Regulation of carbohydrate metabolism during flight in Manduca sexta

Abstract

During the first 5 min of flight in Manduca sexta haemolymph carbohydrate levels decrease by about 8 mg × ml −1 or at a rate of at least 350 μg × min −1 and thereafter they remain more or less unchanged. Before flight about 7% of total fat body glycogen phosphorylase is in the active form, while after 30–60 min about 35% is found in the active form. Even after 1 h of flight, the increased mobilization of carbohydrates by active glycogen phosphorylase can only account for 11–25% of the rate a which carbohydrates are used at the start of flight. The activity of fat body glycogen phosphorylase is not controlled by hormones from the corpora cardiaca. The adipokinetic hormone from these glands does not, therefore, control the activity of glycogen phosphorylase during flight although, it is secreted during flight, and if corpora cardiaca extracts are injected they can activate glycogen phosphorylase. It is suggested that the decrease of haemolymph carbohydrates may control the activation of fat body glycogen phosphorylase.