Hypertrehalosaemic and hyperlipaemic responses to adipokinetic hormone in fifth larval instar locusts,Locusta migratoria

In fifth instar larvae of Locusta migratoria the haemolymph lipid concentration is elevated after injection of adipokinetic hormone (AKH). This hyperlipaemic response in larvae remains substantially lower than in adults; over 75% of the mobilized lipid consists of diacylglycerol. In addition, unlike adult locusts, fifth instar larvae also exhibit a consistent, though moderate, hypertrehalosaemic response to AKH. The increases of both lipid and carbohydrate concentrations in larvae are dose-dependent, showing a significant linear regression on log dose in the range 0.2–20 pmol AKH.Glycogen phosphorylase in the fat body of fifth instar larvae as well as young adults is activated on injection of AKH, the percentage active phosphorylase increasing linearly with log dose in the range 0.04–20 pmol AKH. For a given response, a somewhat higher dose of AKH is needed in larvae than in young adults.Fat body glycogen phosphorylase is strongly activated during the period of the larval-adult ecdysis, when active phosphorylase accounts for almost half of the total enzyme, which is approximately ten times more than it is two days before, and two days after the ecdysis.The corpora cardiaca of fifth larval instar locusts already possess the potencies to elevate carbohydrate and lipid concentrations in larval haemolymph, and to activate fat body glycogen phosphorylase.     

饥饿对东亚飞蝗生长和取食的影响

研究了不同龄期东亚飞蝗Locusta migratoria manilensis(Meyen)的耐饥饿能力和3龄后的东亚飞蝗在不同饥饿程度下的取食量和取食速度。结果表明,东亚飞蝗的耐饥饿能力基本随龄期的增加而增强,平均耐饥饿时间为46～116h;同一龄期的东亚飞蝗,饥饿12h后的取食量和取食速度均大于正常情况,饥饿24h后的取食量和取食速度与正常情况下差异不显著,饥饿36、48h后的取食量和取食速度均明显小于正常情况;饥饿程度越大,取食量就越小,取食速度越慢。     

Carbohydrases and carbohydrate digestion in the gut of Locusta migratoria

The digestion of various carbohydrates and synthetic substrates by the gut of Locusta migratoria was analysed quantitatively. Maltose, starch, and sucrose were found to be hydrolysed most rapidly, whereas the splitting of cellobiose, trehalose, lactose, and melecitose took place at much slower rates.The absolute carbohydrase activities in foregut and midgut are nearly equal. However, specific activities are much higher in the foregut. Only low activities were found in extracts from the hindgut and salivary glands. The latter show a pattern of sugar splitting which is different from that found in gut preparations.The distribution of carbohydrase activities between the epithelia and lumina of the foregut, midgut, and hindgut and between soluble and particulate fractions were studied. The midgut epithelium is shown to have a particularly high content of enzymes, although some carbohydrases are rather active also in the epithelium of the hindgut. During hunger periods the relative enzymatic activities of the epithelium are distinctly increased.The isolation and purification of the carbohydrases were attempted and a partial separation of individual enzymes was obtained by gel-filtration. These results indicate the presence of at least seven distinct carbohydrases in the locust gut. The molecular weights of the enzymes were estimated by gel-filtration, and K_M values and pH-optima are reported.     

Effect of injection of synthetic Hyalophora cecropia juvenile hormone in Locusta migratoria L]

The synthetic racemic C18 Hyalophora cecropia juvenile hormone (JH-I) is injected at does of between 10 and 200 mug/animal at the end of the fourth instar of Locusta migratoria. The effects on mortality, length of the fourth and fifth instars, pigmentation and morphogenesis are reported. Higher doses of JH-I produce a higher mortality than lower doses. But mortality can also occur following the injection of oil which sometimes takes place only a few hours before the ecdysis. In no case is JH-I able to shorten the length of the instar. Many animals moult at the same time as the controls, but some of them, both in the fourth and fifth instars, show an important increase in the length of the instar because of an inhibition of the ecdysis. The effect of JH-I on pigmentation is very important and doses higher than 50 mug/animal present a greater effect than an implantation of one pair of corpora allata, both on the number of insects which turn green and on the intensity of this green pigmentation. At the metamorphosis the larvae injected with JH-I produce imperfect imagos and supernumerary larvae, the number of which depends upon the dose. Nevertheless the morphogenetic effect is considerably lower than that of one pair of corpora allata. We have reason to think that this is only due to the time of injection and not to the activity on morphogeneis of the injected hormone. JH-I is injected at the dose of 200 mug in young females which were allatectomized beforehand to prevent oocytes maturation. The hormone completely counter-balances the lack of the corpora allata and some days after the injection the oocytes are in the same state of development as those of the controls. All the results indicate that the synthetic racemic C18 juvenile hormone of Hyalophora cecropia shows a quite similar activity to the secretion of the corpora allata on Locusta migratoria although it has been said for some time that this hormone was not the principal one in locusts.     

