Rapid Plasma Membrane Changes in Superoxide Radical Formation, Fluidity, and Phospholipase A2Activity in the Corpus Luteum of the Rat During Induction of Luteolysis*

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Abstract
Early luteolytic changes in the plasma membrane of luteal cells were examined in the rat. Treatment with prostaglandin F2 alpha in vivo caused a rapid transient increase in superoxide radical formation and a decrease in fluidity in plasma membrane samples prepared from luteinized rat ovaries. These alterations preceded detection of a significant fall in plasma progesterone concentration. The rise in superoxide radical was not accompanied by changes in activities of free radical scavenging enzymes. Within the first hour of prostaglandin treatment, there was also a significant increase in the activity of phospholipase A2 and ATP-dependent calcium uptake in the membrane samples. These experiments indicate that one of the initial sites affected by the luteolytic process appears to be the plasma membrane. The changes include a transient rise in production of superoxide radicals, which may cause membrane changes that are responsible for disrupting corpus luteum function in the rat.