Three-dimensional diffusion tensor microscopy of fixed mouse hearts

The relative utility of 3D, microscopic resolution assessments of fixed mouse myocardial structure via diffusion tensor imaging is demonstrated in this study. Isotropic 100-microm resolution fiber orientation mapping within 5.5 degrees accuracy was achieved in 9.1 hr scan time. Preliminary characterization of the diffusion tensor primary eigenvector reveals a smooth and largely linear angular rotation across the left ventricular wall. Moreover, a higher level of structural hierarchy is evident from the organized secondary and tertiary eigenvector fields. These findings are consistent with the known myocardial fiber and laminar structures reported in the literature and suggest an essential role of diffusion tensor microscopy in developing quantitative atlases for studying the structure-function relationships of mouse hearts.

Physiological impact of increased expression of the AT1 angiotensin receptor

To test the effect of increased AT1 receptor expression on blood pressure, we used gene targeting to generate mouse lines with a tandem duplication of the AT1A receptor gene locus (Agtr1a) along with >10 kb of 5' flanking DNA. By successive breeding, we generated mice with 3 and 4 copies of the Agtr1a gene locus on an inbred 129/Sv background. AT1A mRNA expression and AT1-specific binding of 125I-angiotensin II were increased in proportion to Agtr1a gene copy number. These animals survived in expected numbers, and their body, heart, and kidney weights were similar to wild-type, 2-copy control mice. Pressor responses to angiotensin II were blunted in the 4-copy mice compared with control mice. In male mice, there was no correlation between resting blood pressure and Agtr1a gene copy number or AT1A mRNA levels. However, in female mice, there was a highly significant positive correlation between blood pressure and AT1A receptor expression, paralleled by significant increases in aldosterone synthase expression with increase in gene copy number. Furthermore, in female but not male mice, there was a positive correlation between kallikrein and AT1A receptor mRNA levels and an inverse correlation between renin mRNA and Agtr1a copy number. Thus, in female but not male mice, genetic variants that increase expression of AT1 receptors affect blood pressure and gene expression programs. The impact of enhanced AT1 receptor expression on blood pressure may be blunted by systemic compensatory responses and altered signal-effector coupling in the vasculature.

Natriuretic peptide receptor A mediates renal sodium excretory responses to blood volume expansion

The deficiency of Npr1 [genetic determinant of natriuretic peptide receptor A (NPRA)] increases arterial pressures and causes hypertensive heart disease in mice similar to those seen in untreated human hypertensive patients. However, the quantitative role of NPRA in mediating the renal responses to blood volume expansion remains uncertain. To determine the specific contribution of NPRA in mediating the signaling mechanisms responsible for natriuretic and diuretic responses to nondilutional intravascular expansion, we administered whole blood to anesthetized Npr1 homozygous null mutant (0-copy), wild-type (2-copy), and gene-duplicated (4-copy) mice. In wild-type (2-copy) animals, urinary flow (microl x min-1 x g kidney wt-1) increased from 4.9 +/- 1.0 to 14.4 +/- 1.8 and sodium excretion (microeq x min-1 x g kidney wt-1) from 1.15 +/- 0.22 to 3.11 +/- 0.60, associated with a rise in glomerular filtration rate (GFR; ml x min-1 x g kidney wt-1) from 0.63 +/- 0.03 to 0.82 +/- 0.09 and renal plasma flow (RPF; ml x min-1. g kidney wt-1) from 2.96 +/- 0.17 to 4.36 +/- 0.41, whereas arterial pressure did not significantly increase. After volume expansion, 0-copy mice showed significantly lesser increases in urinary flow (P < 0.001) and sodium excretory (P < 0.001) responses even though the increases in arterial pressures were greater (P < 0.001) compared with 2-copy mice. The 4-copy mice showed augmented responses in urinary flow (P < 0.01) and sodium excretion (P < 0.001) along with rises in both GFR (P < 0.01) and RPF (P < 0.01) compared with 2-copy wild-type mice. These results establish that NPRA activation is the predominant mechanism mediating the natriuretic, diuretic, and renal hemodynamic responses to acute blood volume expansion.

