Endocrine Abstracts

We have investigated inter-individual transfer of 17β-estradiol (E₂) and progesterone (P-₄), and related it to mammalian ‘pheromonal’ effects. Assays of unconjugated E₂ and P₄ revealed their presence in male and female urine of laboratory mice and big brown bats (Eptesicus fuscus), which are phylogenetically very distant from each other. These small and lipophilic steroids readily pass through biological membranes. After cutaneous or nasal exposure, radiolabeled E₂ (³H-E₂) or P₄ (³H-P₄) arrived in blood and tissues, but only arrived in the brain after nasal exposure^1–4. After 48 h of cohabitation with male stimulus animals treated with doses of ³H-E₂ that represent a small fraction of their endogenous E₂, untreated females showed significant radioactivity in blood serum, uterus, and other tissues in both mice and bats. Seminal emissions of diverse mammals contain E₂, and we found that ³H-E₂ transfers from males directly to the female’s reproductive tract during mating⁵. Ovariectomized female mice were made sexually receptive by E₂ and P₄ injections. When these females were paired with males given ³H-E₂, the amount of radioactivity in females’ serum increased with the number of sexual intromissions, and females that received an ejaculation showed especially high radioactivity in the uterus. In other experiments, females were all mated to the point of insemination with young adult males given ³H-E₂. Substantial radioactivity was observed in the males’ epididymides, preputials, and vesicular-coagulating glands, and their copulatory plugs and semen taken from the females’ reproductive tracts showed high levels of radioactivity that lingered there at least 18 h after mating. The uterus is densely populated with estrogen receptors. Male-to-female transfer of E₂ has been related to suppression of pregnancies sired by other males (Bruce effect) and male-induced acceleration of puberty (Vandenbergh effect), and may also relate to male-induced estrous cycling (Whitten effect) and ovulation⁶. Female-to-female transfer of ³H-P₄ has been observed in mice², and it could possibly explain suppression of estrous cycling in group-housed female mice (Lee-Boot effect)⁶. Female-to-female transfer of ³H-P₄ has also been found in big brown bats, which notably roost in very close contact in predominantly female groups⁴.

References: 1. Guzzo et al. 2012 Reproduction 143:539–48.

2. Guzzo et al. 2013 J Endocrinol 217:1–10.

3. deCatanzaro et al. 2014 Gen Comp Endocrinol 208:126–33.

4. Greville et al. 2017 Gen Comp Endocrinol 247:199–204.

5. deCatanzaro & Pollock 2016 J Endocrinol 231:245–57.

6. deCatanzaro 2015 Horm Behav 68:103–16.