Aromatization and the induction of male sexual behavior in male, female, and androgenized female hamsters

Eight weeks after gonadectomy male, female, and androgenized [10 μg testosterone propionate (TP), 24 hr after birth] female hamsters were given daily treatment with: 150 μg dihydrotestosterone (DHT), 5 μg estradiol benzoate (EB), 150 μg DHT + 5 μg EB, 150 μg DHT + 1 μg EB, 30 μg DHT + 5 μg EB, 30 μg DHT + 1 μg EB, or the oil vehicle. Treatment of castrated male hamsters with 5 μg EB fully restored mounting but relatively few of these animals intromitted and none ejaculated. Treatment with 150 μg DHT restored all components of male sexual behavior but only in a small proportion of the males. Combined treatment with EB and DHT restored mounts, intromissions, and ejaculations in the majority of the males. Although as little as 30 μg DHT + 1 μg EB restored the full complement of male behavior, the males which received 150 μg DHT + 5 μg EB or 150 μg DHT + 1 μg EB required fewer intromissions to achieve ejaculation than the males which received 30 μg DHT + either dose of EB. The response of the androgenized females was similar to that of the males except that the androgenized females had lower intromission rates and none ejaculated. Relatively few of the nonandrogenized females responded to EB and DHT treatment and those that did mounted only a few times each test. These results demonstrate that both EB and DHT can stimulate male sexual behavior in the hamster and that the sensitivity to EB and DHT for copulatory behavior is determined by early postnatal androgen exposure.     

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.     

Androgen- and estrogen-induced copulatory behavior and inhibition of luteinizing hormone (LH) secretion in the male rat

The purpose of the present investigation was to determine if estrogen, aromatizable androgen or nonaromatizable androgen is capable of (1) inducing copulatory behavior and (2) inhibiting the postcastration rise in plasma LH. Castrate male rats were injected daily with either 1 mg testosterone (T), androstenedione (A), dihydrotestosterone (DHT), or 25 μg estradiol benzoate (EB) or oil and tested weekly for masculine behavior and for lordosis behavior after 38 days of steroid treatment. On day 40 blood was collected for radioimmunoassay of plasma LH. At least 89% of the males treated with T, A, or EB and 55% of those treated with DHT displayed ejaculatory behavior whereas none of the oil-treated males showed male copulatory behavior. Only estrogen-treated males displayed lordosis behavior. T and to a lesser extent A treatment reduced high levels of plasma LH; however, DHT and EB further reduced plasma LH to undectable levels. The relative potency of the steroid effect in stimulating accessory sex tissues followed the order: DHT > T > A > EB = oil. Significant dissociation was observed between the effects of these steroids on peripheral morphology, negative feedback, and mating behavior. These results indicate that masculine behavior is facilitated to the greatest extent, although not exclusively, by centrally acting aromatizable androgen or estrogen, whereas under the present conditions only estrogen stimulates feminine behavior.     

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.     

Induction of male mating behavior in androgen-insensitive (tfm) and Normal (King-Holtzman) male rats: effect of testosterone propionate, estradiol benzoate, and dihydrotestosterone

Castrated androgen-insensitive rats exhibited mounting and intromission patterns in response to testosterone propionate (TP), estradiol benzoate (EB), or EB combined with dihydrotestosterone (DHT) treatment in adulthood. Treatment with DHT alone was ineffective in stimulating male mating behavior in the mutant rats. Since androgen-insensitive rats, like normal males, have the potential to show mounting behavior following hormone treatment in adulthood, the neural substrate underlying this behavior must be masculinized during development. The effectiveness of gonadal hormones in activating the entire copulatory sequence in castrated littermate males (King-Holtzman) was also examined. TP treatment induced mating behavior in the control rats. DHT also stimulated the complete copulatory pattern, although it was not as effective as TP. The administration of EB, however, did not induce ejaculation in control rats. These results do not support the hypothesis that the activation of male mating behavior by testosterone requires its metabolite estrogen (aromatization hypothesis).     

Effects of estradiol benzoate in combination with dihydrotestosterone on postejaculatory vocalization and refractory period in castrated male rats

The objective of this experiment was to compare the effects of estradiol ben-zoate (EB) treatment with those of testosterone propionate (TP) on the postejaculatory vocalization and refractory period in castrated dihydrotestosterone (DHT)-treated male rats. Twelve reliable maters were tested, castrated, and then treated with subcutaneous implants of DHT and daily injections of either 200 μg of TP (N = 6) or 200 μg of EB (N = 6). Testing continued weekly for 9 weeks with treatments interchanged after the fourth week. EB treatment resulted in: (1) a reduction in the number of males that vocalized, (2) a reduction in the duration of vocalization, and (3) the exhibition of extraordinarily abbreviated postejaculatory refractory periods by a few males. It was suggested that high doses of estradiol act to counter inhibitory processes during the refractory period.     