Genetic contributions to generalized arousal of brain and behavior

We have identified a generalized arousal component in the behavior of mice. Analyzed by mathematical/statistical approaches across experiments, investigators, and mouse populations, it accounts for about 1/3 of the variance in arousal-related measures. Knockout of the gene coding for the classical estrogen receptor (ER-alpha), a ligand-activated transcription factor, greatly reduced arousal responses. In contrast, disrupting the gene for a likely gene duplication product, ER-beta, did not have these effects. A combination of mathematical and genetic approaches to arousal in an experimentally tractable mammal opens up analysis of a CNS function of considerable theoretical and practical significance.

Induction of hepatic differentiation in embryonic stem cells by co-culture with embryonic cardiac mesoderm

BACKGROUND

Modifications in vitro have been used to direct embryonic stem (ES) cells toward endodermal phenotypes including hepatocytes; however, developmental correlates and evidence of biologic activity is lacking, and critical cell-cell interactions have not been investigated. In this study, we hypothesized that cardiac mesoderm (CM) signals ES cells in co-culture to undergo differentiation toward early hepatocyte lineage as determined by morphology and induction of genes essential for endodermal competence and hepatocyte development.

METHODS

Green fluorescent protein ES derived from A129 mice were cultured with or without embryonic chick cardiac mesoderm. Cultures from day 1, 2, and 4 were analyzed for colony formation and ES morphology and 10(6) ES-derived cells were isolated for mRNA analysis.

RESULTS

ES in co-culture with CM displayed colony formation, polymorphic appearance, and definitive interface with CM. In addition, ES + CM co-culture activated crucial transcription factors (sox 17alpha, HNF3beta, and GATA 4) required for hepatocyte development by day 1. mRNA for albumin and especially a-fetoprotein were also increased by culture days 2 and 4.

CONCLUSIONS

ES cells co-cultured with CM display morphology and gene expression pattern required for hepatocyte differentiation and appear to recapitulate the molecular events of hepatogenesis.

Minireview: computer simulations of blood pressure regulation by the renin-angiotensin system

Gene targeting experiments in mice have been used by us and others to test whether quantitative changes in gene expression in the renin-angiotensin system affect blood pressure. Surprisingly, these studies showed that blood pressure does not change with mild quantitative changes in the expression of the angiotensin converting enzyme (ACE). Yet, ACE inhibitors are widely used for the treatment of hypertension. This apparent paradox motivated us to develop a simple computer simulation, which qualitatively reconciled the paradox. We have now improved the simulation by including blood pressure as an explicit variable and by adding the kallikrein-kinin system and feedback control of plasma renin via plasma angiotensin II levels. The new simulation now matches quantitative aspects of the experimental data and suggests that a decrease in bradykinin plays an important role in the increased risk of diabetic nephropathy associated with genetically determined higher levels of ACE activity. This emphasizes that the value of these types of simulation lies in the thoughts that they provoke rather than in their ability to replicate experimental data.

Why the kidney glomerulus does not clog: a gel permeation/diffusion hypothesis of renal function

Current interpretations of kidney function in terms of a coarse filter followed by a fine filter have difficulty explaining why the glomerulus does not clog. I propose, as an alternative, a semiquantitative hypothesis that assumes that the size-selective property of the glomerulus is a consequence of the limited fraction of space in the glomerular basement membrane (a concentrated gel) into which macromolecules can permeate. The glomerular epithelial cell slits and slit diaphragms are assumed to impose substantial resistance to liquid flow across the glomerulus without acting as a molecular sieve. Calculations based on gel behavior show that proteins cross the glomerular basement membrane mainly by diffusion rather than by liquid flow, whereas water crosses entirely by flow. Thus, diffusion provides most of the protein, whereas flow provides the diluent. As a result, the single-nephron glomerular filtration rate (GFR) becomes a prime factor in (inversely) determining the concentration of proteins in early proximal tubular fluid. Because the reabsorption of proteins from the tubules is a saturable process, the gel permeationdiffusion hypothesis readily accounts for the albuminuria observed when single-nephron GFR is substantially reduced by severe pathological decreases in slit diaphragm length, such as occur in minimal-change nephrotic syndrome in humans, in animals treated with puromycin aminonucleoside, or in humans or animals with mutations in the gene coding for nephrin. My hypothesis predicts that albuminuria will ensue, even with a normal kidney, if the single-nephron GFR falls below approximately 50% of normal.

