Fasting-induced changes in prostaglandin binding in isolated hepatocytes and liver plasma membranes

The effects of fasting on hepatic prostaglandin E (PGE) receptor characteristics were studied in Sprague-Dawley rats. Plasma membranes were isolated from liver homogenates of animals after 0, 12, 18, 24, and 48 h of fasting. The changes observed in body weight, liver weight, plasma glucose, and plasma beta-hydroxybutyrate during the fast were consistent with those previously reported for a similar fasted rat model. During the transition from the fed to the fasted state there was a decrease in hepatic PGE receptor density (from 0.175 +/- 0.011 pmol bound/mg membrane membrane protein in fed rats to 0.060 +/- 0.009 in rats fasted for 24 h), with no change in binding affinity. This change was observed whether the data were expressed per mg membrane protein isolated or were corrected for total membrane recovery and normalized to initial body weight. Isolated hepatocytes prepared from fed and 24-h fasted animals also demonstrated a significant decrease in PGE-binding site density (from 0.98 +/- 0.05 pmol bound/10(6) cells in fed rats to 0.46 +/- 0.14 in fasted rats), with no change in binding site affinity. The change in binding site density in the hepatocytes was of a magnitude similar to that observed in the liver plasma membranes after the membranes were corrected for recovery and normalized to initial body weight (51% vs. 53%, liver plasma membranes vs. isolated hepatocytes). We conclude that fasting is associated with a decrease in the hepatic PGE receptor density and suggest that this decrease may reflect an increase in hepatic E-series PGs during starvation.