Exposure to developing females induces polyuria, polydipsia, and altered urinary levels of creatinine, 17beta-estradiol, and testosterone in adult male mice (Mus musculus)

Quantification of Urinary Sex Steroids in the Big Brown Bat (Eptesicus fuscus)

AbstractBats (order Chiroptera) are the second largest group of mammals, diverging ~52.5 million years ago. Many species exhibit an unusual reproductive cycle and extreme longevity without reproductive senescence, yet steroid profiles exist for few bats. Big brown bats (Eptesicus fuscus) are temperate insectivores found throughout North America. They mate promiscuously in fall, store sperm during winter hibernation, and have delayed ovulation and fertilization in spring. Here, we report the first urinary steroid profile in bats by quantifying 17β-estradiol (E₂) in captive male and female E. fuscus across their reproductive cycle. Male bats had higher urinary E₂ levels than females, and adults had higher levels than yearlings following creatinine adjustment for hydration. In nonpregnant females, several seasonal differences in creatinine-adjusted and unadjusted urinary E₂ levels were observed. Urinary E₂ was higher in males than females in winter for both conditions and in autumn for creatinine-adjusted levels. We quantified progesterone (P₄) in a subset of females. In nonpregnant females, urinary P₄ was constant across seasons except for unadjusted levels, which were highest in the summer. In pregnant females, urinary E₂ and P₄ levels peaked beginning ~20 d before parturition, with both steroids returning to baseline in the following weeks. Knowing how urinary steroid levels fluctuate with age and sex and across the annual season is key to understanding reproductive cycling in bats. Our research furthers the potential for bats as a model for medical reproductive research. Moreover, it complements previous studies on the potential role of steroids in primer pheromonal effects in bats.

Seasonal transfer and quantification of urinary estradiol in the big brown bat (Eptesicus fuscus)

Growing evidence shows that sex steroids not only act within the individual whose glands produce them; they can also act on proximate conspecifics. Previous studies show that exogenous 17β-estradiol (E₂) can be absorbed both nasally and percutaneously, arriving in blood, neural, reproductive, and peripheral tissues. When male bats were injected with radiolabeled E₂ (³H-E₂) and housed with females during the mating season, radioactivity was reliably measured in the females' tissues. The present study was designed to compare E₂ transfer from male to female bats at three time points in the annual reproductive cycle: spring (ovulation and fertilization), summer (maternal season), and autumn (mating season). Pairs of mature female bats were housed with a mature ³H-E₂-treated male (50 μCi). Following 48 h of communal housing, radioactivity was measured in the tissues of female bats. Higher levels of radioactivity were present in the uterus and other tissues during the spring and autumn seasons compared to the summer season. We also measured natural levels of bioactive, unconjugated E₂ in the urine of male bats using enzyme immunoassays, and found that it was present in all three seasons but at lower levels during the summer. Male-excreted E₂ could transfer to females within the close confines of a roost, potentially influencing their reproductive physiology and behavior. These results suggest increased E₂ transfer coincides with female reproduction, with urine as a likely vector. We suggest that sex steroid transfer among interacting individuals may explain several mammalian phenomena historically viewed as "pheromonal".

Male-mediated prenatal loss: Functions and mechanisms

Sexually selected infanticide has been the subject of intense empirical and theoretical study for decades; a related phenomenon, male-mediated prenatal loss, has received much less attention in evolutionary studies. Male-mediated prenatal loss occurs when inseminated or pregnant females terminate reproductive effort following exposure to a nonsire male, either through implantation failure or pregnancy termination. Male-mediated prenatal loss encompasses two sub-phenomena: sexually selected feticide and the Bruce effect. In this review, we provide a framework that explains the relationship between feticide and the Bruce effect and describes what is known about the proximate and ultimate mechanisms involved in each. Using a simple model, we demonstrate that male-mediated prenatal loss can provide greater reproductive benefits to males than infanticide. We therefore suggest that, compared to infanticide, male-mediated prenatal loss may be more prevalent in mammalian species and may have played a greater role in their social evolution than has previously been documented.

