Stimulation of Vascular Na-K Pump with Subpressor Angiotensin II in Rats

Abstract

Abstract

The effect of subpressor doses of angiotensin II (ANG II) on vascular Na-K pump activity and Na-H exchange, two transmembrane signals of trophic stimulation of vascular muscle, was investigated. Male Sprague-Dawley rats (350–400 g) were given subpressor doses of ANG II by osmotic minipump intraperitoneally for 24 hr or 7–10 days. Control rats received sham procedure/vehicle infusion. Na-K pump activity (⁸⁶Rb uptake), total and intracellular (Li exchange at 4°C) Na content, and amiloride-sensitive and -insensitive Na uptake of aortas were measured ex vivo. Ouabain-sensitive ⁸⁶Rb uptake of aortas of rats receiving 80–100, 160–180, and 240–260 ng/kg−⁻¹ of ANG II for 24 hr was 26.6 ± 3.5, 28.8 ± 3.4, and 29.1 ± 2.6 nmol/mg dry wt−15 min⁻¹ (mean ± SD, n = 7–12), respectively, compared with 25.2 ± 3.8 in controls (n = 23, P < 0.01). These increases were maintained at 7–10 days. After 24 hr and 7–10 days of ANG II treatment, the total Na content of aortas was increased by 9.2% (P < 0.01) and 7.6% (P < 0.02), respectively, without a change in intracellular Na content, indicating accumulation of excess extracellular Na. Total and amiloride-sensitive Na uptake of the aorta was unchanged after 24 hr or 7–10 days of ANG II administration. The dry weight of anatomically defined segments of the aorta was 40 ± 3.8 mg/kg body wt (n = 25) after 24 hr and 42 ± 4.4 (n = 20) after 7–10 days of ANG II administration, compared with 37 ± 4.8 (n = 15, P < 0.05) and 37 ± 4.9 (n = 17, P < 0.01) in appropriate controls. Increased Na-K pump activity may signal the onset of trophic stimulation of vascular muscle by ANG II.