Reactive oxygen species generation and histamine release by activated mast cells: modulation by nitric oxide synthase inhibition.

1. We have examined the generation of intracellular reactive oxygen species (ROS) and release of histamine by rat peritoneal mast cells (RPMC) in response to stimulation with antigen (ovalbumin), compound 48/80, nerve growth factor (NGF) and substance P (SP). 2. We have also examined the effects of the non-specific nitric oxide synthase inhibitor, L-NAME (100 microM) upon the release of histamine and generation of intracellular ROS in response to the named secretagogues. 3. Ovalbumin (100 - 1000 microg ml-1), compound 48/80 (0.1 - 100 microg ml-1), NGF (0.1 - 100 microg ml-1), and SP (5 - 50 microM), caused a concentration-dependent release of histamine from RPMC. 4. Ovalbumin (1 ng ml-1 - 0.1 microg ml-1), compound 48/80 (1 - 100 microg ml-1), NGF (1 pg ml-1 - 1 microg ml-1), and SP (0.005 - 50 microM) caused a concentration-dependent generation of intracellular ROS by RPMC. 5. Pre-incubation of RPMC with L-NAME (100 microM) caused a significant enhancement of both histamine release and intracellular ROS from RPMC in response to ovalbumin, compound 48/80, NGF and SP. 6. Our data demonstrate that NGF, SP and ovalbumin are capable of causing intracellular ROS generation by RPMC at lower concentrations than those causing significant histamine release and we speculate that this may contribute to the activation of cytokine production. 7. The data also show that NO modulates histamine release, and ROS generation in response to the secretagogues used. This may have significance in pathologies where NO synthesis is decreased, leading to an increased activation of mast cells.