AUTOREGULATION OF RENAL BLOOD-FLOW, GLOMERULAR-FILTRATION RATE AND PLASMA-RENIN ACTIVITY IN SPONTANEOUSLY HYPERTENSIVE RATS AND NORMOTENSIVE WISTAR RATS

The autoregulation of renal blood flow (RBF), glomerular filtration rate (GFR) and the pressure dependent renin release into the circulation were studied in conscious chronically instrumented spontaneously hypertensive rats (SHR) and normotensive Wistar rats. Renal perfusion pressure was lowered by means of a suprarenal inflatable cuff on the abdominal aorta and was lowered in pressure steps of 10 mm Hg. Breakoff points for RBF- and GFR-autoregulation as well as the threshold for renin release were calculated using non-linear regression (breakpoint analysis). - Wistar rats autoregulated RBF and GFR in a range between 110 and 90 mm Hg (breakoff points: R.BF 88 +/- 2 mm Hg; GFR 92 +/-3 mm Hg). Plasma-renin activity (PRA) showed a threshold of activation at 89 +/-8 mm Hg. Breakoff points and threshold of renin release did not differ significantly from each other. SHR autoregulated RBF and GFR in a range between 160 and 100 mm Hg (breakoff points: RBF 104 +/- 6 mm Hg; GFR 99 +/- 4 mm Hg). The PRA increase had a threshold at 119 +/- 6 mm Hg. Breakoff points of R.BF- and GFR-autoregulation did not differ significantly. In SHR the threshold of renin release was at a significantly higher pressure than the breakoff point of GFR-autoregulation. The comparison between Wistar rats and SHR revealed a significant shift of the RBF-autoregulation curve and the pressure-dependent renin release of SHR towards higher pressures (p < 0,05). - The early increase of PRA in SHR suggests a role of the renin-angiotensin-system (RAS) in the autoregulation of GFR in SHR. Wistar rats seem to autoregulate GFR independently of the PAS. An activation of the sympathetic nervous system might take part in the rightward shift of the R.BF- and GFR-autoregulation curve in SHR. The role of this altered autoregulatory pattern in the development of genetic hypertension remains to be investigated.