AN ULTRASTRUCTURAL-STUDY OF THE FIBROMUSCULAR CAPSULE OF THE CORPUS-LUTEUM IN MICE

The presence and distribution of contractile cells in mature corpora l utea (CL) of pregnant and normal cycling mice were studied by transmis sion (TEM) and scanning (SEM) electron microscopy. In the connective t issue surrounding the CL, SEM observations made after maceration in al kali, revealed long, flat, spindle-shaped elements arranged parallel t o each other, forming a continuous capsule. TEM of these elements reve aled ultrastructural features of mature smooth muscle cells (SMC), as well as structures intermediate between fibroblasts, fibrocytes and SM C. Discrete bundles of SMC were seen to exit the external capsule of t he CL and to penetrate the luteal tissue. The extensive branches of th ese bundles of SMC appeared to make contact with numerous vessels. The refore, three-dimensional reconstruction, based on TEM and SEM analysi s, revealed that the SMC of the CL were organized such that they form a wide fibromuscular skeleton around and within the luteal mass. It is possible that pulsatile or tonic contraction of this structure may he lp to regulate the secretory activity of the luteal tissue by modifyin g the pressure inside the CL.