ABSTRACT
The ability of PRL to modify prostaglandin F2 alpha (PGF2 alpha)-induced membrane changes during functional corpus luteum regression was examined in the pseudopregnant rat. Fluorescence polarization studies conducted 24 h after sc injection of PGF2 alpha revealed a marked and significant increase in the polarization parameter, which is suggestive of reduced plasma membrane fluidity. At the same time, there was a decrease in hCG binding and a significant increase in apparent phospholipase-A2 activity during incubation of dispersed rat luteal cells. Each of these changes was attenuated when the animals were pretreated with PRL 30 min before PGF2 alpha. The decrease in plasma progesterone caused by PGF2 alpha treatment was also inhibited by PRL. PGF2 alpha also stimulated a significant polarization increase in dispersed cells prepared from ovaries removed 1 h after injection of this luteolytic agent, although this effect could not be demonstrated in plasma membrane samples. These results indicate that PRL and PGF2 alpha affect the same membrane pathway in the rat corpus luteum and that this pathway appears to be closely coupled to luteal cell function.
