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Biomedical subjects

M R Jones

Publications and source records attributed to M R Jones.

At least 145 records · Page 8Linked to original sources
PubMed1986

Hypotensive effect of a high calcium diet in the Wistar rat.

In order to study the effects of Ca supplementation upon systolic blood pressure, male weanling Wistar rats were fed rat chow or chow mixed with either CaCO3 (to 2.5% total Ca) or CaHPO4 (to 3.4% total Ca). In the first study rats receiving CaCO3 supplementation had lower systolic pressures after 6 weeks on the diet. Urinary P was reduced, fecal P was increased and urinary Ca was increased with this diet. Ionized Ca in blood was unaltered by Ca supplementation, but total Ca was decreased and plasma P was increased. In the second study with CaCO3, only a transient effect on blood pressure was found. The effects of the diet upon Ca and P metabolism, however, were similar to those found in the first study. In the third study, with CaHPO4 as the vehicle for Ca supplementation, blood pressure was consistently reduced in rats after 8 weeks on the high Ca diet. Plasma P, total Ca and whole blood ionized Ca were unaltered by this diet, but ionized Ca was reduced in plasma. The dietary intake of nutrients other than the Ca salt did not differ between control and and experimental groups in any of the experiments. Urinary Na and K were similar in control and experimental animals in all three experiments. These data suggest that neither increased ionized Ca, P depletion nor increased Na excretion are necessary conditions for expression of the hypotensive effect of supplementary Ca.

Animals↗
PubMed1985

Periplasmic location of p-cresol methylhydroxylase in Pseudomonas putida.

The cellular location of the flavocytochrome c, p-cresol methylhydroxylase was investigated in two strains of Pseudomonas putida. In both cases the enzymes were shown to be located in the periplasmic fraction by their release during treatment of the bacteria with EDTA and lysozyme in a solution containing a high concentration of sucrose. For strain NCIB 9869 the finding is in accord with the suggestion that the physiological acceptor for the enzyme is azurin as this too was shown to be located mostly in the periplasm.

Azurin↗
PubMed1985

On marching to two different drummers: perceptual aspects of the difficulties.

People have remarkable difficulty generating two responses that must follow different temporal sequences, unless the temporal patterns are simply related (e.g., periods in 2:1, 3:1 relation). For example, it is hard to tap to two conflicting rhythms presented concurrently (i.e., a polyrhythm) using the right and left hands (Klapp, 1979), or to tap while articulating a conflicting speech utterance (Klapp, 1981). The present experiments indicate that difficulties in processing conflicting rhythms occur even when people must (a) merely monitor the stimuli and indicate the termination of one rhythmic sequence or (b) tap with a single hand. Responding to polyrhythms is thus difficult even without multiple limb coordination. Furthermore, the difficulty of two-handed tapping to polyrhythms that involve two different tones was found to decrease as the pitch difference between the tones was decreased. This result indicates that the difficulty of rhythmic coordination can be perceptually manipulated in a striking fashion. Polyrhythmic performance thus provides an excellent opportunity for examining possible interactions of perceptual and motor organizations.

Auditory Perception↗
PubMed1985

Health of workers exposed to electric fields.

The results of health questionnaire interviews with 390 electrical power transmission and distribution workers, together with long term estimates of their exposure to 50 Hz electric fields, and short term measurements of the actual exposure for 287 of them are reported. Twenty eight workers received measurable exposures, averaging about 30 kVm-1h over the two week measurement period. Estimated exposure rates were considerably greater, but showed fair correlation with the measurements. Although the general level of health was higher than we have found in manual workers in other industries, there were significant differences in the health measures between different categories of job, different parts of the country, and in association with factors such as overtime, working alone, or frequently changing shift. After allowing for the effects of job and location, however, we found no significant correlations of health with either measured or estimated exposure to electric fields.

Anxiety↗
PubMed1985

Net release or uptake of histidine and carnosine in kidney of dogs.

Previous studies are equivocal as to whether the dog kidney produces histidine. Because one possible source of renal histidine is carnosine (beta-alanyl-L-histidine), we investigated net renal production (release) or utilization (uptake) (Qmet) of histidine and carnosine in 19 female dogs after they were fed histidine-free (9 dogs) or histidine-containing diets (10 dogs). Diets were fed in short-(2-11 days) or long-term (52-57 days) studies. Dogs were infused with half-normal saline for 120 min followed by an infusion of half-normal saline containing carnosine, 50 mumol/min. Renal Qmet histidine, calculated from either plasma or whole blood values, was positive during infusion of half-normal saline. During carnosine infusion, Qmet histidine increased markedly, and there was net renal uptake of carnosine. The Qmet histidine and carnosine were not different in the dogs fed histidine-free vs. histidine-containing diets. Thus there is net renal release of histidine in female dogs that increases when carnosine is administered. Qmet histidine or carnosine do not change adaptively when dogs are fed histidine-free diets.

Animals↗
PubMed1984

Enhanced muscle protein degradation and amino acid release from the hemicorpus of acutely uremic rats.

Protein synthesis and degradation and net uptake and release of amino acids and minerals were investigated in the perfused hemicorpus of acutely uremic and control Sprague-Dawley rats. Rats underwent bilateral nephrectomy or sham surgery and were studied 30 hr after surgery. The uremic rats displayed greater urea N appearance (net urea generation), lower plasma and muscle concentrations of most amino acids, and increased muscle protein degradation as compared to control rats. Muscle protein synthesis was slightly but not significantly decreased in the uremic animals. There was greater net release of phenylalanine, tyrosine, alanine, total nonessential amino acids, total amino acids, potassium and phosphorus from the perfused hemicorpus of uremic rats and greater release of citrulline from sham rats. Muscle ATP, creatine phosphate, cyclic-AMP, and activities of cathepsin B1, cathepsin D, and alkaline protease were not different in the uremic and sham rats. These data provide evidence that acutely uremic rats sustain increased muscle protein wasting which is due to enhanced protein degradation. The increased protein degradation does not appear to be due to enhanced activities of muscle cathepsin B1, cathepsin D or alkaline protease.

