Endocrine factors in haematological changes seen in dogs and ferrets given oestrogens

High doses of oestrogens in the dog and ferret cause myeloid hyperplasia in the bone marrow superseded by hypoplasia affecting all cell lines. In the peripheral blood after an initial leucocytosis, there is thrombocytopenia, anaemia and leucopenia. These effects, which are ultimately lethal, do not occur in cats, rats and monkeys, and their cause is unknown. It is speculated that they may be due to endocrine derangements possibly affecting the pituitary-adrenal axis and that species differences in oestrogen toxicity may be due to species differences in endocrinology.