Biomedical subjects

R C Oudejans

Publications and source records attributed to R C Oudejans.

At least 19 recordsLinked to original sources

PubMed2001

Absence of coupling between release and biosynthesis of peptide hormones in insect neuroendocrine cells.

Adipokinetic hormone (AKH)-producing cells in the corpus cardiacum of the insect Locusta migratoria represent a neuroendocrine system containing large quantities of stored secretory peptides. In the present study we address the question whether the release of AKHs from these cells induces a concomitant enhancement of their biosynthesis. The effects of hormone release in vivo (by flight activity) and in vitro (using crustacean cardioactive peptide, locustamyoinhibiting peptide, and activation of protein kinase A and C) on the biosynthetic activity for AKHs were measured. The intracellular levels of prepro-AKH mRNAs, the intracellular levels of pro-AKHs, and the rate of synthesis of (pro-)AKHs were used as parameters for biosynthetic activity. The effectiveness of in vitro treatment was assessed from the amounts of AKHs released. Neither flight activity as the natural stimulus for AKH release, nor in vitro treatment with the regulatory peptides or signal transduction activators appeared to affect the biosynthetic activity for AKHs. This points to an absence of coupling between release and biosynthesis of AKHs. The strategy of the AKH-producing cells to cope with variations in secretory stimulation seems to rely on a pool of secretory material that is readily releasable and continuously replenished by a process of steady biosynthesis.

Animals↗

PubMed2000

Intracisternal granules in the adipokinetic cells of locusts are not degraded and apparently function as supplementary stores of secretory material.

The intracisternal granules in locust adipokinetic cells appear to represent accumulations of secretory material within cisternae of the rough endoplasmic reticulum. An important question is whether these granules are destined for degradation or represent stores of (pro)hormones. Two strategies were used to answer this question. First, cytochemistry was applied to elucidate the properties of intracisternal granules. The endocytic tracers horseradish peroxidase and wheat-germ agglutinin-conjugated horseradish peroxidase were used to facilitate the identification of endocytic, autophagic, and lysosomal organelles, which may be involved in the degradation of intracisternal granules. No intracisternal granules could be found within autophagosomes, and granules fused with endocytic and lysosomal organelles were not observed, nor could tracer be found within the granules. The lysosomal enzyme acid phosphatase was absent from the granules. Second, biochemical analysis of the content of intracisternal granules revealed that these granules contain prohormones as well as hormones. Prohormones were present in relatively higher amounts compared with ordinary secretory granules. Since the intracisternal granules in locust adipokinetic cells are not degraded and contain intact (pro)hormones it is concluded that they function as supplementary stores of secretory material.

Acid Phosphatase↗

PubMed1999

Differential location of peptide hormones in the secretory pathway of insect adipokinetic cells.

Immunoreactivity of granules containing secretory material in the adipokinetic cells of the insect Locusta migratoria was studied using antisera specific for the adipokinetic hormone-associated peptides (AAP) I, II and III. Immunocytochemical detection of these associated peptides represents a new strategy for studying the intracellular location of the adipokinetic hormones and their prohormones. Fixation with 2% glutaraldehyde and 2% formaldehyde with low-temperature embedding in Lowicryl HM20 allowed highly selective immunogold labelling of both secretory and intracisternal granules. All three associated peptides were co-localized in secretory granules. This indicates that also all three adipokinetic hormones can be co-localized in these granules, which was confirmed by experiments in which, after secretory stimulation, adipokinetic hormone III was released from the adipokinetic cells together with adipokinetic hormones I and II. The immunopositivity of the intracisternal granules was similar to that of the secretory granules, although with the exception that the intracisternal granules did not show any specific reaction with anti-AAP III. The presence of AAP I and AAP II in intracisternal granules indicates that these granules only function as stores of adipokinetic prohormones I and II and not of adipokinetic prohormone III. The observed differences in storage in intracisternal granules among the three adipokinetic prohormones suggest differences in physiological significance of the three adipokinetic hormones in L. migratoria.

Amino Acid Sequence↗

PubMed1999

Adipokinetic hormones. Coupling between biosynthesis and release.

