Adipokinetic hormone and developmental changes of the response of fat body glycogen phosphorylase in Manduca sexta

The maximum percentage of active fat body glycogen phosphorylase which can be induced by the indigenous adipokinetic hormone ( M-AKH) undergoes changes during the development of the tobacco hornworm, Manduca sexta. In intact fifth-instar larvae and pharate pupae a maximum of 60–80% can be achieved. Two picomoles of peptide were required in larvae weighing 2–3 g, pharate pupae and pupae; 20 pmol in larger larvae (5.5–6.5 g). In larvae 1 day before wandering (9–10 g), pupae and adults (both day 1 and day 2) 40% active phosphorylase was the maximum. Ligated abdomens from larvae weighing 9–10 g, however, showed a maximum phosphorylase activation of about 60%. The dilution of the injected peptide in different haemolymph volumes influences the results but cannot explain all the observed differences. Other parameters, e.g. presence of peptidases in the haemolymph and on the surface of tissues bathed in haemolymph or uptake of M-AKH into Malpighian tubules may undergo developmental changes which influence the residence time of the peptide in the haemolymph.