Abstract
The effect of adenosine-3',5'-cyclic monophosphate (cyclic AMP) and N(6),O(2)-dibutyryl adenosine-3',5'-cyclic monophosphate (dibutyryl cyclic AMP) on renal tubular permeability was studied by microinjection techniques in anesthetized diuretic rats. Radioactive inulin and mannitol were microinjected simultaneously into superficial proximal and distal convolutions and recovery of the isotopes was measured in the urine.During control conditions, mannitol and inulin recovery was essentially complete. However, during infusion of cyclic AMP or dibutyryl cyclic AMP, mannitol recovery was significantly less than control after early proximal and late proximal microinjections, averaging 79 and 85%, respectively. There was no loss of mannitol from the nephron after microinjection into distal convolutions. Inulin recovery was complete after all microinjections during cyclic AMP or dibutyryl cyclic AMP infusion. Simultaneous clearances of mannitol and inulin as well as peritubular capillary microinjections studies demonstrated bidirectional fluxes of mannitol across the proximal tubular epithelium during infusion of cyclic AMP or dibutyryl cyclic AMP. Intratubular pressures were not different during control and experimental periods. These studies demonstrate a change in the permeability characteristic of the proximal convoluted tubule during infusion of cyclic AMP and dibutyryl cyclic AMP. This change in permeability of the proximal tubule could account for the effects of cyclic AMP on proximal tubular transport processes.