High phosphate level directly stimulates parathyroid hormone secretion and synthesis by human parathyroid tissue in vitro

Phosphate retention plays an important role in the pathogenesis of secondary hyperparathyroidism in patients with renal failure. In in vitro studies, high extracellular phosphate levels directly stimulate PTH secretion in rat and bovine parathyroid tissue. The present study evaluates the effect of high phosphate levels on the secretion of PTH and the production of prepro PTH mRNA in human hyperplastic parathyroid glands. The study includes parathyroid glands obtained from patients with primary adenomas and from hemodialysis and kidney-transplant patients with diffuse and nodular secondary hyperplasia. The experiments were performed in vitro using small pieces of parathyroid tissue. The ability of high calcium levels to decrease PTH secretion was less in adenomas than in secondary hyperplasia; among the secondary hyperplasia, nodular was less responsive to an increase in calcium than diffuse hyperplasia. In diffuse hyperplasia, PTH secretion was increased in response to 3 and 4 mM phosphate compared with 2 mM phosphate, despite a high calcium concentration in the medium; prepro PTH mRNA levels increased after incubation in 4 mM phosphate. Similar results were obtained with nodular hyperplasia, except that the elevation of PTH secretion in response to 3 mM phosphate did not attain statistical significance. In adenomas, high calcium concentrations (1.5 mM) did not result in inhibition of PTH secretion, independent of the phosphate concentration, and the prepro PTH mRNA was not significantly increased by high phosphate levels. In conclusion, first, the PTH secretory response to an increase in calcium concentration is less in nodular than diffuse hyperplasia; second, high phosphate levels directly affect PTH secretion and gene expression in patients with advanced secondary hyperparathyroidism.     

Applying statistics to find the causes of variability in aluminumevaporation: a case study

A study of the causes of variability in the thickness of aluminum deposited on silicon wafers is presented. A work team was assembled to define and characterize the process, equipment, and measuring techniques adequate to the available means. The most important variables were studied, and, through a variance analysis, the ones that contribute the most to the variability were selected. The relationship among the vital variables was established using the Taguchi technique. A test run was performed and the C_PK showed an increase, effectively reducing the variability     

Blood microdialysis in humans: a new method for monitoring plasma compounds

A new venous microdialysis probe for humans was developed. The active area was made with cellulose membrane (220 mm outside diameter, length 20 mm, and 6000 molecular weight cut off). Glucose measurements were used to test it. The relative recovery was 50% in dialysates obtained in vitro, the step response was 91.8% in the first 2 min. The in vivo recovery was 65.8% obtained by the no net flux method, with the probe placed in the cubital vein of the subjects arms. Corrected glucose in dialysates was non significantly different from plasma glucose simultaneously collected. In healthy male volunteers from 18 to 37 years of age, mean 22.1 years, the glucose levels in the blood dialysates were measured every 30 min, 60 min before and 150 min after an oral load of 75 g of glucose or vehicle. Glucose increased significantly after the load. The differences with the control group were significant at 60 and 90 min after the treatment. The results showed the easy and safe application of this technique to monitor endogenous and exogenous compounds in the extracellular compartment of blood in out patients.     

A new algorithm for process flowsheeting

A new algorithm is described for organizing the computations in a process flowsheeting system designed to handle mixed systems of equations and procedures. It is essentially a depth-first implicit enumeration algorithm based on partitioning and tearing techniques, but also uses automatic algebraic manipulation to take further advantage of the structure.