ROLE OF OUABAIN-LIKE COMPOUND IN RATS WITH REDUCED RENAL MASS-SALINE HYPERTENSION

Ouabainlike compound (OLC) has recently been identified as a likely mammalian endogenous digitalis-like factor (EDLF) from human plasma. In this study, plasma levels of OLC were determined to assess the role of OLC in a model known as volume-expanded, reduced renal mass (RRM)-saline (S) hypertension in rats with use of a newly developed radioimmunoassay for ouabain. In the first experiment, at 3 wk after subtotal nephrectomy and drinking 1% saline solution, systolic blood pressure (SBP) of 18 rats with reduced renal mass (RRM-S rats) was significantly higher than in 17 sham-operated saline-drinking control (C-S) rats [154 +/- 4 (SE) vs. 132 +/- 2 mmHg; P < 0.01]. Plasma OLC levels were 355 +/- 68 pmol/l in RRM-S rats, sevenfold higher than in C-S rats (54 +/- 4 pmol/l; P < 0.01). In the second experiment, we measured plasma OLC levels of 10 RRM-S, 12 sham-operated control (C), and 10 subtotally nephrectomized rats drinking distilled water (RRM rats). Concomitant with a marked increase in blood pressure (203 +/- 5 mmHg), RRM-S rats showed significantly higher plasma OLC levels compared with C and RRM rats (RRM-S 114 +/- 24, C 47 +/- 11, and RRM 52 +/- 9 pmol/l; P < 0.05). In both experiments, plasma OLC levels correlated significantly with SBP (P < 0.05). These findings suggest that plasma OLC shows a similar behavior to that of EDLFs or Na+-K+-adenosinetriphosphatase inhibitors reported in previous publications and may play a role in hypertensive mechanisms in rats with RRM and excess Na intake.