bluuebunny/crossref_metadata_2025 huggingface dataset:
Dopamine regulation of renal Na+,K(+)-ATPase activity is lacking in Dahl salt-sensitive rats.
Authors: Nishi A , Eklöf A C , Bertorello A M , Aperia A
Published: June 2012

Dopamine is a natriuretic hormone that acts by inhibiting tubular Na+, K(+)-ATPase activity by activation of the dopamine-1 receptor (the thick ascending limb [TAL] of Henle) or by a synergistic effect of dopamine-1 and dopamine-2 receptors (the proximal tubule). The dopamine-1 receptor is coupled to adenylate cyclase. In this article we show that prehypertensive Dahl salt-sensitive (DS) rats have a blunted natriuretic response to dopamine determined during euvolemic conditions compared with Dahl salt-resistant (DR) rats. Furthermore, we have examined the renal tubular effects of dopamine in DS and DR rats. Basal Na+,K(+)-ATPase activity was similar in DS and DR rats. In proximal tubule, dopamine (10(-5) M) inhibited Na+,K(+)-ATPase activity in DR but not in DS rats. The dopamine-2 agonist LY171555 (10(-5) M) together with dibutyryl cyclic AMP (10(-6) M) inhibited proximal tubule Na+,K(+)-ATPase activity in both DS and DR rats. LY171555 alone had no effect. In TAL, the dopamine-1 agonist fenoldopam (10(-5) M) inhibited Na+,K(+)-ATPase activity in DR but not in DS rats. Dibutyryl cyclic AMP (10(-5) M) inhibited TAL Na+,K(+)-ATPase activity in both DS and DR rats. In cell suspensions from the cortex and the medulla, activation of the dopamine-1 receptor significantly increased cyclic AMP content in DR but not in DS rats. The results indicate that DS rats lack the capacity to inhibit tubular Na+,K(+)-ATPase activity because of a defective dopamine-1 receptor adenylate cyclase coupling. This defect may contribute to the impaired natriuretic capacity in DS rats.
Gene expression and tissue localization of the two isoforms of angiotensin I converting enzyme.
Authors: Sibony M , Gasc J M , Soubrier F , Alhenc-Gelas F , Corvol P
Published: June 2012

Angiotensin converting enzyme exists in two different isoforms, somatic and germinal, whose respective distributions and intracellular localizations have not been precisely determined. The differing biochemical and molecular characteristics of the two isozymes allowed the preparation of antibodies specific for each of the two angiotensin converting enzyme isoforms and of two nucleic acid probes, one of which was specific for the germinal isoform. Immunohistochemistry and in situ hybridization were used to determine the cell distribution of, respectively, the two isoforms and their corresponding messenger RNAs in the classically studied tissues of male adult humans and marmosets. Results provided by the two different methods were always concordant and were identical in the two species. The somatic angiotensin converting enzyme form was expressed uniquely in somatic tissues (vascular endothelial cells and at the brush border of renal proximal convoluted tubule, jejunal villus, and epididymal duct epithelia), and the germinal form was expressed uniquely in germinal cells with a precise stage-specific pattern, starting in round spermatids and finishing in spermatozoa. In situ hybridization documented the presence of somatic angiotensin converting enzyme messenger RNA in renal tubule epithelium, jejunal enterocytes, and epididymal epithelium and demonstrated that there was no direct correlation between the levels of angiotensin converting enzyme messenger RNA and the enzyme it encodes for, i.e., angiotensin converting enzyme, in a given epithelium. The significance of the ultraselective expression of germinal angiotensin converting enzyme and of its specific messenger RNA at a very precise stage of spermatogenesis remains uncertain.
Alterations in prostaglandin production in spontaneously hypertensive rat smooth muscle cells.
Authors: Jaiswal N , Jaiswal R K , Tallant E A , Diz D I , Ferrario C M
Published: June 2012

