Quantification of adipokinetic hormones I and II in the corpora cardiaca of Schistocerca gregaria and Locusta migratoria

Peptides of the adipokinetic hormone/red pigment-concentrating hormone family with special emphasis on Caelifera: primary sequences and functional considerations contrasting grasshoppers and locusts

The presented work is a hybrid of an overview and an original research paper. First, we review briefly the structure, biosynthesis, release, mode of action and function of those peptides that constitute the adipokinetic/red pigment-concentrating family. Second, we collate the data on primary sequences available for caeliferan orthoptera, i.e. grasshoppers and locusts, and add a number of new data from previously unpublished work. The data are interpreted in conjunction with morphological and molecular biology data with respect to phylogenetic relationships of these various taxa. Finally, we discuss the differences between the adipokinetic response of grasshoppers and locusts to corpus cardiacum extract or synthetic adipokinetic hormone with regard to flight ability, phase polymorphism, age, presence of adipokinetic hormones, lipophorin system and other parameters. It appears that the higher hyperlipaemic response is always correlated with pronounced flight ability.

Relationship of adipokinetic hormone I and II to migratory propensity in the grasshopper, Melanoplus sanguinipes

This report examines three aspects of adipokinetic hormone (AKH) involvement in migratory flight behavior in the grasshopper, Melanoplus sanguinipes. The titer of hemolymph AKH I during long-duration tethered flight was examined using radioimmunoassay (RIA) after narrow bore RP-HPLC. The hemolymph fraction containing AKH I was assayed using commercially available anti-Tyr1-AKH I serum. Titer determinations of hemolymph AKH were done at rest and after various periods of flight. The amount of AKH I released from the corpora cardiaca during flight was estimated. When resting levels of AKH I and II in corpora cardiaca (CC) of migrants and non-migrants were examined with HPLC, no significant differences in AKH levels were detected between non-migrants, animals that had flown for 1 h to identify them as migrants, and animals that had flown to exhaustion (i.e., voluntary cessation). CC levels of both AKH I and II were less in this species than in locusts. When the lipid mobilization in response to AKH I and II was compared in migrants (animals that had self-identified as migrants in a 1-h tethered flight test) and non-migrants (animals that would not perform a 1-h flight in a tethered flight test), the adipokinetic response to AKH I was greater in migrants than in non-migrants, possibly indicating differences in level of sensitivity or number of receptors in the target tissues. AKH II had little effect on hemolymph lipid levels in either flight group, and may not play a significant role in lipid mobilization in this species.

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

The development of an enzyme-linked immunoassay (ELISA) for the adipokinetic neuropeptide hormone, Pya-AKH, from the firebug Pyrrhocoris apterus L. is described. The ELISA measures as little as 20 fmol of Pya-AKH. Tested against a range of synthetic peptides, the assay has a high sensitivity for peptides containing the C-terminal motif FTPNWamide. The amounts of Pya-AKH in the brain, corpora cardiaca, suboesophageal ganglia, and fused thoracic and abdominal ganglionic mass are very small, with only the corpora cardiaca containing appreciable levels of the hormone (ca. 4 pmol per bug). Preliminary estimates of the persistence of the hormone in the haemolymph are consistent with values determined for AKHs in other insects, and suggest that Pya-AKH has a rapid turnover with a half-life of ca. 18 min. Measurements of circulating titres of AKH in Pyrrhocoris are only possible in the ELISA described here by using pooled samples of haemolymph, and after preliminary clean-up of the haemolymph samples. The titre of Pya-AKH in resting reproductive female Pyrrhocoris is ca. 1 fmol/&mgr;l.

Adipokinetic hormones concentrations in the haemolymph of Schistocerca gregaria, measured by radioimmunoassay

A new procedure for the measurement of adipokinetic hormone (AKH) concentrations in locust (Schistocerca gregaria) haemolymph is described: Haemolymph is extracted with chloroform/methanol/water and the aqueous layer is fractionated with reverse-phase cartridges and HPLC. The fractions corresponding to AKH-I (Lom-AKH-I) and AKH-II (Scg-AKH-II) are then measured in a competitive binding assay using specific antibodies and [3H]AKHs. The procedures could be applied to any peptides containing N-terminal pyroglutamate residues including all members of the adipokinetic/hyperglycaemic/red pigment concentrating hormone family. Results show that the concentrations of both AKH-I and AKH-II increase within 5 min of initiation of flight and are maintained at approx. 15-fold (AKH-I) and 6-fold (AKH-II) the resting levels over flights of at least 60 min. Poisoning of locusts with either the insecticide deltamethrin or with potassium chloride also caused release of hormones. Starvation for 6 h caused elevation of hormone levels in 5th instar nymphs, but starvation for 6 or 20 h had little effect on hormones in adults, despite an increase in haemolymph diacylglycerols at 20 h.

