Androgen-dependent regulation of human angiotensinogen expression in KAP-hAGT transgenic mice.
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We previously reported a novel transgenic model expressing human angiotensinogen from the kidney androgen-regulated protein promoter, and demonstrated sexually dimorphic expression. Herein, we investigated the hormonal regulation of this transgene. Testosterone increased transgene expression in female mice in a dose- and time-dependent manner and was not detectable 3-days after treatment was halted. High doses of estrogen were required to induce the transgene. Expression of transgene mRNA decreased after castration of male transgenic mice. As in females, however, transgene expression could be induced after administration of testosterone. Flutamide, an androgen receptor antagonist, dose dependently blocked transgene expression in males and blunted the induction caused by testosterone in females. Neither testosterone nor estrogen altered the proximal tubule cell-specific expression of the transgene. The data suggest that the level of transgene expression in this model can be controlled temporally and in magnitude by manipulating the levels of androgen. The fortuitous androgen regulation of this transgene can be used as a molecular "on-off" switch to control transgene expression and potentially manipulate blood pressure levels in this model. (+info)
Upregulation of immunoreactive angiotensin II release and angiotensinogen mRNA expression by high-frequency preganglionic stimulation at the canine cardiac sympathetic ganglia.
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The possible involvement of the local angiotensin system in ganglionic functions was investigated in the canine cardiac sympathetic ganglia. Positive chronotropic responses to preganglionic stellate stimulation at high frequencies, after intravenous administration of pentolinium plus atropine, were inhibited by the nonpeptide angiotensin AT(1) receptor antagonist forasartan or the angiotensin I-converting enzyme inhibitor captopril, whereas the rate increases elicited by the postganglionic stellate stimulation and norepinephrine given intravenously failed to be inhibited by these antagonists. The levels of endogenous immunoreactive angiotensin II, as determined by radioimmunoassay in the incubation medium of the stellate and inferior cervical ganglia, were increased after the high-frequency preganglionic stimulation of the isolated ganglia. The increment of the peptide was also antagonized by the pretreatment with captopril but not by a chymase inhibitor, chymostatin. The expression of angiotensinogen mRNA was observed in the stellate ganglion, adrenal, liver, and lung but not in the ovary and spleen. The expression of the mRNA in the stellate and inferior cervical ganglia increased after high-frequency preganglionic stimulation of the in vivo dogs for a period of 1 hour. These results indicate that an intrinsic angiotensin I-converting enzyme-dependent angiotensin system exists in the cardiac sympathetic ganglia, which is activated by high-frequency preganglionic stimulation. (+info)
Expression of angiotensinogen mRNA and protein in angiotensin II-dependent hypertension.
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Chronic elevations in circulating angiotensin II (AngII) levels produce sustained hypertension and increased intrarenal AngII contents through multiple mechanisms, which may include sustained or increased local production of AngII. This study was designed to test the hypothesis that chronic AngII infusion increases renal angiotensinogen mRNA and protein levels, thus contributing to the increase in intrarenal AngII levels. AngII (80 ng/min) was infused subcutaneously for 13 d into Sprague-Dawley rats, using osmotic minipumps. Control rats underwent sham operations. By day 12, systolic arterial BP increased to 184 +/- 3 mmHg in AngII-treated rats, whereas values for sham-treated rats remained at control levels (125 +/- 1 mmHg). Plasma renin activity was markedly suppressed (0.2 +/- 0.1 versus 5.3 +/- 1.2 ng AngI/ml per h); however, renal AngII contents were significantly increased in AngII-treated rats (273 +/- 29 versus 99 +/- 18 fmol/g). Western blot analyses of plasma and liver protein using a polyclonal anti-angiotensinogen antibody demonstrated two specific immunoreactive bands, at 52 and 64 kD, whereas kidney tissue exhibited one band, at 52 kD. Densitometric analyses demonstrated that AngII infusion did not alter plasma (52- or 64-kD), renal (52-kD), or hepatic (52-kD) angiotensinogen protein levels; however, there was a significant increase in hepatic expression of the highly glycosylated 64-kD angiotensinogen protein, of almost fourfold (densitometric value/control value ratios of 3.79 +/- 1.16 versus 1.00 +/- 0.35). Renal and hepatic expression of angiotensinogen mRNA, which was examined by semiquantitative reverse transcription-PCR, was significantly increased in AngII-treated rats, compared with shamtreated rats (kidney, densitometric value/glyceraldehyde-3-phosphate dehydrogenase mRNA value ratios of 0.82 +/- 0.11 versus 0.58 +/- 0.04; liver, densitometric value/glyceraldehyde-3-phosphate dehydrogenase mRNA value ratios of 2.34 +/- 0.07 versus 1.32 +/- 0.15). These results indicate that increases in circulating AngII levels increase intrarenal angiotensinogen mRNA levels, which may contribute to the sustained renal AngII-generating capacity that paradoxically occurs in AngII-treated hypertensive rats. (+info)
Prognostic value of angiotensin-I converting enzyme I/D polymorphism for nephropathy in type 1 diabetes mellitus: a prospective study.
