The intrarenal renin-angiotensin system (RAS) contributes to the increased renal vascular resistance and reactivity observed in spontaneously hypertensive rats (SHR) and to the pathogenesis of high blood pressure (BP). Thus, we decided to characterize angiotensin II (ANG II) receptors in the renal arteries and glomeruli of 16-week-old SHR and their age-matched, normotensive Wistar-Kyoto (WKY) controls. SHR had significantly higher BP (153 +/- 4 v 96 +/- 10 mmHg) and heart weight (440 +/- 5 v 327 +/- 4 g/100 g body weight) than WKY rats. There was no difference in plasma renin activity between strains. Radioligand binding assays using non-peptide antagonists for AT1 (losartan) and AT2 (PD 123319) showed that renal preglomerular microvessels and glomeruli expressed a single receptor population (AT1) for ANG II. AT1 density tended to be lower in glomeruli of SHR compared to WKY (377 +/- 45 v 555 +/- 74 fmol/mg protein), but was significantly higher in preglomerular vessels (93 +/- 7 v 57 +/- 1 fmol/mg protein). No difference in receptor affinity was found in either preparation. Isolated kidney perfusion revealed that at low flow (3-10 ml/min), perfusion pressure was similar in both strains; however, at higher flow levels, SHR showed higher reactivity and less compliance than their controls. In addition, SHR presented a higher renal vascular reactivity to ANG II (but not to arterenol) than WKY rats. Thus, upregulation of ANG II receptors in the renal vasculature may mediate the hyperreactivity to ANG II observed in SHR kidney.