Atrial natriuretic peptide during the elevation in blood pressure induced by sodium restriction

This study examined the effects of dietary sodium restriction combined with unilateral nephrectomy on systolic blood pressure (SBP), heart rate, plasma renin activity (PRA) and immunoreactive atrial natriuretic peptide (iANP) in the conscious rat. SBP and heart rate, measured by photoelectric tail-cuff, were elevated in both one- and two-kidney, sodium-restricted rats compared with one- and two-kidney rats maintained on a normal-sodium intake. In addition, the SBP of one-kidney, low-sodium rats was significantly elevated compared with two-kidney, low-sodium rats on days 10 and 14 postnephrectomy. PRA was significantly elevated two- to threefold in one- and two-kidney, low-sodium rats compared with rats fed the normal-sodium chow. Plasma iANP levels in rats fed the normal-sodium diet averaged 291 +/- 45 and 277 +/- 35 pg/ml in one- and two-kidney rats, respectively. Plasma iANP levels were significantly lower in the one- and two-kidney, low-sodium rats and averaged 165 +/- 15 and 182 +/- 22 pg/ml, respectively. These results indicate that dietary sodium restriction can elevate blood pressure in the rat and that this response can be augmented by unilateral nephrectomy. In addition, the exacerbation of the hypertension by unilateral nephrectomy in sodium-restricted rats is not attributable to differences in PRA or plasma levels of iANP between one- and two-kidney, sodium-restricted rats.