An Extrarenal Role of Aldosterone on the Regulation of Blood Pressure

: This study was designed to examine the effects of aldosterone on the distribution of extracellular fluid between the intra- and extra-vascular compartments, and to relate the changes in the fluid distribution to blood pressure in nephrectomized and nephrectomized-adrenalectomized male Wistar rats. Polyethylene catheters were inserted into the right common carotid artery and the right jugular vein, and bilateral nephrectomy with or without adrenalectomy was performed. The animals were divided into three groups: 10 nephrectomized rats (NX), 10 nephrectomized-adrenalectomized rats (NX-AX), and 10 nephrectomized-adrenalectomized and aldosterone treated rats (NX-AX-A). Aldosterone (250 micrograms/rat: Aldocorten, Ciba), mixed with sesame oil, was given subcutaneously in the NX-AX-A. After these procedures, food and water were withheld. Twenty four hours later, blood pressure and body fluid volumes were measured in the unanesthetized unrestricted condition. Mean arterial pressure (MAP) was directly recorded through the carotid catheter using electric manomater. Plasma volume (PV) and extracellular fluid volume (ECFV) were measured according to the dilution principle using 131I-RISA and 35S-Na2SO4, respectively. Interstitial fluid volume (IF) defined as ECFV minus PV and PV/IF ratio was also calculated. In NX, NX-AX and NX-AX-A, the transcapillary escape rate of albumin (TER) was determined after 6 hours. TER was obtained by measuring the disappearance of intravenously injected 131I-RISA for 2 hours after injection. The initial body weight and the changes in body weight were similar among the three groups. MAP was definitely higher in the NX than in the NX-AX and the NX-AX-A. Moreover, it was significantly higher in the NX-AX-A than in the NX-AX (p less than 0.001). Although ECFV and IF were equally and significantly reduced in the NX-AX-A and the NX-AX as compared to the NX, PV was significantly higher in the NX-AX-A than in the NX-AX (p less than 0.01), leading to a significantly lower PV/IF ratio in the latter than in the former (p less than 0.02). When a relationship between MAP and PV was examined in the rats as a whole, a significant positive correlation was found between the two parameters (r = 0.69, p less than 0.001). This relationship still held in the NX-AX and the NX-AX-A in combination (r = 0.69, p less than 0.001). TER was significantly higher in the NX-AX than in the others (p less than 0.001 vs NX, and p less than 0.02 vs NX-AX-A).(ABSTRACT TRUNCATED AT 400 WORDS)