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Biomedical subjects

M Peacock

Publications and source records attributed to M Peacock.

At least 181 records · Page 10Linked to original sources
PubMed1977

Prophylactic 1alpha-hydroxyvitamin D3 therapy in haemodialysis patients.

Twenty-seven patients starting regular haemodialysis were treated with a 1 microgram daily dose of 1alpha-hydroxyvitamin D3 and concurrent aluminium hydroxide therapy to prevent hyperphosphataemia. There was an increase in plasma calcium, but no significant improvement in plasma alkaline phosphatase activity or parathyroid hormone levels. Metastatic calcification progressed but was never a severe clinical problem. Quantitative bone histology showed a significant decrease in resorptive surfaces confirmed radiologically, but there was no significant decrease in forming surfaces. The expected increase in forming surfaces with length of dialysis was however prevented.

Adolescent↗
PubMed1977

The management of hypoparathyroidism with 1alpha-hydroxyvitamin D3.

A retrospective study of the comparative effects of vitamin D, dihydrotachysterol and 1alpha-hydroxyvitamin D3 was undertaken in twenty-eight patients with hypoparathyroidism. The vitamin D compounds restored plasma calcium to the normal range in most patients with comparable actions on the gut, bone and kidney. Although the vitamin D compounds had a direct action on kidney and bone in the absence of PTH, the major action in maintaining plasma calcium was on the gut. Plasma phosphate fell due to a reduction in renal tubular reabsorption. Dihydrotachysterol and 1alpha-hydroxyvitamin D3 had significant practical advantages over vitamin D in their rapid onset of action and their relatively short biological half-life.

Adolescent↗
PubMed1977

Vitamin D resistant hypophosphataemic osteomalacia: treatment with 1alpha-hydroxyvitamin D3.

Ten patients with vitamin D resistant hypophosphataemic osteomalacia are described. They had hypophosphataemia with a decreased tubular reabsorption of phosphate, malabsorption of calcium and phosphorus, proximal myopathy and extensive osteomalacic changes on iliac crest bone biopsy. The plasma alkaline phosphatase and urine hydroxyproline, however, were raised in only some of the patients. Treatment with 1alpha-hydroxyvitamin D3 in high doses rapidly cured the myopathy, increased calcium and phosphorus absorption and retention and healed the osteomalacia. Phosphorus supplements were not required.

Adolescent↗
PubMed1977

Tumoral calcinosis: a manifestation of extreme metastatic calcification occurring with 1, alpha-hydroxycholecalciferol therapy.

Two cases are reviewed, both of which developed tumoral calcinosis whilst receiving 1, alpha-hydroxy-cholecalciferol therapy. Tumoral calcinosis is an extreme form of peri-articular calcification, and its occurrence in patients with chronic renal failure is unusual. These peri-articular masses developed around the shoulders in both patients, and the action of 1, alpha-hydroxycholecalciferol as a possible factor promoting this form of metastatic calcification is discussed.

Adult↗
PubMed1976

Assay of plasma 25-hydroxy vitamin D.

A radio-competitive protein-binding assay for 25-hydroxy vitamin D3 (25-OHD3) is described using diluted plasma from patients with vitamin D deficient osteomalacia as the binding protein. The 25-OHD3 is extracted from plasma with ethanol and assayed directly without further purification. An incubation of two hours is used to give suitable binding. The lower detection limit of the assay is approximately 23 pg, the intra-assay coefficient of variation is 5.4% and the inter-assay variation 15%. Tth a mean of 26.9 mug/l. Levels of plasma 25-OHD3 are undetectable in patients with vitamin D deficient osteomalacia and greater than 110 mug/l in patients taking large doses of vitamin D2.

Binding, Competitive↗
PubMed1976

Saturation-inhibition index as a measure of the risk of calcium oxalate stone formation in the urinary tract.

Studies were carried out on multiple urine samples from eight patients with recurrent idiopathic calcium oxalate stone formation and eight normal persons to define an index of the risk of forming calcium oxalate stones. Under the same conditions of dietary and fluid intake the urine samples of the patients with stone formation were more supersaturated with calcium oxalate (P less than 0.001) and had lower concentrations of protective inhibitors of crystallization (P less than 0.001) than those of the controls. However, the best separation between the groups was defined by a discriminant line relating inhibitory activity and urine saturation. A measure of the risk of forming large crystals, the saturation-inhibition index, was defined as the distance of each urine from the discriminant line. The patients with stone formation had a significantly higher mean saturation-inhibition index than the controls (P less than 0.001). Both the percentage of large calcium oxalate crystals excreted (P less than 0.001) and the stone episode rate (P less than 0.005) were significantly correlated with the saturation-inhibition index.

Calcium↗
PubMed1976

Effect of dialysate calcium concentration on bone disease in patients on hemodialysis.

