Search

1. The effect of plasma and serum from normal subjects on the production of prostacyclin by cultured porcine endothelial cells was investigated. 2. Both plasma and serum from all subjects studied significantly stimulated the production of prostacyclin by cultured endothelial cells, measured by the radioimmunoassay of its stable metabolite 6-oxoprostaglandin F1α. 3. Serum caused a consistently greater stimulation than plasma from the same individual. The stimulation was dose-dependent and inhibited by indomethacin. Heparin added to serum also inhibited this response. 4. Extracts from isolated washed platelets were tested for their ability to increase prostacyclin production. Extracts from platelets which had been induced to aggregate and release their granule contents in response to thrombin, caused stimulation. 5. These results indicated the invariable presence in plasma and serum of factors that stimulate the production of prostacyclin by endothelial cells in vitro. At least one of these factors is derived from platelets. These factors may be involved in the regulation of prostacyclin production by the vascular endothelium under normal conditions and in disease states.

1. The formation of thromboxane B2 and malondialdehyde was studied in human platelet-rich plasma, in gel-filtered platelets and in bovine platelet microsomes. 2. Exogenous sodium arachidonate was converted into thromboxane B2 and malondialdehyde in a concentration-dependent manner. Pre-incubation of platelets with aspirin inhibited the production of both thromboxane B2 and malondialdehyde, although malondialdehyde could apparently be detected in the absence of thromboxane B2. 3. The aggregating agents, thrombin, collagen and the ionophore A23187 also caused production of thromboxane B2 and malondialdehyde. ADP and adrenaline produced a smaller rise whilst the endoperoxide analogue U 46619 had only a slight influence on thromboxane and malondialdehyde, even though they all induced aggregation. 4. Pre-incubation of platelets with imidazole or 1-N-butylimidazole, which inhibit thromboxane synthetase, resulted in an inhibition of both thromboxane B2 and malondialdehyde formation in response to collagen. 5. The results indicate that thromboxane B2 and malondialdehyde are formed in parallel, in comparable quantities. However, under the conditions used in these studies, the apparent amounts of malondialdehyde exceed those of thromboxane B2, especially in the presence of exogenous arachidonate. Thus the thiobarbiturate reaction used to assay malondialdehyde may detect other products of lipid peroxidation. 6. Platelet thromboxane B2 concentrations did not always relate to the extent of aggregation. In particular, platelet aggregation could occur in the absence of detectable thromboxane B2 production.

1. We have studied the early effects of intravenously and orally administered etidronate on vitamin D metabolism and indirect indices of calcium and skeletal metabolism in 17 patients with Paget's disease of bone. 2. Administration of etidronate by mouth (700–1400 mg daily for 1 month) or its intravenous infusion (300 mg daily for 5 days) decreased bone resorption as judged by urinary excretion of hydroxyproline and significantly increased renal tubular reabsorption of phosphate. No significant change in serum activity of alkaline phosphatase was noted with either regimen. 3. When etidronate was given by mouth there was a progressive decrease in fasting urinary calcium excretion and a rise in serum 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3]. In contrast, intravenous etidronate decreased serum values of l,25-(OH)2D3 and was associated with a progressive increase in fasting calcium excretion, suggesting a decrease in the net influx of calcium from the extracellular compartment to bone. Significant inverse correlations were noted between the change induced in 1,25-(OH)2D3 values at 2 weeks and the changes in serum calcium, phosphate and fasting urinary excretion of calcium. 4. These observations suggest that the different effects of intravenous and oral etidronate on l,25-(OH)2D3 values are a consequence of different doses of etidronate used and the different effects of these regimens on the accretion of calcium into bone.

1. A technique is described for the determination of orthophosphate (Pi) in human erythrocytes. The advantages of the technique are that it uses whole blood rather than separated erythrocytes, that it avoids major hydrolysis of organic phosphates, that it takes account of incomplete recovery of Pi and that it minimizes the effects of chilling the cells. 2. In chilled samples from 46 patients in an intensive care unit, the cellular concentration of Pi was proportional to that in plasma. 3. Blood samples from nine normal subjects were incubated at 37°C. The cellular Pi was 0.79 mmol/litre of cells using an external standardization and 0.67 using an internal standardization. When the same cell samples were chilled on ice for 30 min, the internally standardized value decreased further to 0.57 mmol/litre of cells. These results suggest that differences in recovery, and the extent of chilling, contribute to the variability in the previously reported values for erythrocyte Pi. 4. If Pi, like chloride, had distributed passively between cells and plasma in these samples, the cell to plasma molar concentration ratio for Pi should have been 0.29, compared with the measured value of 0.64. This difference suggests that some factor, in addition to passive diffusion, determined the distribution of Pi.