Effect of high potassium concentrations on juvenile hormone release in vitro from corpora allata of Locusta migratoria

ABSTRACT. Incubation of corpora allata (CA) from adult females of Locusta migratoria (L.) in vitro in medium with a potassium concentration of 50 mM results in an elevation of the rate of juvenile hormone (JH) release. This elevation is however delayed, becoming apparent after the glands have been returned to low concentration of potassium but it is also prolonged, lasting up to 270 min. The elevation is initially modest but becomes more marked with time. The response of glands to high concentration of potassium is heterogeneous and appears to some extent to be a function of the initial rate of JH release of the glands. Glands starting with low rates of JH release are stimulated strongly by potassium, those with high rates of JH release much less so. Co-incubation of glands with high concentration of potassium and with calcium channel blockers (both organic and ionic) prevents the elevation of release rates otherwise consequent on high concentrations of potassium.     

Effects of juvenile hormone analogs and 20-hydroxyecdysone on diapause termination in eggs of Locusta migratoria and Oxya yezoensis

To understand the hormonal control of embryonic diapause, juvenile hormone analogs (JHAs), methoprene and hydroprene, and 20-hydroxyecdysone (20E) were applied onto diapause eggs of Locusta migratoria and Oxya yezoensis. These insects enter diapause at the mid-stage of embryogenesis prior to blastokinesis. Topical application of JHAs significantly facilitated diapause termination in both species but JHA-treated embryos underwent abnormal morphogenesis, pigmentation and sclerotization without dorsal closure. The Locusta eggs immersed in the 20E solution for 24h terminated diapause in a dose-dependent manner. We also investigated phosphorylation of extracellular signal-regulated kinase (ERK), a member of mitogen-activated protein kinase (MAPK), during diapause-terminating process of Locusta migratoria and found that ERK was activated either by cold exposure or JHA treatment. The possible involvement of the hormones and ERK in embryonic diapause and the possibility of ecdysteroids synthesis by prothoracic glands of diapause embryo were proposed.     

Physico-chemical (GC-MS) measurements of juvenile hormone III titres during embryogenesis of Locusta migratoria

Summary

The titre fluctuations of juvenile hormone III (JH III) in eggs of Locusta during embryogenesis were investigated by use of a combination of gas chromatography and chemical ionisation mass spectrometry. The results do not favour the idea of a functional transfer of JH III from the adult female to the embryo. JH III was found to be absent during the period of intense, JH-sensitive, organogenesis, roughly at mid-embryogenesis. The hormone titres peak shortly before the deposition of the last (3rd) embryonic cuticle (which corresponds to the first larval cuticle). Hatching occurs in the virtual absence of JH III.     

Lipoprotein transformations during adipokinetic hormone action in Locusta migratoria

ABSTRACT. Detailed studies of lipoprotein A⁺ formation during AKH action have been made in Locusta migratoria L. using gel filtration combined with the use of radiolabeled haemolymph protein probes. In addition, we have assessed the quantitative contribution of the C_L-proteins to A⁺ formation by direct measurement of the changes in concentration of free C_L-proteins and report some properties of the C-I and C-II proteins: they appear to be glycoproteins of 20,000 and 16,000 MW respectively, but do not bind to concanavalin A. We have confirmed earlier observations (using different techniques) which showed that liproprotein A_yellow is not involved per se in A⁺ formation during the first 15 min of AKH action. In contrast, the (two) C_L-proteins take part in A⁺ formation without any apparent delay after hormone injection. Our observations show that A⁺ formation is essentially complete within 30 min of AKH injection, although further C_L-protein binding and lipid-loading do occur subsequently. After 30 min there is no further decrease in the A_yellow titre. It is argued that much, if not all, C_L-protein is located at the surface of the A⁺ particle. From the changes in titres which occur in A_yellow and C_L-proteins during AKH action we estimate that A⁺ is formed from 1 mole of A_yellow and approximately 28 moles of C_L-proteins. Using these figures we calculate an apparent molecular weight for A⁺ within the range of 1.65–2.12×10⁶, which is in reasonable agreement with estimates derived from gel exclusion chromatography data. These studies emphasize the dynamic and fully reversible nature of lipoprotein A⁺ formation and highlight the complex nature of the lipoprotein transformations occurring during hormone-stimulated lipid transport in locusts.     

Influence of age on chiasma number in male Locusta migratoria

The influence of age on chiasma formation in Locusta migratoria has been studied both in wild-type and irradiated males. Samples were obtained on the one hand from different individuals and on the other hand from the same individuals at different ages through repeated biopsies. It was observed that mean chiasmata per cell decreased in ageing animals. Chi-squared tests and correlation coefficients showed that the decrease of chiasmata with age is progressive but not continuous. Intermediate values coincide with the first mating. It seems that older individuals tend to transmit their genetic combinations unaltered, increasing the probability of transmitting gene combinations of adaptive value.     