We have characterized angiotensin binding sites in cultured smooth muscle cells obtained from the aorta of spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats. In both strains of rats the binding of 125I-angiotensin II (125I-Ang II) in smooth muscle cells was time dependent and reached a maximum at 60 minutes. Scatchard analysis revealed a single binding site in both strains with equilibrium constants (KD) of 5.35 nmol/L in SHR and 3.47 nmol/L in WKY rats. Binding capacities (Bmax) in smooth muscle cells averaged 270 and 150 fmol/mg protein in SHR and WKY rats, respectively. Angiotensin peptides competed for 125I-Ang II binding with an order of potency of Ang II > angiotensin-(1-7) = angiotensin I. In smooth muscle cells of the SHR, basal prostaglandin E2 (PGE2) and prostacyclin (prostaglandin I2 [PGI2]) release were threefold and 15-fold lower than that found in WKY rat smooth muscle cells. Ang II as well as angiotensin-(1-7) stimulated PGE2 and PGI2 release in WKY rat smooth muscle cells. In smooth muscle cells from SHR, Ang II increased the production of both PGE2 and PGI2, whereas angiotensin-(1-7) enhanced only PGE2 but not PGI2 release. There was no significant difference between Ang II-stimulated PGE2 and PGI2 release or angiotensin-(1-7)-stimulated PGE2 production in SHR and WKY rat smooth muscle cells. However, angiotensin-(1-7)-stimulated PGI2 release was significantly lower (p < 0.0005) in SHR compared with WKY smooth muscle cells. Collectively, the data suggest that smooth muscle cells of SHR contain a higher number of angiotensin binding sites.(ABSTRACT TRUNCATED AT 250 WORDS)
Role of renal interstitial pressure as a mediator of sodium retention during systemic blockade of nitric oxide.
Authors: Nakamura T , Alberola A M , Granger J P
Published: June 2012

The role of renal interstitial pressure was examined in mediating the sodium retention induced by blockade of nitric oxide synthesis. The effects of intravenous NG-nitro-L-arginine-methyl ester (L-NAME), a synthesis inhibitor, on renal hemodynamics, renal interstitial hydrostatic pressure, and sodium and lithium excretion were determined. L-NAME (50 micrograms/kg per minute) was infused for 75 minutes in Sprague-Dawley rats (n = 7) in which renal perfusion pressure was permitted to rise in parallel with systemic arterial pressure and in rats (n = 8) in which renal perfusion pressure was serocontrolled constant at basal levels. Infusion of L-NAME raised renal perfusion pressure from 122 +/- 6 to 157 +/- 4 mm Hg in the nonservocontrolled group but not in the servocontrolled group (118 +/- 3 mm Hg). L-NAME decreased renal plasma flow and glomerular filtration rate to the same level in both rat groups. L-NAME significantly decreased sodium excretion (1.38 +/- 0.41 to 0.36 +/- 0.14 microEq/min and 1.19 +/- 0.46 to 0.30 +/- 0.05 microEq/min, respectively), fractional excretion of lithium (25.7 +/- 1.7% to 16.7 +/- 2.3% and 25.6 +/- 4.0% to 18.2 +/- 1.7%), and renal interstitial hydrostatic pressure (6.4 +/- 1.4 to 3.2 +/- 0.9 mm Hg and 6.3 +/- 1.8 to 2.7 +/- 0.9 mm Hg) in servocontrolled and nonservocontrolled groups. However, there was no significant difference in the renal hemodynamic and excretory responses to L-NAME between the servocontrolled and nonservocontrolled groups. In summary, reductions in sodium excretion during inhibition of nitric oxide synthesis are associated with significant reductions in renal interstitial hydrostatic pressure.(ABSTRACT TRUNCATED AT 250 WORDS)
Bradykinin B2-receptor blockade facilitates deoxycorticosterone-salt hypertension.
Authors: Madeddu P , Parpaglia P P , Demontis M P , Varoni M V , Fattaccio M C , Tonolo G , Troffa C , Glorioso N
Published: June 2012

