Effect of low sodium diet on the facilitatory effect of angiotensin on 3H-norepinephrine release in the rat portal vein.

The ability of angiotensin to enhance the field-stimulation induced release of 3H-norepinephrine from the superfused rat portal vein was examined in vessels obtained from animals fed a normal (0.5% Na+) or low sodium diet (0.05% Na+). Angiotensin was seen to enhance the field-stimulation (480 pulses, 2 Hz, 1 ms duration, supramaximal voltage) induced release of 3H-norepinephrine from vessels obtained from Sprague-Dawley, Wistar, Wistar-Kyoto (WKY) and the spontaneously hypertensive rats (SHR) maintained on a normal sodium diet. The effect of angiotensin was attenuated when examined in vessels obtained from animals maintained on the low sodium diet. The selectivity of the low sodium diet for angiotensin was demonstrated by a lack of effect of the low sodium diet in altering the facilitatory effect of isoproterenol on the release of 3H-norepinephrine and an enhanced response to the alpha 2-adrenoceptor-selective antagonist, yohimbine. The simultaneous treatment of rats with a low sodium diet plus captopril (estimated to be approximately 50 mg/kg/day for 7 days) prevented the attenuation of the angiotensin-induced enhancement of the release of 3H-norepinephrine seen by sodium alone. These results are consistent with the hypothesis that low sodium treatment increases circulating angiotensin levels which lead to a down-regulation of the angiotensin receptors located on adrenergic nerve varicosities.