Adipokinetic hormone inhibits protein synthesis in Locusta

Role of adipokinetic hormone in the Colorado potato beetle, Leptinotarsa decemlineata infected with the entomopathogenic nematode Steinernema carpocapsae

The effects of the entomopathogenic nematode Steinernema carpocapsae on the Colorado potato beetle (CPB) Leptinotarsa decemlineata and the involvement of adipokinetic hormone (AKH) in the responsive reactions were examined in this study. It was observed that nematode application doubled the amount of AKH (Peram-CAH-I and Peram-CAH-II) in the central nervous system of L. decemlineata, indicating mobilization of anti-stress reactions in the body. Furthermore, the external co-application of Peram-CAH-II with the nematode significantly increased beetle mortality (5.6 and 1.8 times, 1 and 2 days after application, respectively). The mechanism underlying this phenomenon was investigated. As the effect on gut characteristics was equivocal, it was assumed that the nematodes profited from the observed mobilization of metabolites from the fat body into the Peram-CAH-II-induced hemolymph. This phenomenon supplied nematodes with a more nutrient-dense substrate on which they propagated. Furthermore, Peram-CAH-II lowered vitellogenin expression in the fat body, particularly in males, thus limiting the anti-pathogen defense capacity of the protein. However, there could be other possible mechanisms underpinning this chain of events. The findings could be theoretically intriguing but could also aid in developing real insect pest control methods in the future.

Adipokinetic Hormones Enhance the Efficacy of the Entomopathogenic Fungus Isaria fumosorosea in Model and Pest Insects

Insect adipokinetic hormones (AKHs) are neuropeptides with a wide range of actions, including the control of insect energy metabolism. These hormones are also known to be involved in the insect defence system against toxins and pathogens. In this study, our aim was to demonstrate whether the application of external AKHs significantly enhances the efficacy of the entomopathogenic fungus Isaria fumosorosea in a model species (firebug Pyrrhocoris apterus) and pest species (Egyptian cotton leafworm Spodoptera littoralis and pea aphid Acyrthosiphon pisum). It was found that the co-application of Isaria with AKHs significantly enhanced insect mortality in comparison to the application of Isaria alone. The mode of action probably involves an increase in metabolism that is caused by AKHs (evidenced by the production of carbon dioxide), which accelerates the turnover of Isaria toxins produced into the infected insects. However, several species-specific differences probably exist. Intoxication by Isaria elicited the stimulation of Akh gene expression and synthesis of AKHs. Therefore, all interactions between Isaria and AKH actions as well as their impact on insect physiology from a theoretical and practical point of view need to be discussed further.

Adipokinetic hormone promotes infection with entomopathogenic fungus Isaria fumosorosea in the cockroach Periplaneta americana

The adipokinetic hormones (AKHs) are known to be involved in insect immunity, thus their role in the cockroach Periplaneta americana infected with the entomopathogenic fungus Isaria fumosorosea was examined in this study. The application of I. fumosorosea resulted in a significant increase in both Akh gene expression and AKH peptide levels. Further, co-application of I. fumosorosea with Peram-CAH-II significantly enhanced cockroach mortality compared with the application of I. fumosorosea alone. The mechanism of AKH action could involve metabolic stimulation, which was indicated by a significant increase in carbon dioxide production; this effect can increase the turnover and thus efficacy of toxins produced by I. fumosorosea in the cockroach's body. I. fumosorosea treatment resulted in a significant decrease in haemolymph nutrients (carbohydrates and lipids), but co-application with Peram-CAH-II restored control level of lipids or even further increased the level of carbohydrates. Such nutritional abundance could enhance the growth and development of I. fumosorosea. Further, both I. fumosorosea and Peram-CAH-II probably affected oxidative stress: I. fumosorosea alone curbed the activity of catalase in the cockroach's gut, but co-application with Peram-CAH-II stimulated it. Interestingly, the hormone alone had no effect on catalase activity. Taken together, the results of the present study demonstrate the interactions between the fungus and AKH activity; understanding this relationship could provide insight into AKH action and may have practical implications for insect pest control in the future.

