Prolactin-binding capacity, prostaglandin synthesis and fluidity of murine hepatic membranes are modified during pregnancy and lactation

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Abstract
The objective of these studies was to determine whether the changes observed in prolactin-binding capacity of mouse liver microsomal membranes during pregnancy and lactation correlated with those observed in the fluidity and prostaglandin (PG)-synthesizing activity of these membrane preparations. Prolactin-binding capacity increased with the advance of pregnancy to reach a peak at 16 days of gestation and declined thereafter to non-pregnant, non-lactating (NPNL) levels. Membrane microviscosity, studied by fluorescence polarization, was significantly decreased throughout early gestation but returned to NPNL levels by day 20 of gestation and remained unchanged thereafter. The amount of PGE synthesized in vitro by these membranes increased during gestation to reach a peak at 12 days of gestation but declined thereafter to below NPNL levels on the day of parturition and returned to NPNL levels by day 20 of lactation. Synthesis of PGF2α remained at a higher level from day 12 to day 18 followed by a decline in activity at parturition to NPNL levels. These changes and other data suggest an interrelationship of receptor levels, fluidity and PG synthesis during pregnancy. Such modifications in local PG synthesis may influence the fluidity of these membranes, which ultimately play a significant role in maximal exposure of membrane receptors during pregnancy.