Accelerative Effect of Olive Oil on Liver Glycogen Synthesis in Rats Subjected to Water-immersion Restraint Stress

The effects of dietary oils on stress-induced changes in the liver glycogen metabolism of male Wistar rats at 6 weeks of age were investigated. The rats were subjected to repetitive water-immersion restraint and fed with a 20% saturated fatty acid mixture (PSC), olive oil (OLI), safflower oil (SAF), or linseed oil (LIS) diet. Stress loading decresed the body weight gain, although the food intake was hardly changed, and the weights of the liver and spleen generally declined regardless of the elapsed time after stress loading and the type of dietary oil. The adrenal weight was generally enhanced by stress in all deitary groups, and particularly tended to be greater in the OLI and PSC groups than in the other two. The plasma corticosterone concentration increased immediately after stressing (Stress-1), but approached the level of the rats with no stress (No stress) 2 h after releasing the stress load (Stress-2) in all groups. The enhancement of corticosterone level in the Stress-1 animals was large in the PSC and OLI groups, and the decline of this level in the Stress-2 animals was small in the OLI group when compared with the other groups. Although the concentrations of total cholesterol (T-CHOL) and triacylglycerol (TG) in the plasma were decreased by stress loading in all groups, these concentrations in the PSC and OLI groups were nearly always higher than in the other groups. The liver serine dehydratase (SDH) activity enhanced by stress was high in the OLI group and tended to be high in the PSC group when compared with the other groups. The contents of liver glycogen were reduced in the Stress-1 animals and extremely elevated in the Stress-2 animals of all groups, and particularly in the OLI group, the reduction in the Stress-1 animals was smaller and the enhancement in the Stress-2 animals was greater than in the other groups. These results suggest that feeding oleic acid to rats exposed to water-immersion restraint further accelerated liver glycogen synthesis through the rise in liver SDH activity due to inceased corticosterone secretion when compared with the effect from linoleic and α-linolenic acids.