Effect of Ions on the Renal Autoregulation in the Isolated Perfused Kidney of Rabbit

Hwang, Hye Sup

Abstract

The isolated rabbit kidney was perfused with 4 kinds of perfusates which had different ionic compositions, in order to investigate the effects of divalent cations, Mg and Ca, on the renal autoregulation. Four kinds of perfusates are full-balanced perfusate (FBP), perfusate subtracted both CaCl2and MgCI2 from FBP, perfusate subtracted only CaCI, from FBP, and perfusate subtracted only MgCl2 from FBP. The composition of FBP is 6% hydroxyethyl starch in 0.9% NaCl (McGaw Lab. USA) containing Na-acetate 5.0, K2HPO4 5.0, CaCls 1.2, MgCl2 0.5, and glucose 5.O mM/L. Renal Perfusate Flow (RPF) as related to various renal arterial perfusion pressure (RAP) was directly measured with flow-meter attached to the perfusion system. Total renal resistance (Rr) was calculated from RAP & RPF (RT=RAP/RPF). Alterations in renal autoregulation, when different perfusates were perfused, were estimated by pressure-flow curve in every run of perfusion experiments. The results obtained were as follows: 1) Kidney perfused with FBP revealed autoregulation within the range of 100~180 mmHg RAP. Renal Perfusate Flow in the autoregulation zone was 5.0 ml,min/gm. 2) The autoregulation was not appeared in the experiments perfused with the solution subtracted both CaCl2 and MgCI2 from FBP. 3) Kidney perfused with FBP-CaCI2 revealed the autoregulation, which had the autoregulation zone of 110~180 mmHg RAP, and 5. 5 m1/min/gm RPF. However, it was not present in the kidney perfused with FBP-MgCl2. 4) The time course of autoregulation was observed on the pressure-flow curve; autoregulation was continued approximately for 15 minutes, and then deteriorated rapidly. 5) Total renal resistance calculated was proportionately increased as the RAP increased within the regulation zone. Below and above the zone, it was almost inversely related to the RAP. From the above results, it was concluded that Mg is the essential factor in the renal autoregulation and suggested that Mg could have a key role on the neuromuscular transmission, excitability of muscular cell membrane, or the process of intracellular contraction.