Estrogen-induced osteogenesis in intact female mice lacking ERbeta

We recently found that estrogen receptor (ER) antagonists prevent high-dose estrogen from inducing the formation of new cancellous bone within the medullary cavity of mouse long bones. In the present investigation, we studied the role of specific ER subtypes in this response by examining whether this is impaired in female ERbeta(-/-) mice previously generated by targeted gene deletion. Vehicle or 17beta-estradiol (E(2)) (range 4-4,000 microg. kg(-1). day(-1)) was administered to intact female ERbeta(-/-) mice and wild-type littermates by subcutaneous injection for 28 days. The osteogenic response was subsequently assessed by histomorphometry performed on longitudinal and cross sections of the tibia. E(2) was found to cause an equivalent increase in cancellous bone formation in ERbeta(-/-) mice and littermate controls, as assessed at the proximal and distal regions of the proximal tibial metaphysis. E(2) also resulted in a similar increase in endosteal mineral apposition rate in these two genotypes, as assessed at the tibial diaphysis. In contrast, cortical area in ERbeta(-/-) mice was found to be greater than that in wild types irrespective of E(2) treatment, as was tibial bone mineral density as measured by dual-energy X-ray absorptiometry, consistent with previous reports of increased cortical bone mass in these animals. We conclude that, although ERbeta acts as a negative modulator of cortical modeling, this isoform does not appear to contribute to high-dose estrogen's ability to induce new cancellous bone formation in mouse long bones.

Targeted disruption of hsp70.1 sensitizes to osmotic stress

The 70 kDa heat shock protein (Hsp70) plays a critical role in cell survival and thermotolerance in response to various stress stimuli. Two nearly identical genes, hsp70.1 and hsp70.3, in response to environmental stress, rapidly induce Hsp70. However, it remains unclear whether these two genes are differentially regulated by various stresses. To address the physiological role of the hsp70.1 and hsp70.3 genes in the stress response, we generated mice that specifically lack hsp70.1. In contrast to heat shock, which rapidly induced both hsp70.1 and hsp70.3 mRNA, osmotic stress selectively induced transcription of hsp70.1. In hsp70.1-deficient embryonic fibroblasts, osmotic stress markedly reduced cell viability. Furthermore, when osmotic stress was applied in vivo, hsp70.1-deficient mice exhibited increased apoptosis in the renal medulla. Taken together, our results demonstrate that differential expression of hsp70 genes contributes to the stress response and that the hsp70.1 gene plays a critical role in osmotolerance.

Ventricular expression of natriuretic peptides in Npr1(-/-) mice with cardiac hypertrophy and fibrosis

Atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) are cardiac hormones that regulate blood pressure and volume, and exert their biological actions via the natriuretic peptide receptor-A gene (Npr1). Mice lacking Npr1 (Npr(-/-)) have marked cardiac hypertrophy and fibrosis disproportionate to their increased blood pressure. This study examined the relationships between ANP and BNP gene expression, immunoreactivity and fibrosis in cardiac tissue, circulating ANP levels, and ANP and BNP mRNA during embryogenesis in Npr1(-/-) mice. Disruption of the Npr1 signaling pathway resulted in augmented ANP and BNP gene and ANP protein expression in the cardiac ventricles, most pronounced for ANP mRNA in females [414 +/- 57 in Npr1(-/-) ng/mg and 124 +/- 25 ng/mg in wild-type (WT) by Taqman assay, P < 0.001]. This increased expression was highly correlated to the degree of cardiac hypertrophy and was localized to the left ventricle (LV) inner free wall and to areas of ventricular fibrosis. In contrast, plasma ANP was significantly greater than WT in male but not female Npr1(-/-) mice. Increased ANP and BNP gene expression was observed in Npr1(-/-) embryos from 16 days of gestation. Our study suggests that cardiac ventricular expression of ANP and BNP is more closely associated with local hypertrophy and fibrosis than either systemic blood pressure or circulating ANP levels.

