Ejaculatory Performance Research Articles

Peri-ovulatory synchronisation of behaviour in male and female rhesus monkeys

RHESUS monkeys, like many other primates, do not restrict their sexual activity to the ovulatory period, and copulation may occur at any time during the menstrual cycle1,2. Thus, in the laboratory, the male's ejaculatory frequency is generally highest near mid-cycle (although different pairs show different patterns of mounting and ejaculation3) while, in the wild, sexual activity seems to be more or less restricted to the middle part of the cycle4,5. It is difficult to judge the stage of the cycle in troops of feral rhesus monkeys, but during the period of maximum sexual activity females actively approach males and form temporary consort bonds which involve mutual grooming and frequent copulations6. To obtain an independent and objective measure of female sexual motivation, we have used an operant conditioning technique in which the female was required to press a lever for access to her male partner. This has made it possible to relate changes in female motivation precisely to changes in the circulating levels of ovarian hormones. We have also demonstrated a synchronisation and maximisation of female sexual motivation with male ejaculatory performance during the peri-ovulatory (fertile) period of the menstrual cycle.

Effects of Ejaculations By Males On the Sexual Invitations of Female Rhesus Monkeys (Macaca Mulatta)

The effects of ejaculation on female sexual invitations were examined in 6 pairs of adult rhesus monkeys of opposite sexes observed during 1 hr mating tests (552 tests), whereby each of 3 females was tested on alternate days with one of 2 male partners (6 males). Ovariectomized females were given subcutaneous silastic implants of testosterone to maintain female sexual motivation, and the sexual activity of males was altered by the administration and withdrawal of intravaginal oestrogen. Plasma hormone determinations confirmed that females remained under constantly high androgenic and low oestrogenic stimulation throughout the study. Comparison of the number of sexual invitations in pairs of successive tests showed that tests without ejaculation following those in which ejaculations occurred were associated with increased numbers of invitations; conversely, ejaculatory tests following non-ejaculatory tests were associated with decreased numbers of invitations. In contrast, there were no changes in pairs of tests with ejaculations in both tests or ejaculations in neither test. Data from sequences of 4 successive tests showed that where an ejaculatory test was followed by 3 non-ejaculatory tests, the increase in invitations during the latter was short-lived: by the third non-ejaculatory test invitations had declined to levels similar to those in the initial ejaculatory test. In contrast, no changes were observed during 3 successive ejaculatory tests following a test without ejaculation. It was therefore concluded that the occurrence of ejaculation in a test affected invitational behaviour in the next two non-ejaculatory tests. Changes in ejaculatory performance during blocks of 10 or more tests would therefore have no predictive value for changes in invitational behaviour unless the distribution of ejaculatory tests is taken into account; this was confirmed by withdrawing intravaginal oestrogen. As expected, a marked decline in mean numbers of ejaculations per test in 3 animal pairs was not associated with consistent or significant changes in the mean numbers of female sexual invitations per test. The circumstances under which changes in invitational behaviour may be used as an index for a hormone-dependent change in female sexual motivation, and the possible nature of the consummatory event for which invitations are appetitive behaviours, are discussed.

EFFECTS OF 17β-HYDROXY-4-ANDROSTEN-19-OL-3-ONE (19-HYDROXYTESTOSTERONE) AND 5α-ANDROSTAN-17β-OL-3-ONE (DIHYDROTESTOSTERONE) ON ASPECTS OF SEXUAL BEHAVIOUR IN CASTRATED MALE RATS

SUMMARY The ability of 19-hydroxytestosterone propionate (150 μg/day) to maintain sexual behaviour, accessory organ weights and the number of penile spines in experienced adult male rats in the 5 weeks after castration was compared with intact males and castrated animals receiving testosterone propionate (75 μg/day) or oil treatment. In a second experiment a group of male rats receiving dihydrotestosterone propionate (150 μg/day) was also included. 19-Hydroxytestosterone did not maintain ejaculatory performance but animals that ejaculated had refractory periods similar to those in intact and testosterone-treated groups. Dihydrotestosterone, however, slowed the rate of decline of ejaculatory performance but the refractory periods were comparable to those in castrated controls. The former action of dihydrotestosterone was attributed to its stimulatory effect on peripheral structures, especially the penile spines. 19-Hydroxytestosterone was shown to have no peripheral effect at doses up to 1800 μg every other day. The results are discussed in terms of a theory of testosterone action involving aromatization in the brain and 5α-reduction peripherally.

Contraceptive steroids and sexual activity.

Since rhesus monkeys have a true menstrual cycle of 28 days and sexual behavior of males is observed to change in response to the female cycle oral contraceptive steroids were administered to monkeys to measure sexual behavior objectively. 2 sterilized females were exposed to 2 males and the number of thrusts and ejaculations were recorded for 1 hour per pair 2-3 times per week. (Fewer thrusts indicate high sexual stimulation in these monkeys.) .05 mg mestranol and 1.0 mg ethinyl diacetate were injected daily in the females for 21 days followed by 6 days without treatment 6 months; then a sequential regimen of .05 mg mestranol for 11 days and .75 mg chlormadinone acetate for the next 10 days followed by 7 days without treatment was given for 6 months. Male ejaculatory capacity decreased progressively with the combined regimen. Number of thrusts to ejaculation increased accordingly. The sequential regimen decreased male ejaculatory performance to a lesser extent and this decrease was not progressive.