Prostaglandin I2 modifies both prolactin binding capacity and fluidity of mouse liver membranes

The objective of this study was to determine if prostaglandins alter the fluidity of hepatic membranes and if this, in turn, modifies their ability to bind prolactin. Liver homogenates of adult C3H female mice incubated with 1-1000 nM prostaglandin A1, A2, B2, F1 alpha, 6-keto-F1 alpha, E1, E2, I2, or thromboxane B2 provided the 100,000 X g membrane pellets for subsequent ovine prolactin binding and membrane fluidity studies. Only membrane preparations treated with prostaglandin I2 showed an increase in specific binding of ovine prolactin. The effect (40-50%) was maximal at 100 nM prostaglandin I2 after 30 min of incubation and was due to an increase in the number of receptor sites. Under the same conditions, prostaglandin I2 induced a 17% decrease in membrane microviscosity. These data suggest that specific prostaglandins may modulate the number of prolactin receptors in vivo by modifying the fluidity of the lipid bilayer and the subsequent ease with which receptors can assume active configurations within the matrix.