Autoradiographic study of Diodrast-I131 transport in Necturus kidney

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Abstract
Renal tubular transport of Diodrast-I131 was studied in Necturus by newly devised autoradiographic methods used in conjuction with classical clearance methods. Clearance measurements on individual animals indicate different types of over-all tubular transport ranging from secretion into tubular urine, heretofore reported in many species, to reabsorption out of tubular urine, so far reported only in Necturus. Diodrast content of tubular urine as disclosed by autoradiography both corroborates clearance data and provides evidence that proximal tubules are the major site of Diodrast transport irrespective of direction. This view is supported by inulin-C14 autoradiographs. In addition, significant amounts of Diodrast were accumulated within proximal tubular cells during all types of transport. With less than 3 mg Diodrast/100 ml arterial plasma, the estimated intracellular concentration ranged from 2 to 19 times that in plasma. At higher plasma levels, tubular transport was overwhelmed and intracellular concentration no longer exceeded that in plasma. These results support a previously formulated theory of simultaneous, bidirectional movement of Diodrast across tubular cells in Necturus kidney.