Adipokinetic Hormone Receptor Mediates Trehalose Homeostasis to Promote Vitellogenin Uptake by Oocytes in Nilaparvata lugens

Adipokinetic hormones (AKHs) are well known to mobilize lipids and carbohydrates for energy-consuming activities in insects. These neuropeptides exert their functions by interacting with AKH receptors (AKHRs) located on the plasma membrane of fat body cells, which regulates energy mobilization by stimulating lipolysis of triacylglycerols (TAG) to diacylglycerols (DAG) and conversion of glycogen into trehalose. Here, we investigated the roles of AKH/AKHR signaling system in trehalose metabolism and vitellogenesis during female reproduction in the brown planthopper, Nilaparvata lugens. Knockdown of AKHR expression by RNA interference (RNAi) resulted in a decrease of the circulating trehalose in hemolymph and significantly increased levels of two trehalases in fat bodies, indicating that the modulation of hemolymph trehalose levels by AKHR may be mediated by regulating trehalose degradation. In addition, adult females that had been injected with double-stranded RNA (dsRNA) for AKHR exhibited delayed oocyte maturation, prolonged pre-oviposition period, as well as decline in egg number and reduction in fecundity. Considering that these phenotypes resulting from AKHR silencing are similar to those of vitellogenin receptor (VgR) RNAi, we further analyzed a possible connection between AKHR and vitellogenesis. Knockdown of AKHR showed no effects on the Vg synthesis in fat bodies, whereas it significantly reduced the levels of VgR in ovaries. With RNAi-females, we observed an increase of Vg accumulation in hemolymph and a decrease of Vg deposition in ovaries. Moreover, the decrease in VgR expression and Vg incorporation by developing oocytes could be partially rescued by injection of trehalose into AKHR RNAi females. The present study has implicated trehalose in the AKH/AKHR signaling-mediated control of reproduction and provided new insight into mechanisms of AKH/AKHR regulation of trehalose metabolism in insect vitellogenesis, oocyte maturation and fecundity.

Deficiency of Brummer Impaires Lipid Mobilization and JH-Mediated Vitellogenesis in the Brown Planthopper, Nilaparvata lugens

Provisioning of sufficient lipids and vitellogenin to the oocytes is an indispensable process for fecundity of oviparous insects. Acute mobilization of lipid reserves in insects is controlled by the Brummer (Bmm), an orthologous of human adipose triglyceride lipase (ATGL). To investigate the functional roles of brummer-mediated lipolysis in the fecundity of the brown planthopper, Nilaparvata lugens, RNA interference (RNAi) analyses were performed with double-stranded RNA (dsRNA) against NlBmm in adult females. Knockdown of NlBmm expression resulted in obesity and blocked lipid mobilization in the fat body. In addition, NlBmm silencing led to retarded ovarian development with immature eggs and less ovarioles, decreased number of laid eggs, prolonged preoviposition period and egg duration. Furthermore, severe reductions of vitellogenin and its receptor abundance were observed upon NlBmm knockdown. The transcript levels of NlJHE (juvenile hormone esterase) which degrades JH were up-regulated, whereas the expression levels of JH receptors NlMet (Methoprene-tolerant) and NlTai (Taiman) and their downstream transcription factors NlKr-h1 (Krüppel-homolog 1) and NlBr (Broad-Complex) were down-regulated after suppression of NlBmm. JH-deficient females exhibited impaired vitellogenin expression, whereas JH exposure stimulated vitellogenin biosynthesis. Moreover, JH topical application partially rescued the decrease in vitellogenin expression in the NlBmm-deficient females. These results demonstrate that brummer-mediated lipolytic system is essential for lipid mobilization and energy homeostasis during reproduction in N. lugens. In addition to the classical view of brummer as a direct lipase with lipolysis activity, we propose here that brummer-mediated lipolysis works through JH signaling pathway to activate vitellogenesis and oocyte maturation that in turn regulates female fecundity.