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.     

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.     

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.     

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.     

Hysterectomy-induced facilitation of lordosis behavior in the rat

The present study investigated the effect of hysterectomy on hormone-induced lordosis behavior. Lordosis quotients (LQ) were measured in hysterectomized-ovariectomized (HO) and ovariectomized-sham hysterectomized (OSH) rats after several treatments including either estradiol benzoate (EB) alone or EB plus progesterone (P) 44 hr later. Testing consisted of placing the females with sexually active males 48 hr after EB. In Experiment 1, HO animals treated with 5 μg/kg EB and 0.5 mg P had significantly higher LQs than OSH animals; groups treated with 10 μg/kg plus P were not different. Experiment 2 showed that a single injection of 50 μg/kg EB resulted in equally high levels of receptivity in both groups. The LQs of HO animals injected with 3 μg/kg for 4 days did not differ from those of OSH animals; however, the administration of 0.5 mg P 24 hr after the fourth EB injection resulted in significantly higher LQs in the HO group (Experiment 3). In Experiment 4, HO rats injected with 5 μg/kg EB and 0.1 mg P 44 hr later displayed higher levels of lordosis behavior than OSH animals. It was concluded that hysterectomy facilitated the lordosis behavior of ovariectomized rats injected with both EB and P and that the mechanism for this potentiation remains to be determined.     

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.     

Facilitation of female sexual behavior in male rats by septal lesions: an interaction with estrogen.

Although destruction of the septal region markedly facilitates the lordosis behavior of female rats in response to estrogen priming, comparable lesions were found to be ineffective in facilitating the lordotic behavior of estrogen primed male rats. Neither the age at the time of septal destruction nor castration influenced the lordosis behavior of males. However, if prepubertal castrated males were given subcutaneous ovarian grafts or injected daily with 2 μgm estradiol benzoate (EB) during the 30 day period following septal destruction, a prolonged facilitation of the activational effects of EB on lordosis behavior was observed. Male rats subjected to septal destruction alone, chronic exposure to EB alone, exposure to ovarian grafts for 30 days prior to septal destruction, or chronic treatment with EB started 6 mo after septal lesioning, failed to show an increase in behavioral responsiveness to estrogen. Thus, in order for septal lesions to facilitate lordosis behavior of male rats, exposure to EB or ovarian tissue must occur within an apparent critical period following septal destruction. Adult male rats were found to be more responsive to this interaction of septal lesions and EB exposure than pubertal animals. It is suggested that the prolonged facilitation of lordosis behavior which follows septal destruction and estrogen exposure in the male rat may be due to hormonal modifications of the recovery process following brain damage.     

Induction of sexual behavior in ovariectomized rhesus females with 19-hydroxytestosterone

Eight sexually experienced long-term ovariectomized female rhesus monkeys were given tests of sexual behavior following treatment with 19-hydroxytestosterone (19-OH-T, 1 mg/day for 13 days), and their performance was compared with that following treatment with estradiol benzoate (EB, 10 μg/day for 13 days). Each female was tested for 10 min with each of nine adult males. Blood samples were taken on the last day of treatment with EB, at the end of the intervening 3-month period of no treatment, and on the last day of treatment with 19-OH-T. Blood levels of testosterone and estradiol were quantified by radioimmunoassay. Mean rate of presenting at a distance (proceptive behavior) was significantly higher (P < 0.05) when they were treated with 19-OH-T, but the ratio of presents to male contacts (receptive behavior) was significantly higher (P <0.05) when they were treated with EB. All other components of female sexual behavior were the same. Males displayed fewer annoyance responses (rejecting jerk, P < 0.05) when the females were treated with 19-OH-T than when they were treated with EB. All other male responses occurred with the same frequencies under the two female treatment conditions. Injection of 19-OH-T and EB both resulted in plasma testosterone and estradiol levels higher than those found in the untreated condition. Testosterone levels did not differ under the two treatments (P > 0.05), but estradiol levels were higher under EB treatment than under 19-OH-T (P < 0.05). This study suggests that both testosterone and estradiol are essential for maximum sexual performance and that various components of sexual behavior may be differentially influenced by the ratio of testosterone to estradiol in plasma.     

