Thyroid changes in PCB-dosed guillemots and their indication of one of the mechanisms of action of these materials

Abstract

A group of six guillemots Uria aalge, reared in the laboratory, were fed daily doses of PCB (Aroclor 1254) for 45 days at dose rates from 12 to 400 mg/kg/day. A further three birds were maintained as controls. The birds given 12 and 25 mg/kg/day showed increased thyroid weight, follicle size and colloid area. Increasing the dose rates further produced significant dose-related decreases in these parameters until, in the bird which died at 400 mg/kg/day, the thyroids showed atrophy with only 59·6% of the weight and 27·3% of the total colloid area of the controls. These changes suggest a direct effect of the PCB on the avian pituitary, causing a dose-related decrease in the amount of thyrotrophin produced. The large colloid goitre seen at 12 mg/kg/day suggests involution as thyroid hormone depletion is reduced; this is changed to atrophy when TSH production by the pituitary ceases. A dose-related reduction in pituitary weight supports this conclusion. These thyroid changes suggest that PCB-dosed birds would be in a state of hypothyroidism. This action on the pituitary producing secondary hypothyroidism could be one of the main sub-lethal lesions of these materials and could be the mechanism behind many of the sub-lethal effects noted in the literature. The thyroid changes already noted in PCB-dosed lesser black-backed gulls Larus fuscus suggest that guillemots may be much more sensitive to PCB than this species in that they exhibit the same effects more than twice as rapidly.