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Angiotensin-I converting enzyme (ACE) regulates renal hemodynamics. Its insertion/deletion (I/D) polymorphism, which determines most of ACE interindividual variance, was proposed as a genetic marker for diabetic nephropathy. A substitution (M235T) polymorphism in angiotensinogen (AGT) may interact with ACE I/D polymorphism for the risk of diabetic nephropathy, but their prognostic values have to be established by follow-up studies. A total of 310 type 1 diabetes mellitus patients who attended the diabetic clinic in Angers (France) took part in a prospective, observational, follow-up study. Glycohemoglobin, BP, plasma creatinine, and urinary albumin excretion were determined periodically. Nephropathy was classified as absent, incipient (microalbuminuria), established (proteinuria), advanced (plasma creatinine > or = 150 micromol/L), and terminal (renal replacement therapy). The main end point was the occurrence of a renal event defined as the progression to a higher stage of diabetic nephropathy. At baseline, 251 (81%) patients had no nephropathy, 35 (11%) had incipient nephropathy, 18 (6%) had established nephropathy, and 6 (2%) had advanced nephropathy. The ACE I/D and M235T AGT polymorphisms were in Hardy-Weinberg equilibrium in the patients. The median duration of follow-up was 6 yr (range, 2 to 9 yr). The occurrence of renal events was significantly influenced by ACE genotype (log-rank II versus ID versus DD, P < 0.03) with a dominant deleterious effect of the D allele: ID or DD versus II (adjusted hazard ratio, 5.0; 95% confidence interval, 1.5 to 16.6). Other contributors were high glycohemoglobin and systolic BP. In the patients who initially were free of nephropathy, baseline plasma ACE concentration was higher in patients who progressed to microalbuminuria (571 +/- 231 versus 466 +/- 181 microg/L; P = 0.0032); the D allele independently favored the occurrence of incipient nephropathy (adjusted hazard ratio, 4.5; 95% confidence interval, 1.1 to 19.4); other contributors were male gender, baseline systolic BP, and urinary albumin excretion. The AGT M235T polymorphism was not associated with renal events. The D allele of the ACE I/D polymorphism is an independent risk factor for both the onset and the progression of diabetic nephropathy in type 1 diabetes mellitus patients. (+info)
Angiotensinogen in essential hypertension: from genetics to nephrology.
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There is general consensus that genetic variation accounts in part for individual susceptibilities to essential hypertension. In marked contrast to classic mendelian disorders, in which genetic alterations produce a gain or loss of function, genetic determinants of essential hypertension, high blood pressure of unknown cause, are expected to be small, achieving significance through the cumulative effects of environmental exposure over the course of a lifetime. Whether and how genetic factors that contribute to common diseases can be identified remain unclear. Research on a link between angiotensinogen and essential hypertension illustrates a path that began in genetics and is now leading toward nephrology. Various challenges encountered along the way may prove to be characteristic features of genetic investigations of the pathogenesis of common diseases. The implication of a gene by statistical analysis is only the beginning of a protracted process of functional analysis at increasing levels of biologic integration. The ultimate goal is to develop an understanding of the manner in which genetic variation at a locus can affect a physiologic parameter and to extract from this inference new knowledge of significance for the prevention or treatment of disease. (+info)
Influence of sodium intake on the reliability of active renin as a measure of the renin-angiotensin system in essential hypertension.