Progesterone transfer among cohabitating female big brown bats (Eptesicus fuscus)

Experiments using female mice and bats have demonstrated that tritium-labeled 17β-estradiol (³H-E₂) can be absorbed via cutaneous and intranasal routes and distributed to reproductive and neural tissues. Radioactivity has also been measured in tissues of untreated females after 48h cohabitation with ³H-E₂ injected males. The present study was designed to quantify steroid transfer among female bats. Radioactive quantification via liquid scintillation counting revealed absorption of tritium-labeled progesterone (³H-P₄) in adult females 1h after cutaneous and intranasal application (10μCi). Subsequently, pairs of mature females were each housed for 48h with a single mature female that had been administered ³H-P₄ (50μCi) via intraperitoneal injection. Radioactivity was observed in all collected tissues of all non-injected females at levels significantly greater than the control group. Following the same paradigm, radioactivity was not observed in the tissues of untreated female bats that were housed with stimulus females treated with ³H-E₂ (50μCi). Enzyme immunoassays revealed measurable levels of unconjugated progesterone and estradiol in the urine of female bats, suggesting urine as a vector for steroid transfer. Given that bats of this species live in predominantly female roosts in very close contact, progesterone transfer among individuals is likely to occur in natural roosts.

Sources of variance within and among young men in concentrations of 17β-estradiol and testosterone in axillary perspiration

The most potent estrogen, 17β-estradiol (E₂), and its precursor, testosterone (T), play critical roles in mammalian reproductive processes. Evidence indicates that these steroids are present in bioactive form in the excretions of many male mammals. It has been demonstrated that small lipophilic steroids such as E₂ can be absorbed by proximate females from male excretions, arriving in the uterus, brain, and other organs where there are estrogen receptors. We took repeated samples of axillary perspiration from men aged 20-30years during vigorous exercise. Both steroids were consistently measurable, with concentrations that ranged from values comparable to those in facial perspiration and urine of both men and women to values that greatly exceeded concentrations observed in any other substrate of men and women. Inter-individual variance in axillary E₂ was positively correlated with the extent of intimate experience with women, as assessed by a questionnaire, but unrelated to subjective measures of stress, exercise habits, or phytoestrogen content of diet. In addition, higher levels of axillary E₂ were observed in participants when samples were collected by a female (as compared to a male) experimenter. These data are concordant with an hypothesis that male excretion of sex steroids could exert pro-reproductive influences on proximate females.

Absorption and distribution of estradiol from male seminal emissions during mating

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.

Sex steroids as pheromones in mammals: the exceptional role of estradiol

This article is part of a Special Issue (Chemosignals and Reproduction). Whether from endogenous or exogenous sources, 17β-estradiol (E2) has very powerful influences over mammalian female reproductive physiology and behavior. Given its highly lipophilic nature and low molecular mass, E2 readily enters excretions and can be absorbed from exogenous sources via nasal, cutaneous, and other modes of exposure. Indeed, systemic injection of tritiated estradiol ((3)H-E2) into a male mouse or bat has been shown to produce significant levels of radioactivity in the reproductive tissues and brain of cohabiting female conspecifics. Bioactive E2 and other steroids are naturally found in male mouse urine and other excretions, and males actively direct their urine at proximate females. Very low doses of E2 can mimic the Bruce effect (disruption of peri-implantation pregnancy by novel males), the Vandenbergh effect (early reproductive maturation induced by novel males), and male-induced estrus and ovulation. Males' capacities to induce the Bruce and Vandenbergh effects can both be diminished by manipulations that reduce their urinary E2. Uterine dynamics during the Bruce and Vandenbergh effects are consistent with the actions of E2. Collectively, these data demonstrate a critical role of male-sourced E2 in these major mammalian pheromonal effects.

Estradiol transfer from male big brown bats (Eptesicus fuscus) to the reproductive and brain tissues of cohabiting females, and its action as a pheromone

The powerful estrogen, 17β-estradiol, has been found to pass from male excretions to the reproductive organs, brain, and other tissues of cohabiting females in laboratory mice. The current studies were designed to examine whether this phenomenon also occurs in big brown bats (Eptesicus fuscus), a mammal appropriate for testing cross-species generality because of its phylogenetic distance from mice. When tritiated estradiol ((3)H-E2) was administered directly on the nasal area of adult female bats, radioactivity was reliably observed in the uterus and ovaries, and also in the brain and other tissues. When (3)H-E2 was applied to the skin, radioactivity was observed in reproductive and other peripheral tissues. We injected male bats with minute quantities of (3)H-E2 and housed each of them directly with groups of adult females for 48h. We then measured radioactivity in male and female bat tissues. In each of several replications of one male housed with three females, radioactivity was reliably observed in the uterus of all females, and in many other tissues in almost every female. Measurement in the organs of males directly exposed to (3)H-E2 showed high levels of radioactivity in the testes and especially the epididymides. These data indicate that estradiol is transferred from males to females, likely via absorptions from males' excretions and potentially also via intravaginal exposure during mating. Given the potency of estradiol in regulating female reproductive physiology and behavior, our data strongly suggest the potential for pheromonal action whereby male mammals induce sexual receptivity and ovulation in females.

