Effect of nitrite on blood pressure in anaesthetized and free-moving rats

The effect of nitrite on blood pressure and heart rate was studied in anaesthetized (non-telemetric method) and free-moving rats (biotelemetry system). In anaesthesized rats, NaNO₂ (10-1000 μmol/kg), infused over 5 min, induced a dose-related decrease in blood pressure. The maximal decrease in mean arterial blood pressure (MAP), caused by 1000 μmol/kg NaNO₂ and measured 15 min after infusion was 55.9 ± 3.2% (n = 3). After NaNO₂ infusion, in the plasma, rapid conversion of nitrate was observed. However, sodium nitrate (NaNO₃, 100 μmol/kg) did not decrease blood pressure and there was no conversion of nitrate into nitrate. Free-moving rats received KNO₂ which was added to drinking water (36 mmol/litre) for a period of 3 days. KNO₂ decreased the MAP and increased the heart rate during the rat's activity phase at night but not during their resting phase in the day. An equal concentration of potassium (KCl, 36 mmol/litre added to drinking water) for 3 days did not decrease blood pressure. It is concluded that nitrite decreases blood pressure in rats, which probably induces, by renin-angiotensin system activation, hypertrophy of the adrenal zona glomerulosa.