Analysis of lipolysis underlying lactation in the tsetse fly, Glossina morsitans

Female tsetse flies undergo viviparous reproduction, generating one larva each gonotrophic cycle. Larval nourishment is provided by the mother in the form of milk secretions. The milk consists mostly of lipids during early larval development and shifts to a balanced combination of protein and lipids in the late larval instars. Provisioning of adequate lipids to the accessory gland is an indispensable process for tsetse fecundity. This work investigates the roles of Brummer lipase (Bmm) and the adipokinetic hormone (AKH)/adipokinetic hormone receptor (AKHR) systems on lipid metabolism and mobilization during lactation in tsetse. The contributions of each system were investigated by a knockdown approach utilizing siRNA injections. Starvation experiments revealed that silencing of either system results in prolonged female lifespan. Simultaneous suppression of bmm and akhr prolonged survival further than either individual knockdown. Knockdown of akhr and bmm transcript levels resulted in high levels of whole body lipids at death, indicating an inability to utilize lipid reserves during starvation. Silencing of bmm resulted in delayed oocyte development. Respective reductions in fecundity of 20 and 50% were observed upon knockdown of akhr and bmm, while simultaneous knockdown of both genes resulted in 80% reduction of larval production. Omission of one bloodmeal during larvigenesis (nutritional stress) after simultaneous knockdown led to almost complete suppression of larval production. This phenotype likely results from tsetse's inability to utilize lipid reserves as loss of both lipolysis systems leads to accumulation and retention of stored lipids during pregnancy. This shows that both Bmm lipolysis and AKH/AKHR signaling are critical for lipolysis required for milk production during tsetse pregnancy, and identifies the underlying mechanisms of lipid metabolism critical to tsetse lactation. The similarities in the lipid metabolic pathways and other aspects of milk production between tsetse and mammals indicate that this fly could be used as a novel model for lactation research.

RNA interference unveils functions of the hypertrehalosemic hormone on cyclic fluctuation of hemolymph trehalose and oviposition in the virgin female Blattella germanica

Hypertrehalosemic hormone (HTH) is a neuropeptide within the adipokinetic hormone (AKH) family that induces a release of trehalose from fat body into hemolymph in a number of insects. In this study, we first showed that female adult German cockroach, Blattella germanica, displayed a cyclic fluctuation of hemolymph trehalose levels correlated to the maturation of oocytes in the reproductive cycle. After cloning the HTH cDNA from the German cockroach (Blage-HTH), expression studies indicated that Blage-HTH mRNA showed the cyclic changes during the first reproductive cycle, where peak values occurred in 8-day-old virgin female cockroaches, which were going to produce oothecae. The functions of Blage-HTH were studied using RNA interference (RNAi) to knockdown its expression. Adult virgin females of B. germanica injected with Blage-HTH dsRNA increased hemolymph trehalose levels in the late period of vitellogenesis more slowly than control. Furthermore, RNAi of Blage-HTH delayed oviposition time and some (10%) individuals did not produce the first ootheca until 15 days after eclosion, whereas the control group produced ootheca before 9 days in all cases.

Bombyx adipokinetic hormone receptor activates extracellular signal-regulated kinase 1 and 2 via G protein-dependent PKA and PKC but β-arrestin-independent pathways

Neuropeptides of the adipokinetic hormone (AKH) family are among the best studied hormone peptides. They play important roles in insect hemolymph sugar homeostasis, larval lipolysis, and storage-fat mobilization. Mechanistic investigations have shown that, upon AKH stimulation, adipokinetic hormone receptor (AKHR) couples to a Gs protein and enhances adenylate cyclase activity, leading to intracellular cAMP accumulation. However, the underlying molecular mechanism by which this signaling pathway connects to extracellular signal-regulated kinase 1/2 (ERK1/2) remains to be elucidated. Using HEK293 cells stably or transiently expressing AKHR, we demonstrated that activation of AKHR elicited transient phosphorylation of ERK1/2. Our investigation indicated that AKHR-mediated activation of ERK1/2 was significantly inhibited by H-89 (protein kinase A inhibitor), Go6983, and GF109203X (protein kinase C inhibitors) but not by U73122 (PLC inhibitor) or FIPI (PLD inhibitor). Moreover, AKHR-induced ERK1/2 phosphorylation was blocked by the calcium chelators EGTA and BAPTA-AM. Furthermore, ERK1/2 activation in both transiently and stably AKHR-expressing HEK293 cells was found to be sensitive to pretreatment of pertussis toxin, whereas AKHR-mediated ERK1/2 activation was insensitive to siRNA-induced knockdown of β-arrestins and to pretreatment of inhibitors of EGFR, Src, and PI3K. On the basis of our data, we propose that activated AKHR signals to ERK1/2 primarily via PKA- and calcium-involved PKC-dependent pathways. Our current study provides the first in-depth study defining the mechanisms of AKH-mediated ERK activation through the Bombyx AKHR.

