Renin Depletion Research Articles

Renin Enhancer Is Critical for Control of Renin Gene Expression and Cardiovascular Function

Renin Enhancer Is Critical for Control of Renin Gene Expression and Cardiovascular Function

Renin Enhancer Is Critical for Control of Renin Gene Expression and Cardiovascular Function

The important cardiovascular regulator renin contains a strong in vitro enhancer 2.7 kb upstream of its gene. Here we tested the in vivo role of the mouse Ren-1c enhancer. In renin-expressing As4.1 cells stably transfected with Ren-1c promoter with or without enhancer, expression of linked beta-geo reporter, stable expression, and colony formation were dependent on the presence of the enhancer. We then generated mice carrying a targeted deletion of the enhancer (REKO mice) and found marked depletion of renin in renal juxtaglomerular and submandibular ductal cells, as well as hyperplasia of macula densa cells. Plasma creatinine was increased, but electrolytes were normal. Male REKO mice implanted with telemetry devices had 9 +/- 1 mm Hg lower mean arterial pressure (p < 0.001), which was partly normalized by a high NaCl diet. Locomotor activity was lower, and baroreflex sensitivity was normal. Markedly reduced mean arterial pressure variability in the midfrequency band indicated a contribution of reduced sympathetic vasomotor tone to the hypotension. In conclusion, the renin enhancer is critical for renin gene expression and physiological sequelae, including response to alteration in salt intake. The REKO mouse may be useful as a low renin expression model.

Regulation of renin in mice with Cre recombinase-mediated deletion of G protein Gsα in juxtaglomerular cells

By crossing mice with expression of Cre recombinase under control of the endogenous renin promoter (Sequeira Lopez ML, Pentz ES, Nomasa T, Smithies O, Gomez RA. Dev Cell 6: 719-728, 2004) with mice in which exon 1 of the Gnas gene was flanked by loxP sites (Chen M, Gavrilova O, Liu J, Xie T, Deng C, Nguyen AT, Nackers LM, Lorenzo J, Shen L, Weinstein LS. Proc Natl Acad Sci USA), we generated animals with preferential and nearly complete excision of Gsalpha in juxtaglomerular granular (JG) cells. Compared with wild-type animals, mice with conditional Gsalpha deficiency had markedly reduced basal levels of renin expression and very low plasma renin concentrations. Furthermore, the acute release responses to furosemide, hydralazine, and isoproterenol were virtually abolished. Consistent with a state of primary renin depletion, Gsalpha-deficient mice had reduced arterial blood pressure, reduced levels of aldosterone, and a low glomerular filtration rate. Renin content and renin secretion of JG cells in primary culture were drastically reduced, and the stimulatory response to the addition of PGE(2) or isoproterenol was eliminated. Unexpectedly, Gsalpha recombination was also observed in the renal medulla, and this was associated with a vasopressin-resistant concentrating defect. Our study shows that Cre recombinase under control of the renin promoter can be used for the excision of floxed targets from JG cells. We conclude that Gsalpha-mediated signal transduction is essential and nonredundant in the control of renin synthesis and release.

Effects of Anesthesia on Plasma and Kidney ANG II Levels in Normotensive and ANG II-Dependent Hypertensive Rats

Background: Previous studies have implicated that normotensive rats with normal renal renin activity respond to anesthesia and surgery with greater increases in plasma and kidney angiotensin II (ANG II) concentrations than ANG II-dependent hypertensive rats with intrarenal renin depletion. In the present study, we therefore compared plasma and kidney ANG II levels in anesthetized and conscious normotensive and ANG II-dependent hypertensive rats. Methods: Salt-replete Hannover-Sprague-Dawley rats (HanSD) served as controls. As models of ANG II-dependent hypertension we used: 1st, transgenic rats harboring the Ren-2 renin gene (TGR); 2nd, two-kidney, one-clip (2K1C) Goldblatt hypertensive rats, and, 3rd, ANG II-infused hypertensive rats. As additional model with enhanced renin-angiotensin system (RAS) activity, salt-depleted HanSD and TGR were employed. Results: In anesthetized salt-repleted HanSD, plasma and kidney ANG II levels were higher than in salt-repleted TGR, ANG II-infused and 2K1C rats. Salt depletion caused marked increases in ANG II levels in HanSD but did not alter them in TGR. In contrast, in conscious animals immediately after decapitation plasma and kidney ANG II levels were similar in salt-repleted and salt-depleted TGR, in ANG II-infused rats, in the clipped kidney of 2K1C rats and in salt-depleted HanSD and in all these groups they were significantly higher than in salt-repleted HanSD. Conclusions: These findings indicate that anesthesia increases plasma and kidney ANG II levels in HanSD to a greater degree than in ANG II-dependent models of hypertension. Therefore, the results from studies employing anesthetized animals must be interpreted with caution.