Characterization of juvenile hormone-binding proteins of hemolymph of Locusta migratoria

The binding of juvenile hormone (JH) by components from hemolymph of adult female Locusta migratoria was characterized to establish whether hemolymph JH-binding proteins could be distinguished from a protein of fat body (BP-1) that may be a JH receptor. Hemolymph was analyzed by the hydroxyapatite assay, gel separation chromatography, polyacrylamide gel electrophoresis, and density gradient centrifugation. Three fractions that bound JH were separated from whole hemolymph by DEAE cellulose column chromatography, and these differed from all three cytosol-binding components. The major hemolymph component (H-A) showed relatively stable binding of JH, a slight loss of binding capacity after delipidation, and a K_d for JH-I of 16 nM. The K_ds for JH-l and JH-lll with unfractionated hemolymph were 26 and 42 nM respectively. The order of effectiveness of competitors for binding of [³H]JH-l was JH-lll > JH-l ? methoprene > hydroprene ? acids of methoprene and hydroprene. The data indicated that unlabeled JH-lll was bound more effectively than its radioactive counterpart. The sedimentation values determined by sucrose density gradient ultracentrifugation were 13-14 S for hemolymph, and the sedimentation value was not altered by the inclusion of 0.4 M KCl throughout the gradient. The data indicated that H-A resembled the specific JH carriers and differed from the putative receptor of fat body cytosol by several criteria.     

High-molecular-weight serum proteins from Locusta migratoria: identification of a protein specifically binding juvenile hormone III

ABSTRACT. Tritiated 10,11-epoxyfarnesyl diazoacetate (EFDA), a photoaffinity label, can be covalently attached to the binding site of a JH-III-specific binding protein in the haemolymph of Locusta migratoria migratorioides (R & F). The specificity of the binding of EFDA to the binding protein is verified by displacement with excess unlabelled JH-III, and EFDA can be used to identify the binding protein in native pore-limiting gradient poly(acrylamide) gel electrophoresis (PAGE) and sodium dodecyl sulphate-PAGE. The native binding protein has a molecular weight of 575,000 and is composed of seemingly identical subunits of molecular weight 81,000.
Three other high-molecular weight serum proteins are identified by native PAGE: a lipophorin, composed of two kinds of apolipophorins, a larval storage protein and a cyanoprotein. The molecular weights and subunit structures of these proteins are investigated, but none of these other high-molecular weight proteins bind JH-III to an appreciable extent.     

Identification of a diuretic hormone of Locusta migratoria.

We have isolated a peptide from brains and corpora cardiaca of Locusta migratoria which is immunologically related to the diuretic hormone of Manduca sexta. We determined its structure as a 46 amino acid linear peptide with 43-50% identity to the M. sexta hormone. Moreover, we showed that the new peptide functions as a diuretic hormone in L. migratoria, stimulating urine production by Malpighian tubules and elevating levels of cAMP in tubules.     

Effect of topical application of a juvenile hormone mimic on the duration of the moulting cycle in fifth instar Rhodnius

Fifth instar Rhodnius prolixus given a single topical application of synthetic juvenile hormone (JH) on one of the first 12 days after feeding showed a sigmoid relationship between day of treatment and duration of the moulting cycle. A similar relationship was observed between day of treatment and mean ‘juvenile score’ in subsequently emerging insects. The linear relationship between mean ‘juvenile score’ and duration of the moulting cycle suggests that the increased time from feeding to ecdysis for late-treated insects is a result of the morphogenetic effects of the JH treatment. Some of the partially juvenilized insects obtained by treatment after day 5 produced an odour characteristically detected only from adult insects. The possible significance of this observation is discussed.     

Identification of an arginine vasopressin-like diuretic hormone from Locusta migratoria

We have identified two neuropeptides (F1 and F2) from suboesophageal and thoracic ganglia of Locusta migratoria, which we isolated earlier based on their immunological similarity to arginine vasopressin. The more abundant and hydrophilic factor, F1, has sequence Cys-Leu-Ile-Thr-Asn-Cys-Pro-Arg-Gly-NH2, but its biological role is unknown. The less abundant factor, F2, is an antiparallel dimer of F1, and functions as a diuretic hormone of this species. It appears to act through the intermediacy of cyclic AMP. The properties of the native neuropeptides were identical with those of samples synthesized from appropriately protected L-amino acids.     

Age-related changes in the response to adipokinetic hormone in Locusta migratoria

ABSTRACT. In fifth instar nymphs of Locusta there is only a feeble adipokinetic response to extracts of corpora cardiaca. In fledglings, this poor response persists for a few days but then increases dramatically to reach a plateau by day 8. The response declines to almost zero as the locusts age beyond 35 days of adult life. This pattern of change in response is similar in both males and females but there are some differences in magnitude depending upon whether the response is measured as changes in haemolymph total lipid (vanillin-positive material) or total diglyceride (gas liquid chromatography). The poor response to adipokinetic hormone in nymphs and newly fledged locusts is not a result of shortage of stored lipid in the fat body and cannot be improved by injection of extra hormone.     

Changes in haemolymph osmotic pressure in Locusta migratoria larvae in relation to feeding

An account is given of the effect of feeding on haemolymph osmotic pressure in larvae of Locusta migratoria. Changes in concentration of solutes and haemolymph volume are investigated and discussed.