Physiological and biochemical aspects of flight metabolism in cocoon-enclosed adults of the fruit beetle, Pachnoda sinuata

We studied several aspects of flight metabolism in cocoon-enclosed adults of the fruit beetle Pachnoda to investigate their flight capability. The majority of adults which were forcefully removed from their pupal cocoon flew off within 5 min of exposure to bright sunlight. Most of the beetles which did not fly voluntarily were, however, capable of flight. Compared with 2-4 week old adults of the same species, cocoon-enclosed adults have higher reserves of glycogen in flight muscles and fat body, whereas the level of total carbohydrates in the haemolymph and the concentration of proline in haemolymph, flight muscles and fat body were similar.Enzymes involved in carbohydrate breakdown (MDH, GAPDH) were more active in flight muscles and fat body of cocoon-enclosed adults compared with adults, while enzymes of proline metabolism in the flight muscles (AlaT, NAD-ME) and fat body (AlaT, NADP-ME) had similar activities in cocoon-enclosed adults and adults. An enzyme of the beta-oxidation of fatty acids (HOAD) had similar activities in flight muscles and fat body of cocoon-enclosed adults and adults.Mitochondria isolated from flight muscles of adults removed prematurely from their cocoon favour the oxidation of proline and pyruvate. Pyruvate, however, is oxidized at higher rates than by mitochondria isolated from flight muscles of adults.During a short lift-generating flight, cocoon-enclosed adults proved that their flight muscles are capable of strong flight performance. During these flights, cocoon-enclosed adults consume proline and carbohydrates at a similar rate to that of adults.The endogenous AKH peptide, Mem-CC, has hyperprolinaemic and hypertrehalosaemic activity in cocoon-enclosed adults. The hypertrehalosaemic effect, however, is stronger in cocoon-enclosed adults than in adults.The content of Mem-CC in corpora cardiaca of larvae (3rd instar), cocoon-enclosed adults and 1 day-old adults is similar at 5-6 pmol per pair of corpora cardiaca, whereas it is higher in 10 day-old adults and 20 day-old adults (37 and 15 pmol per pair corpora cardiaca, respectively).From these results we conclude that cocoon-enclosed adults comply with all the prerequisites for flight performance before they leave their pupal cocoon. Furthermore, cocoon-enclosed adults have a more pronounced carbohydrate-based metabolism before they leave their cocoon compared with adults, which suggests that carbohydrate breakdown is mainly involved in such activities as leaving the cocoon and burrowing activity thereafter.

Physiological effectors of hyperglycemic neurohormone biosynthesis in an insect

Biosynthesis of hypertrehalosemic hormone (HTH) by isolated corpora cardiaca (CC) from Blaberus discoidalis cockroaches was measured for the 3-week period following adult ecdysis using an in vitro bioassay based on the incorporation of [3H]tryptophan. Synthetic rates for both males and females were highest following the molt and declined with age. Rates of HTH secretion and levels of stored HTH followed a similar pattern. We found no neural or endocrine brain effects or photophase influence on HTH synthesis. Synthesis was unaffected by treatment with 20-hydroxyecdysone or the juvenile hormone analog methoprene. In starved insects, HTH synthesis doubled and secretion increased 66% relative to fed controls.

