Delayed recovery from NG-nitro-L-arginine in the conscious sheep

1. In the chronic, awake, instrumented sheep model NG-nitro-L-arginine (NOLA) an inhibitor of nitric oxide synthesis, injected at a dose of 40 mg/kg, produced a significant increase in systolic blood pressure (from 110 +/- 6 to 145 +/- 8 mmHg after 5 min) which persisted for at least 1 h but returned to baseline after 24 h. 2. When NOLA was repeated 1 and 4 days after the first injection, the blood pressure response was significantly attenuated, and at 1 day was no greater than the response to an equivalent volume of saline. The blood pressure response returned to the initial response with an 8 day interval between injections. 3. There was no significant blood pressure response to 100 mL of saline before the NOLA injection; however, 1 and 4 days after NOLA there was a significant rise in blood pressure.