Changes in luteal cells distribution, apoptotic rate, lipid peroxidation levels and antioxidant enzyme activities in buffalo (Bubalus bubalis) corpus luteum

Buffalo (Bubalus bubalis) is known for its weak/silent estrous behaviour, lower conception rate and longer inter-calving interval as compared to cattle. Understanding the kinetics and functional properties of luteal cells may be helpful to improve reproductive efficiency in the buffalo. Hence the present study was designed to assess the size and distribution of steroidogenic luteal cells along with biochemical properties during different phases of corpus luteum (CL) in the buffalo. The ovaries collected from the local abattoir were classified into three phases, early, mid and late, based on the morphological appearance of the CL as well as the follicles in the ovary. The proportion (%) of the luteal cells (>10 μm diameter) increased (P < 0.01) from early (30.7 ± 1.3) to mid (36.30 ± 1.6), and then decreased (P < 0.01) in late luteal (31.46 ± 1.8) phases. Percentage of small luteal cells (10–20 μm diameter) was higher (P < 0.05) in early (58.47 ± 0.61) and mid (61.29 ± 0.67) than late luteal (37.18 ± 1.50) phases of CL. However, the percentage of large luteal cells (20–50 μm diameter) was higher (P < 0.05) only in late (62.82 ± 1.50) than early (41.53 ± 0.61) and mid (38.71 ± 0.67) phases of CL. The average size (μm) of the large luteal cells increased (P < 0.05) from early (25.46 ± 0.62) to mid (27.15 ± 0.5) and late (28.86 ± 0.47) luteal phases. The percentage of luteal cells expressing in situ DNA fragmentation was significantly (P < 0.05) higher in the late luteal (41.17 ± 5.8) than mid-luteal (21.15 ± 4.9) phase of the CL. In the early stage, half of the steroidogenic luteal cells had significantly (P < 0.05) less 3β-HSD activity than the other two phases. In the mid stage, the steroidogenic luteal cells had significantly higher (P < 0.05) intense 3β-HSD activity than the other two phases. Further in the late phase, a significant (P < 0.05) reduction in intense 3β-HSD activity was observed in the large luteal cells. The lipid peroxidation (μmol/g of CL) levels were significantly (P < 0.05) higher in late luteal (3.46 ± 0.2) than the mid-luteal (1.43 ± 0.16) phases. The superoxide dismutase and catalase enzyme levels (U/mg of protein) were also significantly (P < 0.05) higher in late luteal (0.9 ± 0.015 and 3.37 ± 0.45, respectively) than the mid-luteal (0.1 ± 0.01 and 2.34 ± 0.3, respectively) phases. In contrast, the GPx activity (U/mg of protein) decreased significantly (P < 0.05) from mid-luteal (1.85 ± 0.4) to late luteal (1.22 ± 0.2) phases. The present study suggests that (i) the decrease in progesterone levels in late CL may be associated with loss of 3β-HSD activity in large luteal cells and (ii) demise of the buffalo CL may be mediated by apoptosis despite the high levels of luteal antioxidant enzymes.