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Biomedical subjects

M R Jones

Publications and source records attributed to M R Jones.

At least 163 records · Page 9Linked to original sources
PubMed1982

14CO2 expiration after 14C-histidine administration in normal and uremic men ingesting two levels of histidine.

The rates of histidine degradation were investigated in six normal and three chronically uremic men who were not undergoing dialysis therapy. The nine men were studied in the postabsorptive state after they had ingested one or more of the following diets for the indicated periods of time: a 40 g protein diet providing about 1100 mg/day of histidine for 27 +/- 9 SD days (seven studies), an amino acid diet providing only 65 mg/day of histidine (histidine-deficient diet) for 33 +/- 3 days (eight studies), and an amino acid diet providing about 1125 mg/day of histidine (histidine-replete diet) for 32 +/- 7 days (six studies). Diets are listed in the order of administration; five men received all three diets. After fasting overnight, subjects received an intravenous injection of 25 microCi/70 kg body weight of L-[ring-2-14C]-histidine (eight men) or L-carboxyl-14C]-histidine (one man), and expiration of 14CO2 was measured continuously for 2 h. With both tracers, expiration of 14CO2 fell with ingestion of the histidine-deficient diet (p less than 0.005) and then increased with intake of the histidine-replete diet (p less than 0.05). Free histidine in plasma and muscle also decreased with the histidine-deficient diet and rose with the histidine-replete diet. If other tissue free histidine pools changed similarly and protein turnover was not very different with the three diets, then the 14CO2 expiration data and the estimated specific activity of 14C-histidine indicate that histidine degradation fell markedly with the histidine-deficient diet and then increased with the histidine-replete diet. In uremic patients as compared to normal subjects no differences in the magnitude of 14C-histidine degradation or in the pattern of 14CO2 expiration were observed.

Adult↗
PubMed1982

Plasma amino acid levels and amino acid losses during continuous ambulatory peritoneal dialysis.

Free amino acid losses into dialysate during a 24-h collection period and postabsorptive plasma amino acid concentrations were measured in 14 studies in nine clinically stable men undergoing continuous ambulatory peritoneal dialysis. Patients ingested diets containing 97 +/- 18 (SD) g/day of protein in a metabolic research unit. Total amino acid losses were 3.4 +/- 1.2 g/24 h and represented 3.9 +/- 1.9% ot total nitrogen output (in dialysate, urine and feces). The sum of plasma essential, nonessential, and total amino acid concentrations was normal, although plasma valine, leucine, and isoleucine were decreased and several amino acids were elevated. Neither plasma nor dialysate amino acids, varied with protein intake. Dialysate amino acid concentrations averaged 72 +/- 18% of plasma levels, and 29.0 +/- 3.6% of dialysate amino acids were essential. Dialysate concentrations and 24 h losses of individual amino acids each correlated with plasma levels (r = 0.83 and 0.78, respectively). Thus during continuous ambulatory peritoneal dialysis, postabsorptive plasma amino acids are, in general, well maintained. Daily losses of free amino acids during continuous ambulatory peritoneal dialysis are rather small and are easily replaced by food intake.

Adult↗
PubMed1982

Arginine metabolism and urea synthesis in cultured rat skeletal muscle cells.

Skeletal muscle is known to contain arginase, but, because this enzyme is also present in erythrocytes, the exact origin of arginine-derived ornithine in peripheral tissues is uncertain. In the present studies, skeletal muscle cells obtained from regenerating hindlimb muscle of adult rats were grown in primary tissue culture for approximately 3 wk and then studied in regard to changes in medium amino acid concentrations over a 48-h period. The consumption of arginine and serine was observed in parallel with the production of ornithine, proline, citrulline, glycine, and urea. Medium threonine and methionine concentrations were relatively constant over 48 h. Incubation of muscle cells with [U-14C]arginine resulted in the formation of [14C]ornithine and [14C]proline at rates at least 10-fold greater than could be accounted for by enzyme constituents of fetal calf serum. In addition, [guanido-14C]arginine was converted to [14C]urea and [U-14C]serine was converted to [14C]glycine. These studies indicate that cultured skeletal muscle cells contain a high arginase capacity and actively synthesize ornithine and urea from arginine.

Ammonia↗
PubMed1981

Evidence for rhythmic attention.

