Hydrostatic pressure in the subcapsular interstitial space of rat and dog kidneys

Summary Experiments were performed in rats and dogs in order to reevaluate the concept of a high renal interstitial pressure. Assuming that the renal subcapsular pressure represents the pressure 2 of the superficial interstitium, catheters were implanted in the subcapsular space and the pressure was continuously recorded with a transducer of a very low volume displacement. In 17 rats a mean subcapsular pressure of 3.8 cm H₂O±2.0 was measured, while 6 dogs had an average subcapsular pressure of 10.8 cm H₂O±3.0. The subcapsular pressure was found to increase during renal venous constriction and ureteral pressure elevation, procedures which are very likely to lead to a rising renal interstitial pressure.To demonstrate a functional communication between the subcapsular and the deep renal interstitium I¹³¹-labelled albumin was injected into the subcapsular space of 5 rats, while the hilar lymph was collected through a cannulated lymph vessel. It was found that already in the first collection period of 20 min duration a considerable I¹³¹ activity was present in the lymph which consisted mainly of albumin-bound iodide. It is concluded that the low subcapsular pressure is probably valid for the entire renal interstitial compartment.