Lack of effect of vaginal lavages and aliphatic acids on ejaculatory responses in rhesus monkeys: Behavioral and chemical analyses

Four behavioral experiments involving a total of 19 adult male and 27 adult spayed female rhesus monkeys failed to reveal significant sexual stimulatory properties of vaginal lavages obtained from estrogen-treated donor females when the material was applied to spayed nonestrogenized recipient females. However, all but one of the males copulated to ejaculation when paired with estrogenized females. Two of three males showed moderate increases in sexual behavior with recipients when the vaginal lavage tested was contaminated with 24-hr-old ejaculate. When purified aliphatic acids were applied to spayed nonestrogenized recepients, one of two males showed increased frequencies of mounting behavior, but intromissions and ejaculations were not displayed.Quantitative analyses of short chain aliphatic acids in vaginal lavages, the hypothesized active component, revealed that (a) spayed females had nondetectable levels of aliphatic acids; (b) daily estradiol benzoate treatment for 6–10 days (25 μg/day i.m.) induced detectable levels of acetic, propionic, and butyric acids; (c) exposure to estradiol for six months resulted in a fairly constant plateau of aliphatic acid concentrations; and (d) ejaculate from the male caused up to fivefold elevations in the aliphatic acid concentrations.Three intact females were studied throughout a menstrual cycle, and the peak values of aliphatic acids occurred in the luteal phase, several days after presumed ovulation. Three spayed females treated chronically with estradiol were given four daily injections of 5 mg progesterone, and the mean concentrations of aliphatic acids increased from 199.7 to 801.0 μg/ml. However, the endocrine conditions associated with maximum concentrations of aliphatic acids in either intact or spayed females are known from other studies to be associated with decreased likelihood of copulation.We conclude that for the majority of males studied, the application of vaginal lavages obtained from estrogenized donors did not significantly increase copulatory behavior with spayed, nonestrogenized recipient females. Moreover, the data from aliphatic acid determinations suggest that increases in concentrations of these substances are not always associated with facilitation of copulation, since the largest increases were found either (1) following copulation to ejaculation, (2) during the luteal phase in cycles free of copulation, or (3) following progesterone treatment of spayed, estrogenized females. Finally, comparison of our results with those from other laboratories suggests that the mechanism involved in positive effects may depend upon associative learning or upon extinction and disinhibition of sexual interest.