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In mammals, the corpus luteum (CL) is an essential endocrine gland for the establishment and maintenance of pregnancy. If pregnancy is not established, the CL regresses and disappears rapidly from the ovary. A possible explanation for the rapid disappearance of the CL is that luteal cells are transported from the ovary via lymphatic vessels. Here, we report the presence of cells positive for 3β-hydroxysteroid dehydrogenase (3β-HSD), an enzyme involved in progesterone synthesis, in the lumen of lymphatic vessels at the regressing luteal stage and in the lymphatic fluid collected from the ovarian pedicle ipsilateral to the regressing CL. The 3β-HSD positive cells were alive and contained lipid droplets. The 3β-HSD positive cells in the lymphatic fluid were most abundant at days 22–24 after ovulation. These findings show that live steroidogenic cells are in the lymphatic vessels drained from the CL. The outflow of steroidogenic cells starts at the regressing luteal stage and continues after next ovulation. The overall findings suggest that the complete disappearance of the CL during luteolysis is involved in the outflow of luteal cells from the CL via ovarian lymphatic vessels.

Abstract. The objective of this study was to investigate the relationship between the plasma concentrations of vitamin A (VA), vitamin E (VE) and β-carotene (BC) during embryo collection in Japanese Black cows that had undergone superovulation treatment and the embryo collection results. Following superovulation treatment in 116 Japanese Black cows, we collected 1317 embryos by nonsurgical means seven days after artificial insemination. The collected embryos were classified into transferable embryos, unfertilized oocytes and degenerated embryos. After embryo collection, we collected blood samples from the cows and measured the plasma concentrations of VA, VE and BC. The cows were then divided into 2 groups depending on the plasma concentration of VA (L and H: < 80 IU/dl and ≥ 80 IU/dl), VE (L and H: < 150 μg/dl and ≥ 150 μg/dl) and BC (L and H: < 150 μg/dl and ≥ 150 μg/dl). As a result, the number of collected embryos in the H group of VE was significantly (P<0.01) higher than that in L groups. Furthermore, the number of transferable embryos was higher (P<0.05) in all VA, VE and BC H groups than in the L groups. The H group for BC showed a high ratio of transferable embryos compared with the L group (P<0.05). Consequently, the present study suggests that the plasma VE and BC concentrations are positively correlated with the embryo collection results.

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