Sodium load increases renal angiotensin type 1 receptors and decreases bradykinin type 2 receptors

The regulation of both angiotensin receptors and bradykinin receptors during sodium intake is poorly understood. We hypothesized that an altered balance between renal angiotensin type 1 (AT(1)) receptors and bradykinin type 2 (B-2) receptors might contribute to an increase in blood pressure during periods of high-sodium intake. We studied the effects of high-sodium intake on renal AT(1) receptors and B-2 receptors in 5-6-week-old spontaneously hypertensive rats (SHR) receiving high-sodium chloride (6% NaCl) or mineral salts (10.5%, composition: 57% NaCl, 28% KCl, 12% MgSO4) compared to those receiving a low-sodium (NaCl 0.125%) diet for 10 weeks. Mineral salt intake was included due to its beneficial effects on blood pressure and cardiac hypertrophy. Receptor densities were measured by quantitative autoradiography. AT(1) receptors were quantified using incubation with I-125-Sar(1)-Ile(8)-angiotensin II and displacement was measured with PD123319 (10 mumol/1), whereas B-2 receptors were quantified using I-125-HPP-icatibant and displacement was measured with icatibant (3 mumol/l). Compared to the SHR controls, a further increase in blood pressure occurred after 2 weeks in the 6% NaCl group and after 6 weeks in the mineral salt group. AT, receptor density increased in the renal cortex by 41% (p<0.01) in the 6% NaCl group and by 26% (p<0.05) in the mineral salt group. B-2 receptor density decreased in the renal medulla by 26% (p<0.01) in the 6% NaCl group, and decreased even more i.e., by 45% (p<0.001), in the mineral salt group. It was shown that a 6% NaCl or a 10.5% mineral salt loading was capable of increasing renal AT(1) receptor density and decreasing renal B-2 receptor density. An altered balance between these receptors might be associated with hypertension under conditions of sodium loading.