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Plasma renin activity (PRA), active renin (AR), prorenin, and angiotensinogen were assessed in 486 hypertensive and 175 normotensive subjects with a sodium intake of 10 or 200 mEq/d during supine and upright posture and after infusion of angiotensin II. PRA and AR levels were compared in hypertensive subjects in each condition. With low sodium intake, particularly while upright, there was a significant correlation between PRA and AR. In upright subjects with low sodium intake who had a PRA of 2.4 ng/mL per hour or less (1.85 nmol.L-1.h-1 or less), the correlation was also strong. With high sodium intake, the correlation was weaker. With intermediate sodium excretion, the correlation was intermediate. Prorenin was less predictive of PRA than was AR, and angiotensinogen had a marginal role. Using PRA during sodium restriction while upright as the standard for determining renin status, the precision of AR for predicting renin status was excellent. AR may be used for surrogate assessment of the renin-angiotensin system activity when the system is activated. (+info)
T+31C polymorphism of angiotensinogen gene and essential hypertension.
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A common variant at codon 235 of the angiotensinogen gene with methionine to threonine amino acid substitution (AGT M235T) has been reported as a genetic risk for essential hypertension. However, the frequency of AGT T235 was heterogeneous among races, and a positive association between AGT M235T and hypertension was not settled. To examine the association in a general population of Japanese (n=4013), we introduced the TaqMan polymerase chain reaction method and examined the relation between hypertension and T+31C polymorphism, which was in absolute linkage disequilibrium with AGT M235T. The C+31 allele of AGT was significantly associated with the positive family history of hypertension (FH) but not with the presence of hypertension or blood pressure. The subjects with CC tended to have hypertensive relatives, especially a hypertensive father or siblings, and its statistical significance was stronger in men. Adjustment of confounding factor did not alter the results of simple association study, suggesting that this positive association with FH is independent and significant. Our findings revealed that the TaqMan polymerase chain reaction method is a powerful tool for genetic association study with a large number of subjects and that AGT T+31C is significantly associated with paternal FH. (+info)
Antisense inhibition of brain renin-angiotensin system decreased blood pressure in chronic 2-kidney, 1 clip hypertensive rats.
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The systemic renin-angiotensin system (RAS) plays an important role in blood pressure (BP) regulation during the development of 2-kidney, 1 clip (2K1C) hypertension. Its contributions decrease with time after constriction of the renal artery. During the chronic phase, the peripheral RAS returns to normal, but the hypertension is sustained for months. We hypothesized that in this phase the brain RAS contributes to the maintenance of high BP. To test the hypothesis, we studied the role of brain RAS by decreasing the synthesis of angiotensinogen (AGT) and the angiotensin II (Ang II) type 1a receptor (AT(1)R) with intracerebroventricular injections of antisense oligonucleotides (AS-ODNs). The response of systolic BP (SBP) to AS-ODNs to AGT mRNA was studied in 2K1C rats at 6 months after clipping, and the response to AS-ODNs to AT(1)R mRNA was studied at 10 months after clipping. Intracerebroventricular injection of AS-ODN-AGT (200 microgram/kg, n=5) significantly decreased SBP (-22+/-6 mm Hg, P<0.05) compared with the sense ODN (n=5) and saline (n=3) groups. Intracerebroventricular injection of AS-ODN-AGT reduced the elevated hypothalamic Ang II level. The hypothalamic Ang II content in sense ODN and saline groups was significantly (P<0.05) higher than in the nonclipped group. Compared with inverted ODN, intracerebroventricular injection of AS-ODN-AT(1)R (250 microgram/kg, n=6) significantly decreased SBP (-26+/-8 mm Hg, P<0.05) for 3 days after injection. This was a brain effect because intravenous AS-ODN-AT(1)R at a dose of 250 to 500 microgram/kg did not affect SBP. These results suggest that the brain RAS plays an important role in maintaining the elevated SBP in chronic 2K1C hypertension. (+info)