The effect of saline loading on uranium-induced acute renal failure in rats

Studies were performed to examine the effect of saline loading on uranium-induced acute renal failure (ARF) in rats. Forty-eight hours after the i.v. injection of uranyl acetate (UA, 5 mg/kg), inulin clearance rate (Cin) decreased to approximately 43% of the control value in water drinking rats (P less than 0.005). Animals receiving continuous isotonic saline infusion following UA showed higher urine flow and Cin (60% of control, P less than 0.01), and lessened intratubular cast formation when compared with water-drinking ARF rats. A short-term saline infusion following UA did not attenuate the decline in Cin (43% of control). An inverse relationship was found between Cin and the number of casts (r = -0.75, P less than 0.01). Multiple regression analysis showed that standardized partial regression coefficient is statistically significant between Cin and cast formation (-0.69, P less than 0.05), but not between Cin and tubular necrosis (-0.07, P greater than 0.05). Renin depletion caused by DOCA plus saline drinking did not attenuate the decline in Cin in ARF (47% of control). No significant difference was found in urinary uranium excretion between water-drinking and saline-infused ARF rats. The findings suggest that continuous saline infusion following UA attenuates the decline in Cin in ARF rats; and that this beneficial effect of saline loading is associated with lessened cast formation rather than with suppressed renin-angiotensin activity or enhanced urinary-uranium excretion.

Hgcl2-induced acute renal failure in the rat. Effect of water diuresis, saline loading, and diuretic drugs.

A variety of pretreatment-treatment protocols were applied to rats with ARF induced by the subcutaneous injection of 6 mg of HgCl2 per kilogram body weight. Renin depletion induced by DOCA-saline pretreatment was associated with protection against HgCl2-induced ARF only when the saline diuresis was maintained by drinking 1% NaCl after injury. Twenty-four dehydration followed by free access to tap water annihilated the protective effect of DOCA-saline pretreatment despite maintained depletion of renal renin. Continuous intravenous loading with saline and furosemide, although increasing renal renin levels, afforded as much protection as saline loading alone. Ethacrynic acid, which did not increase salt excretion in our rats, as well as water diuresis, failed to be protective. A loose correlation was found between he amount of histological damage to the convoluted parts of the proximal tubules and the degree of renal functional impairment. Thus protection against HgCl2-induced ARF was independent of the renal renin level but closely related to urinary NaCl excretion after the injury. Saline diuresis could act by relieving or preventing tubular obstruction.

Effect of chronic treatment with desoxycorticosterone on the dipsogenic response of rats to isoproterenol and angiotensin.

Administration of desoxycorticosterone (DOC) at a dose of 0.5 mg/kg/day to male rats for 6 weeks attenuated significantly the drinking response to acute subcutaneous administration of 5, 10 and 20 microgram isoproterenol/kg body weight. Chronic administration of DOC did not prevent the drinking response to acute intraperitoneal administration of angiotensin II (200 microgram/kg body weight). In contrast, the drinking response was enhanced compared with that of control rats given angiotensin II acutely. While attenuation of the drinking response to isoproterenol in DOC-treated rats may be attributed to depletion of renin from their kidneys, the mechanisms responsible for the enhanced drinking response to angiotensin II are not clearly understood.

Reversal of renal hypertension: effects on renin, salt and water balance.

The effect of removal of one renal artery stenosis on renal sodium and fluid excretion and on the activity of the renin-angiotensin system (RAS) has been investigated in three types of renal hypertension of rats. Blood pressure fell in all experimental models after declamping, independently of changes in urinary sodium and water excretion or plasma angiotensin II (ANG II). Plasma concentrations of ANG II did not rise in response to salt and fluid loss induced by declamping when the contralateral kidney had been removed or when it was depleted from renin. A high renin content of the declamped kidney prevented major salt and fluid loss, whereas renin depletion of this kidney was accompanied by an exaggerated natriuresis and diuresis. Besides this tubular modulation of renal salt and water handling by the local RAS, glomerular filtration rate could be reduced by a stimulated activity of this system in plasma, indicated by a close relationship between serum urea and plasma ANG II levels.