Hormonal regulation of energy metabolism in insects as a driving force for performance

Since all life processes depend on energy, the endocrine control of energy metabolism is one of the driving forces for the performance of an individual. Here, we review the literature on the key players in the endocrine regulation of energy homeostasis in insects, the adipokinetic hormones. These pleiotropic peptides not only control dynamic performance traits (flight, swimming, walking) but also regulatory performance traits (egg production, larval growth, and molting). Adipokinetic hormone is released into the hemolymph during intense muscular activity (flight) and also during apparently less energy-demanding locomotory activities, such as swimming and even walking, and, finally, activates the catabolic enzymes phosphorylase and/or triacylglycerol lipase that mobilize carbohydrates and/or lipids and proline, respectively. At the same time, anabolic processes such as the synthesis of protein, lipid, and glycogen are inhibited. Furthermore, adipokinetic hormones affect locomotory activity via neuromodulatory mechanisms that apparently employ biogenic amines. During oogenesis, it is thought that adipokinetic hormone performs similar tasks, because energetic substrates have to be mobilized and transported from the fat body to the ovaries in order to support oocyte growth. Inhibition of anabolic processes by exogenous adipokinetic hormone results in females that lay fewer and smaller eggs. Much less is known about the role of adipokinetic hormones during larval development and during molting but in this case energy homeostasis has to be tightly regulated as well: in general, during the early phase of a larval instar intake of food prevails and the energy stores of the fat body are established, whereas, prior to the molt, insects stop feeding and mobilize energy stores in the fat body, thereby fueling energy-demanding processes such as the formation of the new cuticle and the emergence from the old one. From the few data available to date, it is clear that adipokinetic hormones are involved in the regulation of these events in larvae.

Age-dependent changes of fat body stores and the regulation of fat body lipid synthesis and mobilisation by adipokinetic hormone in the last larval instar of the cricket, Gryllus bimaculatus

Data on the hormonal regulation of the formation and mobilisation of fat body stores are presented and discussed in relation to general parameters of last instar larval development such as growth, food intake, and moulting. Crickets feed voraciously during the first half of the last larval stage. With the onset of feeding, fat body lipid synthesis increases, leading to increasing lipid stores in the fat body with a maximum reached on day 5. Lipid (42% of fat body fresh mass) is the main constituent of the fat body stores, followed by protein (6%) and glycogen (2%). During the second half of the last larval stage, feeding activity dramatically decreases, the glycogen reserves are depleted but lipid and protein reserves in the fat body remain at a high level except for the last day of the last larval stage when lipid and protein in the fat body are also largely depleted. The process of moulting consumes almost three quarters of the caloric equivalents that were acquired during the last larval stage. Adipokinetic hormone (AKH) inhibits effectively the synthesis of lipids in the larval fat body. Furthermore, AKH stimulates lipid mobilisation by activating fat body triacylglycerol lipase (TGL) in last larval and adult crickets. Both effects of AKH are weaker in larvae than in adults. This is the first report on the age-dependent basal activity of TGL in larval and adult insects. In addition, for the first time, an activation of TGL by AKH in a larval insect is shown.

Adipokinetic hormone inhibits the formation of energy stores and egg production in the cricket Gryllus bimaculatus

Adipokinetic hormones (AKHs) mobilise lipids, carbohydrates and/or proline from insect fat body stores. In addition, AKHs inhibit lipid and protein synthesis in the fat body. In the current study, 100 pmol homologous Grybi-AKH was injected twice daily into adult female crickets, Gryllus bimaculatus, starting on the day of adult emergence. The effects of the injected AKH on the formation of energy reserves in the fat body and on egg production were measured on day 4 after adult emergence. In comparison to water-injected control animals, lipid and protein content in the fat body of the AKH-injected crickets was significantly reduced, suggesting an inhibitory effect of AKH on the formation of lipid reserves and protein stores. The content of glycogen and free carbohydrate in the fat body was significantly higher in the AKH-injected animals. The most pronounced effect of the AKH-injections was a significant reduction of ovary mass, due to the retarded maturation of the oocytes and the significantly lower number of terminal oocytes produced. It is concluded that AKH inhibits egg production indirectly by interference with the formation of energy stores in the fat body that are mobilised to fuel egg production.

