Although the establishment of toxic levels of BA is difficult
since this depends on the characteristics of different individuals,
W¨ohrl et al. (2004) report that 75 mg of pure liquid oral
histamine—a dose found in normal meals—can provoke immediate
as well as delayed symptoms in 50% of healthy females
with no history of food intolerance.
An additional problem in determining toxic levels of BA
is their synergistic effects. For example, experiments in rats
and guinea pigs indicate that cadaverine and other amines act
as potentiators of histamine toxicity. These amines play a role
as diamine oxidase inhibitors (Lehane and Olley, 2000) and
their presence may explain why the intake of aged cheese is
more toxic than an equivalent amount of histamine in aqueous
solution (Taylor and Sumner, 1986).
Secondary amines such as putrescine and cadaverine can also
react with nitrite to form carcinogenic nitrosamines (Ten Brink
et al., 1990), and the adherence to intestinal mucosa of some
enteropathogens, such as E. coli O157:H7 is increased in the
presence of tyramine (Lyte, 2004).