Human large luteal cells in the menstrual cycle and early pregnancy express leukotriene A4 hydrolase.

Leukotriene (LT) A4 hydrolase (EC3.3.2.6) converts LTA4 to LTB4 which shows a chemotactic activity to leukocytes. To investigate the involvement of LTB4 in human corpus luteum (CL) function, the localization of LTA4 hydrolase in human ovarian tissues was examined by immunohistochemistry with a rabbit polyclonal antibody against LTA4 hydrolase. The enzyme was weakly expressed on granulosa cells of the follicles. After ovulation, the intensity of LTA4 hydrolase on large luteal cells increased and was highest in the midluteal phase. High expression was also observed in the CL of early pregnancy. In theca interna and small luteal cells, LTA4 hydrolase was weakly detected in all developmental stages. Immunoblot analysis demonstrated that the molecular mass of LTA4 hydrolase expressed in CL was 62 kDa, and confirmed that LTA4 hydrolase expression increased during CL formation and remained high in early pregnancy. The sequence encoding mRNA of LTA4 hydrolase, which was isolated from CL and amplified by polymerase chain reaction, was shown to be identical to the previously reported one. Immunocytochemistry showed that LTA4 hydrolase expression in cultured granulosa cells increased over 4 days in vitro and was enhanced by human chorionic gonadotrophin treatment. These expression profiles of LTA4 hydrolase suggest the involvement of LTB4 in luteal cell function during CL formation and early pregnancy.