Three studies compared effects of different rhythmic contexts on order judgments of targets embedded in auditory patterns designed to manifest auditory stream segregation. Of interest was the effect of rhythmic structure upon the frequency-based captor effect, wherein tones in one stream "capture" those of similar frequencies from another. Three rhythmic structures were studied. Experiment 1 compared a rhythm conducive to pairwise-target stream formation with one conducive to a four-tone stream, and one based on an isochronous rhythm in a within-subjects design. Patterns embedding the target tone pair contained a preliminary string of captor tones at frequencies either close or far from frequencies of distracting tones that flanked the target pair. No effect of captor distance was found. Experiments 2 and 3 varied rhythm between subjects using 9- and 11-tone patterns, respectively. In general, the magnitude of the captor effect was found to vary with temporal predictability of flanking and/or target tones. The pairwise rhythm was most likely to improve order judgments by facilitating frequency-based capture. Results are discussed in terms of a rhythmic attentional hypothesis.

Attention↗
PubMed1981

Protein losses during peritoneal dialysis.

The losses of protein into dialysate have been considered a major limitation of maintenance peritoneal dialysis. We, therefore, undertook a comprehensive evaluation of protein losses in 30 patients undergoing maintenance intermittent peritoneal dialysis (IPD), 12 patients undergoing acute IPD, and 8 patients undergoing continuous ambulatory peritoneal dialysis (CAPD). The weekly loss of protein based upon the usual treatments per week was relatively similar with the three modes of dialysis. Protein losses during repeated dialyses were similar for a given patient, but there was repeated dialyses were similar for a given patient, but there was marked interpatient variation. During maintenance IPD, protein loss was 12.9 +/- (SD) 4.4 g per 10 hours of dialysis; albumin loss was 8.5 g, and IgG loss was 1.3 g. Approximately 50% of the protein loss was from the ascitic fluid accumulated during the interdialytic interval, and concentrations of most proteins in the ascitic fluid correlated with their serum levels. Serum protein concentrations were in the low, normal range and did not change during dialysis. The development of peritonitis markedly increased protein losses. During acute IPD, 23.3 +/- 16.5 g of protein were lost per 36 hours of dialysis, lower losses than those previously reported. With CAPD, 8.8 +/- 1.7 g of protein were removed per 24 hours; also immunoglobulin losses correlated with their serum concentrations. The results of these studies suggest that, in the absence of peritonitis, dialysate protein losses do not appear to limit the usefulness of peritoneal dialysis.

Adult↗
PubMed1981

Daily requirement for pyridoxine supplements in chronic renal failure.

Vitamin B6 deficiency was evaluated in 37 patients with chronic renal failure and in 71 patients undergoing maintenance hemodialysis (HD) or intermittent peritoneal dialysis (PD). Vitamin B6 deficiency was assessed by the in vitro activity of erythrocyte glutamic pyruvic transaminase (EGPT), without (basal) and with (stimulated) the addition of pyridoxal-5-phosphate to the assay, and the EGPT index (stimulated activity ./. basal activity). Basal and stimulated EGPT activities were below normal in the HD patients, and the EGPT index was increased in each group of patients, indicating vitamin B6 deficiency. Supplemental pyridoxine hydrochloride was given to 30 HD patients who received 1.25 to 50 mg/day (37 studies), 6 PD patients who were given 1.25 or 2.5 mg/day (7 studies), and 8 nondialyzed patients with mild to severe renal failure who received 2.5 mg/ day. In all HD patients, 10 or 50 mg/day of pyridoxine hydrochloride rapidly corrected the abnormal EGPT index and maintained normal values; with supplements of 5.0 mg/day or less, the index was often abnormal, particularly in those who were septic or taking pyridoxine antagonists. In PD patients and nondialyzed patients with renal failure, 2.5 mg/day of pyridoxine hydrochloride was inadequate to correct rapidly the abnormal index in all patients. These findings suggest that HD patients should receive 10 mg/day of supplemental pyridoxine hydrochloride (8.2 mg/day pyridoxine). PD patients and patients with chronic renal failure should receive about 5.0 mg/day of supplemental pyridoxine hydrochloride (4.1 mg/day pyridoxine). When sepsis intervenes or vitamin B6 antagonists are taken, 10 mg/day of pyridoxine hydrochloride may be a safer supplement for all patients.

Adult↗
PubMed1981

Histidine, an essential amino acid for adult dogs.

