Forearm vasoconstrictor response to ouabain: studies in patients with mild and moderate essential hypertension

The dependence of arteriolar vasoconstrictor tone on the activity of Na+,K+-ATPase was studied in 17 normotensive subjects (NT) and 28 patients with essential hypertension (EH) by measuring the response in forearm blood flow and vascular resistance to intraarterial infusion of the Na+,K+-ATPase inhibitor ouabain. Basal plasma aldosterone concentrations were elevated in mild (n = 14) and moderate (n = 14) EH patients as compared with NT (p less than 0.001 for both) and correlated positively with intraarterial diastolic blood pressure (r = 0.551, p less than 0.001). Ouabain in incremental doses of 0.4-16 micrograms/100 ml tissue induced a vasoconstrictor 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. The vasoconstrictor response to ouabain, 8 micrograms/100 ml, expressed as the percentage change in the ratio of forearm vascular resistance (FR) on the experimental side versus the control side, was 29.6 +/- 6.8% in NT (p less than 0.001); 51.9 +/- 8.4% in mild EH (p less than 0.001), and 36.0 +/- 12.7% in moderate EH (p less than 0.05). The vasoconstrictor response was greater (p less than 0.05) in patients with mild EH than in NT but did not differ in NT and patients with moderate EH. Vascular reactivity in the forearm, as assessed by intraarterial infusions of noradrenaline (3, 8, and 20 ng/min/100 ml tissue), did not differ in NT (n = 9) and patients with mild (n = 9) or moderate (n = 9) EH. The results suggest increased activity of arteriolar Na+,K+-ATPase in mild EH, which may represent a mechanism counteracting an accumulation of intracellular sodium and thereby an early increase in forearm vascular resistance (FR).(ABSTRACT TRUNCATED AT 250 WORDS)