In mammals, which blood vessel would normally carry largest amount of urea?

In mammals, the hepatic vein is the blood vessel that would normally carry the largest amount of urea. The hepatic portal vein carries nutrient-rich blood from the alimentary canal to the liver. In the liver, deamination of amino acids produced ammonia which is converted into less toxic urea through the ornithine cycle. So, urea is synthesised in the liver. Hepatic veins drain blood from the liver into the inferior vena cava. Hence, the concentration of urea is maximum in the blood passing through the hepatic veins. Inferior vena cava also receives urea-less blood from the kidneys through renal veins. So the concentration of urea in the blood passing from the inferior vena cava into the right atrium is lesser than that in the hepatic veins. The same blood reaches the left side of the heart through the pulmonary circuit and is pumped by the aorta into the dorsal aorta.