During long-distance flight of migratory locusts, the dramatic energy demand of the flight muscles is controlled by three adipokinetic hormones (AKHs). These peptide hormones regulate the mobilization of lipid and carbohydrate stored in the fat body to serve as energy substrates for the flight muscles. Despite the relatively huge quantities of the three AKHs that are stored in the corpora cardiaca, flight induces a differential 2-4-fold increase in the mRNAs for the three hormones. Moreover, newly synthesized AKHs can be released only during a restricted period of time, suggesting that by far most of the stored hormones are physiologically inactive. This raises the question of how the biosynthetic activity in the AKH-producing cells is coupled to their secretory activity. The present review discusses the potential mechanisms by which generation and release of mixtures of bioactive neurohormones are controlled and how peptidergic neuroendocrine cells cope with variations in physiological stimulation, with the AKH-producing cells serving as a model system.

Amino Acid Sequence↗

PubMed1996

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

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 -III were 51, 40, and 5 min, respectively, for rest conditions and 35, 37, and 3 min, respectively, during flight. The rapid and differential degradation of structurally related hormones leads to changes in the ratio in which they are released and therefore will have important consequences for concerted hormone action at the level of the target organ or organs, suggesting that each of the known AKHs may play its own biological role in the overall syndrome of insect flight.

Amino Acid Sequence↗

PubMed1996

Preferential release of newly synthesized, exportable neuropeptides by insect neuroendocrine cells and the effect of ageing of secretory granules.

The release of newly synthesized neuropeptides was studied in an in vitro system using the adipokinetic hormone (AKH)-producing cells of an insect (Locusta migratoria) as a model system. Tritiated phenylalanine incorporated into three hormonal neuropeptides, AKH I, II and III, was used to distinguish newly synthesized hormones from older, preexisting ones. After pulse-chase labeling experiments of varying duration, the secretion of AKHs by the AKH cells was stimulated. Both hormones released into the incubation medium after stimulation and non-released hormones extracted from the tissue were separated by reversed-phase high performance liquid chromatography. Their radioactivity was measured by scintillation counting of the column eluate. The ratio between the specific radioactivities of the released and the non-released neuropeptides was always greater than 1.0, which indicates that the newly synthesized peptides are preferentially released. The percentages of newly synthesized (radioactive) AKHs which are released, increased until 8 1/4 h and decreased thereafter. The results indicate that after the packaging of the prohormones into secretory granules and their processing to bioactive AKHs, some further maturation of the secretory granules is required before they can release their content. After an 8 1/4 h incubation, secretory granules with radioactive AHKs enter a non-releasable pool consisting of older secretory granules.

1-Methyl-3-isobutylxanthine↗

PubMed1995

Molecular cloning of three distinct cDNAs, each encoding a different adipokinetic hormone precursor, of the migratory locust, Locusta migratoria. Differential expression of the distinct adipokinetic hormone precursor genes during flight activity.

Three distinct cDNAs encoding the preproadipokinetic hormones I, II, and III (prepro-AKH I, II, and III), respectively, of Locusta migratoria have been isolated and sequenced. The three L. migratoria AKH precursors have an overall architecture similar to that of other precursors of the AKH/red pigment-concentrating hormone (RPCH) family identified so far. The AKH I and II precursors of L. migratoria are highly homologous to the Schistocerca gregaria and Schistocerca nitans AKH precursors. Although the L. migratoria AKH III precursor appears to be the least homologous to the Manduca sexta, Drosophila melanogaster, and Carcinus maenas AKH/RPCH precursors, we favor the opinion that the L. migratoria AKH III precursor is evolutionary more related to the M. sexta, D. melanogaster, and C. maenas AKH/RPCH precursors than to the AKH I and II precursors of S. gregaria, S. nitans, or L. migratoria. In situ hybridization showed signals for the different AKH mRNAs to be co-localized in cell bodies of the glandular lobes of the corpora cardiaca. Northern blot analysis revealed the presence of single mRNA species encoding the AKH I precursor (approximately 570 bases), AKH II precursor (approximately 600 bases), and AKH III precursor (approximately 670 bases), respectively. Interestingly, flight activity increased steady-state levels of the AKH I and II mRNAs (approximately 2.0 times each) and the AKH III mRNA (approximately 4.2 times) in the corpora cardiaca.

Amino Acid Sequence↗

PubMed1993

Isolation, identification, and synthesis of AKH-I4-10 from Locusta migratoria.

