Development of a simplified assay for determination of the antimineralocorticoid activity of compounds dosed in rats. 
Mineralocorticoid receptor (MR) antagonists are useful for the treatment of hypertension and heart failure.  In the present work we sought to develop a simplified protocol for measuring the acute activity of MR antagonists on urinary excretion of sodium and potassium in rats based on the original studies of mineralocorticoids in adrenalectomized rats reported by Kagawa et al. ( Kagawa, C. M., & Jacobs Jr., R. S. (1960) Mineralocorticoid effects of 9 alphafluorodeoxycorticosterone in adrenalectomized rats.  Proceedings of the Society for Experimental Biology and Medicine, 104, 60-62).  Rats with intact adrenal glands were treated with test compounds and challenged with a bolus oral dose of saline.  Urine was collected over 4 h in metabolism cages and urinary sodium and potassium concentrations were measured.  Aldosterone had no significant effect on sodium or potassium excretion and MR antagonists dose-dependently increased the ratio of sodium to potassium.  Diuretics with distinct mechanisms of action were differentiated via their relative effects on sodium, potassium and urine volumes and the new assay protocol was used to characterize a novel MR antagonist.  A facile and robust protocol for the measurement of antagonism of renal MRs was established.  This protocol used fewer animals than previously described methods and did not require preparative surgery, factors which contributed favorably to cost, experimental throughput and animal use.