The ovarian-uterine vasculature in relation to unilateral endometrial growth in flying foxes (genus Pteropus, suborder Megachiroptera, order Chiroptera).

The ovarian-uterine vasculature was examined in three Australian species of flying fox (Pteropus scapulatus, P. poliocephalus and P. alecto). Vascular casts and histological sections were used to determine the relationship between the blood supply and the localized endometrial reaction, which occurs ipsilateral to the ovulating ovary. The ovarian artery coils extensively just cranial to the ovary, gives off a branch to the ovary and continues caudally as the major vessel supplying the cranial tip of the uterus, where it anastomoses with the smaller uterine artery. The coil of the ovarian artery is completely enclosed by a venous sinus that drains the cranial pole of the ovary. The ovary is heavily encapsulated, with primordial follicles restricted to the caudal pole; thus, the corpus luteum is completely internal and placed cranially, close to the coil of the ovarian artery. This arrangement would allow countercurrent or crosscurrent transfer of ovarian steroids from ovarian vein to ovarian artery and on to the cranial tip of the ipsilateral uterine horn. The steroids could thus reach high concentrations locally and generate localized endometrial growth. Cranial to the coil, the ovarian artery is enclosed in a venous sinus that derives from uterine as well as ovarian veins. This would allow countercurrent transfer of bioactive substances from uterus to ovary.