| Glutamine synthetase (GSase) in the brains of rainbow trout ( Oncorhynchus mykiss) is suspected to play a critical role in ammonia detoxification. It was hypothesized that trout depend on brain GSase for detoxification during ammonia exposure. Fish were injected with either 0.9% saline or 6 mg/kg fish methionine sulfoximine (MSOX), a GSase inhibitor, and then exposed to either control water or elevated ammonia. Saline-ammonia fish had increased brain glutamine concentrations but no increase in brain GSase activity. MSOX reduced brain GSase activity by 75%, but did not affect brain ammonia or glutamate concentrations. Fish treated with MSOX had reduced plasma cortisol concentrations during ammonia exposure relative to untreated fish, though concentrations remained elevated over time during high exposure. Results do not support the hypothesis, indicating that while trout use GSase to detoxify ammonia during exposure, they are still able to cope with only 25% brain GSase activity. |