Amino Acids↗
PubMed1984

Oral cholecystographic contrast media--a comparative study.

Three oral cholecystographic contrast media have been compared, mainly with regard to their ability to outline the gall bladder and also the frequency of undesirable side-effects that they produce. No significant differences were found between the media, and the final choice of a suitable medium for use in X-ray departments may depend on their relative cost. In times of financial restraint, such a decision might increasingly involve hospital pharmacists.

Administration, Oral↗
PubMed1984

Some effects of rhythmic context on melody recognition.

The effects of rhythmic context on the ability of listeners to recognize slightly altered versions of 10-tone melodies were examined in three experiments. Listeners judged the melodic equivalence of two auditory patterns when their rhythms were either the same or different. Rhythmic variations produced large effects on a bias measure, indicating that listeners judged melodies to be alike if their rhythms were identical. However, neither rhythm nor pattern rate affected discriminability measures in the first study, in which rhythm was treated as a within subjects variable. The other two studies examined rhythmic context as a between subjects variable. In these, significant effects of temporal uncertainty due to the number and type of rhythms involved in a block of trials, as well as their assignment to standard and comparison melodies on a given trial, were apparent on both discriminability and bias measures. Results were interpreted in terms of the effect of temporal context on the rhythmic targeting of attention.

Adult↗
PubMed1983

Protein and amino acid metabolism in posterior hemicorpus of acutely uremic rats.

Protein synthesis and degradation and net uptake and release of amino acids and minerals were examined in the perfused hemicorpus of bilaterally nephrectomized and sham-operated control rats. Animals were studied 30 h after surgery. In comparison with controls, uremic rats had greater urea N appearance (net urea generation) and lower plasma and muscle concentrations of most amino acids. Muscle protein synthesis was not altered, but protein degradation was greater in uremic versus sham rats. There was greater net release of phenylalanine, tyrosine, alanine, total nonessential amino acids, total amino acids, potassium, and phosphorus from the perfused hemicorpus of uremic rats and greater release of citrulline from sham rats. ATP, creatine phosphate, cAMP, and activities of cathepsin B1, cathepsin D, and alkaline protease were not different in muscles of the uremic versus sham rats. Thus, in acutely uremic rats there is increased protein wasting in the hemicorpus due to enhanced protein degradation. The enhanced protein degradation does not appear to be due to increased muscle cathepsin B1, cathepsin D, or alkaline protease activities.

Adenosine Triphosphate↗
PubMed1983

Effect of acute uremia on protein degradation and amino acid release in the rat hemicorpus.

Protein synthesis and degradation and net uptake and release of amino acids and minerals were investigated in the perfused hemicorpus of acutely uremic and sham-operated control Sprague-Dawley rats. Rats underwent bilateral nephrectomy or sham surgery and were studied 30 hours after surgery. The uremic rats displayed greater urea nitrogen appearance (net urea generation), lower plasma and muscle intracellular concentrations of most amino acids, and increased protein degradation in the hemicorpus as compared with control animals. Muscle protein synthesis was slightly but not significantly decreased in the uremic animals as compared with controls. There was greater net release of phenylalanine, tyrosine, alanine, total nonessential amino acids, total amino acids, potassium, and phosphorus from the perfused hemicorpus of uremic rats and greater release of citrulline from sham rats. Muscle ATP, creatine phosphate, and cyclic AMP, and muscle cathepsin B1, cathepsin D, and alkaline protease activities were not different in the uremic and control rats. These data provide evidence that acutely uremic rats have increased muscle protein wasting which is due to enhanced protein degradation. The cause of the increased muscle protein degradation is unknown.

Acute Disease↗
PubMed1982

Amino acid losses during hemodialysis with infusion of amino acids and glucose.

This study evaluated the effects during hemodialysis of intravenous infusion of amino acids and glucose on plasma amino acid and glucose concentrations and amino acid losses. Eight men undergoing maintenance hemodialysis were each studied during two dialyses using glucose-free dialysate. During one hemodialysis, they were infused with 800 ml of normal saline. During the other hemodialysis, they were infused with an equal volume of water which contained 39.5 g of essential and non-essential free L-amino acids and 200 g of d-glucose. The solutions were infused throughout the dialysis procedure into the drip chamber of the venous outflow from the dialyzer. Subjects were fasted from the night before until the end of hemodialysis, and the order of administration of the two solutions was determined randomly. Plasma essential, non-essential, and total amino acids fell significantly during the infusion of normal saline and rose during the administration of amino acids and glucose. Dialysate total-free amino acid losses averaged 8.2 +/- 3.1 SD g during the infusion of normal saline and 12.6 +/- 3.6 g with the administration of amino acids and glucose. These findings indicate that the intravenous infusion of amino acids and glucose during hemodialysis prevents a fall in plasma amino acid and glucose concentrations and leads to only a slight increase in the losses of free amino acids into dialysate. Because most of the infused amino acids are retained, this technique may be used during hemodialysis to avoid a net outflow of amino acids, minimize disruption of amino acid and glucose pools, and provide a nutritional supplement.

Amino Acids↗