6 research outputs found
Blood pressure and renal failure in the Fawn-Hooded rat: combining physiology and genetics
The question why not all patients with hypertension develop end-stage renal
failure (ESRF) has become a major issue in nephrology and hypertension
research over the past decade. There are indications for a relationship between
hypertension and impaired renal fimction in individuals with no underlying renal
disease.31 It is widely believed that genetic factors play an important role in the
susceptibility to hypertension-induced renal failure.18.IOO Epidemiological studies
indicate that the risk for hypertension-associated renal failure varies with the
ethnic background. 14.28 For instance, the presence of ESRF in an AfricanAmerican
individual results in a nine-fold increased risk of ESRF in a firstdegree
relative, even after controlling hypertension in the relative.32
Most information on familial clustering of renal failure and hypertension is
derived from studies in patients with diabetic nephropathy, for which Seaquist et
al. recently showed the involvement of genetic factors in its pathogenesis. I08
Other studies have reported a greater prevalence of hype11ension and/or
cardiovascular disease in the parents of children who developed diabetic
nephropathy later in Iife.27
•
133 Furthermore, Schmidt et al. found that a familial
history of hypertension is not only more frequent in patients who develop chronic
renal failure caused by diabetes but also in patients with different histologic types
of primary glomel1llonephritis. lo7
The factors responsible for an association between blood pressure and renal
failure are not known, but an increased blood pressure is: (a) necessmy and
sufficient to cause ESRF, or (b) necessmy but not sufficient to cause ESRF, or (c)
neither nec~ssmy nor sufficient to cause ESRF; it accelerates the risk in
individuals who are otherwise predisposed. Renal failure is hypertension-induced
in the first two suppositions and hypertension-associated in the latter. 12
In this context, we have to consider the possibility that hypertension and the
predisposition to develop glomel1llar damage due to hypertension are influenced
by different genes. Gene-gene and gene-environment interactions determine the
final phenotype. It could be that hype11ension alone and renal failure due to
hypertension are two different phenotypes.
The genetic basis of complications in human diseases deserves more attention,
and it would be usefill to asce11ain a large number of hypertensive affected sibpairs
to study whether risk of renal failure correlates between these sib-pairs and,
if so, to map human susceptibility factors. Using the candidate gene approach, an
insertion/deletion polymorphism of the angiotensin converting enzyme (ACE)
gene was recently discovered, significantly influencing circulating ACE levels.
These levels might playa role in the development of target organ damage, such as
left ventricular hYfelirophy in essential hypeliension and microalbuminuria in
diabetes mellitus. I .29.83 However, simple comparisons do not provide answers to
these complex problems. Combining physiology and genetics, we might be able
to dissect the susceptibility to hypeliension and renal damage
Altered renal hemodynamics and impaired myogenic responses in the fawn-hooded rat
The present study examined whether an abnormality in the myogenic response
of renal arterioles that impairs autoregulation of renal blood flow (RBF)
and glomerular capillary pressure (PGC) contributes to the development of
renal damage in fawn-hooded hypertensive (FHH) rats. Autoregulation of
whole kidney, cortical, and medullary blood flow and PGC were compared in
young (12 wk old) FHH and fawn-hooded low blood pressure (FHL) rats in
volume-replete and volume-expanded conditions. Baseline RBF, cortical and
medullary blood flow, and PGC were significantly greater in FHH than in
FHL rats. Autoregulation of renal and cortical blood flow was
significantly impaired in FHH rats compared with results obtained in FHL
rats. Myogenically mediated autoregulation of PGC was significantly
greater in FHL than in FHH rats. PGC rose from 46 +/- 1 to 71 +/- 2 mmHg
in response to an increase in renal perfusion pressure from 100 to 150
mmHg in FHH rats, whereas it only increased from 39 +/- 2 to 53 +/- 1 mmHg
in FHL rats. Isolated perfused renal interlobular arteries from FHL rats
constricted by 10% in response to elevations in transmural pressure from
70 to 120 mmHg. In contrast, the diameter of vessels from FHH rats
increased by 15%. These results indicate that the myogenic response of
small renal arteries is altered in FHH rats, and this contributes to an
impaired autoregulation of renal blood flow and elevations in PGC in this
strain
Impaired autoregulation of renal blood flow in the fawn-hooded rat
The responses to changes in renal perfusion pressure (RPP) were compared
in 12-wk-old fawn-hooded hypertensive (FHH), fawn-hooded low blood
pressure (FHL), and August Copenhagen Irish (ACI) rats to determine
whether autoregulation of renal blood flow (RBF) is altered in the FHH
rat. Mean arterial pressure was significantly higher in conscious,
chronically instrumented FHH rats than in FHL rats (121 +/- 4 vs. 109 +/-
6 mmHg). Baseline arterial pressures measured in
ketamine-Inactin-anesthetized rats averaged 147 +/- 2 mmHg (n = 9) in FHH,
132 +/- 2 mmHg (n = 10) in FHL, and 123 +/- 4 mmHg (n = 9) in ACI rats.