Spontaneous voiding by mice reveals strain-specific lower urinary tract function to be a quantitative genetic trait

Lower urinary tract (LUT) symptoms become prevalent with aging and affect millions; however, therapy is often ineffective because the etiology is unknown. Existing assays of LUT function in animal models are often invasive; however, a noninvasive assay is required to study symptom progression and determine genetic correlates. Here, we present a spontaneous voiding assay that is simple, reproducible, quantitative, and noninvasive. Young female mice from eight inbred mouse strains (129S1/SvImJ, A/J, C57BL/6J, NOD/ShiLtJ, NZO/H1LtJ, CAST/EiJ, PWK/PhJ, and WSB/EiJ) were tested for urination patterns on filter paper. Repeat testing at different times of the day showed minimal within-individual and within-strain variations, but all parameters (spot number, total volume, percent area in primary void, corner voiding, and center voiding) exhibited significant variations between strains. Calculation of the intraclass correlation coefficient, an estimate of broad-sense heritability, for each time of day and for each voiding parameter revealed highly significant heritability [spot number: 61%, percent urine in primary void: 90%, and total volume: 94% (afternoon data)]. Cystometrograms confirmed strong strain-specific urodynamic characteristics. Behavior-voiding correlation analysis showed no correlation with anxiety phenotypes. Diagnostically, the assay revealed LUT symptoms in several systems, including a demonstration of voiding abnormalities in older C57BL/6J mice (18-24 mo), in a model of protamine sulfate-induced urothelial damage and in a model of sucrose-induced diuresis. This assay may be used to derive pathophysiological LUT readouts from mouse models. Voiding characteristics are heritable traits, opening the way for genetic studies of LUT symptoms using outbred mouse populations.

Novel male exposure reduces uterine e-cadherin, increases uterine luminal area, and diminishes progesterone levels while disrupting blastocyst implantation in inseminated mice

Exposure to novel male mice disrupts blastocyst implantation in inseminated female mice, and evidence increasingly implicates the female's absorption of male urinary estrogens. We observed implantation sites in male-exposed and isolated control female mice during gestation days (GD) 2-8, observing a significant reduction in male-exposed females compared to controls, particularly on GD 6 and 8. We also measured transitions in uterine luminal area and e-cadherin expression, as these processes are modulated by estrogens. Luminal area was greater in male-exposed females than in controls during the post-implantation period (GD 5-7). E-cadherin levels were suppressed by male exposure, particularly during GD 4-6 Serum progesterone levels were also reduced in male-exposed females. The effects of male exposure on uterine closure and e-cadherin levels are consistent with established effects of estrogens, and suggest a possible mechanism that could contribute to implantation failure. This article is part of a Special Issue entitled 'Pregnancy and Steroids'.

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.

Oestradiol transmission from males to females in the context of the Bruce and Vandenbergh effects in mice (Mus musculus)

Male mice actively direct their urine at nearby females, and this urine reliably contains unconjugated oestradiol (E2) and other steroids. Giving inseminated females minute doses of exogenous E2, either systemically or intranasally, can cause failure of blastocyst implantation. Giving juvenile females minute doses of exogenous E2 promotes measures of reproductive maturity such as uterine mass. Here we show that tritium-labelled E2 (3H-E2) can be traced from injection into novel male mice to tissues of cohabiting inseminated and juvenile females. We show the presence of 3H-E2 in male excretions, transmission to the circulation of females and arrival in the female reproductive tract. In males, 3H-E2 given systemically was readily found in reproductive tissues and was especially abundant in bladder urine. In females, 3H-E2 was found to enter the system via both nasal and percutaneous routes, and was measurable in the uterus and other tissues. As supraoptimal E2 levels can both interfere with blastocyst implantation in inseminated females and promote uterine growth in juvenile females, we suggest that absorption of male-excreted E2 can account for major aspects of the Bruce and Vandenbergh effects.

