Two common non-steroidal anti-inflammatory drugs (NSAIDs) and their nitric oxide (NO) adducts were evaluated for effects on mol/kg of ibuprofen caused stomach and thymus. Following 4-h duration (acute) oral dosing of fasted male Wistar rats, 1.33 x 10(-4) significant visual irritation score and microscopic thinning, although an ulceration assay proved insensitive. Ibuprofen esterified with NO abolished irritation and significantly reduced thinning. Gastro-protective effects of NO-linked ibuprofen were associated with higher levels of diaphorase by optical density, an enzymatic marker of local synthesis of nitric oxide. Both indomethacin and its congener at 2 x 10(-5) mol/kg produced microscopic signs of thinning only, not visible irritation or alteration of diaphorase staining. Results suggest that NO-linked ibuprofen can promote resistance to mucosal injury, possibly via local synthesis of NO. All NO-congeners and parent NSAIDs produced comparable reductions in the abundance of medullary nitrergic cells, those synthesising NO in thymus, without significantly lowering T-cellularity, the relative size of cortex wherein T-cells are produced. Findings indicate disturbance of T-cell tolerance, consistent with increased risk of autoimmune susceptibility. (c) 2005 Elsevier Inc. All rights reserved.