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

Abstract

Since concomitant release of structurally related peptide hormones with apparently similar functions seems to be a general concept in endocrinology, we have studied the dynamics of the lifetime of the three known adipokinetic hormones (AKHs) of the migratory locust, which control flight-directed mobilization of carbohydrate and lipid from fat body stores. Although the structure of the first member of the AKHs has been known for 20 years, until now, reliable data on their inactivation and removal from the hemolymph are lacking, because measurement requires AKHs with high specific radioactivity. Employing tritiated AKHs with high specific radioactivity, obtained by catalytic reduction with tritium gas of the dehydroLeu2 analogues of the AKHs synthesized by the solid-phase procedure, studies with physiological doses of as low as 1.0 pmol per locust could be conducted. The AKHs appear to be transported in the hemolymph in their free forms and not associated with a carrier protein, despite their strong hydrophobicity. Application of AKHs in their free form in in vivo and in vitro studies therefore now has been justified. We have studied the degradation of the three AKHs during rest and flight. The first cleavage step by an endopeptidase is crucial, since the resulting degradation -products lack any adipokinetic activity. Half-lives for AKH-I, -II and -m were 51, 40, and 5 min, respectively, for rest conditions and 35, 37, and 3 min, respectively, during flight.

Regulation of carbohydrate metabolism and flight performance by a hypertrehalosaemic hormone in the mosquito Anopheles gambiae

“…This high dose was administered with the hope that its action would persist for a few hours, because the half-life of AKHs is limited to tens of minutes by the action of endopeptidases in locusts (Oudejans et al, 1996). By 1 h post injection, glycogen levels had significantly decreased relative to that of control females, and this effect persisted up to 4 h post injection.…”

“…2 A), both intact and decapitated females were injected with this dose, prior to being mounted on the flight mills. Another reason for using this higher dose was that the half-life of AKHs in flying locusts is much shorter that in resting ones (Oudejans et al, 1996). To optimize the effect of injected peptides, females were decapitated to remove the CC, the putative source of Anoga-AKH-I, and the brain, the source of Anoga-AKH II .…”

“…Since the half-life of AKHs has been reported to vary from a few minutes to one hour in locusts during flight (Oudejans et al, 1996) and around 18 min in the firebug, Pyrrhocoris apterus (Goldsworthy et al, 2002), a pharmacological dose of Anoga-HrTH (50 pmol/female) was used to achieve a long-lasting hypertrehalosaemic response in the flight experiments (Fig. 4).…”

Methoprene modifies adipokinetic hormone characteristics in the firebug Pyrrhocoris apterus (Heteroptera: Pyrrhocoridae)

“…The rapid changes in the level of AKH in the haemolymph also reflect the rapid turnover of AKHs. A half-life in the order of a few minutes is proposed for several insect species: for Pyrap-AKH in P. apterus 18 min (Goldsworthy et al, 2002) and Locmi-AKH-I, -II and -III in L. migratoria 51, 40 and 5 min at rest, and 35, 37 and 3 min during flight (Oudejans et al, 1996;Van der Horst et al, 1999). All these data and the above conclusions accord with the suggestion that a coupling between release and biosynthesis of the AKHs in the adipokinetic cells is very loose or does not exist (Diederen et al, 2002).…”

A quantitative study of adipokinetic hormone of the firebug, Pyrrhocoris apterus

“…Half-lives in the order of a few minutes have also been proposed for AKHs from other insects. For example in locusts the endogenous AKHs are inactivated by cleavage of their Asn 3 -Phe 4 bond (Siegert and Mordue, 1992) and their rates of degradation are different for each particular hormones and are influenced by locomotory activity: half-lives of AKH-I, -II and -III at rest are 51, 40 and 5 min; and 35, 37 and 3 min respectively during flight (Oudejans et al, 1996;Van der Horst et al, 1999).…”