Plasma biochemistry, bone radiology and morphometry were studied in a group of 20 patients receiving maintenance hemodialysis. The aim was to determine if increasing the dialysate calcium concentration would decrease plasma parathyroid hormone and improve the radiologic appearances of bone in patients without producing serious side effects. Dialysate calcium concentration was increased stepwise from 4.5 to 6.0 and then to 7.0 mg/100 ml. Mean predialysis plasma calcium concentration increased from 9.4 to 9.7 and then to 10.0 mg/100 ml and mean predialysis phosphate concentration increased from 5.3 to 5.6 mg/100 ml. Parathyroid hormone concentration was elevated in all patients but the mean concentration did not change significantly although in seven patients a decrease occurred. Six patients had radiologic signs of renal bone disease, two patients showed improvement and three patients developed bone disease during the study. The patients with radiologic bone disease had the highest parathyroid hormone concentrations and the majority were female. Morphometric bone measurements showed that bone loss during the study occurred mainly in the male patients. Soft tissue calcification continued to appear during the study. Although the response to some patients to an increased dialysate calcium concentration was favorable, it was impossible to predict which types of patient would benefit from the use of a dialysate calcium concentration of 7.0 mg/100 ml.

Adult↗
PubMed1975

Seasonal variations in the composition of urine in relation to calcium stone-formation.

1. A retrospective cross-sectional study was carried out on data derived from single 24 h urine collections from 246 male idiopathic calcium stone-formers. 2. The daily urine volume and pH and the exretions of calcium, oxalate, phosphate, creatinine and magnesium were related to the time of year when the urine was collected, and the saturation of urine with calcium oxalate and octocalcium phosphate calculated for each month. 3. There were significant seasonal variations in the urinary excretion of calcium and oxalate, each showing a maximum during the summer months and a minimum in the winter. There was no significant seasonal variation in urinary pH, volume, creatinine, phosphate or magnesium. 4. There was a significant increase in the saturation of urine with calcium oxalate and a trend towards higher saturation levels of octo-calcium phosphate in the summer. These changes were dependent only on the seasonal variation in urinary calcium and oxalate and not on urine volume. 5. A retrospective study of the seasonal incidence of stone episodes among these 246 stone-formers showed that the rate of stone passage per month was 50% higher in the summer than in the winter. There was no significant seasonal variation in the incidence of stones removed surgically.

Calcium↗
PubMed1975

A comparison of the effects of the calcitonins, steroid hormones and thyroid hormones on the response of bone to parathyroid hormone in tissue culture.

A bone culture system was used to compare the effects of several hormones on the response of 5-day-old mouse calvaria to parathyroid hormone (PTH). The results showed that salmon calcitonin was almost 10-5 times more active than any other hormone in preventing the PTH-induced release of calcium and caused a dose-related inhibition of calcium release over a range of 0-2-200 milli MRC units/culture. A high dose of calcitonin (200 milli MRC units) caused a net accretion of calcium in the absence of PTH. Progesterone and testosterone were more active than the naturally occurring oestrogens although a synthetic oestrogen (stillboestrol diphosphate) had approximately the same potency. High concentrations of these hormones caused a net accretion of calcium whether or not PTH was present. Cortisol was only effective at high doses, as was the steroid precursor cholesterol. In the present culture system the thyroid hormones (triiodothyronine and thyroxine) inhibited the action of PTH. It was concluded that these agents acted in a similar fashion to the oestrogens. That is, they prevented the accumulation of citric acid induced by PTH by reducing the rate of glycolysis. None of the hormones affected the inhibition of citrate oxidation caused by PTH. The results also showed that, whilst these hormones inhibited PTH-mediated bone resorption, they had an action on bone independent of PTH. Experiments with clomiphene citrate failed to demonstrate an oestrogen receptor in bone.

Animals↗
PubMed1974

Seasonal variations in urinary excretion of calcium.

A retrospective study over a three-year period has shown a noticeable seasonal variation in the daily urinary excretion of calcium in healthy men, healthy women, and men prone to form stones. This reached a maximum in July or August and a minimum in December or January in all three groups. For any given month the stone formers had higher urinary calcium values than healthy men, who, in turn, had higher values than healthy women.

Adult↗
PubMed1974

Plaque assay of rickettsiae in a mammalian cell line.

Clear-cut and repeatable plaque assays were obtained for three rickettsiae of the spotted fever group (Rickettsia rickettsi, R. conori, and R. montana) in Vero cells used in a manner similar to that for arboviruses. In addition, three typhus group agents (R. typhi, R. canada, R. prowazeki) induced plaques in these cells. In preliminary tests Coxiella burneti (Nine Mile strain) failed to produce plaques. Comparable results were obtained in plastic flasks and plastic culture trays incubated in ambient air with or without addition of N-2-hydroxyethyl-piperazine-N'-2-ethanesulfinic acid buffer. Larger and more well defined R. rickettsi plaques were produced when cultures were overlaid with Leibovitz (L15) medium than with either medium 199 or Eagle medium. Phosphate-buffered saline containing bovine plasma albumin (fraction V), in contrast to brain heart infusion broth, as a diluent for preparing inocula consistently permitted development of larger and more numerous plaques with three agents: R. rickettsi, R. conori, and R. montana. When R. rickettsi and R. typhi were assayed in parallel in primary chicken embryo cultures and Vero cells, comparable results were obtained, but with R. canada results in Vero cells were superior. In contrast, R. prowazeki produced inconsistent results in Vero cells.

Animals↗