A genetically clamped renin transgene for the induction of hypertension

Experimental analysis of the effects of individual components of complex mammalian systems is frequently impeded by compensatory adjustments that animals make to achieve homeostasis. We here introduce a genetic procedure for eliminating this type of impediment, by using as an example the development and testing of a transgene for "genetically clamping" the expression of renin, the major homeostatically responding component of the renin-angiotensin system, one of the most important regulators of blood pressure. To obtain a renin transgene whose expression is genetically clamped at a constant level, we have used single-copy chosen-site gene targeting to insert into a liver-specific locus a single copy of a modified mouse renin transgene driven by a liver-specific promoter/enhancer. The resulting transgene expresses renin ectopically at a constant high level in the liver and leads to elevated plasma levels of prorenin and active renin. The transgenic mice display high blood pressure, enhanced thirst, high urine output, proteinuria, and kidney damage. Treatment with the angiotensin II type I receptor antagonist, losartan, reduces the hypertension, albuminuria, and kidney damage, but does not affect expression of the transgene. This genetically clamped renin transgene can be used in models in which hypertension and its complications need to be investigated in a high prorenin/renin environment that is not subject to homeostatic compensations by the animal when other factors are changed.

Genotype/age interactions on aggressive behavior in gonadally intact estrogen receptor beta knockout (betaERKO) male mice

Estrogen, as an aromatized metabolite of testosterone, has a facilitatory effect on male aggressive behavior in mice. Two subtypes of estrogen receptors, alpha (ER-alpha) and beta (ER-beta), in the brain are known to bind estrogen. Previous studies revealed that the lack of ER-alpha gene severely reduced the induction of male aggressive behavior. In contrast, mice that lacked the ER-beta gene tended to be more aggressive than wild type (WT) control mice, although the behavioral effects of ER-beta gene disruption were dependent on their social experience. These findings lead us to hypothesize that estrogen may facilitate aggression via ER-alpha whereas it may inhibit aggression via ER-beta. In the present study, we further investigated the role of ER-beta in the regulation of aggressive behavior by examining developmental changes starting at the time of first onset, around the age of puberty. Aggressive behaviors of ER-beta gene knockout (betaERKO) mice were examined in three different age groups, puberty, young-adult, and adult. Each mouse was tested every other day for three times in a resident-intruder paradigm against olfactory bulbectomized intruder mice and their trunk blood was collected for measurements of serum testosterone after the completion of the study. Overall, betaERKO mice were significantly more aggressive than WT. These genotype differences were more pronounced in puberty and young adult age groups, but not apparent in the adult age group, in which betaERKO mice were less aggressive than those in two younger age groups. Serum testosterone levels of betaERKO mice were significantly higher than those of WT mice only in the pubertal age group, but not in young adult (when betaERKO mice were still significantly more aggressive than WT mice) and adult (when no genotype differences in aggression were found) age groups. These results suggest that ER-beta mediated actions of gonadal steroids may more profoundly be involved in the inhibitory regulation of aggressive behavior in pubertal and young adult mice.

