Stimulation of glycogenolysis by three locust adipokinetic hormones involves Gs and cAMP

Identification and Functional Characterization of Two Orphan G-protein-coupled Receptors for Adipokinetic Hormones from Silkworm Bombyx mori

“…In general, binding of AKH to its receptor leads to dissociation of the G s protein the ␤␥ subunit, which in turn activates an adenylate cyclase, resulting in an increase in intracellular cAMP levels (16,37). cAMP stimulates lipase activity via activation of PKA.…”

“…Previous biochemical characterization with isolated fat body suggested that AKH binds to its receptor and activates adenylyl cyclase via the G s protein, which results in an increase of intracellular cAMP levels. In addition, AKH activates phospholipase C to induce the release of Ca 2ϩ from intracellular Ca 2ϩ stores (16,17). Our previous studies have demonstrated that AKH stimulation not only led to a ligand concentration-dependent mobilization of intracellular Ca 2ϩ and cAMP accumulation but also elicited PKA and PKC pathway-mediated transient activation of the extracellular signal-regulated kinase 1 and 2 (ERK1/2) pathways in HEK293 cells stably expressing AKHR (18).…”

Endocrine control of TAG lipase in the fat body of the migratory locust, Locusta migratoria

“…2B) 60 min after injection of analogues of IP 3 and cAMP. These two compounds are known to be involved in the activation of glycogen phosphorylase in locusts (Vroemen et al 1995(Vroemen et al , 1997. For comparison, the activation state of glycogen phosphorylase was measured 15 min after injection of the respective second messengers using a different group of locusts (Fig.…”

“…Trehalose released from the fat body does not accumulate in the haemolymph, probably because consumption and mobilization are balanced. The carbohydrate concentration in the haemolymph is, therefore, not useful for observing the hypertrehalosaemic effect (see Ga¨de and Auerswald 2003) but the activation of glycogen phosphorylase in the fat body of locust has been extensively studied (see, for example, Ga¨de 1981;Vroemen et al 1995Vroemen et al , 1997. Only scattered information, however, is available on the action of TAG lipase in the fat body of insects in general.…”

Locust adipokinetic hormones: carrier-independent transport and differential inactivation at physiological concentrations during rest and flight.

“…The most important target tissue for the AKHs is the fat body, in which they stimulate the hormone-dependent triacylglycerol lipase and glycogen phosphorylase (13), though with different potencies (14). Since physiological responses of AKHs in the fat body include an increase in cAMP level (15) as well as stimulation of phosphoinositide turnover (16) and depend on intra-and/or extracellular calcium ions (17)(18)(19), it is most likely that-like other receptors for peptide hormones-also the AKH receptor or receptors are linked to G proteins for their intracellular responses (15). The titer of the AKHs in the hemolymph is very low (20,21), and their hydrophobic nature suggests their transport to be in association with specific transport or carrier molecules or with the lipid-transporting lipophorins, though this has never been postulated.…”