Influence of progesterone on sexual behavior in castrated male Rhesus monkeys treated with testosterone

Long-term effects of castration on the skeleton of male rhesus monkeys (Macaca mulatta)

While osteopenia (OPE) and osteoporosis (OPO) have been studied in various species of aging nonhuman primates and extensively in ovariectomized rhesus and cynomolgus macaques, there is virtually no information on the effects of castration on the skeleton of male nonhuman primates. Most information on castrated male primates comes from a few studies on the skeletons of eunuchs. This report used a subset of the Caribbean Primate Research Center's (CPRC) Cayo Santiago (CS) rhesus macaque skeletal collection to qualitatively and quantitatively compare the bone mineral density (BMD) of castrated and age-matched intact males and, thereby, determine the long-term effects of castration (orchidectomy) on bone. Lumbar vertebrae, femora, and crania were evaluated using dual-energy X-ray absorptiometry (DEXA or DXA) and digital radiography augmented, when fresh tissues were available, with autoradiography and histology. Results confirmed physical examinations of long bones that castration causes changes in the skeleton of male rhesus macaques similar to those found in eunuchs, including OPE and OPO of the vertebrae and femora, thinning of the skull, and vertebral fractures and kyphosis of the spine more severe than that caused by normal aging alone. Also like eunuchs, some castrated CS male rhesus monkeys had a longer life span than intact males or females. Based on these results and the effects of castration on other tissues and organs of eunuchs, on behavior, hormone profiles and possibly on cognition and visual perception of human and nonhuman primates, and other mammals, castrated male rhesus macaques should be used with caution for laboratory studies and should be considered a separate category from intact males. Despite these caveats, the castrated male rhesus macaque should make an excellent animal model in which to test hormone replacement therapies for boys and men orchidectomized for testicular and prostate cancer.

Effects of progesterone on the sexual behavior of castrated, testosterone-treated male cynomolgus monkeys (Macaca fascicularis)

In male cynomolgus monkeys the synthetic progestin, medroxyprogesterone acetate (MPA), decreases testosterone (T) levels and sexual behavior, binds to progestin receptors in brain, and reduces by about 70% the uptake of [3H]androgens by both brain and genital tract tissues. To examine the behavioral effects of progesterone (P) itself, eight castrated, T-treated males were each tested twice weekly with an estrogenized female before, during, and after they were treated with two SC Silastic P implants. Data from six 4-week treatment periods were analyzed to facilitate comparisons with our previous data using MPA: i) baseline, ii) weeks 4-7 of P treatment, iii) weeks 8-11 of P treatment, iv) weeks 1-4 after P implants were removed, v) weeks 5-8 after P withdrawal, and finally vi) weeks 9-12 after P withdrawal (384 1 h behavior tests). Weekly blood samples (N = 192) were analyzed by radioimmunoassay to determine plasma levels of both T and P. P treatment, which resulted in high plasma P levels (about 44 ng/ml), produced decrements in measures of male sexual behavior and motivation that were both qualitatively and quantitatively similar to those produced by MPA treatment but, unlike MPA, P did not decrease plasma T levels or change them in any way (about 850 ng/100 ml throughout). The findings suggest that P implants may be preferable to weekly MPA injections in the treatment of male sex offenders because they require less patient compliance and may not have MPA's troubling side effects.

Behavioral responses to Depo-Provera, Fadrozole, and estradiol in castrated, testosterone-treated cynomolgus monkeys (Macaca fascicularis): the involvement of progestin receptors

Sexual motivation and behavior decreased in male cynomolgus monkeys given either Depo-Provera (medroxyprogesterone acetate, MPA), which reduces androgen uptake by brain, or the nonsteroidal aromatase inhibitor, Fadrozole, which virtually eliminates the conversion of testosterone (T) to estradiol (E2) in brain. This suggested that both unchanged T and E2 are important for the control of male primate sexual behavior, but combined treatment with MPA and Fadrozole did not have the anticipated summatory effects in intact males: the behavioral decrements when MPA-treated males were given Fadrozole were about half those observed when Fadrozole was given alone. The present study tested the hypothesis that Fadrozole suppressed the behavioral effects of MPA by preventing the induction by E2 of progestin receptors in the brain to which MPA binds. Eight castrated, T-treated males were each tested with an estrogenized female i) during baseline, ii) during MPA treatment, iii) during treatment with MPA and Fadrozole together, and iv) with E2 treatment added to condition (iii) (256 1-h behavior tests). All dosages were those used in previous studies. Sexual motivation, as reflected in mounting attempts and mounting attempt latencies, was further diminished by E2 treatment in males receiving both MPA and Fadrozole, but ejaculatory activity was not changed. Immunocytochemistry demonstrated that the distributions of progestin and androgen receptors were little affected by MPA treatment, and that progestin receptor immunoreactivity was almost completely abolished in the brains of males receiving both MPA and Fadrozole but present in those receiving additional E2 treatment, findings that supported the hypothesis.

Ethopharmacological studies on the effects of antihormones on rodent agonistic behavior with especial emphasis on progesterone

The effects of a range of antiandrogens and antiestrogens on conflict behaviors in laboratory rats and mice are reassessed in the light of recent studies applying ethophamacological analyses (recording the full spectrum of behaviors) to such investigations. It is argued that any antihostility properties of the antiandrogen cyproterone acetate are largely a consequence of indirect actions on odor communication, whereas antiestrogens (e.g., tamoxifen and CI 680) seem to have more fundamental motivational effects in addition to communicatory actions. A detailed example of the approach is provided in which progesterone (which can be antiandrogenic) is given to rats paired in different ways. The type of pairing has a very substantial effect on the actions seen after treatment, and the ethopharmacological approach generates a better picture of antihormone effect than traditional psychopharmacological tests.

Progesterone, estradiol, testosterone and dihydrotestosterone: effects on rate of extinction of a conditioned taste aversion in rats

An investigation was made to determine why the prolonged rate of extinction of a conditioned taste aversion induced by testosterone is diminished when the ovarian system is intact. In the first experiment, 36 gonadectomized female rats received injections of progesterone, testosterone propionate (TP), progesterone plus TP, or sesame oil. Progesterone did not reduce the slow extinction rate induced by TP. In a second experiment, 36 gonadectomized female rats received injections of estradiol dipropionate (EP), TP, EP plus TP, or sesame oil. Estradiol dipropionate reduced the effectiveness of TP in prolonging the extinction rate. These same results (the ineffectiveness of progesterone and the effectiveness of EP in blocking TP-induced slow extinction) were also observed in male rats in a third experiment. Dihydrotestosterone, as well as testosterone, has been shown to prolong extinction: hence, in a fourth experiment 30 gonadectomized female rats received injections of EP, TP, dihydrotestosterone propionate (DHTP), EP plus DHTP, or sesame oil. Estradiol dipropionate reduced the DHTP-induced slow extinction. All the above data are consistent with the hypothesis that it is estradiol from the ovaries that diminishes the effect of testosterone on the rate of extinction of a conditioned taste aversion in intact females.