The fate of nitrogen from N-15-labeled nitrate after single intravenous administration of (NaNO3)-N-15 in sheep

The metabolic fate of nitrogen from N-15-labeled sodium nitrate has been in vestigated in four healthy Polish Merino ewes. N-15-labeled sodium nitrate was administered intravenously at the dosage of 400 mu mol.kg(-1) body weig ht. Blood plasma and urine concentrations of nitrate, ammonia, and urea and N-15 enrichment of ammonia and urea were estimated over a 50-h period foll owing N-15-nitrate administration. Nitrate (NO3-) was slowly eliminated fro m the blood plasma, and the presence of NO3- in the blood plasma above the nitrate "background" was observed for 50 h. N-15 enrichment of blood plasma urea already appeared at 15 min and reached the maximum 6 h after N-15-nit rate administration. The urinary excretion of nitrate occured during 50 h a fter N-15-nitrate injection; the total urine excretion of NO3- was 23.63 +/ - 2.39% of the administered dose. The mean urinary recoveries of nitrogen a s N-15-urea and N-15-ammonia were 14.76 +/- 1.32% and 0.096 +/- 0.015% of t he administered N-15-nitrate dose, respectively. It should be pointed out t hat in total only 38.49% of the administered nitrate-N was excreted in urin e las nitrate, ammonia and urea nitrogen) during 50 h. The results obtained indicate that sheep are able to store nitrate nitrogen in their body. The fate of the remaining approximately 60% of the (NO3-)-N-15 administered dos e is unknown. The results obtained do not allow one to conclude what fracti on of the unrecovered approximately 60% of the (NO3-)-N-15 dose was utilize d by gastrointestinal microorganisms, and (or) metabolized, or stored in sh eep tissues.