Expression patterns of endothelial and inducible nitric oxide synthase isoforms in corpora lutea of pseudopregnant rabbits at different luteal stages

Total activity of nitric oxide (NO) synthase (NOS) and expression of both endothelial (eNOS) and inducible (iNOS) isoforms,were examined in corpora lutea (CL) of rabbits across pseudopregnancy by quantitative RT-PCR, analysis, Western blot and immunohistochemistry. CL were collected at early (day 4), mid- (day 9) and late- (day 13) luteal phases of pseudopregnancy. The PCR product of rabbit luteal eNOS was cloned and its direct Sequence exhibited 90%, homology with those of other species. The steady-state mRNA levels encoding eNOS remained fairly constant throughout both early- and mid-luteal stages of pseudopregnancy but dropped almost to half (Pless than or equal to0(.)05) by day 13. By contrast, luteal eNOS proteins increased 2-fold (Pless than or equal to0(.)05) from the early to late-lureal phase. Independently of CL age. iNOS mRNA was very poorly expressed awhile protein levels gradually declined from the early- to late-luteal stage. Intense eNOS-like immunoreactivity, was detected in large luteal cells, while iNOS staining was targeted to a few, isolated cells, probably inacrophages. Basal NOS activity was greater in day 4 CL than in both day 9 and day 13 CL. These data are the first to characterize in rabbit CL the temporal expression patterns of NOS isoforms across different luteal stages of pseudopregnancy and, collectively, suggest the existence of an expressional control for thin constitutive isoform, which might have a physiological role in regulating CL Function during development.