Enhanced Renal Angiotensin II Subtype 1 Receptor Responses in the Spontaneously Hypertensive Rat

Results from renal transplantation experiments demonstrate that a renal defect is responsible for the development of hypertension in the spontaneously hypertensive rat (SHR). In addition, studies with inhibitors of the renin-angiotensin system have shown that angiotensin II (Ang II) is required for the development and maintenance of hypertension in the SHR. These observations prompted us to propose the hypothesis that hypertension in these rats is due to an enhanced renal responsiveness to Ang II. The purpose of the present study was to determine whether an enhanced renal responsiveness to Ang II exists in adult (12- to 14-week-old) SHR relative to Wistar-Kyoto control rats. To prevent hypertension-induced changes in renal function in SHR, we maintained both strains in the normotensive state from 4 weeks of age with long-term captopril treatment (100 mg/kg per day). Intrarenal Ang II infusions induced a significantly greater decrease in renal blood flow and glomerular filtration rate and a significantly greater increase in renal vascular resistance in SHR compared with Wistar-Kyoto rats. DuP 753 (Ang II subtype 1 [AT1] receptor antagonist), but not PD 123177 (Ang II subtype 2 receptor antagonist), blocked the renal responses to Ang II in SHR, suggesting that the enhanced renal responsiveness to Ang II was mediated solely by the AT1 receptor subtype. Unlike renal responses to Ang II, renal responses to periarterial renal nerve stimulation were similar in both strains, suggesting a selective renal hyperresponsiveness to Ang II in the SHR rather than a general hyperresponsiveness toward all vasoconstrictors. From these studies in chronically captopril-treated rats, we conclude that 1) SHR have a genetically determined, enhanced renal responsiveness to Ang II; 2) the enhanced renal responsiveness to Ang II is mediated by the AT1 receptor; and 3) renal responses to periarterial nerve stimulation are not significantly enhanced, suggesting a selective hyperresponsiveness to Ang II in the kidneys of SHR.