Twenty-seven adult female mongrel dogs were studied to evaluate whether histidine is an essential amino acid. Dogs were tube-fed isocaloric, isonitrogenous amino acid diets which provided either no histidine or 67 mg histidine/kg body weight/day. The histidine-free diet was fed to 10 dogs for 5.6 +/- 3.6 (SD) days and to six dogs for 59.2 +/- 6.0 days. In the short-term studies, there were no differences between the responses of the dogs fed the histidine-free and histidine-replete diets. In the long-term studies, dogs fed the histidine-free diet developed a significant decrease in plasma and muscle histidine, muscle carnosine, body weight, hematocrit and serum albumin. The dogs fed the histidine-free diet tried to avoid the feedings, and after several weeks, they often manifested reduced activity and listlessness. One dog died on the 72nd day. None of these manifestations occurred in the dogs fed the histidine-replete diet in the long-term studies. Plasma zinc and copper were not different in the two groups of dogs. However, at the end of the long-term studies, the dogs fed the histidine-free diet had significantly lower final whole blood zinc and copper concentrations as compared to the histidine-replete dogs. These findings indicate that histidine is an essential amino acid in adult female dogs. The syndrome associated with histidine-deficiency tends to develop slowly over many days to several weeks.

Amino Acids↗
PubMed1981

Effects of clofibric acid on amino acid metabolism in cultured rat skeletal muscle.

Well-differentiated cultured skeletal muscle cells (myotubes) obtained from adult rats were incubated for up to 48 h in Dulbecco's modified Eagle's medium. Medium glucose decreased from 4.9 +/- 0.1 mM at 0 h to 13 +/- 1 microM by 24 h; approximately 60% of glucose was converted to lactate. Pyruvate, alanine, and citrate were continuously produced, even during the period of 24-48 h when no glucose or lactate utilization was observed. Branched-chain amino acid utilization increased more than fourfold during the incubation period of 24-48 h; during this time, intracellular ATP, pyruvate, alpha-ketoglutarate, malate, and citrate levels were constant despite the absence of glucose or lactate consumption. Incubation of muscle cells with 2 mM clofibric acid resulted in a 76% inhibition of leucine metabolism. Coincident with the drug-induced inhibition of a branched-chain amino acid utilization, alanine and citrate production was blocked, and cell levels of pyruvate, alpha-ketoglutarate, malate, and citrate were markedly reduced. These studies suggest branched-chain amino acids contribute significantly to anaplerotic pathways in cultured skeletal muscle cells and that these pathways lead to the net production of alanine and citrate during periods of minimal carbohydrate utilization.

Alanine↗
PubMed1980

Repair of mycotic aneurysms of the aorta involving the aortic valve.

This report summarizes our successful management of 6 patients who underwent repair of mycotic aneurysms of the ascending aorta within a four-year period. Repairs have been successful despite involvement of as much as two-thirds of the circumference of the aortic valve annulus, involvement of the origin of the right coronary artery, and development of heart block. Three patients required surgical intervention because of hemodynamic decompensation before they had completed antibiotic therapy for endocarditis. In 3 patients, the aneurysm was buttressed with the valve skirt so that aneurysm repair and valve replacement were accomplished in continuity. In 2 patients, the aneurysm was repaired separately and the valve seated on the repair. In 1 patient, a large defect between the left and right coronary arteries was repaired with a woven Dacron patch secured to the valve skirt. The valve was seated to the left ventricle and the graft to the aorta. There were no operative or postoperative deaths. Our data suggest that mycotic aneurysms of the aortic annulus can be successfully repaired despite extensive damage.

Adolescent↗
PubMed1979

AHR-6646: a new, long-acting neuroleptic.

1. AHR-6646 blocked d-amphetamine lethality in mice under aggregated conditions when the pretreatment interval was between one hour and seven days. 2. Conditioned avoidance responding in mice and cats was suppressed by AHR-6646 in doses that did not impair escape behavior. The duration of this effect was markedly prolonged. 3. AHR-6646 produced catalepsy in rats. The onset of this effect was delayed and the duration was prolonged when compared with that of chlorpromazine. 4. Apomorphine-induced pivoting in mice with unilateral lesions of the caudate nucleus was suppressed by AHR-6646. 5. AHR-6646 was a potent antiemetic agent in dogs, with a delayed onset and prolonged duration of action.

Animals↗