Adipokinetic hormone (AKH) mobilizes carbohydrates
and lipids from storage into the hemolymph for energy
demands such as a long flight. Thus, AKH is a functional
counterpart of vertebrate glucagon. The red pigment concentrating
hormone (RPCH), structurally related to AKH,
controls the granule of the crustacean chromatophore, eventually
changing the body color.
AKH has been identified in more than 40 insect species
so far.In most insect species, several AKH subtypes are
present. In L. migratoria, two structurally related subtypes
(AKH-II and -III) have been identified.Some AKH subtypes
are exceptionally nonapeptides and decapeptides.
The number of subtypes differs according to species.
No subtypes of crustacean RPCH are known.
AKH stimulates the fat body, where lipids and carbohydrates
are stored, eventually resulting in lipid and carbohydrate
mobilization into the hemolymph. The
increase in hemolymph lipids is accompanied by the activation
of the lipid transfer system. According to the
effects of the increase in hemolymph carbohydrates and
lipids, locomotor and flight muscles are concomitantly
activated.AKH is also required for proper food digestion,
enhancing the protease and amylase activities in
the midgut of Sarcophaga crassipalpis and Periplaneta americana,
respectively.RPCH, however, influences the
concentration of the pigment chromatophore, causing
drastic body color changes in the crustacean species.
Regulation of synthesis and release
AKH is released from the secretary granule in the CC.
AKH secretion is modulated by nutritional status, including
the need for extra loading of lipids and carbohydrates
for long migratory flights.In a recent study, a glucosesensing
neuron pair was identified as regulating AKH
release in Drosophila.AKH is released from the CC by
a high concentration of potassium in vitro.
