Inhibition of the arteriolar smooth muscle NA+ -K+-pump induces an enhanced vasoconstriction in borderline but not in established essential hypertension.

1. The dependency of arteriolar tone on the activity of the Na+ -K+-pump was studied in 17 normotensive (NT) males, aged 20-71 yr, without heredity for essential hypertension and 28 male patients with essential hypertension, aged 18-63 yr, by measuring forearm blood flow response to intra-arterial infusion of the Na+-K+-pump inhibitor ouabain. 14 of the patients were classified as borderline essential hypertensives (BHT) and 14 as established essential hypertensives (EHT). 2. Ouabain in incremental dosages 0.4-16 micrograms/100 ml tissue induced a vasoconstrictive response in the forearm with a maximal effect to 8 micrograms/100 ml tissue, which was not associated with an increase in regional noradrenaline release. 3. The vasoconstriction to ouabain 8 micrograms/100 ml was 29.6 +/- 6.8% in NT (P less than 0.001); 51.9 +/- 8.4% in BHT (P less than 0.001) and 36.0 +/- 12.7% in EHT (P less than 0.05). This response was greater in BHT than in NT (P less than 0.05) but not different in NT and EHT and did not correlate with age either in NT or in BHT and EHT taken together. 4. Our findings suggest an increased activity of the arteriolar Na+ -K+-pump in the early phase of essential hypertension which may to some extent correct a raised intracellular Na+; the latter being the consequence of an increased passive permeability to Na+. The activity of the arteriolar Na+ -K+-pump appears to be decreased in the later as compared to the early phase of essential hypertension.