Estradiol-17β (E2) plays critical roles in female maturation, sexual receptivity, ovulation and fertility. In many mammals, contact with males can similarly affect these female parameters, whereas male excretions contain significant quantities of E2. We administered radiolabeled estradiol ([3H]E2) to male mice in doses representing a small fraction of their endogenous E2. These males were paired with sexually receptive females, and radioactivity was traced into the females’ systems. In Experiment 1, males were given [3H]E2 at 24 and 1 h before mating. Male-to-female [3H]E2 transfer intensified with increasing numbers of intromissions and spiked in the uterus after insemination. In Experiment 2, sexually experienced young males received [3H]E2 at 72 and 24 h before mating, and all mated to ejaculation. The copulatory plug deposited in the female reproductive tract contained substantial levels of radioactivity. The uteri, other tissues and blood serum of females displayed radioactivity indicative of E2 transfer. In Experiment 3, radioactivity was observed 3 and 18 h after insemination in the females’ uteri and other tissues, including parts of the brain. In Experiment 4, we observed substantial levels of radioactivity in semen as well as the copulatory plugs retrieved from the females after mating. Transferred E2 could directly affect abundant estrogen receptors in the female reproductive tract without potential metabolism by the liver. Sexually transferred E2 may facilitate uterine preparation for blastocyst implantation. These data converge with several lines of evidence indicating that male-sourced E2 can transfer to proximate females in bioactive form, contributing to various mammalian pheromonal effects.
Denys deCatanzaro and Tyler Pollock
Adam C Guzzo, Tyler Pollock and Denys deCatanzaro
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.