Renal blood flow autoregulation in developing swine

Pressure-flow relationships (P/F) in the renal circulation were determined in 62 swine, aged 1 day-2 mo, anesthetized with pentobarbital sodium. Aortic and inferior vena caval pressures and renal and femoral arterial flows were recorded. Blood gas composition and pH and body temperature were monitored. The P/F was first determined while perfusion pressure was decreased for 2 min at each pressure by suprarenal aortic occlusion. The left renal artery in 38 of these animals was then cannulated for in situ perfusion of the kidney with blood withdrawn from a carotid artery by a Masterflex pump. The P/F was subsequently determined by changing pump flow for 2 min at each flow while recording perfusion pressure. Records were analyzed for transient and steady-state effects. Readjustments in renal vascular resistance (RVR) were apparent within 5 s after changing pressure or flow. The RVR stabilized at a new level within 2 min. Graphs of steady-state data delineated an autoregulatory range in the P/F for animals as young as 2 wk of age. We conclude that renal blood flow autoregulation in this mammal is negligible at birth and develops progressively during the first postnatal month.