[ 196] Glycogenolysis in the Liver of the Common Frog, Rana Temporaria

INTRODUCTION It has been known for many years that the metabolism of the frog is subject to seasonal variations. Liver glycogen and total body glycogen attain a maximum value in autumn, and a minimum in spring (Athanasiu, 1899; Pfluger, 1907; Kato, 1910; Bleibtreu, 1911; Goldfederowa, 1926). A few seasonal estimations of blood sugar were reported (Lesser, 1913; Slome, 1936), but the first comprehensive study of the problem was conducted by Smith (1950), who investigated the seasonal changes in blood-sugar level, fat-body development, liver-glycogen content and gonad condition in Rana temporaria. In view of these seasonal changes, it was felt that temperature might be an important factor in the regulation of amphibian carbohydrate metabolism. It was therefore decided to investigate the fundamental relationship between temperature and glycogenolysis in the frog's liver, with a view to establishing the role of changing environmental temperature in the observed seasonal changes in carbohydrate metabolism. For this purpose a tissue-slice technique had many advantages, as the number of variables can be greatly reduced. For example, by incubating slices from the same liver at different temperatures, not only can individual variation be controlled, but simultaneous readings over a wide temperature-range are obtainable. Such a technique also lends itself to the in vitro study of the action of drugs and hormones on glucose production.