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A J Shaw

Publications and source records attributed to A J Shaw.

50 records · Page 3Linked to original sources
PubMed1989

Kinetics of rapid 45Ca uptake into chick skeleton in vivo: effects of microwave fixation.

We have investigated uptake kinetics for 45Ca labels acutely administered as single intravenous injections into twelve-day-old chicks in vivo. Effects of microwave fixation on this process have also been studied. Rapid uptake of 45Ca was demonstrated into the skeleton with approximately 40% of injected label being found in the skeleton within the first 15 min. By 45 min tissue 45Ca levels had stabilized and showed little change during the following 90 min. Soft tissue isotope levels declined during the period from 3 to 135 min following injection. These data were obtained from animals in which tissue isotope levels were stabilized by fixation with microwaves at the point of killing by cervical dislocation. In animals where the microwave fixation step was omitted and tissues were dissected for counting at least 1 h after killing, 45Ca levels in both skeletal and soft tissues were 15-20% higher than in those from microwave groups during the period 3-15 min after injection. In a separate experiment, groups of chicks killed by cervical dislocation 3 min after isotope injection were fixed with microwaves at time intervals ranging from 0 to 45 min post-mortem. Isotope levels in femur increased with time and were significantly higher in groups in which fixation was carried out 12 and 45 min after death when compared with those fixed at the point of death. Data in calvarium reflected those in femur but were not statistically significant at the time intervals tested.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Cytotoxicity and metabolism of the hepatotoxin N-methylformamide and related formamides in mouse hepatocytes.

Some N-alkylformamides such as N-methylformamide (NMF) possess hepatotoxic properties in vivo. To study the mechanism of this toxicity, suspensions of mouse hepatocytes were tested as an in vitro model system suitable for the study of the relationship between (i) the toxic potential of formamides, (ii) their metabolism to N-alkylcarbamoylating species, and (iii) their ability to deplete hepatic glutathione pools. The effects of NMF were compared with those of its analogs N-ethylformamide (NEF), N,N-dimethylformamide (DMF), formamide (F), N-methylacetamide (NMA), and N-methyldeuteroformamide ([2H]NMF). Only NEF and [2H]NMF share with NMF the ability to cause liver damage in vivo in mice. Hepatocellular toxicity was determined by measuring LDH leakage into the extracellular medium; metabolism to N-alkylcarbamoylating species was measured by GLC after derivatization with propanol to form propyl N-alkylcarbamate; glutathione concentrations were determined spectrophotometrically. Of the formamide analogs studied, only NMF and NEF caused cytotoxicity, being apparently equipotent. NMF, NEF, and [2H]NMF gave rise to the formation of detectable levels of N-alkylcarbamoylating metabolites and depleted glutathione pools. Toxicity, metabolism, and glutathione depletion were dependent on NMF concentration. [2H]NMF was markedly less cytotoxic than NMF, yielding only 35% of the amount of N-methylcarbamoylating metabolite compared to NMF and caused less depletion of glutathione than did NMF. These results parallel closely the in vivo hepatotoxic potential of NMF and its analogs, their metabolism to urinary S-(N-alkylcarbamoyl)mercapturates and their ability to deplete hepatic glutathione in mice. The results provide support for the contention that metabolism is involved with formamide-induced hepatotoxicity and suggest that suspensions of isolated mouse hepatocytes are an appropriate in vitro model for the further study of the mechanism by which formamides cause toxicity.

Acetylcysteine↗
PubMed1988

Effects of synthetic bovine parathyroid hormone (1-34) and its analogues on 45Ca uptake and adenylate cyclase activation in bone and plasma calcium levels in the chick.

We have previously demonstrated that intravenous injection of synthetic bovine parathyroid hormone (1-34) (bPTH(1-34)), but not necessarily bPTH(1-84), into chicks rapidly (3 min) inhibits skeletal uptake of an acute 45Ca label. In the present study hydrogen peroxide oxidation of bPTH(1-34) abolished this response and reduced its ability to activate adenylate cyclase in bone and kidney. Oxidised bPTH(1-34) did, however, exhibit the full hypercalcaemic activity of untreated hormone. In contrast, the analogue [Nle8, Nle18, Tyr34]-bPTH(1-34)amide reduced chick bone 45Ca uptake but failed to raise plasma Ca levels. Cyclic AMP formation in response to this analogue was also slight. Another analogue, [Nle8, Nle18, Tyr34]-bPTH(3-34)amide, failed to inhibit 45Ca uptake or stimulate cyclic AMP formation in chick bone. It was also without hypercalcaemic activity. These data suggest that the hypercalcaemic response to bPTH(1-34) in chicks is not merely a reflection of its inhibitory effect on bone 45Ca uptake. They also question the relevance of cyclic AMP in the former action. A model is proposed by which PTH could rapidly inhibit bone net 45Ca uptake by stimulating release and turnover of intracellular calcium stores in bone lining cells, thereby creating a gradient for Ca out of bone.

