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Biomedical subjects

J G Mercer

Publications and source records attributed to J G Mercer.

90 records · Page 5Linked to original sources
PubMed1989

Studies on the biosynthesis and fate of ecdysteroids in filarial nematodes.

Experiments were performed to investigate whether adult Dirofilaria immitis and Brugia pahangi were capable of synthesising ecdysteroids from cholesterol or various intermediates from the biosynthetic pathway functioning in insects. Metabolites of radioactively-labelled cholesterol and 5 beta-ketodiol (2,22,25-trideoxy-ecdysone) were detected in the filarial nematodes, but there was no radioactivity corresponding to ecdysteroid. Uptake of tritiated 2-deoxyecdysone was poor and metabolism was not observed. [3H]Ecdysone was absorbed sparingly by adult D. immitis, but was metabolised efficiently to several less polar products. There was no evidence of C-20 hydroxylation capability.

Animals↗
PubMed1989

Analysis of ecdysteroids in Onchocerca gibsoni, O. volvulus and nodule tissues.

Free ecdysteroids were detected in Onchocerca gibsoni, in tissues constituting O. volvulus and O. gibsoni nodules and in unrelated bovine tissues. Ecdysone and 20-hydroxyecdysone were identified by HPLC-RIA and GC/MS(SIM). The concentration of free ecdysteroids in the nodule tissue immediately surrounding the parasites was at least an order of magnitude higher than that detected in the worms themselves, or in adjacent nodular tissues or other bovine tissues.

Abattoirs↗
PubMed1988

Caenorhabditis elegans: occurrence and metabolism of ecdysteroids in adults and dauer larvae.

1. Ecdysteroids were detected in extracts of egg-producing adult Caenorhabditis elegans, in dauer larvae and in dietary bacteria. 2. Similar concentrations of free ecdysteroids were recorded in adults and larvae, although the two life cycle stages differed in their ratio of ecdysone: 20-hydroxyecdysone. 3. Patent adults metabolized [3H]ecdysone into apolar products and putative [3H]ecdysone 22-phosphate.

Animals↗
PubMed1987

Capillary gas chromatography-mass spectrometry of ecdysteroids.

Fully trimethylsilylated ecdysteroids have been analysed by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS) using flexible fused-silica capillary columns. Best results were obtained using columns coated with cross-bonded apolar (OV-1 type) stationary phases. By employing capillary GC-MS with selected-ion monitoring (SIM), very sensitive and selective analyses for ecdysteroids are possible. Detection limits of 10 and 100 pg have been determined for 20-hydroxyecdysone and ecdysone, respectively. At this level of sensitivity, capillary GC-SIM-MS constitutes a complementary means of ecdysteroid analysis to high-performance liquid chromatography (HPLC) with monitoring of the eluent fractions by radioimmunoassay (RIA), but with the advantage of enhanced selectivity. Examples are given of the application of capillary GC-SIM-MS and HPLC-RIA in combination to investigate the nature and concentration of ecdysteroids at the picogram level in three helminth species.

Animals↗
PubMed1987

Analysis of ecdysteroids in different developmental stages of Hymenolepis diminuta.

Prepatent and patent adult Hymenolepis diminuta from the intestines of rats, H. diminuta eggs recovered from the faeces of rats harbouring patent infections, and infective cysticercoids from the beetle intermediate host were analysed for free and conjugated ecdysteroids. Adult worms and eggs contained both free ecdysteroids and hydrolysable polar conjugated ecdysteroids, with comparatively large amounts of immunoreactive material also being detected following hydrolysis of the possible apolar conjugated ecdysteroid fraction. Free ecdysteroids were not detected in the cysticercoid sample. The concentration of free ecdysteroids in H. diminuta eggs was higher than that detected in the tissues of the adult worms. Ecdysone and 20-hydroxyecdysone were the major identified compounds of the free ecdysteroid fraction, whereas in the hydrolysed polar conjugated ecdysteroid fraction these two compounds were accompanied by 20,26-dihydroxyecdysone. The free ecdysteroid fraction also contained comparatively large amounts of unidentified immunoreactive material.

Animals↗
PubMed1987

Ecdysteroid excretion by adult Hymenolepis diminuta in vitro.

Both patent and prepatent adult Hymenolepis diminuta excreted 20-hydroxyecdysone into the culture medium when maintained in vitro. Patent worms also excreted ecdysone and comparatively large quantities of unidentified immunoreactive material of a relatively apolar nature. This latter material was shown to be depleted from the endogenous free ecdysteroids of patent adults during the culture period. Ecdysteroid excretion was affected both qualitatively and quantitatively when culturing conditions were varied.

Animals↗
PubMed1987

Echinococcus granulosus: occurrence of ecdysteroids in protoscoleces and hydatid cyst fluid.

Both free ecdysteroids and hydrolysable polar conjugated ecdysteroids were detected in protoscoleces of Echinococcus granulosus from the equine host, and in hydatid cyst fluid from the same source. Comparisons were made of hydatid cyst fluid from E. granulosus infections of three intermediate host species: horses, sheep and humans. Ecdysone and 20-hydroxyecdysone were identified in both protoscoleces and hydatid cyst fluids by high-performance liquid chromatography monitoring fractions by radioimmunoassay, and by capillary gas chromatography/mass spectrometry (selected ion monitoring). The free ecdysteroid fractions of hydatid cyst fluid from horses and sheep also contained several unidentified, chromatographically unique, immunoreactive compounds which were refractory to hydrolysis with a crude Helix pomatia aryl sulphatase enzyme preparation.

