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At least 19 recordsLinked to original sources
PubMed1993

The effect of invertebrate hormones and potential hormone inhibitors on the third larval moult of the filarial nematode, Dirofilaria immitis, in vitro.

The effects of the insect hormones, ecdysone and 20-hydroxyecdysone, certain non-steroidal ecdysteroid agonists (RH compounds) and the inhibitor, azadirachtin, on the timing of the 3rd-stage moult of Dirofilaria immitis were investigated. 20-Hydroxyecdysone and RH 5849 when used at a concentration of 10(-5) M, resulted in a premature timing of this moult. Azadiracthin, at a similar concentration, prevented moulting of most of the larvae to the 4th stage. The results are discussed in relation to the possibility of a hormonal role for ecdysteroids and neuropeptide-like compounds in the control of ecdysis in filarial nematodes, that maybe somewhat comparable to the system which is found in insects.

Aedes↗
PubMed2005

Gonadotropin-releasing hormone in invertebrates: structure, function, and evolution.

Gonadotropin-releasing hormone (GnRH) is central to the initiation and maintenance of reproduction in vertebrates. GnRH is found in all major groups of Phylum Chordata, including the protochordates. Studies on functional and structural evolution of GnRH have, in the past, focused exclusively on chordates. However, the recent structural elucidation of an octopus GnRH-like molecule and increasing evidence that GnRH-like substances are present in multiple invertebrate phyla suggest GnRH is an ancient peptide that arose prior to the divergence of protostomes and deuterostomes. The extraordinary conservation of GnRH structure and function raises interesting questions regarding the functional role assumed by GnRH over the course of evolution. This review will focus on the current understanding of GnRH structure and function in non-chordate invertebrates. Special emphasis will be placed upon the possible and speculated functions of GnRH in mollusks.

Amino Acid Sequence↗
PubMed1983

Invertebrate neuropeptide hormones.

The development of a long-term research program on the neurosecretory hormones of arthropods is described. The purification and full characterization of the first invertebrate neurohormones, the red pigment-concentrating hormone (RPCH) and the distal retinal pigment hormone (DRPH) demonstrated that they are peptides, an octapeptide and an octadecapeptide, respectively. Physiological function studies with the pure hormones and their synthetic preparations showed that the RPCH acts as a general pigment-concentrating hormone (PCH), and that the DRPH, in addition to its light-adaptive function, also constitutes a general pigment-dispersing hormone (PDH). In the regulation of the color-adaptation of the animals, the two hormones act as antagonists. The chromatophorotropic activities are widely distributed within the arthropod neuroendocrine systems. Purification of the pigment-concentrating activities from the locust corpora cardiaca lead to the isolation and characterization of the first insect neurohormones, the adipokinetic hormones (AKH I and AKH II). These two hormones, AKH I being a decapeptide and AKH II being an octapeptide, are close structural analogs to the crustacean PCH, demonstrating a common evolution of arthropod neurohormones. The hormones of this PCH-family all cross-react, but structure-function studies of the hormones show that quite different parts of their structure are involved in their binding to the various receptors.

Animals↗
PubMed1990

Activation of membrane guanylate cyclase by an invertebrate peptide hormone.

Peptide hormones can stimulate cyclic GMP synthesis through either of two general mechanisms: some peptides activate the cytoplasmic form of guanylate cyclase via a coupling factor called EDRF (endothelium-derived relaxation factor), while others activate the membrane form by interacting directly with an extracellular binding domain of the cyclase molecule itself. We have investigated the mechanism(s) by which crustacean hyperglycemic hormone (CHH), a neuropeptide that regulates energy metabolism in crustaceans, elevates cyclic GMP levels in lobster muscle. Phosphodiesterase inhibitors potentiate the response in intact tissue. This indicates that the primary effect of the peptide is to activate a cyclase rather than inhibit a phosphodiesterase. Methylene blue, a specific inhibitor of the EDRF pathway, does not block the actions of CHH. In addition, nitroprusside, an agent that directly activates the EDRF pathway in vertebrate animals, does not activate guanylate cyclase either in intact or homogenized lobster muscle. This indicates that the EDRF pathway, although prominent in vertebrate muscle, is not found in crustaceans and further suggests that the membrane cyclase is the most likely target of CHH. Membrane and soluble cyclases can be isolated from homogenates of lobster muscle (in a 3.5:1 ratio), and both are stimulated by Mn2+ and inhibited by Ca2+. CHH has no effect on the soluble enzyme. Coupling of CHH receptors to the particulate cyclase, however, remains intact in isolated membranes, thus providing a new model system for the study of receptor/cyclase interactions.

