Prostaglandin Induction of Mitochondrial Respiration and Adaptive Changes of Enzymes in the Perfused Rat Liver

1 Prostaglandins stimulate mitochondrial resting respiration and, over a restricted range of phosphate concentrations, increase the Ca 2+ ‐stimulated respiration. 2 Prostaglandins added to mitochondrial suspensions after Ca 2+ + Mn 2+ increase citrate production. 3 Fluorescence studies indicate that prostaglandins can cause a transient change in the fluorescence yield, mimicking the effect of energised Ca 2+ uptake. 4 Prostaglandin F2α reduces perfusate glucose levels from fasted rat livers perfused with either high lactate or low glucose concentrations. With the former, urea synthesis is depressed, while with the latter, increased depletion of endogenous lipid occurs. 5 Prostaglandin F2α halves the tissue malic enzyme level: both prostaglandin and lactate reduce isocitrate dehydrogenase contents while lactate alone as substrate increases the level of pyruvate carboxylase. Phosphofructokinase and fructose 1:6‐bisphosphatase activities both drop slightly when prostaglandin is given to these perfusions. 6 Enzyme changes when prostaglandin F2α is given to low glucose perfusions reflect (a) energy conservation with decreases in phospho enol pyruvate carboxykinase, glucokinase and glucose 6‐phosphatase coupled with a rise in pyruvate kinase, and (b) reduced capacity for lipogenesis with decreased malic enzyme and isocitrate dehydrogenase, and a lowered response to citrate activation by acetyl‐CoA carboxylase.