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The importance of endogenous histamine relative to dietary histamine in the aetiology of scombrotoxicosis.

Deliberately spoiled mackerel samples and mackerel samples implicated in outbreaks of scombrotoxicosis were, under medical supervision, tested blind on normal, healthy volunteers of both sexes. These experiments identified batches of fish which could induce nausea/vomiting and/or diarrhoea when 50 g samples were consumed. It was also established that the fillets in a batch were neither of equal potency nor homogeneous with respect to histamine content. Strong evidence was obtained that dietary histamine is not a major determinant of scombrotoxicosis since potency was not positively correlated with the dose, and volunteers appeared to fall into susceptible and non-susceptible subgroups. However, there is no reason to suspect allergy as being solely responsible for these differences in sensitivity. It is also possible to discount body weight as a factor. While the data suggest that females may be more susceptible than males, this effect cannot be confirmed at the present time. Studies with susceptible volunteers predosed with either placebo or H1 antagonist (chlorpheniramine 4 mg) demonstrated convincingly that the antihistamine can abolish vomiting and diarrhoea associated with the ingestion of 50 g of scombrotoxic fish. It is therefore postulated that endogenous histamine released by mast cell degranulation has a significant role in the aetiology of scombrotoxicosis, whereas the role of dietary histamine is minor. The nature and origin of the agent responsible for mast cell degranulation is being investigated.