ENDOGENOUS IMMUNOREACTIVE OUABAIN-LIKE AND DIGOXIN-LIKE FACTORS IN REDUCED RENAL MASS HYPERTENSIVE RATS

We evaluated the urinary excretion of immunoreactive endogenous ouabai n-like factor(OLF) and digoxin-like factor (DLF) to investigate their pathophysiological roles in sodium metabolism and blood pressure in 5/ 6-reduced renal mass rats, a model of volume-expanded hypertension. Ab out five-sixths of the kidney mass (5/6 RRM, n = 9) was removed from m ale Sprague-Dawley rats, or the rats were sham operated (control, n=10 ). Both groups were fed regular diets with tap water for 1 wk as a con trol period, followed by 1% saline solution for 4 wk. Systolic blood p ressure(SBP), urine volume (UV), urinary sodium excretion (UNaV), DLF, and OLF were measured on the last 2 d of every week throughout the ex perimental period. SEP and UNaV were significantly higher in 5/6 RRM r ats than in control rats. Urinary DLF significantly increased, reachin g peak value in the first week, while OLF increased continuously, reac hing peak value in the fourth week. In the first week, there were a si gnificant positive correlations between the change in DLF and the chan ges in UNaV and SEP. However, the change in OLF was not correlated,vit h changes in either UNaV or SEP. Both SEP and UNaV showed a significan t positive correlation with OLF (p<0.001, r = 0.547, p<0.001, r = 0.65 8, respectively), whereas DLF significantly correlated with UNaV (p < 0.001, r = 0.584) but not with SEP in 5/6 RRM. These findings suggest that endogenous OLF and DLF coexist in rat urine and that an increased level of OLF, but not DLF, may contribute to the development and main tenance of hypertension. DLF may contribute to renal sodium excretion in this volume-expanded hypertensive rat model.