Hemolymph ecdysteroids do not affect vitellogenesis in the lubber grasshopper

The role of hemolymph ecdysteroids in the reproduction of non-dipteran insects is unclear. We examine the role(s) of hemolymph ecdysteroids during egg production in the lubber grasshopper, Romalea microptera. In all individuals, hemolymph ecdysteroids rose to a sharp peak with similar maxima and then fell to undetectable levels. The time from the adult molt to the maximum ecdysteroid titer (E(max) titer) varied in response to food availability, whereas the time from E(max) titer to oviposition was unrelated to food availability. Because both the timing of egg production and the timing of E(max) responded similarly to environmental changes, ecdysteroids may be involved in egg production. We hypothesized that this role is the stimulation of vitellogenesis. Ovariectomized females had vitellogenin but no ecdysteroids, so ecdysteroids are not necessary for vitellogenin production. In addition, treatment of females with ecdysteroids altered neither Vg titers nor ovarian growth. Ovarian ecdysteriods increased at the same age in development as hemolymph ecdysteroids. In contrast to hemolymph ecdysteroids, ovarian ecdysteroids persisted until oviposition. Despite this, [(3)H]ecdysone injected into the hemolymph was detected later only at very low levels in the ovary, suggesting that hemolymph ecdysteroids are not sequestered by the ovary. In summary, our studies indicate that hemolymph ecdysteroids in adult females of the lubber grasshopper are associated with the timing of egg production, but they neither regulate vitellogenesis nor act as a source of ecdysteroids for the ovary.

Synthesis of lipids in the fat body of Gryllus bimaculatus: age-dependency and regulation by adipokinetic hormone

The free abdominal fat body of adult female Mediterranean field crickets, Gryllus bimaculatus, synthesizes lipids from [1-(14)C]-acetate in vitro. Up to an age of 12h, the incorporation of acetate into lipids is very low and then rises to a maximum 24h after adult emergence. Thereafter, the incorporation of acetate decreases to moderate levels at day 2 and then slowly decreases until day 30. The adipokinetic hormone of G. bimaculatus (Grb-AKH) significantly inhibits the incorporation of acetate at a concentration of 10(-11) M; maximum inhibition (approximately 95%) is reached at 10(-8) M. The inhibiting effect of Grb-AKH is fast, dose-dependent, and reversible. The periovaric fat body shows a similar pattern of acetate incorporation, although rates of incorporation are lower; the incorporation can be inhibited by Grb-AKH as well. The segmental abdominal fat body and the fat body from the head both incorporate acetate into lipids at low rates that cannot be inhibited significantly by AKH. Prepurified brain extracts significantly inhibit acetate incorporation by free abdominal fat bodies at a concentration of 0.1 brain equivalent. Allatostatins and crustacean cardioactive peptide, which are both present in cricket brains, are not responsible for this inhibiting effect. Octopamine causes a dose-dependent inhibition of acetate incorporation whereas synephrine had no such effect. The inhibiting effect of Grb-AKH on the formation of lipid stores in the fat body and its consequences for reproductive processes are discussed.

Synthesis and biological activity of adipokinetic hormone analogues with modifications in the 4-8 region

Several structural characteristics in the molecule of the locust adipokinetic hormone, AKH-I, have been investigated in terms of their importance in determining biologic activity. All modifications tested in this study resulted in analogues with decreased potency in comparison with the parent molecule. However, all analogues that were found to be active gave a full response, although often only at very high doses of peptide. This study has highlighted for the locust receptor(s) the vital role of the side chain of Thr(5), and the importance of positions 4 and 8. For example, when Trp(8) and Phe(4) were exchanged, the resulting analogue (Trp(4),Phe(8)-AKH-I) was one of the least active analogues tested in this study. Although Trp is tolerated quite well as a substitute for Phe(4), with only a 10-fold loss of potency, Phe is not favored as a substitute for Trp(8) (>300 times decrease in potency). On the other hand, 3-[2-napthyl] alanine (Nal) is a better substitute for Trp(8) (only a 100-fold loss in potency). We conclude that position 4 requires a phenyl ring in the side chain, and position 8 an indole ring.

