Abstract
In the search for the biochemical abnormality which might be associated with the susceptibility to audiogenic seizures in strains of rabbits previously described (1,2), the conversion of phenylalanine to tyrosine by these rabbits was studied. This investigation was carried out because Coleman had reported greatly reduced in vivo production of tyrosine in 2 dilute strains of mice susceptible to audiogenic seizures (3).
Materials and methods. All animals came from intensely inbred lines of seizure-susceptible and seizure-resistant rabbits. The L-phenylalanine was obtained from Mann Research Laboratories. In preliminary studies phenylalanine determinations were made by Bio-Science Laboratories; the later phenylalanine and tyrosine determinations were made at Children's Memorial Hospital(4). On the basis of the initial studies, it was hypothesized that phenylalanine metabolism in the rabbit related to coat pigmentation, but not to seizure-susceptibility.
To test this hypothesis 6 nonpigmented and 6 pigmented convulsant rabbits, aged 50–66 days, their period of greatest seizure susceptibility, were matched for age, sex, coat color, and number of times tested with rabbits from seizure-resistant lines. The seizure-susceptible rabbits had each convulsed 85% to 100% of the time in 10 or more tests. All animals were fasted overnight, but were allowed water. Blood samples were taken from the central ear artery immediately prior to, and at 15, 30, 45, 60 and 90 minute intervals following intraperitoneal injection of 100 mg L-phenylalanine/kg body weight.
Results. The phenylalanine and corresponding tyrosine values were pooled for each of the 4 groups, i.e., the 6 nonpigmented and 6 pigmented convulsant rabbits and their respective controls. Two graphs were plotted: the values for the 12 seizure-susceptible vs the 12 seizure-resistant rabbits, and the values for the 12 nonpigmented, albino rabbits vs the 12 pigmented ones.
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