Plasma concentration of atrial natriuretic peptide after acute reduction in functioning renal mass in the rat

Both acute unilateral nephrectomy (UNX) and unilateral ureteral obstruction (UUO) result in a prompt rise in cation excretion from the contralateral kidney. An important role for atrial natriuretic peptide (ANP) has been recently proposed in the acute functional adaptation to UNX. The possible involvement of endogenous ANP in the response to UUO was investigated in anesthetized euvolemic SpraguenDawley rats. Both UNX and UUO resulted in a twofold increase in urinary sodium (from 0.93 ± 0.23 to 2.14 ± 0.34 and from 0.83 ± 0.37 to 1.88 ± 0.58 μequiv./min, respectively; both p < 0.05) and potassium (from 1.12 ± 0.14 to 2.21 ± 0.23 and from 1.18 ± 0.14 to 2.12 ± 0.18 μequiv./min, respectively; both p < 0.05) excretion, whereas no significant change was detected after the sham procedure (from 0.87 ± 0.19 to 0.83 ± 0.23 and from 1.27 ± 0.13 to 1.18 ± 0.13 μequiv./min for urinary sodium and potassium excretion, respectively; both p = ns). In separate experiments, circulating levels of ANP increased by threefold (from 23.5 ± 3.6 to 66.3 ± 12.8 fmol/mL; p < 0.01) within 2 min after UNX, but they did not change not after either the sham or UUO maneuvers (from 22.2 ± 4.1 to 25.3 ± 5.1 and from 21.5 ± 5.8 to 20.7 ± 5.0 fmol/mL, respectively; both p = ns). Moreover, UNX was associated with an immediate, significant (by 13 ± 2 mmHg (1 mmHg = 133.3 Pa); p < 0.05) and transient (<20 min) rise in mean arterial pressure, whereas no significant change was detected after the sham or UUO maneuvers. These observations indicate that ANP release is stimulated immediately after UNX but not after UUO. In conclusion, the results of the present study suggest that ANP might be an important mediator for the acute functional response of the remaining kidney to contralateral nephrectomy but not to contralateral ureteral obstruction.