Methaemoglobin reductase deficiency in dogs

Erythrocyte methaemoglobin reductase deficiency is described in a toy Alaskan Eskimo dog, a miniature poodle dog and a cocker/poodle cross dog. Blood methaemoglobin contents ranged from 19% to 36% of total haemoglobin, with methaemoglobin reductase values between 13% and 33% of normal. There appeared to be a negative linear correlation between erythrocyte methaemoglobin content and methaemoglobin reductase activity. A single intravenous injection of methylene blue (1 mg/kg body weight) resulted in a dramatic decrease in methaemoglobin content within 1 hour when given to two of the deficient dogs in the present study. Following the disappearance of methylene blue from blood, methaemoglobin content increased linearly at 3.2% and 2.5% per day in these dogs, suggesting that about 3.0% of erythrocyte haemoglobin is normally oxidised to methaemoglobin each day in dogs, as has been estimated in humans. Oral riboflavin therapy was not effective in reducing blood methaemoglobin content in deficient dogs.