Transfer of [3H]estradiol-17β and [3H]progesterone from conspecifics to cohabiting female mice

Estradiol-17β (E₂) and progesterone (P₄) play critical roles in female reproductive physiology and behavior. Given the sensitivity of females to exogenous sources of these steroids, we examined the presence of E₂ and P₄ in conspecifics' excretions and the transfer of excreted steroids between conspecifics. We paired individual adult female mice with a stimulus male or female conspecific given daily injections of [³H]E₂ or [³H]P₄. Following 48  h of direct interaction with the stimulus animal, we measured radioactivity in the uterus, ovaries, muscle, olfactory bulbs, mesencephalon and diencephalon (MC+DC), and cerebral cortex of the untreated female cohabitant. Radioactivity was significantly present in all tissues of female subjects after individual exposure to a stimulus male or female given [³H]E₂. In females exposed to males given [³H]P₄, radioactivity was significantly present in the uterus, ovaries, and muscle, but not in other tissues. In females exposed to stimulus females given [³H]P₄, radioactivity was significantly present in all tissues except the MC+DC. In mice directly administered [³H]steroids, greater radioactivity was found in the urine of females than of males. Among females directly administered [³H]steroids, greater radioactivity was found in urine of those given [³H]P4 than of those given [³H]E₂. When females were administered unlabeled E₂ before exposure to [³H]E₂-treated females, less radioactivity was detected in most tissues than was detected in the tissues of untreated females exposed to [³H]E₂-treated females. We suggest that steroid transfer among individuals has implications for the understanding of various forms of pheromonal activity.