SUMMARY A thermostable urinary homologue of the plasma aldosterone-binding globulin (ABG), designated ABG-TsU, was isolated and purified by differential ultrafiltratlon, ion exchange chromatography, and gel filtration to electrophoretic homogeneity. Scatchard plot analysis using highly purified ABG-TsU demonstrated reversible high-affinity low-capacity binding at separate sites for aldosterone and dehydroepiandrosterone sulfate (DHEA-SO 4 ). ABG-TsU injected intraperitoneally (i.p.) in male rats resulted in sustained hypertension after 5 to 8 days, characterized after 12 days by no changes in plasma Na + K + , aldosterone, or plasma renin activity (PRA). No histological changes could be detected in the kidneys, brains, or hearts, nor evidence of adrenocortical hyperplasia. This hypertension appears to be aldosterone-dependent since it is prevented by bilateral adrenalectomy or administration of a spironolactone, but not by adrenalectomy when aldosterone is given concomitantly with ABG-TsU. Hemodynamic characterization of this hypertension was carried out in rats after treatment with ABG-TsU or saline i.p. for 14 days. Cardiac output (CO) was measured using the reference sample microsphere method. ABG-TsU-treated rats had significantly higher mean arterial pressure (MAP), systolic blood pressure (SBP), diastolic blood pressure (DBP), and CO, while no difference in total peripheral resistance (TPR) was detected. This new animal model of borderline essential hypertension (EH) induced by ABG-TsU, which has a reversible high-affinity binding for aldosterone, results in adrenal-dependent hypertension due at this early phase to an increase in CO without any change in TPR, which remains inappropriately normal. Increased plasma levels of aldosterone in subjects with EH were found to be linked to a decrease in the metabolic clearance rate (MCR) of aldosterone in the face of a normal or decreased secretion rate.1 The decrease in the MCR of aldosterone wasFrom the

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1. A human urinary thermostable glycoprotein (ABG-TsU) believed to be a homologue of the plasma aldosterone-binding globulin (ABG) was isolated and purified by differential ultrafiltration, ion-exchange chromatography and gel filtration to electrophoretic homogeneity; it showed a charge heterogeneity in electrofocussing. 2. ABG-TsU was administered intraperitoneally to male rats in small daily doses (7 microgram/day per rat). Sustained hypertension developed in 5--8 days. 3. The treated rats showed no changes in plasma electrolytes, aldosterone or plasma renin activity; however, a significant increase in heart weight was observed. 4. This hypertension appears to be adrenal dependent since it is prevented by bilateral adrenalectomy or administration of an aldosterone antagonist, but not by adrenalectomy when aldosterone is given concomitantly with ABG-TsU.