Apparent and true vascular resistances to flow in SHR and NCR kidneys as related to the pre/postglomerular resistance ratio

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Abstract
In maximally vasodilated SHR [spontaneous hypertensive rat] and NCR [normotensive control rat] kidneys perfused with filtrable and non-filtrable perfusates, analyses were performed on the extent of the average renal tissue pressure (Pt) elevation which occurs on glomerular filtration and causes passive flow autoregulation. It is important to distinguish between apparent (PA-PV[arterial pressure-venous pressure]/flow) and true (PA-Pt[arterial pressure-tissue pressure]/flow) renal resistance to flow, particularly when the compared SHR and NCR renal vascular beds differ in true total renal resistance and the structurally determined ratio between the pre- and postglomerular resistances. Apparently this ratio is considerably elevated in adult SHR kidneys due to structural vascular changes, perhaps the most efficient way of resetting the long term barostat function of the kidneys in hypertension. The altered pre/postglomerular ratio in SHR in combination with Pt rises can distort the results of apparently precise in vitro comparisons of SHR and NCR renal vascular beds to give misleading results which underestimate the structurally based vascular hyperreactivity of the preglomerular section in SHR.