Effect of Progressive Starvation on Rat Liver Enzyme Activities

Abstract

The patterns of decreases in total liver enzyme activities, body weight and some selected liver constituents in young and old rats were studied during progressive starvation. The following were observed in young rats: total liver protein, liver glycogen, phosphoglucomutase, fructose diphoshatase, aldolase, succinic dehydrogenase and fumarase decreased in activity after one day of starvation and remained relatively constant during the next 3 days of starvation. A decrease on days 1 and 4 of starvation was noted with soluble liver protein, phosphohexoseisomerase, glyceraldehyde 3-phosphate dehydrogenase, lactate dehydrogenase, α-glycerolphosphate dehydrogenase, malic enzyme (TPN), isocitric dehydrogenase (TPN) and malic dehydrogenase. A decrease in the activities of phosphorylase, glucose 6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase and the pentose phosphate-metabolizing enzymes was observed on days 1, 2 and 4 of starvation. Glucose 6-phosphatase and uridine diphosphate glucose dehydrogenase activities remained relatively constant during 3 days of starvation and decreased on day 4. The patterns of decreases in total liver enzyme activities in old rats were similar to those for young rats with a few notable exceptions. The most striking of these was the sharp decrease in the activity of uridine diphosphate glucose dehydrogenase on day 1 of starvation in old rats. The activities of glucose 6-phosphatase and lactate dehydrogenase were maintained to a greater extent in young rats than in old rats. But the activities of aldolase, α-glycerolphosphate dehydrogenase, isocitrate dehydrogenase (TPN) and glucose 6-phosphate dehydrogenase appeared to be more resistant to decreases during starvation in old rats. In general, the activities of enzymes involved in gluconeogenesis, the citric acid cycle, and the pentose phosphate-metabolizing enzymes were equally stable to starvation. The activities of enzymes of the Embden-Meyerhoff pathway (phosphoglucomutase, aldolase, glyceraldehyde 3-phosphate dehydrogenase and lactic dehydrogenase) were somewhat less stable. The activities of those enzymes which are thought to be associated with lipogenesis (glucose 6-phosphate dehydrogenase, malic enzyme and α-glycerolphosphate dehydrogenase) were the least stable. The possible physiological importance of this order of stability is discussed.