Chloromethyl ketones are insulin-like stimulators of lipid synthesis in locust fat body

N alpha-tosyl-L-lysine chloromethyl ketone (TLCK) stimulates lipid synthesis in locust fat body in vitro, and is able to reverse the inhibitory effects of AKH-I on lipid synthesis. Effective stimulatory concentrations of TLCK were in the range of 0.2-1.0 mM. Similar stimulatory effects were also achieved with phenylalanine chloromethyl ketone (PheCK) and leucine chloromethyl ketone (LeuCK), but not with tosyl-phenylalanine chloromethyl ketone (TPCK), dansyl-glu-gly-arg-CK, chloroacetone, chloroacetic acid, chloroacetamide, chloroacetaldehyde, chloroacetyl-L-leucine or acetylated or fluorescamine-labelled TLCK, PheCK, and LeuCK. The level of stimulation caused by TLCK was dependent on incubation time, so that after a 5-h preincubation of fat body tissue with TLCK the stimulated rate was severalfold higher than the control. TLCK also increased the rate of uptake of trehalose and uridine, but not glucose, deoxyglucose or glycine. Increasing concentrations of bovine serum albumin (BSA) in the incubation medium caused a reduction in the rate of TLCK-stimulated acetate uptake, such that levels of uptake were no higher with 1% BSA than in the controls. A range of more specific protease and kinase inhibitors was tested, but none caused stimulation; thus the mode of action of TLCK on the stimulation of acetate uptake has yet to be identified. Elucidation of the mode of action of TLCK may facilitate the development of novel compounds for insect pest control.

Structures, assays and receptors for locust adipokinetic hormones

This review is concerned mainly with the adipokinetic hormones (AKHs) of locusts: their molecular conformations, actions and functions and the development of microfiltration assays in vitro. The physiological significance of having multiple hormones with overlapping actions whose efficacy changes during development is discussed in relation to the possibility that these reflect variations in populations of receptors and/or the pharmacokinetics of the peptides. The involvement of second messengers in the transduction mechanism of AKHs is reviewed, and we describe hormone-induced changes of intracellular calcium in single dispersed fat body cells. The structure activity relationships of the three locust AKHs and a number of analogues with variations at the N- and C-termini are discussed. A number of areas are identified where there are gaps in our understanding of these hormones, and some of these will be the focus of our future research.

Hypertrehalosemic hormone effects on transcriptional activity in the fat body of the cockroach, Blaberus discoidalis

Gene expression was examined in the fat body of adult male Blaberus discoidalis cockroaches in response to the hypertrehalosemic hormone (HTH). HTH regulates a natural peak of heme synthesis in the fat body at day 4 of adult life. Inhibition of transcriptional activity by alpha-amanitin suppressed both the natural increase in heme biosynthesis at day 4, and the increase that was induced in decapitated animals by HTH administration. In contrast, the regimen of alpha-amanitin treatments that suppressed HTH-responsive heme biosynthesis had no effect on the ability of HTH to increase hemolymph carbohydrate. HTH administration to decapitated animals produced a 25% increase in total fat body RNA and a 3-fold increase in [3H]uridine incorporation. In vitro translation of fat body RNA showed that HTH increased the synthesis of polypeptides at 24, 60 and 77 kDa. The results suggest that HTH affects fat body heme synthesis through gene expression, and evidence was obtained for three polypeptides that increase in the fat body in response to HTH.

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.

Structure-activity relationships on hyperglycemia by representatives of the adipokinetic/hyperglycemic hormone family in Blaberus discoidalis cockroaches

Several members of the adipokinetic/hyperglycemic neurohormone family from several different invertebrate species have been prepared by solid-phase peptide synthesis and assayed by a modified in vivo hyperglycemic bioassay in Blaberus discoidalis cockroaches. The hypertrehalosemic hormone (HrTH) is the endogenous hypertrehalosemic factor for B. discoidalis and was the most potent peptide in the assay. The more divergent the sequence of a family member from Blaberus HrTH, the less potent was the bioanalog. Manduca adipokinetic hormone is the most divergent peptide of the family and was totally inactive in the bioassay. Locusta adipokinetic hormone I had reduced maximum activity in the assay, which suggests that Ser5 is an important residue for the transduction of the hyperglycemic response. The direct relation between bioanalog similarity to Blaberus HrTH sequence and potency suggests that the hormone and target cell receptor for HrTH have evolved to maintain an "optimal fit".

