To prove that exogenous nitric oxide prevented this phenomenon, the nitric oxide donor SNAP (10 mg/kg/min intravenously for 30 mins, L-NNA plus SNAP plus LPS group) was applied to restore the due course of endotoxemia in L-NNA plus LPS rats (Figure 2, dotted line). On the contrary, pretreatment of rats with the preferential NOS-II inhibitor AGD (15 mg/kg) instead of L-NNA in the ADG plus LPS group was not only protective but also elongated the survival time (P<0.05 compared with the LPS group) (Figure 2, dashed line).These data suggest that inhibition of NOS-III was responsible for the early death of LPS-treated nitric oxide-deficient rats owing to nitric oxide deficiency during the early phase of endotoxemia. Detection of NOS-III in control and LPS-treated lung: Total RNA (1 |ig) isolated from freshly homogenized lung of control rats was analyzed by RT-PCR. Rat gene-specific primers for NOS-III and NOS-II were used, and RT-PCR products were visualized on ethidum bromide-stained agarose gels (Figure 3).
Figure 3 Recombinant Thermus thermophilus reverse transcription polymerase chain reaction (RT-PCR) amplification of inducible nitric oxide synthase (NOS-II) and constitutive NOS (NOS-III) mRNA in control rat lung. Freshly isolated total RNA from rat lung was reverse transcribed and amplified with rat gene-specific primers for NOS-II or NOS-III isoforms and analyzed by agarose gel electrophoresis stained with ethidium bromide. A single 324 base pair (bp) band of NOS-III transcript was obtained (lane 2), but no PCR product for NOS-II was detected (lane 4). In lane 3, the expected 308 bp product of beta-actin was observed (positive control). No signal was obtained in the absence of any primers (negative control, lane 5). Marker M1 is shown in lane 1 (pUC 19/MspI with bands 501/489, 404, 331, 242, 190 and 147 bp long). The size of the predicted amplified products is indicated on the right