Na transport and blood pressure in the adrenalectomized rat

The transmembrane distribution of Na, K, and water in freshly excised rat tail artery was measured 7 days after adrenalectomy, 3 days after withdrawal of support with 1% NaCl as drinking water. Cell Na decreased from 35.8 +/- 0.9 to 31.6 +/- 0.7 mmol/kg dry wt, tissue water increased from 2.93 +/- 0.03 to 3.08 +/- 0.04 l/kg dry wt, and tissue K remained unchanged. As concentration, [Na]i decreased from 22.5 +/- 0.9 to 18.3 +/- 1.0 mM in parallel with [Na]o which fell from 140.6 +/- 0.3 to 133.6 +/- 1.0. Conversely, while [K]i fell from 140 +/- 2 to 128 +/- 3, [K]o rose from 2.15 +/- 0.12 to 5.40 +/- 0.33 so that EK dropped from -109 to -83 mV. Aldosterone (120 micrograms X 100 g-1 X 24 h-1 sc; 3 X 10(-7) M if immediately distributed in the extracellular fluid) partially restored blood pressure, plasma [Na] and [K], and tissue water within 24-26 h but did not increase cell Na. Similar effects were produced with corticosterone at 400 microgram X 100 g-1 X 24 h-1 (3 X 10(-6) M if immediately distributed in the extracellular fluid). We conclude that the restoration of blood pressure in the adrenalectomized rat is independent of [Na]i or [Na]o/[Na]i but is associated with enhanced Na transport activity.