Developmental changes in the response of the fat body of Manduca sexta to injections of Corpora cardiaca extracts.

The Corpora cardiaca of larval and adult Manduca sexta contain glycogen phosphorylase-activating and adipokinetic activity. Depending on the age of the injected animal, injection of Corpora cardiaca extracts induces different responses. In larvae of the 1st and 2nd day of the Vth instar, phosphorylase is activated strongly by injections of Corpora cardiaca extracts, whereas in older animals it is only slightly activated. Mobilization of lipids in response to Corpora cardiaca extract injections is found only in animals injected after the imaginal molt; in younger animals this response is absent. It is argued that this difference in responsiveness may be due to a change in the properties of the target organ fat body.