1-Methyl-3-isobutylxanthine↗
PubMed2001

Common phytochemicals are ecdysteroid agonists and antagonists: a possible evolutionary link between vertebrate and invertebrate steroid hormones.

Many plant compounds are able to modulate growth and reproduction of herbivores by directly interacting with steroid hormone systems. In insects, several classes of phytochemicals, including the phytoestrogens, interfere with molting and reproduction. We investigated whether the anti-ecdysone activity may be due to interaction with the ecdysone receptor (EcR) using a reporter-gene assay and a cell differentiation assay of an ecdysone-responsive cell line, Cl.8+. We tested rutin (delays molt in insects); four flavones: luteolin and quercetin (metabolites of rutin), and apigenin and chrysin; and three non-flavones, coumestrol and genistein (both estrogenic) and tomatine (alters molt in insects). None of the phytochemicals tested were ecdysone agonists in the reporter-gene assay, but the flavones were able to significantly inhibit EcR-dependent gene transcription. In the Cl.8+ cells, quercetin and coumestrol were mixed agonists/antagonists, while genistein, tomatine and apigenin showed a synergistic effect with ecdysteroid in the reduction of cell growth. We suggest that the rutin effects on molting in insects are most likely due to the metabolites, luteolin or quercetin, while tomatine acts via a non-EcR pathway. Flavones not only interact with EcR and estrogen receptor (ER), but also signal nitrogen-fixing bacteria to form root nodules. The NodD protein which regulates this symbiosis has two ligand-binding domains similar to human ERalpha. The evolutionary significance of these findings are discussed.

Animals↗
PubMed1991

Uptake, distribution and binding of vertebrate and invertebrate steroid hormones and time-dependence of ponasterone A binding in Calliphora vicina. Comparisons among cholesterol, corticosterone, cortisol, dexamethasone, 5 alpha-dihydrotestosterone, 1,25-dihydroxyvitamin D3, ecdysone, estradiol-17 beta, ponasterone A, progesterone, and testosterone.

The presence of specific binding sites for radiolabelled vertebrate-type and arthropod-type steroid hormones was investigated in several organs including salivary gland, and central nervous system of third instar Calliphora vicina larvae by thaw-mount autoradiography. Ponasterone A, a 20-hydroxyecdysone agonist and 20-hydroxyecdysone are the only steroids which bind to nuclear high affinity binding sites. These binding sites are DNA associated while nucleoli show no tracer binding. Ecdysone, an endogenous 20-hydroxyecdysone precursor, is taken up by target cells but no significant nuclear binding occurs. 1,25-Dihydroxyvitamin D3 concentrates in cytoplasm only and its uptake is highest compared to all other steroids. Progesterone and testosterone show weak accumulation in the cytoplasm, while for cholesterol, corticosterone, cortisol, dexamethasone, dihydrotestosterone and estradiol-17 beta, no noticeable uptake occurs. For ponasterone A, a clear time dependence of uptake and intracellular distribution is visible, suggesting the existence and involvement of specific ecdysteroid uptake and transport mechanisms. These results suggest the presence of binding sites for various mammalian steroids in insects. Whether vertebrate steroid hormones or metabolites of them play a role in insects or whether the uptake and binding is based on chemical similarities alone without biological significance remains to be further investigated.

Animals↗
PubMed1991

Circadian regulation of synthesis of ecdysteroids by prothoracic glands of the insect Rhodnius prolixus: evidence of a dual oscillator system.

