Chemical studies of hamster vaginal discharge: Male behavioral responses to a high molecular weight fraction require physical contact

This report describes the isolation and behavioral testing in normal male hamsters of a high molecular weight fraction (HMF) of vaginal discharge which accounts for much of the aphrodisiac activity in the discharge. The HMF encompasses a group of proteins which elute as a relatively narrow, major peak upon agarose gel filtration of estrous vaginal discharge. The crude fraction from gel filtration retains a variety of volatiles including sulfur-containing compounds which we have previously found to account for much of the initial attraction of males to the female but which do not, themselves, facilitate overt copulatory behavior. Procedures for markedly reducing the presence of such volatiles to yield the HMF are described. In behavioral assays using anesthetized males as surrogate females, scenting the hindquarters of the surrogates with the HMF elicits intense genital investigation by experimental males, although this effect on investigatory behavior is not as dramatic as that of the unfractionated vaginal discharge. Like the unfractionated discharge, the HMF significantly increases the incidence of intromission attempts toward scented surrogates. To assess whether physical contact with the HMF is required for behavioral activity, as would be expected if the active material is proteinaceous, series of preference tests were performed using vanillin as a competing stimulus under conditions in which physical contact with the stimuli either was possible or was prevented. The unfractionated discharge was preferred in both conditions, whereas significant preferences for the HMF were exhibited only if it could be contacted by the snout of experimental males. The active material in the HMF thus appears to be of extremely low volatility, at least prior to physical contact with it by the male.