Systemic inhibition of nitric oxide and prostaglandins in volume-induced natriuresis and hypertension.

Nitric oxide (NO) synthesis inhibition with N G-nitro-l-arginine methyl ester (l-NAME) (10 μg ⋅ kg-1 ⋅ min-1iv), cyclooxygenase inhibition with meclofenamate (Meclo; 5 mg/kg iv bolus), and combination of drugs (l-NAME+Meclo) were used to investigate the roles of NO and prostaglandins (PG) in the hemodynamic and natriuretic responses to isotonic saline volume expansion (VE; 5% body wt over 60 min) in anesthetized dogs. Before VE,l-NAME ( n = 6), Meclo ( n = 6), andl-NAME+Meclo ( n = 6) produced significant increments in mean arterial pressure (MAP) of 12 ± 2, 15 ± 3, and 17 ± 3 mmHg, respectively. VE did not change MAP in Meclo-treated dogs, but produced a significant elevation in the control dogs (14 ± 6 mmHg), inl-NAME-treated dogs (17 ± 6 mmHg), and in dogs pretreated withl-NAME+Meclo (12 ± 5 mmHg). VE alone induced marked natriuretic responses in the control (38 ± 9 to 562 ± 86 μmol/min),l-NAME (31 ± 9 to 664 ± 65 μmol/min), and Meclo groups (41 ± 10 to 699 ± 51 μmol/min). However, this natriuretic response was attenuated in dogs pretreated with l-NAME+Meclo (12 ± 4 to 185 ± 52 μmol/min). These results indicate that 1) blockade of both NO and PGs has significant diminishing effects on volume-induced natriuresis, 2) NO blockade alone impairs volume-induced natriuresis in a manner that requires further increases in MAP to restore the natriuresis, and 3) PG blockade alone does not curtail volume-induced natriuresis.