Animals↗
PubMed1986

Schistosoma mansoni: uptake in vitro and incorporation of adenine by adults.

The rates of adenine uptake and incorporation into nucleic acids by adult male and female Schistosoma mansoni were determined during periods of up to 10 days in vitro, and comparisons were made between paired and separated worms. Adenine uptake by separated males and females exceeded that exhibited by equivalent paired worms. The rate of incorporation of adenine into nucleic acids was higher in separated females than in paired females. In contrast, the state of pairing had little effect on adenine incorporation by male S. mansoni. There was no correlation between rates of adenine uptake and incorporation and the reproductive activity of S. mansoni adults in vitro. Uptake and incorporation rates appeared to reflect the changing somatic requirements of both male and female worms.

Adenine↗
PubMed1985

Schistosoma mansoni: effect of maintenance in vitro on the uptake and incorporation of leucine by adult worms.

The rates of leucine uptake and incorporation into protein by adult male and female Schistosoma mansoni were not affected by maintenance in vitro for up to 10 days' duration, despite the decline in the protein content of male and female worms of approximately 35 and 55%, respectively, during this period. The effect of maintenance in vitro was obscured in paired female schistosomes by the apparent shielding of the female tegument within the gynaecophoral canal of the male. Incorporation rates were reduced by 50% in the presence of 2 mM cycloheximide whereas uptake rates were unaffected. Adult schistosomes are unable to maintain their in vivo protein levels purely by recourse to exogenous amino acids absorbed across the tegument in vitro, and the rates of uptake and incorporation of leucine appear to reflect the changing somatic requirements of the worms and are probably not correlated with the reproductive activity of adult worms in vitro. The possible role of alimentary rather than tegumental nutrition in egg production in vivo is discussed.

Alanine↗
PubMed1985

Schistosoma mansoni: effect of maintenance in vitro on the physiology and biochemistry of adult worms.

In Medium 199 supplemented with calf serum (+10%), adult Schistosoma mansoni produced a mean total of 400 eggs/worm pair during maintenance for 10 days in vitro. During the period of egg deposition in vitro, the dry weight of worm pairs decreased by 35%. Biomass decreases were proportionally greater in female worms than in males. Declines in the dry weight of female worms were mainly due to decreases in protein content, while biomass decreases in males resulted from losses of both protein and glycogen. Glucose was depleted from the maintenance medium at a rate of approximately 200 micrograms/worm pair/day during each of the first 3 days in vitro, while concentrations of glucose in the medium of above 1 g/litre did not affect the degree of glycogen depletion observed in adult S. mansoni during culture for 24 h. The contribution of the loss of schistosome gut contents in vitro to the observed changes is discussed. The work described represents part of an attempt at logical design of in vitro culture.

Animals↗
PubMed1982

Transmission of Schistosoma mansoni from man to snail: experimental studies of miracidial survival and infectivity in relation to larval age, water temperature, host size and host age.

We report the results of experimental work on (a) the influence of temperature on the age-dependent survival and infectivity of the miracidia of Schistosoma mansoni and (b) the relationship between snail age, snail size and susceptibility to infection. The death rate of miracidia declined exponentially with age where life-expectancy was maximal (approximately 16 h) at 15 degrees C. Infectivity also declined rapidly with larval age but, in contrast to larval survival, the rate of infection was at a maximum at 25 degrees C. Snail susceptibility was shown to be more closely correlated with host size rather than host age. Susceptibility declined exponentially with increased host size. Size-dependent susceptibility was shown to generate concave age-prevalence curves for infection within snail populations, where the maximum prevalence is generated in snails of intermediary age. Simple mathematical models are developed to aid estimation of larval survival and infection rates and experimental results are discussed in relation to the overall transmission success of the parasite from man to snail.

Aging↗
PubMedDate not supplied

Hypothalamic neuropeptide systems and anticipatory weight change in Siberian hamsters.

Seasonal animals are able both to programme changes in body weight in response to annual changes in photoperiod (anticipatory regulation) and to correct changes in body weight caused by imposed energetic demand (compensatory regulation). Experimental evidence from the Siberian hamster suggests that seasonally appropriate body weight is continually reset according to photoperiodic history, even when actual body weight is driven away from this target weight by manipulation of energy intake. These characteristics constitute the "sliding set point" of seasonal body weight regulation. To define the mechanisms and molecules underlying anticipatory body weight regulation, we are investigating the involvement of hypothalamic systems with an established role in the compensatory defence of body weight. Weight loss or restricted growth induced by short days (SD) results in low circulating leptin compared with long day (LD) controls. However, this chronic low leptin signal is read differently from acute low leptin resulting from food deprivation; leptin receptor gene expression in the hypothalamic arcuate nucleus (ARC) is lower in SD, whereas food deprivation increases expression levels, suggesting changes in sensitivity to leptin feedback. SD alterations in mRNA levels for a number of hypothalamic neuropeptide and receptor genes appear counter-intuitive for a SD body weight trajectory. However, early increases in ARC cocaine-and amphetamine-regulated transcript (CART) gene expression in SDs could be involved in driving body weight loss or growth restriction. The sites of photoperiod interaction with energy balance neuronal circuitry and the neurochemical encoding of body weight set point require full characterisation. Study of anticipatory regulation in seasonal animals offers new insight into body weight regulation across mammalian species, including man.

Animals↗