of results obtained with TP, T, E₂, and E₂B suggests that an appreciable, but not necessarily sustained, elevation of E₂ levels in the brain may be critical in the facilitation of male copulatory behavior in mice.     

Mounting behavior and lordosis behavior in castrated male rats treated with testosterone propionate, or with estradiol benzoate or dihydrotestosterone in combination with testosterone propinonate.

Treatment of prepuberally castrated male rats with testosterone propionate (TP, 50, 200, 500, or 1000 μg for 30 days) in adulthood stimulated the display of both mounting behavior and lordosis behavior. No correlation between mounting and lordosis behavior could be detected at any TP dose level. Treatment of prepuberally castrated male rats with either 1 μg estradiol benzoate (EB) or 500 μg dihydrotestosterone (DHT) for 60 days stimulated the display of mounting behavior in three of eight and four of eight rats, respectively. Treatment with 200 μg TP for the last 30 days of rats receiving either EB or DHT for 60 days resulted in an abrupt onset on mounting behavior as compared to rats treated with oil for 60 days. These results show additive effects of EB or DHT and TP upon mounting behavior by male rats and are interpreted as a support for the suggestion that testosterone to estrogen as well as testosterone to DHT conversion may be involved in the mechanism whereby testosterone activates the mounting behavior of castrated rats.     

Effect of prenatal stress and gonadal hormone condition on depressive behaviors of female and male rats

Whether prenatal stress (PNS) and gonadal hormones may influence depressive behavior of rats in the forced swim test was investigated. In Experiment I, adult diestrous female rats had increased immobility, which is indicative of depression, but did not show any significant difference in the duration of struggling compared to intact adult males. In Experiment 2, the behavior of adult intact, castrated, or castrated dihydrotestosterone (DHT)- or estrogen (E2)-replaced offspring of dams that were restrained under lights for 45 min on gestational day 18 (PNS) or were not subjected to gestational stress (non-PNS, control condition) were compared. There were no effects of PNS, but DHT and E2 produced anti-depressant effects on behavior of male rats. Castration decreased struggling and increased immobility compared to intact rats. DHT or E2 replacement was able to partially reinstate struggling and immobility behavior but not to levels of intact males. In Experiment 3, behavior of PNS or control rats that were in proestrus or were ovariectomized and DHT, E2, or vehicle-replaced were compared. Ovariectomy decreased struggling and increased immobility compared to that of proestrous rats. E2 or DHT to control females increased anti-depressant struggling behavior compared to ovariectomized control or PNS rats administered vehicle, which demonstrated greater duration of struggling than did E2-primed, PNS rats. E2 or DHT administration decreased immobility of PNS and control females. These findings suggest that E2 and DHT have some anti-depressant effects but that modest PNS may alter E2's ability to alleviate some depressive behavior in female, but not male rats.     

Differential effect of testosterone and dihydrotestosterone on the sexual behavior of prepuberally castrated male rabbits

The effect of testosterone propionate (Tp) and dihydrotestosterone propionate (DHTp) at doses of 1, 3 and 9 mg daily for 30 days on the copulatory behavior of prepuberally castrated male New Zealand white rabbits was studied. Tp was significantly more effective than DHTp in eliciting copulatory behavior at each dose level tested. Three milligrams Tp was the minimal dose required to elicit mounting consistently. DHTp at the high dose level (9 mg) only elicited sexual activity comparable to that observed with the low dose of Tp (1 mg). The results suggest that T does not need to be reduced to DHT to stimulate sexual behavior in the male rabbit.     

Castration inhibits exercise-induced accumulation of Hsp70 in male rodent hearts

Intense exercise leads to accumulation of the inducible member of the 70-kDa family of heat shock proteins, Hsp70, in male, but not female, hearts. Estrogen is at least partially responsible for this difference. Because androgen receptors are expressed in the heart and castration leads to decreases in calcium regulatory proteins and altered cardiac function, testosterone (T) or its metabolites could also be involved. We hypothesized that removal of endogenous T production through castration would reduce cardiac Hsp70 accumulation after an acute exercise bout, whereas castrated animals supplemented with 5alpha-dihydrotestosterone (DHT) would show the intact male response. Fifty-four 8-wk-old male Sprague-Dawley rats were divided into intact, castrated, or castrated + DHT groups (n = 18/group). At 11 wk of age, 12 animals in each group undertook a 60-min bout of treadmill running at 30 m/min (2% incline) while the remaining 6 in each group remained sedentary. At 30 min or 24 h after exercise (n = 6/time point), blood and hearts were harvested for analysis. Serum T was undetectable in castrated and DHT-treated castrated rats, whereas serum DHT was significantly reduced in castrated animals only (approximately 60% reduction) (P < 0.05). Although there were no differences in constitutive levels of Hsp70 protein, exercise significantly increased cardiac hsp70 mRNA and protein in intact and DHT-supplemented rats, but not in castrated animals (P < 0.05). To examine whether castration eliminated the ability to respond to stress, another six intact and six castrated animals were subjected to a 15-min period of hyperthermia (core temperature raised to 42 degrees C) and killed 24 h later. As opposed to exercise, castrated animals subjected to heat shock exhibited increases in Hsp70 above nonshocked (i.e., sedentary) animals, similarly to intact males (P < 0.05). These data suggest that androgens, in addition to estrogen, play a role in the sexual dimorphism observed in the stress response to exercise but not heat shock.