Oestradiol treatment restores the capacity of castrated males to induce both the Vandenbergh and the Bruce effects in mice (Mus musculus)

Androgen-dependent urinary constituents from males hasten reproductive maturation (the Vandenbergh effect) and disrupt peri-implantation pregnancy (the Bruce effect) in nearby females. Each of these effects can be mimicked in socially isolated females by direct administration of exogenous oestrogens. The current experiments were designed to determine the role of males' urinary 17β-oestradiol (E2) in their capacities to induce these effects. A preliminary experiment showed that both males on a phyto-oestrogen-rich soy-based diet and those on a phyto-oestrogen-free diet could induce both effects. For subsequent experiments, males were castrated and treated with either oil vehicle or E2. Enzyme immunoassay was conducted on non-invasively collected urine samples from these males. Concentrations of urinary testosterone were subnormal in both conditions, but urinary E2 was restored to the normal range for intact males in castrates given E2. Urinary creatinine was also quantified as a measure of hydration and was significantly reduced in males treated with E2. Castration diminished the capacity of males to promote growth of the immature uterus and also their capacity to disrupt blastocyst implantation in inseminated females. Injections of E2 to castrated males restored both capacities. These data converge with other studies indicating that E2 is the main constituent of male urine responsible for induction of both the Vandenbergh and the Bruce effects.

Excretion and binding of tritium-labelled oestradiol in mice (Mus musculus): implications for the Bruce effect

Male mouse urine contains 17beta-oestradiol (E(2)) and other steroids. Given that males actively direct urine at proximate females and intrauterine implantation of blastocysts is vulnerable to minute amounts of exogenous oestrogens, males' capacity to disrupt early pregnancy could be mediated by steroids in their urine. When male mice were implanted with osmotic pumps containing tritium-labelled E(2) ((3)H-E(2)) or injected i.p. with (3)H-E(2), radioactivity was reliably detected in their urine. Following intranasal administration of (3)H-E(2) to inseminated females, radioactivity was detected in diverse tissue samples, with there being significantly more in reproductive tissues than in brain tissues. When urine was taken from males injected with (3)H-E(2), and then intranasally administered to inseminated females, radioactivity was detected in the uterus, olfactory bulbs, and mesencephalon and diencephalon (MC+DC). When inseminated and ovariectomised females were perfused at the point of killing to remove blood from tissues, more radioactivity was detected in the uterus than in muscle, olfactory bulbs, MC+DC and cerebral cortex. Pre-treatment with unlabelled E(2) significantly reduced the uptake of (3)H-E(2) in the uterus. Taken with evidence that males deliver their urine to the nasal area of females, these results indicate that male urinary E(2) arrives in tissues, including the uterus, where it could lead to the disruption of blastocyst implantation.

Preputialectomised and intact adult male mice exhibit an elevated urinary ratio of oestradiol to creatinine in the presence of developing females, whilst promoting uterine and ovarian growth of these females

Exposure to novel adult males and their urine can hasten the onset of sexual maturity in female mice. Some evidence implicates chemosignals from males’ preputial glands, while other evidence suggests that male urinary steroids, especially 17β-oestradiol, contribute to this effect. The present experiment was designed to determine whether preputial gland removal would influence the capacity of males to accelerate female sexual development, and to measure male urinary oestradiol and testosterone in the presence or absence of these glands. Juvenile females aged 28 days were housed for two weeks in isolation or underneath two outbred males that had undergone preputialectomy or sham surgery. Urine samples were collected non-invasively from males that were isolated or exposed to females, then assayed for oestradiol, testosterone and creatinine. Combined uterine and ovarian mass from females sacrificed at 43 days of age was increased by exposure to males, regardless of whether or not these males had been preputialectomised. Male urinary creatinine was reduced by exposure to developing females. Creatinine-adjusted oestradiol and testosterone were significantly greater in female-exposed than in isolated males, in both preputialectomised and intact males. These data suggest that the preputials are not necessary for the capacity of males to hasten female uterine and ovarian growth. As exogenous oestrogens can promote uterine growth and other parameters of female reproductive maturation, oestradiol in males’ urine may contribute to earlier sexual maturity in male-exposed females.