Rhythmic synthesis of moulting hormones (ecdysteroids) by prothoracic glands (PGs) of the insect Rhodnius prolixus during the last larval instar was studied in vitro following explantations every 4-5 hr for up to 96 hr. Ecdysteroid synthesis was measured by radioimmunoassay as the quantity of ecdysteroid produced during 4 hr in vitro. A massive daily rhythm is seen, with synthesis at night being three- to fivefold higher than during the day. This rhythm of ecdysteroid synthesis by PGs free-runs in continuous darkness with a temperature-compensated period length close to 24 hr and is therefore controlled by a circadian system. This is the first report of circadian regulation of synthesis of an invertebrate hormone. The synthesis rhythm also free-runs in continuous light, but with an inverted phase and shorter period length. It is argued that the circadian system controlling synthesis comprises two oscillators which free-run in antiphase, occupy different anatomical locations, and are coupled by a humoral factor, possibly prothoracicotropic hormone. The ecdysteroid synthesis rhythm in PGs appears to drive the previously reported circadian rhythm in the haemolymph ecdysteroid titre. It is concluded that the circadian system controlling synthesis of ecdysteroids constitutes a pacemaker which drives various rhythms in the target cells of ecdysteroids via the rhythm in the haemolymph titre. Ecdysteroids are viewed as "hormonal Zeitgebers," imposing temporal order on development.

Animals↗
PubMed2006

Non-genomic ecdysone effects and the invertebrate nuclear steroid hormone receptor EcR--new role for an "old" receptor?

The ecdysteroids (Ec), invertebrate steroid hormones, elicit genomic but also non-genomic effects. By analogy to vertebrates, non-genomic responses towards Ec may be mediated not only by distinct membrane-integrated but also by membrane-associated receptors like the classical nuclear ecdysteroid receptor (EcR) of arthropods. This is supported by a comparison of physiological properties between invertebrate and vertebrate steroid hormone systems and recent findings on the subcellular localization of EcR. The measured or predicted high degree of conformational flexibility of both Ec and the ligand binding domain (LBD) of EcR give rise to a conformational compatibility model: the compatibility between conformations of the cognate receptor's ligand binding domain and structures or conformations of the ligand would determine their interaction and eventually the initiation of genomic versus non-genomic pathways. This model could also explain why specific non-genomic effects are generally not observed with non-steroidal agonists of the bisacylhydrazine group.

Animals↗
PubMed1983

The effects of 20-hydroxyecdysone and juvenile hormone III on tick cells.

Two cell lines isolated from Rhipicephalus appendiculatus ( RAE 25) and Anocentor (= Dermacentor) nitens (ANE 58) responded to the invertebrate hormones 20-hydroxyecdysone (20-HE) and juvenile hormone III (JH III) in vitro. In the presence of 0.2 or 2 nMolar 20-HE, the cells of the continuous line RAE 25 attached to the culture substrate at a rate of 9% per hr for the first 8 hr, as did cells in growth medium. Twenty or 200 nMolar of 20-HE reduced the rate of cell attachment to 6% per hr, and in the higher hormone concentration the cells ceased to attach after 4 hr. Low concentrations (0.2 and 2 nMolar ) of 20-HE stimulated the growth of the RAE 25 line (P less than 0.02), but 200 nMolar or more inhibited growth (P less than 0.001). Twenty-HE suppressed the growth of the young line ANE 58 in a dose-dependent manner, but the decrease in cell growth was less pronounced than in RAE 25. Ten to 100 times more (2 and 20 mu Molar) 20-HE was needed to achieve significant growth suppression (P less than 0.025 and less than 0.005). The growth of both lines declined (P less than 0.01) by 20% ( RAE 25) or 30% (ANE 58) when the medium contained 38 mu Molar of JH III. The bimodal growth response of line RAE 25 to 20-HE also occurred in the presence of 3.8 and 38 mu Molar JH III, and 2 nMolar 20-HE counteracted the suppressive effect of 38 mu Molar JH III.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