Dissociation of renal blood flow and filtration rate autoregulation by renin depletion

Renal blood flow (RBF) and glomerular filtration rate (GFR) autoregulation during changes in renal artery pressure (RAP) were examined in dogs fed a "normal" diet (group 1, n = 10) and in renin-depleted dogs (group 2, n = 11) which received a high-sodium diet and deoxycorticosterone acetate (DOCA) injections for a minimum of 21 days prior to the study. Renal venous plasma renin activity was undetectable in group 2 by radioimmunoassay of angiotensin I and did not increase even when RAP was reduced to less than 70 mmHg. Autoregulation of RBF was not impaired by renin depletion. However, GFR autoregulation, which was very effective in group 1 dogs, was markedly impaired in group 2. Average GFR in group 2 decreased progressively to 58 +/- 7% of the control value as RAP was reduced in steps from the control value of 137 +/- 3 to 69 +/- 1 mmHg. In normal dogs, the filtration fraction either increased slightly or did not change when RAP was reduced in steps, whereas in renin-depleted dogs the filtration fraction decreased progressively during reductions in RAP. Thus, chronic sodium loading and DOCA administration causes renin depletion and dissociates the autoregulation of RBF and GFR. These data are consistent with the hypothesis that the renin-angiotensin system participates in the control of GFR, possibly by an efferent arteriolar mechanism.

Resistance to acute renal failure afforded by prior renal failure: examination of the role of renal renin content.

In this study, rats recovering from glycerol-induced acute renal failure were found to be protected from mercury-induced nephropathy, and HgCl2 poisoning protected rats from developing myohemoglobinuric renal failure. In view of the widely disparate nature of the renal failure models used, refractoriness appears to relate to an altered sensitivity of the organism itself rather than reflecting resistance to a particular nephropathic challenge. Renal renin content of the rats at the time of rechallenge was normal or high, a finding which contrasts sharply with that of chronically saline-loaded animals which also are refractory to ARF but have a maximally suppressed renal renin content. Renal renin depletion is not essential to the prevention of acute renal failure in the rat.

Impaired autoregulation of blood flow and glomerular filtration rate in the isolated dog kidney depleted of renin.

The effect of renin depletion on autoregulation of renal blood flow and glomerular filtration rate was examined in an isolated perfused kidney preparation. Group 1 dogs received a normal-sodium diet, group 2 dogs received deoxycorticosterone acetate (DOCA) and a high-sodium diet, group 3 dogs received DOCA and a sodium-deficient diet, group 4 dogs received a high-sodium diet without DOCA, and dogs in groups 5 and 6 were treated just like dogs in groups 1 and 2, respectively. Renin release was stimulated by decreasing renal arterial pressure to 50 mm Hg. An increase in renal arterial pressure from 100 to 160 mm Hg was associated with an impaired autoregulatory response in kidneys from group 2 dogs and in two kidneys from group 4 dogs; these kidneys exhibited suppressed or absent renin release in response to a decrease in renal arterial pressure. A separate group of experiments demonstrated that DOCA plus a high-sodium diet completely depleted the kidney of renin stores, indicating that decreased renin secretion reflected depletion of renal renin content. Infusing angiotensin II (0.22 ± 0.06 µg/min) into the renal artery of group 2 kidneys did not normalize the autoregulatory response. A decrease in renal arterial pressure from 150 to 50 mm Hg was associated with impaired autoregulation of glomerular filtration rate and renal blood flow in kidneys from group 6 dogs; renin secretion was undetectable in these kidneys. All kidneys from groups 1, 3, and 5 and the remaining six kidneys from group 4 exhibited a normal autoregulatory response and normal renin release. In groups 1-3, zonal blood flow was measured using the radiolabeled microsphere technique. Only in group 2 did a significant redistribution of fractional blood flow from the inner to the outer cortex occur. These experiments demonstrate that renin depletion impairs the capacity of the kidney to autoregulate blood flow and glomerular filtration rate; thus the data are consistent with the hypothesis that the renin-angiotensin system participates in the autoregulatory response.

The replenishment of the juxtaglomerular renin store after temporary renin depletion

Renal cortical and plasma renin activities and the electron microscopic appearance of juxtaglomerular epitheloid cells were investigated in the unclamped renin-depleted kidney of rats with two-kidney-Goldblatt hypertension after removal of the clamped kidney. Within 24 h the renal renin content fell to still lower values, on the 2d day, it rose to one half its normal value, on the 7th day it reached its control value. Renin activity of plasma did not significantly differ from zero until the 3d day after removing the clamped kidney, reached 20% of normal on the 7th day and normal values between the 7th and the 21 st day. Sparse secretory granules appeared in the remaining renal cortex 12 h after removal of the clamped kidney. After 24 h secretory granules were formed by confluence of Golgi vesicles. After 2 days cisternae appeared in the rough-surfaced endoplasmic reticulum. After 4 days the electron-microscopic picture became normal. Renin appears to be elaborated in the rough-surfaced endoplasmic reticulum and concentrated into granules by the Golgi-apparatus. A fraction of the renal renin does not appear to be available for secretion.

