Alterations in the cellular membranes of regressing rat corpora lutea

Wide angle x-ray diffraction and fluorescence polarization were used to determine the structural properties of membranes from rat luteal cells. Examination of a plasma membrane fraction by x-ray diffraction revealed a significant increase in the gel phase melting temperature during luteal regression. The membrane fluidity of this fraction as well as that of a preparation of microsomes was also studied by fluorescence polarization. Using a fluorescent probe, membrane fluidity was observed to decrease during luteolysis. The temporal correlation between structural changes in the membrane and decreased progesterone secretion suggests that alterations in the physical properties of cellular membranes may be involved in the process of luteal cell regression.