A hormone from the corpora cardiaca controls fat body glycogen phosphorylase during starvation in tobacco hornworm larvae

Abstract

Steele has demonstrated the presence of a factor in the corpora cardiaca (Cc) of the adult male cockroach, Periplaneta americana, which increases the trehalose concentration in haemolymph¹. This factor, which was shown to be a peptide², activates fat body glycogen phosphorylase³, and glucose-1-phosphate which is liberated from glycogen is used for trehalose synthesis within the fat body. Peptides having similar properties were found in several other insects, including bees², locusts⁴, stick insects^5,6 and a lepidopteran, Manduca sexta (tobacco hornworm)⁷. These peptides have been called hyperglycaemic¹ or phosphorylase activating factor⁷ or trehalogon⁸. Their physiological significance during an insect's life cycle is unknown^9,10, and consequently it is uncertain whether these compounds are hormones or not. We have examined the activity of fat body glycogen phosphorylase during late larval development of M. sexta¹¹. During the moult from the fourth to the fifth instar, when the animals were unable to ingest food for a period of about 25 h, 45% of the enzyme was in an active form. Before and after the moult, only 10% of the enzyme was active. We suggested that reduced feeding activity leads to the activation of fat body glycogen phosphorylase by releasing the phosphorylase activating peptide from the Cc¹¹. We now substantiate this hypothesis in reporting results obtained with fifth instar larvae of M. sexta that were starved during their normally active feeding period.