Transport of uric acid and hypoxanthine across the isolated guinea pig placenta.

Transport of uric acid and hypoxanthine across the isolated guinea pig placenta is investigated quantitatively. The clearances measured are independent of concentration. It is shown that the uric acid transport is not greatly influenced by variations in flow, so it is concluded that the uric acid transport is membrane limited. The clearance of hypoxanthine is even less than the uric acid clearance, so hypoxanthine transport is also membrane limited. Xanthine oxidase is shown to be present in the uterine tissues, and an apparent Km and a maximum velocity have been determined.