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 48 h 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 1 h after cutaneous and intranasal application (10 μCi). Subsequently, pairs of mature females were each housed for 48 h with a single mature female that had been administered 3H-P4 (50 μCi) 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 (50 μCi). 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.