1. Orthophosphate (Pi), adenosine 5′-diphosphate (ADP), adenosine 5′-triphosphate (ATP) and 2,3-diphosphoglycerate (2,3-DPG) were measured in the erythrocytes of patients in an intensive care unit. 2. The patients’ plasma concentration of Pi varied from 0.1 to 4.2 mmol/l, and the corresponding concentration in erythrocytes varied from 0.1 to 2.0 mmol/litre of cells. 3. Marked ATP depletion (less than 1 mmol/litre of cells) was only observed when erythrocyte Pi was less than 0.3 mmol/litre of cells and plasma Pi was less than 0.35 mmol/l. No dependence of 2,3-DPG concentration on the cellular concentration of Pi was detected. 4. The phosphorylation potential [ATP]/([ADP] × [Pi]) varied inversely with the erythrocyte concentration of Pi. Hence the calculated free energy of hydrolysis of ATP in the cell increased from −58 kJ/mol in the most hypophosphataemic samples to −51 kJ/mol in the most hyperphosphataemic. Such changes may adversely affect cell function by altering the steady state mass-action ratios of ATPase reactions. 5. When erythrocytes from normal donors were incubated in solutions containing 1 or 5 mmol/l Pi, the cellular concentrations of Pi stabilized at 1.09 and 2.85 mmol/litre of cells respectively. The corresponding rates of lactate production were 2.09 and 3.11 mmol h−1 litre−1 of cells. 6. In spite of this stimulation of glycolysis (and hence of the flux through ATP synthesizing steps of the Embden-Meyerhof pathway), no significant change in ATP concentration was observed. As in the patients' cells, this indicates that, when extracellular Pi concentrations are perturbed, the concentrations, in erythrocytes, of organic phosphates are more closely regulated than the concentration of Pi.

1. Bone loss was assessed by measurement of cortical thickness of metacarpal bone by X-ray and of trabecular bone area in serial bone biopsies in 49 patients with chronic renal failure, six before and 45 during maintenance haemodialysis treatment. 2. Metacarpal cortical measurements (MCM) were very reproducible (coefficient of variation 1·95%), whereas bone area measurements by histology showed great variability. There was no correlation between rates of change of MCM and bone area over the same period, although both tended to fall with time. 3. The mean annual rate of bone loss measured by MCM for patients on dialysis was 2·08 ± 0·32 mm/year (mean ±1 sem) and this rate was not significantly different from the mean rate of loss of 2·49 ± 0·78 mm/year for the six patients who were not on maintenance haemodialysis. 61% of all patients showed a significant decrease during the period of study (1–6 years), but none had symptoms attributable to bone loss. 4. The loss tended to be greatest in women over the age of 40 years. The initial amount of bone and the rate of loss measured by MCM or bone histology were not influenced significantly by the presence or absence of histological or radiological evidence of parathyroid overactivity or of osteomalacia, nor by differences in the causes of renal disease. 5. Loss of metacarpal cortical bone correlated with heparin consumption during haemodialysis in men but not in women. The amount of bone and its rate of loss was not influenced by the presence of an arteriovenous shunt in one arm compared with the other. In neither sex did bone loss correlate with physical activity. 6. A relative deficiency of calcium due to a low dietary calcium intake and intestinal malabsorption of calcium, together with a dialysate calcium of only 1·5 mmol/l, may be more important causes of bone loss in patients in this study.

1. In this study, cells derived from explants of human trabecular bone were treated with the anabolic steroid stanozolol in order to determine whether the potential therapeutic effect of this agent might be explained by direct effects on skeletal tissue. 2. Stanozolol at a concentration of 10−10 mol/l to 10−6 mol/l consistently stimulated the incorporation of [3H]thymidine into DNA of human bone cells and increased proliferation. 3. Stanozolol had variable effects on the expression of two other markers of the osteoblast phenotype, namely the bone-specific vitamin-K-dependent protein osteocalcin, and the enzyme alkaline phosphatase. Although stanozolol tended to increase the values, this was not seen in all experiments. 4. We conclude that human bone cells respond to stanozolol. The effects of this agent on cell proliferation may be important in understanding the mode of action of this drug in the treatment of osteopenic disorders.