Abolition, by Dopamine Blockade, of the Natriuretic Response Produced by Lower-Body Positive Pressure

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Abstract
In a preliminary study, a positive pressure of 25 mm Hg applied to the lower body raised right atrial pressure by a mean of 7 mm Hg. Sustained application of lower-body positive pressure (LBPP) in 6 normal adult males increased Na excretion ([Na]V) from a control level of 126.5 .+-. 10 to 213 .+-. 21 .mu.mol/min (P = 0.003), and fractional Na excretion (EFNa) from 0.7 .+-. 0.1 to 1.2 .+-. 0.1 (P = 0.001). Urine flow (UF) increased from 0.85 .+-. 0.07 to 4.1 .+-. 0.8 ml/min (P = 0.002), osmolar clearance (Cosm) from 2.6 .+-. 0.13 to 4.2 .+-. 0.4 ml/min (P = 0.003) and free H2O clearance (CH2O) from -1.75 .+-. 0.1 to -0.1 .+-. 0.01 ml/min (P = 0.001). Creatinine clearance (Ccr) showed no significant change. After dopamine blockade with domperidone, LBPP did not cause a rise in [Na]V or EFNa. Urine flow, Cosm and CH2O remained significantly above control values, implying persistent suppression of antidiuretic hormone. Dopamine blockade without positive pressure did not affect basal Na excretion.