Adenylyl Cyclases↗
PubMed1987

Studies of the rapid effects of parathyroid hormone and prostaglandins on 45Ca uptake into chick and rat bone in vivo.

The rapid effects of parathyroid hormones and a variety of prostaglandins on net uptake of 45Ca into the skeleton have been investigated in chicks and, in a limited parallel study, in immature rats. Intravenous injection of bovine (b) parathyroid hormone(1-34) (bPTH(1-34)) or 16,16-dimethyl prostaglandin E2 (16,16-dimethyl PGE2) in a 45Ca-labelled vehicle, combined with subsequent microwave fixation of tissue isotope levels, resulted in rapid (3-15 min) net inhibition of 45Ca uptake into endochondral bone (femur) in chicks (12 days old) and rats (4 weeks old). Use of 125I-labelled albumin and [14C]mannitol indicated that these responses were not a reflection of gross changes in tissue vascular or extracellular space. In rats, bPTH(1-84) also caused significant net inhibition of 45Ca uptake into femur at 10 min. Both bPTH(1-34) and 16,16-dimethyl PGE2 produced generally smaller decreases in 45Ca uptake into chick dermal bone (calvarium) at 3-15 min. In rat calvarium, however, these agents stimulated net uptake of 45Ca at these times. When microwave fixation was omitted, inhibitory responses were reduced or disappeared, while the stimulatory response in rat calvarium was enhanced. Responses to natural prostaglandins (PGE1, PGE2, PGF2 alpha and PGI2) in chicks at 3 min were similar but less marked than those to 16,16-dimethyl PGE2; 45Ca uptake into femur and, to a lesser extent in calvarium, being inhibited. In rats, PGE1, PGE2 and PGF2 alpha showed a tendency to decrease 45Ca uptake into femur while PGE1 and PGE2 both increased 45Ca uptake into calvarium.

Animals↗
PubMed1987

Metabolism of N-methylformamide in mice: primary kinetic deuterium isotope effect and identification of S-(N-methylcarbamoyl)glutathione as a metabolite.

S-(N-Methylcarbamoyl)glutathione has been identified by cesium ion liquid secondary ion mass spectrometry as a biliary metabolite in mice of the experimental antitumor agent and hepatotoxin N-methylformamide. Metabolism of N-methylformamide to urinary methylamine, urinary N-acetyl-S-(N-methylcarbamoyl)-cysteine and biliary S-(N-methylcarbamoyl)glutathione was found to be subject to large intermolecular primary kinetic isotope effects when hydrogen was replaced by deuterium in the formyl group (kH/kD = 5.5 +/- 0.2, 4.5 +/- 1.0 and 7 +/- 2, respectively), as shown by mass spectrometry of derivatives of these metabolites. These values indicate the existence of a common metabolic precursor for each of these metabolites. In particular, methylamine is shown not to arise from simple enzymatic hydrolysis of N-methylformamide but is associated with an oxidative process. Therefore, it is highly likely that N-methylformamide is oxidized and conjugated to form S-(N-methylcarbamoyl)glutathione which is metabolized further to N-acetyl-S-(N-methylcarbamoyl) cysteine. Either of these thiocarbamates could be hydrolyzed to give the parent thiol and the observed metabolic end products, methylamine and carbon dioxide. The presence of deuterium in the formyl moiety of N-methylformamide reduced markedly the hepatotoxicity of the compound, as shown by measurements of the activities of appropriate hepatic enzymes in plasma.

Acetylcysteine↗
PubMed1987

An investigation of the relationship between the hepatotoxicity and the metabolism of N-alkylformamides.

