Fig. 3

Representative staining of SMA in the CL during luteal stages. The walls of all vessels in the regressed (Reg) CL exhibited strong immunoreactivity for SMA (a, b). Tunica media of the large vessels at the periphery of the CL contains SMA immunoreactivity (arrows in a). Cells in the wall of typical AVA-like vessels with a diameter of 100–200 μm are immunolabeled with SMA (asterisks in a, b). In the CL during the mid-luteal (ML) stages, the immunoreactivity for SMA is largely restricted to the tunica media of arteries and arterioles (asterisks in c and arrows in c, d). Pericytes surrounding capillary vessels also immunoreactive for SMA (asterisk in d). Weak immunoreactivity for SMA is found in fibroblast-like cells lying between steroidogenic luteal cells but not being associated with blood vessels (arrowheads in d). During the late-luteal (LL) stage, abundant SMA-positive fibroblast-like cells are observed in the CL parenchyma and accumulate around the arteries (asterisks in e). Smooth muscle cells in the arteries (asterisks in e) and arterioles (arrows in e, f) as well as pericytes (asterisks in f) are immunolabeled with SMA. Capillary vessel network is more visible in the CL at the LL stage (asterisks in g). Fibroblastic cells with elongated cytoplasmic processes also contain SMA immunoreaction (arrowheads in f, h). Inserts in (d and f) show traverse images of capillary vessels. Dotted lines in (d and f) display changing points from arterioles to capillary vessels. Cont: negative control image