NADPH-d-positive mast cells in the canine paranal sinus.

This study aimed to investigate the enzyme histochemical expression of NADPH-d in mast cells in the wall of the paranal sinus in male and female dogs. NADPH-d-positive cells with weak, medium and strong enzyme histochemical expression were observed in the stroma of the sinus near the blood vessels of the microcirculatory bed and around the apocrine and sebaceous glands. In the same areas, mast cells with similar dimensions and morphology were demonstrated by metachromasia on paraffin and cryostat cross-sections and stained with 0.1% toluidine blue in McIlvane's buffer (pH 3). These findings suggest that the mast cells that are located in the stroma near the blood vessels, the lining epithelium and the glands correspond with the cells with marked NADPH-d activity. The possibility of mast cells having nitric oxide activity could be used in the regulation of mast cells function when treating paranal sinus tumours and inflammations.