Sexual differentiation of reproductive behavior in pigs: defeminizing effects of prepubertal estradiol

The present study sought to determine (1) whether estrogen by itself can defeminize the behavior of pigs during the late juvenile-early pubertal period, and (2) whether the progressive late defeminization reported for pigs is a true organizational effect, as opposed to an artifact of the time between castration and testing. Male pigs were castrated at 19-22 days or left intact and females were ovariectomized at 3 months. Additional males castrated at 19-22 days and females ovariectomized at 3 months were implanted with estradiol benzoate (EB) from 3 to 5.5 months. After castration of the previously intact males at the age of 5.5 months, all subjects were tested beginning at 6.5 months for proceptivity (choice of a male versus a female in a T-maze) and receptivity (immobilization to a mounting male) following an injection of EB. EB administered during development significantly defeminized proceptivity and receptivity in both sexes. The decrease in proceptivity was more pronounced in males than in females and was more pronounced than the decrease in receptivity, as if differentiation ends earlier for proceptivity than for receptivity; the decrease in receptivity was more pronounced in females. To see whether the capacity to display female-typical behavior is a function of time since castration, we castrated additional males at 4 months and tested for receptivity 9 days later following an injection of EB, then tested again with the other subjects at 6.5 months. The proceptivity and receptivity scores for males castrated at 4 months fell between those for intact males and males castrated at 3 weeks, and thus these animals were not completely defeminized. They were more receptive at 6.5 months than at 4 months, but the difference was not significant. These results indicate that in pigs estradiol defeminizes both receptive and proceptive behavior and that this defeminization can occur relatively late in development.     

Female lordosis pattern in the male rat induced by estrogen and progesterone: effect of interruption of the dorsal inputs to the preoptic area and hypothalamus.

Lordosis behavior was very rare in castrated male rats which had been pretreated with 50 mug estradiol benzoate (EB) for successive 2 days and 1 mg progesterone (P) 6-8 hr prior to testing on the third day. Only one out of 8 rats displayed lordosis in response to mounts by the sexually matured males. However, the occurrence of lordosis behavior was markedly increased in similarly treated castrated males in which the dorsal afferents to the preoptic area (POA) and hypothalamus were removed by the surgical cut. Twelve out of 19 rats of the group showed lordosis response. The incidence was less frequent in rats receiving sham deafferentation. These results suggest that the dorsal inputs to the POA and hypothalamus may exert a tonic inhibitory influence on the lordosis mediating system in the male rat.     

Testosterone implanted in the preoptic area of male Japanese quail must be aromatized to activate copulation

Intracranial implantation of minute pellets of gonadal steroids was combined with aromatase inhibitor treatment to determine if aromatization within the preoptic area (POA) is necessary for androgens to activate sexual behavior in the Japanese quail (Coturnix japonica). In this species, implantation of pellets of testosterone propionate (TP) or estradiol benzoate (EB) in the POA of castrated males restores male-typical copulatory behavior. In Experiment 1, adult male castrated quail were implanted intracranially with 200-micrograms pellets of equimolar mixtures of crystalline TP + cholesterol (CHOL), TP + 1,4,6-androstatriene-3,17-dione (ATD, an aromatase inhibitor), EB + ATD, or CHOL and behavior-tested with intact males and females. Copulation was stimulated by POA implants containing TP or EB (three of six CHOL + TP males and two of seven ATD + EB males copulated vs zero of four CHOL males), but copulation was not inhibited by combining ATD with TP (three of four ATD + TP males copulated). In Experiment 2, adult male castrated quail were injected systemically with ATD or oil for 6 days prior to and 14 days after intracranial implantation of 200-micrograms pellets containing the same amounts of TP or EB as in Experiment 1. The ATD injections completely blocked copulatory behavior in males with TP implants in the POA such that ATD/TP and Oil/TP mount frequencies differed significantly, but failed to block copulation in males with EB implants in the POA (proportions of males copulating were ATD/EB, 6/8; ATD/TP, 0/6; Oil/TP, 4/7). The cloacal foam gland, an androgen-sensitive secondary sex character, was unaffected by the dose of ATD used. We conclude that activation of copulatory behavior by TP implants in the POA is not due to nonspecific effects of high local testosterone concentrations but rather to aromatization. These results support the hypothesis that cells within the POA aromatize testosterone to estrogens, which directly stimulate the cellular processes leading to activation of male-typical copulatory behavior.     

