Seasonal and sex-bound variation in the carbohydrate metabolism of the liver of the whitefish

Abstract

Seasonal variations in the weight of the liver, its glycogen content and two carbohydrate enzyme activity values were studied in specimens of Coregonus nasus (Pallas), sensu Svärdson. 1. 1. The results obtained for virgin fish and for maturing or spent males revealed similar patterns of variation, though the figures for the virgin fish were generally somewhat higher. 2. 2. The group of males in spawn, measured in October, stood out by virtue of the high liver glycogen content recorded. 3. 3. Compared with the other groups, the mature or spent females had larger livers from July (the onset of rapid gonadal development) to January, lower liver glycogen content during the winter, lower G6Pase activity during September-November and lower glycogen phosphorylase activity from August until the spring. 4. 4. The main reasons for these sexual differences are thought to be the vitellogenetic role of the liver and an estrogen-induced inhibition in the carbohydrate metabolism. 5. 5. The high glycogen content observed in November and the winter months, the increased liver size found in virgin fish and the increase in G6Pase activity in midwinter are all associated with seasonal acclimatization. The increase in glycogen phosphorylase activity in virgin fish and in males took place during the autumn. 6. 6. On one occasion very low G6Pase activities were found, together with rapidly increasing glycogen content in the liver. 7. 7. In general, the liver glycogen content decreased considerably in the spring while the sea was still frozen over, though this decrease was completed between taking the May and June samples. The phenomenon was accompanied by high glycogen phosphorylase activity, especially in the virgin fish.