Baseline RBF was significantly higher in FHH than in FHL and ACI rats and
averaged 9.6 +/- 0.7, 7.4 +/- 0.5, and 7.8 +/- 0.9 ml. min-1. g kidney
wt-1, respectively. RBF was autoregulated in ACI and FHL but not in FHH
rats. Autoregulatory indexes in the range of RPPs from 100 to 150 mmHg
averaged 0.96 +/- 0.12 in FHH vs. 0.42 +/- 0.04 in FHL and 0.30 +/- 0.02
in ACI rats. Glomerular filtration rate was 20-30% higher in FHH than in
FHL and ACI rats. Elevations in RPP from 100 to 150 mmHg increased urinary
protein excretion in FHH rats from 27 +/- 2 to 87 +/- 3 microg/min,
whereas it was not significantly altered in FHL or ACI rats. The
percentage of glomeruli exhibiting histological evidence of injury was not
significantly different in the three strains of rats. These results
indicate that autoregulation of RBF is impaired in FHH rats before the
development of glomerulosclerosis and suggest that an abnormality in the
control of renal vascular resistance may contribute to the development of
proteinuria and renal failure in this strain of rats
New rat model that phenotypically resembles autosomal recessive polycystic kidney disease
Numerous murine models of polycystic kidney disease (PKD) have been
described. While mouse models are particularly well suited for
investigating the molecular pathogenesis of PKD, rats are well established
as an experimental model of renal physiologic processes. Han:SPRD-CY: rats
have been proposed as a model for human autosomal dominant PKD. A new
spontaneous rat mutation, designated wpk, has now been identified. In the
mutants, the renal cystic phenotype resembles human autosomal recessive
PKD (ARPKD). This study was designed to characterize the clinical and
histopathologic features of wpk/wpk mutants and to map the wpk locus.
Homozygous mutants developed nephromegaly, hypertension, proteinuria,
impaired urine-concentrating capacity, and uremia, resulting in death at 4
wk of age. Early cysts were present in the nephrogenic zone at embryonic
day 19. These were localized, by specific staining and electron
microscopy, to differentiated proximal tubules, thick limbs, distal
tubules, and collecting ducts. In later stages, the cysts were largely
confined to collecting ducts. Although the renal histopathologic features
are strikingly similar to those of human ARPKD, wpk/wpk mutants exhibited
no evidence of biliary tract abnormalities. The wpk locus maps just
proximal to the CY: locus on rat chromosome 5, and complementation studies
demonstrated that these loci are not allelic. It is concluded that the
clinical and renal histopathologic features of this new rat model strongly
resemble those of human ARPKD. Although homology mapping indicates that
rat wpk and human ARPKD involve distinct genes, this new rat mutation
provides an excellent experimental model to study the molecular
pathogenesis and renal pathophysiologic features of recessive PKD
Blood pressure and the susceptibility to renal damage after unilateral nephrectomy and L-NAME-induced hypertension in rats
BACKGROUND: Fawn-hooded hypertensive (FHH) rats carry several genes which
determine the susceptibility to develop renal damage, while renal damage
resistant August x Copenhagen Irish (ACI) rats do not. Kidneys from
heterozygous (FHH x ACI) F(1) rats, appear to be largely, but not
completely, protected after blood pressure elevation with
N(omega)-nitro-L-arginine methyl ester (L-NAME). We examined the role of
an increased haemodynamic burden on the development of renal damage
combining unilateral nephrectomy (UNx)- and L-NAME-induced hypertension in
F(1) and ACI rats. Additionally, we investigated whether a general toxic
effect of L-NAME, independent from a blood pressure elevation, caused
renal damage in F(1) rats in animals simultaneously treated with L-NAME
and the ACE inhibitor lisinopril. METHODS: Surgery was performed and
L-NAME treatment (50 or 150 mg/l) was started at the age of 15 weeks.
Systolic blood pressure (SBP) and urinary albumin excretion (UaV) were
measured at 6 and 12 weeks post-UNx, followed by autopsy to determine the
incidence of focal glomerulosclerosis (FGS). Using lisinopril (LIS) and
L-NAME, another group of rats was evaluated at 12, 18, and 24 weeks after
start of treatment. RESULTS: At similar L-NAME intake, F, rats developed
more severe hypertension and more UaV than ACI rats. The increase in UaV
per mmHg increase in SBP was fivefold higher in F(1) compared with ACI
rats. In F(1) rats, the increase in UaV per percentage incidence increase
in FGS was three times higher. In LIS treated F(1) rats, no significant
UaV or FGS was measured at low blood pressure levels, indicating that
renal damage in hypertensive F(1) rats is not a direct effect of L-NAME,
but the result of the high blood pressure or another action of the
renin-angiotensin system. CONCLUSION: We conclude that heterozygosity for
the genes influencing the development of renal damage in the FHH strain
increases the susceptibility of the kidney to develop damage after UNx
combined with systemic hypertension