The hepatotoxicity and metabolism of the following close analogs of the hepatotoxic antitumor agent N-methylformamide (NMF) were investigated in CBA/CA mice: N-ethylformamide (NEF), dimethylformamide (DMF), formamide and N-methylacetamide (NMA). Apart from NMF only NEF was potently hepatotoxic as measured by the elevation of plasma activities of the enzymes sorbitol dehydrogenase and alanine and aspartate aminotransferases 24 hr after drug administration. In freeze-dried urine samples of mice which had received NEF or NMF, but not in the case of DMF, formamide or NMA, thioesters were detected by thin-layer chromatography. Evidence based on high-pressure liquid chromatography analysis and 400 MHz 1H-NMR and mass spectrometry suggests that the thioester metabolite of NEF is S-(N-ethylcarbamoyl)-N-acetylcysteine. It has been shown previously that NMF is metabolized to S-(N-methylcarbamoyl)-N-acetylcysteine. NEF also underwent extensive metabolism to ethylamine; similarly NMF was biotransformed to methylamine. In contrast, the urine of mice which had received DMF contained only very small amounts of dimethylamine and methylamine could not be detected as a metabolite of NMA. Instead, the major metabolite of NMA was identified by 400 MHz 1H-NMR spectrometry as N-(hydroxymethyl)acetamide. DMF is known to undergo extensive metabolism to its N-hydroxymethyl derivative. The results suggest that two metabolic pathways of N-alkylformamides can be distinguished: Hydroxylation at the alpha-carbon of the N-alkyl group and oxidation of the formyl moiety. The former pathway presumably constitutes a detoxification route, and the latter may well be associated with hepatotoxicity, and affords a glutathione conjugate, excreted in the urine as a mercapturate.

Acetamides↗
PubMed1986

A comparison of the effects of bovine parathyroid hormone 1-34 and methylated prostaglandin E2 analogues on plasma calcium and inorganic phosphate levels in immature chickens and rats.

The relative effects of bovine parathyroid hormone 1-34 (bPTH-(1-34] and prostaglandin (PG)E2 analogues, 16,16-dimethyl PGE2 and 11,16,16-trimethyl PGE2, on plasma calcium, inorganic phosphate (Pi), and osmolality in 12-day-old chickens were compared. bPTH-(1-34) and 16,16-dimethyl PGE2 were similarly tested for effects on plasma Ca and Pi in immature (3-week-old) rats. PGs administered iv in a saline vehicle (20 micrograms 16,16-dimethyl PGE2 or 125 micrograms 11,16,16-trimethyl PGE2/100 g body wt, respectively) produced significant hypercalcaemic effects in chicks compared with vehicle-injected controls at times ranging from 15 to 90 min, similar to those obtained with bPTH-(1-34) (3.3 micrograms/100 g body wt). The PGE2 analogues injected in chicks also produced significant increases in plasma Pi compared with controls at 15 and 45 min, while those treated with PTH showed smaller, nonsignificant plasma Pi responses. Little change in plasma osmolality was seen in chicks following injection with either bPTH-(1-34) or 16,16-dimethyl PGE2, although a small but significant increase in this parameter was seen in chicks treated with 11,16,16-trimethyl PGE2. Acute labelling of chicks with 32P incorporated into the 16,16-dimethyl PGE2 injection vehicle indicated a decreased exit of Pi from the blood as the mechanism underlying the PG-mediated hyperphosphataemic response. This type of response was not seen following bPTH-(1-34) injection in chicks.(ABSTRACT TRUNCATED AT 250 WORDS)

16,16-Dimethylprostaglandin E2↗
PubMed1985

Evidence for a novel inhibition of calcium uptake into chick bone in response to bovine parathyroid hormone (1-34) or 16, 16-dimethyl prostaglandin E2 in vivo.

Mechanisms of initial hypercalcaemic responses to parathyroid hormone (PTH) and 16,16-dimethyl prostaglandin (PG) E2 have been investigated in 10-to 12-day-old chicks in vivo using a combination of acute 45Ca injection and microwave fixation to stabilize tissue isotope levels. Single i.v. injection of 16,16-dimethyl PGE2 (20 micrograms/100 g body wt) caused an approximately 100% increase in soft tissue 45Ca levels compared with vehicle control injected chicks at 30 min. 45Ca levels were lowered in calvarium by 26% and in femur by 60% with this treatment. Bovine PTH (1-34) (3.3 micrograms/100 g body wt) had no effect on soft tissue 45Ca levels, but in calvarium it had a similar effect to the PG. In femur this dose of PTH lowered 45Ca by 19%. When expressed on an absolute basis (c.p.m./100 mg tissue wt), responses to the PG in soft tissue were only 3 and 10% respectively of those in femur and calvarium. The duration of inhibitory responses in bone were examined and those to PTH found to be transient (less than 45 min) compared with the responses to the PG (greater than 135 min). Dose-response curves for PTH- and PG-induced inhibition of 45Ca uptake into femur at 15 min were essentially parallel and indicated that the lowest doses of PTH and PG used (0.74 micrograms and 1.1 micrograms/100 body wt respectively) produced significant responses. In a separate experiment it was found that inhibition of 45Ca uptake into femur was evident as early as 3 min following PTH or PG injection.(ABSTRACT TRUNCATED AT 250 WORDS)

16,16-Dimethylprostaglandin E2↗
PubMedDate not supplied

Metabolic engineering of propanediol pathways.