Molecular phenotyping for analyzing subtle genetic effects in mice: application to an angiotensinogen gene titration

The angiotensinogen M235T polymorphism in humans is linked to differential expression of the human angiotensinogen gene (AGT) gene and hypertension, but the homeostatic responses resulting from this polymorphism are not known. We therefore investigated how mice respond to five genetically determined levels of mouse angiotensinogen gene (Agt) expression covering the range associated with the M235T variants. By using high-throughput molecular phenotyping, tissue RNAs were assayed for expression of 10 genes important in hypertension. Significant positive and negative responses occurred in both sexes as Agt expression increased twofold, including a three-fold increase in aldosterone synthase expression in adrenal gland, and a two-fold decrease in renin expression in kidney. In males, cardiac expression of the precursor of atrial natriuretic peptide B and of adrenomedullin also increased approximately twofold. The relative expression of all genes studied except Agt differed significantly in the two sexes, and several unexpected relationships were encountered. A highly significant correlation between renal expression of the angiotensin type 1a receptor and kallikrein, independent of Agt genotype, is present in females (P < 0.0001) but not males (P = 0.4). The correlation between blood pressure (BP) and liver Agt expression within the five Agt genotypes is significant in females (P = 0.0005) but not in males (P = 0.2), whereas correlation of BP with differences between the genotypes is less in females (P = 0.06) than in males (P = 0.001). The marked gender differences in gene expression in wild-type mice and the changes induced by moderate alterations in Agt expression and BP emphasize the need to look for similar differences in humans.

Multiple roles of adrenomedullin revealed by animal models

The newly identified adrenomedullin (AM) gene codes for a potent, highly conserved vasodilator that is expressed in many tissues. Many biological functions have been ascribed to AM based on its broad expression pattern and numerous in vitro studies, and it is currently viewed as a multifunctional peptide hormone. Recent advances in gene manipulation have permitted the development of experimental animal systems to help distinguish between gene causes and effects in the context of otherwise normal physiology, and so the normal biological function of the AM gene can be studied within the intact physiological milieu of a whole animal. In this review article, we summarize the recent findings from three different types of genetic experiments involving the AM gene.

Posttranscriptional compensation for heterozygous disruption of the kidney-specific NaK2Cl cotransporter gene

Mice homozygous for a loss of function mutation of the kidney-specific NaK2Cl cotransporter, BSC1/NKCC2, do not survive. Here the effects of loss of one copy of the gene are studied. NKCC2 mRNA of NKCC2 +/- kidney was 55 +/- 6% of +/+, yet no differences were found between NKCC2 +/+ and +/- mice in BP, blood gas, electrolytes, creatinine, plasma renin concentration, urine volume and osmolality, ability to concentrate and dilute urine, and response to furosemide. When mice were challenged with 180 mM NH(4)Cl, plasma ammonia and urinary ammonia excretion were increased twofold and fivefold, respectively, but there was still no difference between the two genotypes. NKCC2 +/- mice had a near-normal level of NKCC2 protein and no clear change in the distribution of NKCC2 in the thick ascending limb (TAL) cells. In vitro microperfusion of isolated TAL showed no significant difference between the two genotypes in the basal and vasopressin-stimulated capacity to reabsorb NaCl. There was no difference in the mRNA expressions of thiazide-sensitive NaCl cotransporter, epithelial Na channel (ENaC), aquaporin-2, ROMK, and NaKATPase. Halving the mRNA expression of NKCC2 does not affect BP or fluid balance because of compensatory factors that restore the protein level to near normal. One possible factor is a regulated increase in the movement of cytoplasmic protein to the luminal membrane leading to a restoration of functional transporter to an essentially wild type level.

Impaired T cell function in RANTES-deficient mice

The chemokine RANTES is a chemoattractant for monocytes and T cells and is postulated to participate in many aspects of the immune response. To evaluate the biological roles of RANTES in vivo, we generated RANTES-deficient (-/-) mice and characterized their T cell function. In cutaneous delayed-type hypersensitivity assays, a 50% reduction in ear and footpad swelling was seen in -/- mice compared to +/+ mice. In vitro, polyclonal and antigen-specific T cell proliferation was decreased. Quantitative analysis using the fluorescent dye carboxy-fluorescein succinimidyl ester revealed that this proliferative defect was due both to fewer antigen-reactive T cells and to a reduction in the capacity of these cells to proliferate. In addition, IFN-gamma and IL-2 production by the -/- T cells was dramatically decreased. Together, these data suggest that RANTES is required for normal T cell functions as well as for recruiting monocytes and T cells to sites of inflammation.