A heptapeptide was isolated from brain-corpora cardiaca-corpora allata-suboesophageal ganglion extracts of the locust, Locusta migratoria. Biological activity was monitored during HPLC purification by observing the myotropic effect of column fractions on the isolated hindgut of Leucophaea maderae. The primary structure of this myotropic peptide was established as: Phe-Thr-Pro-Asn-Trp-Gly-Thr-NH2. The chromatographic and biological properties of the synthetic peptide were the same as those of the native peptide, thus confirming structural analysis. This heptapeptide is identical to the carboxyterminal heptamer of AKH-I and therefore designated as AKH-I4-10. AKH-I4-10 has no adipokinetic activity. AKH-I4-10 is most likely a breakdown product of Lom-AKH-I, suggesting that an endopeptidase which cleaves between Asn and Phe is present in the brain complex of L. migratoria. Such an endopeptidase has recently been characterized in in synaptic membranes of the nervous system of Schistocerca gregaria.

Amino Acid Sequence↗

PubMed1991

Isolation and structure elucidation of a novel adipokinetic hormone (Lom-AKH-III) from the glandular lobes of the corpus cardiacum of the migratory locust, Locusta migratoria.

A new adipokinetic hormone (named Lom-AKH-III) was isolated from the glandular lobes of the corpora cardiaca of Locusta migratoria. At the N-terminus it is blocked by a 5-oxoproline (pyroglutamic acid) residue (less than Glu). After enzymatic deblocking, the amino acid sequence of the N-terminus was partly established by automatic Edman degradation to be [less than Glu]-Leu-Asn-Phe-Thr-Pro-. Fast-atom-bombardment spectrometry (FAB-MS) revealed that the new hormone is an octapeptide, which is amidated at the C-terminus, and has a relative molecular mass of 1072. Based on the FAB-MS data the complete sequence is less than Glu-Leu-Asn-Phe-Thr-Pro-Trp-Trp-NH2, which was confirmed by chemical synthesis. All characteristics from HPLC, FAB-MS and biological activity of the natural hormone and the synthetic peptide appeared to be identical. Although the structure of this new hormone resembles that of Lom-AKH-I (less than Glu-Leu-Asn-Phe-Thr-Pro-Asn-Trp-Gly-Thr-NH2), its amino acid sequence points to a completely different route for its biosynthesis, involving a third prohormone. High-[K+]-containing media can cause release of all three adipokinetic hormones in vitro. Interestingly, the new hormone is absent in another locust species. Schistocerca gregaria. Based on in vitro biosynthesis experiments the turnover for this hormone is very high, suggesting an important physiological function. Locusta migratoria is the first insect species in which three different adipokinetic hormones have been demonstrated.

Amino Acid Sequence↗

PubMed1984

Kinetics of individual polychlorinated biphenyl (PCB) components in juvenile sole (Solea solea) in relation to their concentrations in food and to lipid metabolism.

PCBs were administered to juvenile soles (Solea solea) with food. Homogenates of gut, liver, brain, dark skin, muscle and gills were analysed for their contents of individual PCB components. The relative contributions of individual components to total PCB were virtually identical in the various organs sampled at the same day in a 275-day period. During the experiment concentrations on a (pentane-extractable) lipid basis of most PCB components declined in all organs regardless of lipid metabolism. The results suggest that PCB patterns in organs are determined by equilibrium partitioning. So components remained mobilizable from organs whose lipid contents increased. This is in contrast with the idea that PCBs are taken up and stored in lipids under circumstances of increasing lipid content in organs. The plateau-values of the steady-states of lipid based concentrations of PCB components decreased in all organs. This might have been due to changes in lipid contents or lipid composition in some organs.

Animal Feed↗

PubMed1982

Changes in the activities of selected enzymes of intermediary metabolism in the pyloric caeca and ovaries of asterias rubens during the annual reproductive cycle.

1. Activities of several enzymes of glycolysis, glycerolphosphate cycle, TCA-cycle, beta-oxidation and pentose phosphate cycle were determined in pyloric caeca and ovaries of Asterias rubens during the reproductive cycle. 2. In the ovaries activities of CS and LDH were significantly decreased during ovarian stages 3 and 4, and those of GDH and GAPDH during stage 3 and 4, respectively. 3. In the pyloric caeca activities of GAPDH and LDH were lower in stage 4 and that of GDH in stage 3, whereas those of G6PDH and HOAD were increased in stage 3. 4. Changes observed in enzyme activities are discussed in relation to the reproductive cycle and to the multiple function of the pyloric caeca.

3-Hydroxyacyl CoA Dehydrogenases↗

PubMed1976