We examined the changes in glomerular hemodynamics produced by angiotensin II (AII) in both normal Munich-Wistar rats and rats which were unilaterally renal denervated (measured kidney) 4-6 d prior to the measurement periods. Measurements of glomerular dynamics were performed in a control period after plasma volume expansion and during infusion of 11 ng. 100 g body wt-1 * min-' of AI. The glomerular hydrostatic pressure gradient increased from 38±1 to 49±1 mmHg in denervated rats compared with a lesser response in controls (from 39±1 to 45±1 mmHg, P < 0.05). Single nephron plasma flow decreased from 213±17 to 87±4 nl * min-' g kidney wt (KW)-' in denervated kidneys versus a more modest decrease in control kidneys (from 161±9 to 102±5 nl* min * gKW-1). These changes were due to a greater increase in both afferent and efferent arteriolar resistance after AII infusion in denervated compared with control kidneys. Glmerular AII receptor maximum binding was 1,196±267 fmol/ mg protein in denervated kidneys compared with 612±89 fmol/ mg protein (P < 0.01) in controls with no change in receptor affinity. We conclude the subacute unilateral renal denervation (a) results in renal vasodilation, (b) denervation magnifies the vasoconstrictive effect of AII infusion on glomerular hemodynamics, and (c) the observed increased response to AII after denervation is associated with increases in glomerular AII receptors.

To gain greater insight into sites of action of circulating angiotensin II (Ang II) within the adrenal, we have localized the [125I]-Ang II binding site using in vitro autoradiography. Autoradiograms were generated either by apposition of isotope-sensitive film or with emulsion-coated coverslips to slide-mounted adrenal sections labeled in vitro with 1.0 nM [125I]-Ang II. Analysis of the autoradiograms showed that Ang II binding sites were concentrated in a thin band in the outer cortex (over the cells of the zona glomerulosa) and in the adrenal medulla, which at higher power was seen as dense patches. Few sites were evident in the inner cortex. The existence of Ang II binding sites in the adrenal medulla was confirmed by conventional homogenate binding techniques which revealed a single class of high affinity Ang II binding site (Kd = 0.7nM, Bmax = 168.7 fmol/mg). These results suggest that the adrenal medulla may be a target for direct receptor-mediated actions of Ang II.

Receptors for thiazide diuretic drugs in the rat renal cortex have recently been identified through the binding of [3H]metolazone, a potent diuretic with a thiazide-like mechanism of action. The present studies describe the rapid and reversible alterations that occur in thiazide receptors following acute renal ischemia in the rat. The apparent density of thiazide receptors in kidney membranes as measured by the binding of [3H]metolazone was reduced by 90% following 10 min of renal ischemia produced by clamping the renal pedicle. With release of the clamp and subsequent reperfusion for 10 min, thiazide receptor density returned to within 40% of control levels. Ischemia did not alter apparent affinity of receptors for [3H]-metolazone. Sections prepared from renal cortex and incubated in oxygenated media in vitro displayed similar rapid changes in thiazide receptors. Hypoxia of 10- to 30-min duration produced by incubating sections in vitro in nitrogen-saturated media caused a significant decrease in [3H]metolazone binding that was reversible with return to oxygenated media. Similar decreases were obtained in oxygenated sections that were incubated with mitochondrial inhibitors, dinitrophenol and rotenone, but not in sections incubated with ouabain. These results indicate that renal thiazide receptors undergo a rapid and reversible form of regulation and that controlling mechanisms are dependent on metabolic energy.

The radiolabeled angiotensin II (ANG II) antagonist, [¹²⁵I]-sar¹, ile⁸-ANG II, was used to study brain ANG II receptors by both homogenate binding and in vitro autoradiography. In homogenate preparations of the hypothalamus, thalamus, septum and midbrain (HTSM), [¹²⁵I]-sar¹ ile⁸-ANG II bound to a single class (Hill slope 0.84 ± 0.05) of high affinity binding sites (K_D 0.42 ± 0.03 nM, B_max 5.98 ± fmol/mg protein). Competition for the [¹²⁵I]-sar¹ ile⁸-ANG II binding site in HTSM membranes demonstrated a rank order potency characteristic of binding to the ANG II receptor, with the unlabeled antagonist being slightly more potent than ANG II (Ki 0.22 ± 0.03 vs. 0.95 ± 0.06 nM, respectively). Brain slices from the region of the rostral third ventricle were incubated with 0.5 nM [¹²⁵I]-sar¹, ile⁸-ANG II in the presence or absence of 1 µM ANG II and exposed to LKB Ultrofilm. Autoradiographic images of [¹²⁵I]-sar’, ile⁸-ANG II binding revealed that structures situated within the anterior wall of the third ventricle, i.e. the lamina terminalis, were heavily labeled; including the subfornical organ, median preoptic nucleus and organum vasculosum laminae terminalis. These results show the utility of [¹²⁵I]-sar¹, ile⁸-ANG II as a probe to study brain ANG II receptors and provides pharmacological evidence for the rostral third ventricle as a possible site for central ANG II actions.