NITRATE AND NITRITE ANION CONCENTRATION IN THE INTACT CEREBRAL-CORTEXOF PRETERM AND NEARTERM FETAL SHEEP - INDIRECT INDEX OF IN-VIVO NITRIC-OXIDE FORMATION

Pregnant sheep with a microdialysis probe implanted in the fetal cereb ral cortex were used to determine if nitrate and nitrite anions (nitra te/nitrite) could be quantitated in the microdialysate as an indirect index of in vivo nitric oxide formation. Pregnant ewes (term, about 14 7 days) were surgically instrumented at gestational day (GD) 90 (n = 3 ; preterm) and GD 121 (n = 3; nearterm). Three days later, following a n overnight probe equilibration period, five dialysate samples were co llected continuously on ice at l-h intervals (infusion rate of 1 mu l/ min). The nitrate/nitrite concentration was determined by reducing a 1 0-mu l aliquot of each dialysate fraction with hot acidic vanadium fol lowed by chemiluminescence quantitation of the nitric oxide product. T he lower limit of quantitative sensitivity of the method is 25 picomol es. Nitrate/nitrite concentration was 16.6 +/- 7.3 mu M for the preter m fetus and 19.7 +/- 1.9 mu M for the nearterm fetus. The data demonst rate that nitrate/nitrite, as an index of in vivo nitric oxide formati on, can be quantitated in microdialysate samples collected from the in tact fetal sheep cerebral cortex. (C) 1998 Elsevier Science Inc.