Microbial fermentation is an important technology for the conversion of renewable resources to chemicals. In this paper, we describe the application of metabolic engineering for the development of two new fermentation processes: the microbial conversion of sugars to 1,3-propanediol (1,3-PD) and 1,2-propanediol (1,2-PD). A variety of naturally occurring organisms ferment glycerol to 1,3-PD, but no natural organisms ferment sugars directly to 1,3-PD. We first describe the fed-batch fermentation of glycerol to 1,3-PD by Klebsiella pneumoniae. We then present various approaches for the conversion of sugars to 1,3-PD, including mixed-culture fermentation, cofermentation of glycerol and glucose, and metabolic engineering of a "sugars to 1,3-PD" pathway in a single organism. Initial results are reported for the expression of genes from the K. pneumoniae 1,3-PD pathway in Saccharomyces cerevisiae. The best naturally occurring organism for the fermentation of sugars to 1,2-PD is Thermoanaerobacterium thermosaccharolyticum. We describe the fermentation of several different sugars to 1,2-PD by this organism in batch and continuous culture. We report that Escherichia coli strains engineered to express either aldose reductase or glycerol dehydrogenase convert glucose to (R)-1,2-PD. We then analyze the ultimate potential of fermentation processes for the production of propanediols. Linear optimization studies indicate that, under aerobic conditions, propanediol yields that approach the theoretical maximum are possible and CO2 is the primary coproduct. Without the need to produce acetate, final product titers in the range of 100 g/L should be possible; the high titers and low coproduct levels should make product recovery and purification straightforward. The examples given in this paper illustrate the importance of metabolic engineering for fermentation process development in general.

Biotechnology↗
PubMedDate not supplied

The reaction of alkylnitronates with glutathione.

Nitroalkanes are agents of occupational importance, and 2-nitropropane has been shown to be mutagenic and hepatotoxic. Here the reaction of alkylnitronates, such as propyl-2-nitronate, with glutathione and other thiol nucleophiles has been studied by using TLC, HPLC, and spectroscopic methods. Propyl-2-nitronate, but not 2-nitropropane, reacted with glutathione in acidic media. The reaction yielded an inseparable mixture of oxidized glutathione and a product that was identified as S-nitrosoglutathione. S-Nitrosoglutathione is known to be generated by reaction of nitrous acid with glutathione and furnishes a characteristic UV spectrum, but its NMR and mass spectral properties are described here for the first time. The 1H NMR spectrum of S-nitrosoglutathione showed in principle the resonance signals of glutathione except that the cysteine beta-protons gave two broad signals shifted downfield by 1 ppm as compared to the resonance frequencies of the glutathione cysteine beta-protons. The interpretation of the spectrum was aided by investigation of the properties of S-nitroso-N-acetylcysteine, the product of the reaction of N-acetylcysteine with propyl-2-nitronate. The nitronates of primary nitroalkanes, such as nitromethane, nitroethane, or 1-nitropropane, did not react with glutathione. The reaction between propyl-2-nitronate and glutathione did not occur at pH values greater than 5; therefore, the relevance of these findings to the disposition of propyl-2-nitronate in vivo is unclear.

Chromatography, High Pressure Liquid↗
PubMedDate not supplied

The use of hypnosis in a sedation clinic for dental extractions in children: report of 20 cases.

We report on the use of informal hypnotic imagery in a group of children who were unable to accept dental extractions under inhalation sedation and local anesthesia. Over the last two and a half years, one hundred and seventy-nine children have been seen in a sedation clinic at Newcastle Dental Hospital. In thirty-four cases it was necessary to stop treatment and from this group, twenty children were selected for the use of hypnotic imagery. Treatment was successfully completed in sixteen children and all parents who completed a written questionnaire (twelve) reported they were happy with their child's treatment. Our preliminary findings show hypnotic imagery can be used successfully as an adjunct to inhalation sedation and conventional management skills for dental extractions in children.

Adolescent↗