Secretory granule formation and membrane recycling by the trans-Golgi network in adipokinetic cells of Locusta migratoria in relation to flight and rest

The influence of flight activity on the formation of secretory granules and the concomitant membrane recycling by the trans-Golgi network in the peptidergic neurosecretory adipokinetic cells of Locusta migratoria was investigated by means of ultrastructural morphometric methods. The patterns of labelling of the trans-Golgi network by the exogenous adsorptive endocytotic tracer wheat-germ agglutinin-conjugated horse-radish peroxidase and by the endogenous marker enzyme acid phosphatase were used as parameters and were measured by an automatic image analysis system. The results show that endocytosed fragments of plasma membrane with bound peroxidase label were transported to the trans-Golgi network and used to build new secretory granules. The amounts of peroxidase and especially of acid phosphatase within the trans-Golgi network showed a strong tendency to be smaller in flight-stimulated cells than in non-stimulated cells. The amounts of acid phosphatase in the immature secretory granules originating from the trans-Golgi network were significantly smaller in stimulated cells. The number of immature secretory granules positive for acid phosphatase tended to be higher in stimulated cells. Thus, flight stimulation of adipokinetic cells for 1 h influences the functioning of the trans-Golgi network; this most probably results in a slight enhancement of the production of secretory granules by the trans-Golgi network.

Adipokinetic peptide hormone content and biosynthesis during locust development

The content and biosynthesis of adipokinetic hormones (Lom-AKH-I, -II. and -III) were studied in larval stages and adults of Locusta migratoria. The amount of all three AKHs increases with age, although the patterns found for AKH-I and -II differ from that for AKH-III. Biosynthetic capacity of the corpus cardiacum for the three AKHs increases with age, particularly in larvae, whereas in adults this increase is only observed for AKH-III. The amounts of AKH-I and -II stored and their active biosynthesis greatly surpass the small quantities needed for mobilization of fuels during flight. The data for AKH-III suggest that this hormone may be important also during larval stages.

Postembryonic proliferation of neuroendocrine cells expressing adipokinetic hormone peptides in the corpora cardiaca of the locust

Neuroendocrine glands that synthesize and secrete peptide hormones regulate the levels of these peptide messengers during development. In this article we describe a mechanism for regulating neuropeptide levels in the corpora cardiaca of the locust Schistocerca gregaria, a neuroendocrine gland structurally analogous to the vertebrate adenohypophysis. A set of five colocalized peptide hormones of the adipokinetic hormone family is synthesized in intrinsic neurosecretory cells in the corpora cardiaca. During postembryonic development there are progressive changes in the absolute and relative levels of these five peptide hormones. We show that the ability of the gland to increase peptide synthesis is due to a 100-fold increase in the number of cells which make up the gland. The gland grows by the addition of new cells derived from symmetrical division of undifferentiated precursor cells within the corpora cardiaca. We show, using double-label immunocytochemistry, that cells born in the glandular lobe mature into cells that express adipokinetic hormone peptides. The pattern of cell birth and peptide expression can account for the dramatic increase in postembryonic peptide levels.

Isolation and structure elucidation of neuropeptides of the AKH/RPCH family in long-horned grasshoppers (Ensifera)

An identical neuropeptide was isolated by reversed-phase high-performance liquid chromatography from the corpora cardiaca of the king cricket, Libanasidus vittatus, and the two armoured ground crickets, Heterodes namaqua and Acanthoproctus cervinus. The crude gland extracts had adipokinetic activity in migratory locusts, hypertrehalosaemic activity in American cockroaches and a slight hypertrehalosaemic, but no adipokinetic, effect in armoured ground crickets. The primary structure of this neuropeptide was determined by pulsed-liquid phase sequencing employing Edman chemistry after enzymically deblocking the N-terminal 5-oxopyrrolidine-2-carboxylic acid residue. The C-terminus was also blocked, as indicated by the lack of digestion by carboxypeptidase A. The peptide was assigned the structure [symbol: see text]Glu-Leu-Asn-Phe-Ser-Thr-Gly-TrpNH2, previously designated Scg-AKH-II. The corpora cardiaca of the cricket Gryllodes sigillatus contained a neuropeptide which differed in retention time from the one isolated from the king and armoured ground crickets. The structure was assigned as [symbol: see text]Glu-Val-Asn-Phe-Ser-Thr-Gly-TrpNH2, previously designated Grb-AKH. This octapeptide caused hyperlipaemia in its donor species. The presence of the same peptide, Scg-AKH-II, in the two primitive infraorders of Ensifera, and the different peptide, Grb-AKH, in the most advanced infraorder of Ensifera, supports the evolutionary trends assigned formerly from morphological and physiological evidence.