Renin-angiotensin role in thirst: paradoxical enhancement of drinking by angiotensin converting enzyme inhibitor.

A competitive angiotensin converting enzyme antagonist SQ 20, 881 (SQ), was used to examine the role of the renin-angiotensin system in putative renin-dependent thirst in the albino rat. Significant enhancement of "renin-dependent" as well as renin-independent drinking was observed in the presence of peripheral SQ. Intraventricular SQ obviated this enhancement of drinking but did not affect the water intake caused by the original stimulus itself, whereas it sharply reduced drinking evoked by peripheral renin in nephrectomized rats. Prior renin depletion likewise had no influence on so-called renin-dependent thirst.

Renal clearance studies of effect of left atrial distension in the dog.

Investigation of the water diuresis of left atrial distension in 16 dogs on the basis of clearance studies employing hydration, chronic and acute salt loading, deoxycorticosterone (DOCA) in excess, and distal tubular nephron blockade with diuretics. The diuresis was found in hydrated and salt-loaded dogs and was independent of DOCA and presumed renin depletion. It was not found in five dogs after distal tubular blockade. No significant reproducible saluresis was ever documented. The water diuresis was always stopped by exogenous vasopressin (seven dogs). Antidiuretic hormone inhibition with distal tubular nephron water permeability changes appears to be the sole mechanism of the diuresis of left atrial distension in the dog.

Effects of renal denervation and renin depletion on the renal responses to intravascular volume expansion.

From the Departments of Physiology and Surgery, University of Virginia, School of Medicine, Charlottesville, Virginia Surgical Fellow supported by Grant HE 05815–01 from National Institutes of Health, U. S. Public Health Service. Recipient of Research Career Development Award 1-K3-HE 36,005–1 from the National Institutes of Health, U. S. Public health Service. Present address: Department of Physiology, University of Nebraska School of Medicine, Omaha, Nebraska.

Renin depletion in the dog.

Renin depletion in the dog.

Micropuncture studies of the basis for protection of renin depleted rats from glycerol induced acute renal failure.

Rats depleted of renin by chronic saline loading are largely protected from glycerol induced acute renal failure. For some 4 h after glycerol injection, these animals showed the same apparent renal ischemia, cessation of filtration and tubule collapse seen in rats that are not renin depleted. Despite this ischemia, renal function returned rapidly, individual nephron GFR reaching 75 % of normal within the succeeding 12 h. Significant outflow obstruction was evident transiently early in recovery, but was found not to be the prime cause of the low GFR. Recovery of glomerular filtration occurred quickly despite the presence of grossly elevated hydrostatic pressure in some nephrons. It is suggested that renin depletion produced by long term saline ingestion may prevent the protracted afferent arteriolar constriction which is chiefly responsible for the pathophysiologic events in this model of acute renal failure in the rat.

The Prevention of Acute Renal Failure in the Rat by Long-Term Saline Loading: A Possible Role of the Renin-Angiotensin Axis

SummarySubstitution of 1% saline for drinking water largely prevents the development of established acute renal failure in rats given glycerol intramuscularly. Control experiments indicate that this protection from acute renal failure is not due to the blood volume expansion, polyuria, polydypsia, lower urine osmolality, or other parameters studied. It is suggested that the depletion of renin, associated with chronic saline-loading, may have played a protective role, and that the renin-angiotensin axis may be a potent factor in the development of glycerol-induced acute renal failure in the rat.

Hypertensive Vascular Disease Induced by Heterologous Renin

Chronic treatment with crude hog, or rat, renin administered subcutaneously to uninephrectomized rats elicits hypertension, renal and vascular lesions, hypertrophy of the zona glomerulosa of the adrenals, and renin depletion in the remaining kidney. Semipurified hog renin given in equipressor doses also causes renin depletion and stimulation of the zona glomerulosa, but no hypertension nor vascular disease. However, semipurified hog renin becomes as effective as the crude preparation after addition of retarding substances such as gelatin, oil, or cholesterol. Thus, a prolonged and sustained resorption of renin seems to be a prerequisite for the development of hypertension. Since hypertension takes place only after a latent period during which arterial pressure remains within the normal range, it does not appear that hypertension can be attributed to the acute pressor effect of renin. It is proposed as a working hypothesis that renin, through angiotensin, initiates nervous mechanisms which are responsible for the development of benign hypertension and that the acute pressor effect of angiotensin is more specifically associated with the malignant phase of hypertension.