Neuroendocrine and juvenile hormone effects on fat body protein synthesis during the reproductive cycle in female Blaberus discoidalis cockroaches

Ovarian protein content and fat body protein synthesis were measured during the first gonotrophic cycle in virgin female Blaberus discoidalis cockroaches. Protein synthesis was measured for in vitro fat bodies from animals treated with combinations of a juvenile hormone analog (JHA = methoprene) and corpora cardiaca (CC) extracts. Ovarian protein content began to increase on Day 5 of adult life and reached its maximum at Days 20-22. Synthesis of proteins secreted by the in vitro fat body increased by 12-fold between emergence and its maximum on Day 18, then declined to nearly its original level by Day 33. Synthesis of nonsecreted, fat body proteins increased by 4-fold between emergence and a maximum on Day 21, then declined. CC extracts and JHA were administered to decapitated females to determine their regulative effects on fat body protein synthesis. The synthesis by the fat body of nonsecreted proteins was increased by both JHA and CC extracts. In contrast, synthesis of secreted proteins increased only in the presence of JHA. CC extracts, alone, had no effects on the synthesis of secreted proteins, but administration of CC extracts in combination with JHA increased the synthesis of the secreted proteins by 55% above that observed with JHA alone. SDS-PAGE of proteins secreted into the medium by the in vitro fat body demonstrated that JHA stimulated the synthesis of specific polypeptides, whereas CC extracts did not affect the synthesis of specific-secreted polypeptides. These results suggest that JH regulates specific protein synthesis by the fat body of B. discoidalis; neurohormones elevate the general capacity of the fat body for protein synthesis and amplify the specific effects of JH.

The effects of synthetic locust adipokinetic hormone on dispersed locust fat body cell preparations: cAMP induction, lipid mobilization, and inhibition of protein synthesis

A procedure for the preparation of functional cells from adult locust fat bodies by collagenase treatment has been developed. The high variability of replicates encountered when whole fat bodies are incubated in vitro is greatly reduced in incubation of the dispersed cells. Synthetic locust adipokinetic hormone (AKH) (40 nM) stimulated release of lipids from the dispersed fat body cells at a rate comparable to that observed using whole fat bodies in vitro. Synthetic AKH elevated cAMP levels sixfold in dispersed cells. In addition, AKH inhibited protein synthesis to a maximum of 50-70% in a concentration-dependent manner. None of these actions of AKH required the presence of locust hemolymph components. These results demonstrate the utility of the isolated locust fat body cells for investigating hormonal action in vitro.

Preparation of a specifically tritiated locust adipokinetic hormone analog with full biological potency

A synthetic peptide related to locus adipokinetic hormone ( AKH ) and shrimp red pigment concentrating hormone ( RPCH ) containing a tyrosine residue in place of phenylalanine was iodinated and the 3,5- diiodotyrosyl derivative was isolated by reverse phase HPLC. Catalytic dehalogenation of the diiodo derivative in the presence of tritium yielded the tritiated AKH analog which was isolated by gel filtration on Sephadex LH-20 and reverse phase HPLC. The tritiated peptide was formed to be identical to AKH in its ability to stimulate lipid release into the hemolymph of locusts in vivo where the diiodotryrosyl derivative was inactive. The specific radioactivity of the tritiated peptide was 57.2 Ci/mmol, or 99% of the theoretical value.

The external anion binding site of the human erythrocyte anion transporter: DNDS binding and competition with chloride

The interaction between chloride and the anion transport inhibitor DNDS (4,4'-dinitro stilbene-2,2'-disulfonate) at the external anion binding site of the human erythrocyte anion transporter was examined by two techniques: a) chloride tracer flux experiments in the presence of varying concentrations of DNDS, and b) DNDS equilibrium binding experiments in the presence of varying concentrations of intracellular and extracellular chloride, Cli and Clo. DNDS inhibited competitively the Clo-stimulated chloride efflux from intact red cells at 0 degree C and pH 7.8 with an inhibitor constant of 90 nM. Under the same conditions DNDS bound reversibly to one class of binding sites on intact cells with a capacity of 8.5 X 10(5) molecules/cell. Clo competitively inhibited DNDS binding with an inhibitor constant of 6 mM. In the absence of Clo the DNDS binding constant was 84 mM. The competition between chloride and DNDS was also tested in nystatintreated cells in which Clo always equaled Cli. Under these conditions the values of the DNDS binding constant and the chloride inhibitor constant were significantly larger. All these data were in quantitative agreement with a single-site, alternating access kinetic scheme with ping-pong-type kinetics that we have previously developed for modeling chloride exchange transport. The data also served to rule out special cases of an alternative two-sited sequential-type kinetic scheme. DNDS binding experiments were also performed at 10 and 20 degree C. We found that neither the DNDS binding constant nor the Clo inhibitor constant were significantly changed compared to 0 degree C.