-Our data suggest that salt-depleted salt-sensitive hypertensives with blunted renin responses exhibit enhanced catecholamine-stimulated endothelin levels and may therefore respond better than unselected patients with essential hypertension to endothelin receptor blockers.

Serum LDH activities assayed spectrophotometrically by the "forward" (lactate + DPN to pyruvate + DPNH + H) method have linear reaction rates, activity proportional to the amount of serum added, and a reproducibility of 1.3%. The reagent mixture can be stored frozen for 6 months and in the lyophilized state indefinitely. Poor separation of normal from abnormal serum LDH activities results from the nonlinear calibration curves and decreasing reaction rates of the "backward" spectro-photometric assay. The dinitrophenylhydrazine colorimetric assay is deemed unsuitable for clinical use because large variations in activity result from minor variations in the reagent calibration curve, and because colorimetric activities are inaccurate as compared to activities obtained with the "forward" spectrophotometric assay.

Serum phosphorus can be measured by continuous-flow uv spectrophotometry without reduction of the phosphomolybdate complex. The dilute sample is dialyzed into dilute (1 ml/100 ml) sulfuric acid, then mixed with an ammonium molybdate— sulfuric acid—"Tween 80" solution. The absorbance of the sample peaks is measured at 340 nm with a linear-absorbance spectrophotometer. Peak heights are directly proportional to concentration, because logarithmic conversion is performed within the spectrophotometer. The method obeys Beer’s law up to 10 mg of P per deciliter, and results correlate closely with those for standard methods based on reduced phosphomolybdate blue. The miniature manifold uses a 12-in. dialyzer. The sampling rate can be 60 to 120 samples per hour when a Gilford one-piece debubbler flow cell is used.