VASCULAR PROVISIONS FOR A LOCAL UTEROOVARIAN CROSS-OVER PATHWAY IN NEW-WORLD CAMELIDS

The right uterine horn of alpacas causes luteolysis in the right ovary , whereas the left horn causes luteolysis in both ovaries. Female repr oductive tracts were studied in 32 adult Ilamas, 12 adult alpacas, and 21 mid-gestation female fetuses to determine if there is a dichotomy in the vascular anatomy between the 2 sides. Adult tracts were studied by either injection of colored latex into the veins and arteries foll owed by tissue clearing or by injection of colored fluids during trans illumination. Fetal uteri were studied by transillumination. The angio architecture of the ovarian vascular pedicle was similar to that repor ted for ewes. There was no vessel comparable to the middle uterine art ery, which is the largest uterine artery in the other farm species. A striking difference from the uterine vascular of other farm species wa s the presence of a major branch of the right uterine artery that cros sed the cranial intercomual area to supply much of the left uterine ho rn. A corresponding major vein originated from the left horn, crossed the mid-line, and terminated as a branch of the right uterine vein. Th us, the vascular anatomy indicated that much venous blood from the lef t horn drained to the right side. This was confirmed by injection of c olored fluid into a small venous branch at the tip of the left horn. T he prominent cross-over vessels were observed in the fetal uteri, and the diameter of the left uterine fetal horn (6.7+/-0.6 mm) was greater (P<0.001) than the diameter of the right horn (5.8+/-0.5 mm). The pre sence of a large cross-over vein traversing from the left horn to the right side is compatible with the hypothesis that the left horn can ex ert luteolytic control over the corpus luteum in the right ovary throu gh a veno-arterial pathway. The area of veno-arterial transfer of the luteolysin from a vein containing blood from the left horn into an art ery supplying the right ovary was not defined in this study. However, the results provide an anatomical basis for functional testing of the cross-over hypothesis and defining the area of veno-arterial transfer in camelids.