Testosterone and estrogen differently effect Th1 and Th2 cytokine release following trauma-haemorrhage.

The object of the study was to determine whether male and female sex steroids produce divergent effects on Th1 and Th2 cytokine release following trauma-haemorrhage. Recent studies indicate that androgens are responsible for the depressed splenocyte Th1 cytokine release in males following trauma-haemorrhage. In contrast, female mice maintain their Th1 cytokine release capacity following trauma-haemorrhage. Nonetheless, the effect of male and female sex steroids on Th1 and Th2 cytokine release following trauma-haemorrhage remains unknown. Male C3H/HeN mice were castrated and treated with pellets containing either vehicle, 5alpha-dihydrotestosterone (DHT), 17beta-estradiol (estradiol), or a combination of both steroid hormones, for 14 days prior to soft-tissue trauma (i.e. laparotomy) and haemorrhagic shock (35+/-5 mmHg for 90 min followed by adequate fluid resuscitation) or sham operation. Untreated male and female mice, as well as DHT treated female mice, served as control groups. Twenty-four hours later the animals were sacrificed, plasma obtained and splenocytes harvested. Plasma DHT and estradiol levels in treated animals were comparable with intact male and female mice, respectively. A significant depression of splenocyte Th1 cytokines, i.e. IL-2, IFN-gamma, was observed in DHT treated castrated animals, DHT treated females, and untreated males following trauma-haemorrhage, as opposed to maintained Th1 cytokine release in estradiol treated and estradiol/DHT treated castrated animals and females. The release of the anti-inflammatory cytokine IL-10 was markedly increased in DHT treated mice and males subjected to trauma-haemorrhage compared to shams, but decreased in estrogen treated mice and females under such conditions. These results suggest that male and female sex steroids differentially affect the release of Th1 and Th2 cytokines following trauma-haemorrhage and should be further studied for their potential to modulate splenocyte function in trauma victims.     

Hormonal regulation of male reproductive behavior in the lizard Anolis sagrei: a test of the aromatization hypothesis

This study examined the hypothesis that aromatization of testosterone (T) to estradiol (E) is required to activate reproductive behavior in castrated male lizards (Anolis sagrei). Adult, reproductively active males were assigned to an intact control group or to one of four treatment groups. Treatment males were castrated and 1 week later three of the four castrated groups were implanted with subcutaneous pellets containing either 0.05 mg of E, 0.5 mg of T, or 0.5 mg of dihydrotestosterone (DHT). Two weeks after pellet implantation, males were tested with stimulus males, and 2 days later were tested with stimulus females. Behavioral tests were of 15-min duration and were videotaped. Significantly fewer E-treated castrates erected a crest in tests with stimulus males than did intact males. In tests with stimulus females, significantly fewer E-treated castrates displayed, neck-gripped, and intromitted than did intact males. Estradiol-treated castrates also showed significantly less display behavior than did intact males. However, aggressive and sexual behavior of DHT-treated castrates was not significantly different from that of intact males. The same was true for T-treated castrates with the exception that display behavior in tests with stimulus females was reduced compared to that of intact males. The results suggest that aromatization of T to E is not required for induction of androgen-dependent reproductive behavior in this lizard.     

Differential effects of testosterone metabolites in the neonatal period on open-field behavior and lordosis in the rat

Two experiments were done to compare the effects of neonatal exposure to testosterone and its major metabolites, dihydrotestosterone (DHT) and estradiol (E₂), on the development of sex differences in open-field behavior in the rat. In Experiment 1 female rats administered either testosterone propionate (TP), DHT, or estradiol benzoate (EB) were found as adults to have low activity scores, more typical of adult males, when compared to the high scores of oil-treated females. In Experiment 2 the adult open-field behavior of female rats treated neonatally with testosterone or the metabolites was compared to that of male rats treated from Day 1 to 10 of life with the aromatizing enzyme inhibitor, androst-1,4,6-triene-3,17-dione (ATD). These same animals were later tested for lordotic behavior after gonadectomy and priming with EB and progesterone. All male animals and female animals exposed neonatally to testosterone or to either of the metabolites had suppressed open-field activity scores compared to oil-treated females. However, the lordotic behavior of females exposed to DHT and of males exposed to ATD was not defeminized and was comparable to that of oil-treated females. These observations were discussed in terms of a role for the androgenic actions of testosterone in establishing sex differences in nonreproductive behavior in the rat.