Interactions between endothelial nitric oxide synthase and sex hormones in vascular protection in mice

The vasculoprotective effects of sex hormones, particularly estrogens, have been attributed to their ability to increase the bioavailability of nitric oxide through activation of endothelial nitric oxide synthase (eNOS). To dissect the relative contribution in vivo of eNOS, sex hormones, and their interaction in two complex vascular phenotypes, hypertension and atherosclerosis, we used mice doubly deficient in eNOS and apoE (nnee) or lacking only apoE (NNee). Females and males were gonadectomized at 1 month of age and implanted either with control pellets or pellets releasing 17beta-estradiol (E2). Hormonally intact nnee mice have elevated blood pressure (BP) and increased atherosclerosis compared with NNee mice, but on removal of gonads, BP and atherosclerosis decreased significantly in nnee mice but not in NNee mice. Three months of treatment with exogenous E2 dramatically reduced atherosclerosis and significantly lowered BP in both NNee and nnee mice compared with animals treated with control pellets. Thus exogenous E2 has strong BP-lowering and atheroprotective effects in apoE-deficient mice, but eNOS is not essential for either effect. Endogenous sex hormones, on the other hand, cause significant damage to the vasculature in the absence of eNOS, but these effects are overridden by interactions between eNOS and sex hormones.

Abnormal vascular function and hypertension in mice deficient in estrogen receptor beta

Blood vessels express estrogen receptors, but their role in cardiovascular physiology is not well understood. We show that vascular smooth muscle cells and blood vessels from estrogen receptor beta (ERbeta)-deficient mice exhibit multiple functional abnormalities. In wild-type mouse blood vessels, estrogen attenuates vasoconstriction by an ERbeta-mediated increase in inducible nitric oxide synthase expression. In contrast, estrogen augments vasoconstriction in blood vessels from ERbeta-deficient mice. Vascular smooth muscle cells isolated from ERbeta-deficient mice show multiple abnormalities of ion channel function. Furthermore, ERbeta-deficient mice develop sustained systolic and diastolic hypertension as they age. These data support an essential role for ERbeta in the regulation of vascular function and blood pressure.

Targeted disruption of the gene for natriuretic peptide receptor-A worsens hypoxia-induced cardiac hypertrophy

Targeted disruption of the gene for natriuretic peptide receptor-A (NPR-A) worsens pulmonary hypertension and right ventricular hypertrophy during hypoxia, but its effect on left ventricular mass and systemic pressures is not known. We examined the effect of 3 wk of hypobaric hypoxia (0.5 atm) on right and left ventricular pressure and mass in mice with 2 (wild type), 1, or 0 copies of Npr1, the gene that encodes for NPR-A in mice. Under normoxic conditions, right ventricular peak pressure (RVPP) was greater in 0 than in 2 copy mice, but there were no genotype-related differences in carotid artery PP (CAPP). The left ventricular free wall weight-to-body weight (LV/body wt) ratio was greater in 0 than in 2 copy mice and there was a trend toward a greater right ventricular weight-to-body weight (RV/body wt) ratio. Three weeks of hypoxia increased RVPP and RV/body wt in all genotypes. The increase in RVPP was similar in all genotypes (11-14 mmHg), but the hypoxia-induced increase in RV/body wt was more than twice as great in 0 copy mice than in 2 copy mice (1.11 +/- 0.06 to 2.65 +/- 0.46 vs. 0.96 +/- 0.04 to 1.4 +/- 0.09, P < 0.05). Chronic hypoxia had no effect on CAPP in any genotype and did not effect LV/body wt in 1 or 2 copy mice, but increased LV/body wt 41% in 0 copy mice. We conclude that absent expression of NPR-A worsens right ventricular hypertrophy and causes left ventricular hypertrophy during exposure to chronic hypoxia without increasing pulmonary or systemic arterial pressure responses.

