Blood plasma response and urinary excretion of nitrite and nitrate in milk-fed calves after oral nitrite and nitrate administration

There is marked endogenous production of nitrate in young calves. Here we have studied the contribution of exogenous nitrate and nitrite to plasma concentrations and urinary excretion of nitrite and nitrate in milk-fed calves. In experiment 1, calves were fed 0 or 200 μmol nitrate or nitrite/kg0.75 or 100 μmol nitrite plus 100 μmol nitrate/kg0.75 with milk for 3 d. In experiment 2, calves were fed 400 μmol nitrate or nitrite/kg0.75 with milk for 1 d. Plasma nitrate rapidly and comparably increased after feeding nitrite, nitrate or nitrite plus nitrate. The rise of plasma nitrate was greater if 400 than 200 μmol nitrate or nitrite/kg0.75 were fed. Plasma nitrate decreased slowly after the 3-d administration of 200 μmol nitrate or nitrite/kg0.75 and reached pre-experimental concentrations 4 d later. Urinary nitrate excretions nearly identically increased if nitrate, nitrite or nitrite plus nitrate were administered and excreted amounts were greater if 400 than 200 μmol nitrate or nitrite/kg0.75 were fed. After nitrite ingestion plasma nitrite only transiently increased after 2 and 4 h and urinary excretion rates remained unchanged. Plasma nitrate concentration remained unchanged if milk was not supplemented with nitrite or nitrate. Nitrate concentrations were stable for 24 h after addition of nitrite to full blood in vitro, whereas nitrite concentrations decreased within 2 h. In conclusion, plasma nitrate concentrations and urinary nitrate excretions are enhanced dose-dependently by feeding low amounts of nitrate and nitrite, whereas after ingested nitrite only a transient and small rise of plasma nitrite is observed because of rapid conversion to nitrate.