Ouabain-like factor and acute salt loading in low-renin hypertension

In these years an ouabain -like factor (OLF), structurally similar to cardiac glycoside ouabain, has been isolated in human plasma. OLF has been implicated in states of volume expansion and in essential hypertension, especially as a factor of salt sensitivity of blood pressure. On the other hand, salt sensitivity has been described particularly in low-renin hypertension. Aim of this study was to determine the response of plasma OLF to acute sodium expansion in low renin hypertension. To this purpuse, an acute intravenous sodium load ( two litres saline in four hours) was performed in 14 subjects with low-renin hypertension. OLF was measured in plasma extracts (C18 extracted samples) by a radioimmunoassay (previously described except for having employed filter separation of bound/ free 3H ouabain) and compared with other endocrine parameters (aldosterone, ANP, cortisol, ACTH). Variable responses to the saline load were observed in the individual patients for blood pressure, which significantly increased (p 0.05 for both diastolic and systolic levels). Only a modest non significant change was observed after four hours saline infusion for OLF (mean SEM); 894 207 pM against 749 171 pM ouabain equivalents before treatment, whereas plasma aldosterone showed a significant decrement (p 0.0007), paralleled by an increase in ANP levels (p 0.007). A positive relationship was observed between OLF and ACTH (p 0.02). In conclusion, our results do not support the hypothesis that ouabainlike factor is stimulated in low renin hypertension by acute volume expansion obtained with intravenous saline loading; ACTH could be a factor modulating OLF secretion in this condition.