Albuminuria in mice after injection of antibodies against aminopeptidase A: role of angiotensin II

It has been shown that injection of combinations of anti-aminopeptidase A (APA) monoclonal antibodies (mAb) that inhibit the enzyme activity induces an acute albuminuria in mice. This albuminuria is not dependent on inflammatory cells, complement, or the coagulation system. APA is an important regulator of the renin-angiotensin system because it is involved in the degradation of angiotensin II (Ang II). This study examined the potential role of glomerular Ang II in the induction of albuminuria. The relation among renal Ang II, glomerular APAX enzyme activity, and albuminuria was examined first. Injection of the nephritogenic combinations ASD-3/37 and ASD-37/41 in BALB/c mice induced albuminuria, whereas the non-nephritogenic combination ASD-3/41 had no effect. There was no clear relation between the inhibition of glomerular APA activity and albuminuria, yet it was evident that intrarenal Ang II levels were significantly increased in albuminuric mice and not in nonalbuminuric mice. As a next step, anti-APA mAb were administered to angiotensinogen-deficient mice that do not produce Ang II, and kidney morphology and albuminuria were determined. Angiotensinogen-deficient mice also developed albuminuria upon ASD-37/41 administration. Altogether, these findings clearly demonstrate that Ang II is not required for the induction of albuminuria upon injection of enzyme-inhibiting anti-APA mAb.

Deficiency of COX-1 causes natriuresis and enhanced sensitivity to ACE inhibition

BACKGROUND

Prostanoid products of the cyclo-oxygenase (COX) pathway of arachidonic acid metabolism modulate blood pressure (BP) and sodium homeostasis. Conventional non-steroidal anti-inflammatory drugs (NSAIDs), which inhibit both COX isoforms (COX-1 and -2), cause sodium retention, exacerbate hypertension, and interfere with the efficacy of certain anti-hypertensive agents such as angiotensin-converting enzyme (ACE) inhibitors. While a new class of NSAIDs that specifically inhibit COX-2 is now widely used, the relative contribution of the individual COX isoforms to these untoward effects is not clear.

METHODS

To address this question, we studied mice with targeted disruption of the COX-1 (Ptgs1) gene. Blood pressure, renin mRNA expression, and aldosterone were measured while dietary sodium was varied. To study interactions with the renin-angiotensin system, ACE inhibitors were administered and mice with combined deficiency of COX-1 and the angiotensin II subtype 1A (AT1A) receptor were generated.

RESULTS

On a regular diet, BP in COX-1-/- mice was near normal. However, during low salt feeding, BP values were reduced in COX-1-/- compared to +/+ animals, and this reduction in BP was associated with abnormal natriuresis despite appropriate stimulation of renin and aldosterone. Compared to COX-1+/+ mice, the actions of ACE inhibition were markedly accentuated in COX-1-/- mice. Sodium sensitivity and BP lowering also were enhanced in mice with combined deficiency of COX-1 and AT1A receptor.

CONCLUSIONS

The absence of COX-1 is associated with sodium loss and enhanced sensitivity to ACE inhibition, suggesting that COX-1 inhibition does not cause hypertension and abnormal sodium handling associated with NSAID use.

Genetically increased angiotensin I-converting enzyme level and renal complications in the diabetic mouse

Diabetic nephropathy is a major risk factor for end-stage renal disease and cardiovascular diseases and has a marked genetic component. A common variant (D allele) of the angiotensin I-converting enzyme (ACE) gene, determining higher enzyme levels, has been associated with diabetic nephropathy. To address causality underlying this association, we induced diabetes in mice having one, two, or three copies of the gene, normal blood pressure, and an enzyme level range (65-162% of wild type) comparable to that seen in humans. Twelve weeks later, the three-copy diabetic mice had increased blood pressures and overt proteinuria. Proteinuria was correlated to plasma ACE level in the three-copy diabetic mice. Thus, a modest genetic increase in ACE levels is sufficient to cause nephropathy in diabetic mice.