The contribution of endogenous kinins to the regulation of blood pressure, urinary volume, and renal sodium excretion was evaluated in Wistar rats on high sodium intake by using the new bradykinin receptor antagonist Hoe 140 (D-Arg,[Hyp3,Thi5,D-Tic7,Oic8]-bradykinin). Neither Hoe 140 (3 nmol/hr s.c. for 4 weeks) nor its vehicle altered systolic blood pressure (tail-cuff plethysmography) or renal function in rats given saline solution (0.15 mol/L NaCl) to drink ad libitum. Four-week administration of deoxycorticosterone (DOC), combined with high sodium intake and uninephrectomy, increased systolic blood pressure from 127 +/- 3 to 160 +/- 3 mm Hg (p < 0.01). When long-term infusion of Hoe 140 was combined with DOC, high sodium intake, and uninephrectomy, systolic blood pressure rose from 127 +/- 3 to 175 +/- 3 mm Hg (p < 0.01). The hypertensive effect was greater in the Hoe 140 group (48 +/- 4 versus 33 +/- 3 mm Hg in controls, p < 0.05). This difference was confirmed by direct measurement of mean blood pressure (Hoe 140 group, 154 +/- 4 mm Hg; vehicle group, 139 +/- 4 mm Hg; p < 0.05). The antagonist blunted the increase in urinary volume induced by salt load and DOC in uninephrectomized rats, whereas it did not alter the increase in urinary sodium excretion. These results suggest that endogenous kinins do not play a major role in the regulation of normal blood pressure in sodium-loaded rats, whereas they may attenuate the hypertensive effect induced by long-term administration of mineralocorticoids and salt in uninephrectomized rats.
Renal nerves affect rate of achieving sodium balance in spontaneously hypertensive rats.
Authors: Greenberg S G , Enders C , Osborn J L
Published: June 2012

The spontaneously hypertensive rat (SHR) has an elevated efferent sympathetic nerve activity, suggesting that the renal handling of sodium and water may be altered. This study evaluated the renal neurogenic influence on the rate of achieving sodium balance in adult SHRs and Wistar-Kyoto (WKY) rats after either a step increase or step decrease in fixed sodium intake. Conscious, unrestrained rats with either innervated or denervated kidneys were initially placed on a low-sodium (0.3 mEq/d) or high-sodium (5.0 mEq/d) intake by intravenous infusion. Hourly urinary sodium excretion was determined 24 hours before and 72 hours after sodium intake had been increased from low to high or decreased from high to low. After either step change in fixed sodium intake, both innervated SHRs and innervated WKY rats achieved sodium balance within 24 hours. Similarly, the time course of achieving sodium balance was nearly identical between WKY rats with innervated and denervated kidneys after either switch in sodium intake. In SHRs receiving a step increase in sodium intake, both innervated and denervated kidneys increased urinary sodium excretion equally for 9 hours; however, at this time, innervated SHRs continued to increase sodium excretion rapidly, whereas denervated rats were delayed in a further response. Thus, innervated SHRs achieved sodium balance approximately 18 hours sooner than denervated SHRs. Differences in urinary sodium excretion did not result from concomitant changes in plasma renin activity or mean arterial pressure.(ABSTRACT TRUNCATED AT 250 WORDS)
A gene-environment interaction between inferred kallikrein genotype and potassium.
Authors: Hunt S C , Hasstedt S J , Wu L L , Williams R R
Published: June 2012

Urinary kallikrein excretion has been shown statistically to be partially determined by a major gene in large Utah pedigrees with the use of segregation analysis. A previous twin analysis of environmental factors influencing urinary kallikrein level showed that urinary potassium twin differences were strongly related to differences in urinary kallikrein. The present study uses 769 individuals in 58 Utah pedigrees to analyze the association of urinary potassium with urinary kallikrein within statistically inferred kallikrein genotypes. Fitting genotype-specific curves relating urinary kallikrein level to 12-hour urinary potassium amount within a major gene, polygene, and common environment model, we showed a significant statistical urinary potassium interaction with the inferred major gene for kallikrein (P = .0002). The heterozygotes (with a frequency of 50%) had a significant association between urinary kallikrein and potassium (slope, 0.51 +/- 0.04 SD), whereas there was no association with potassium in the low homozygotes, suggesting a genetic defect involving the kallikrein response to potassium. The model predicted that an increase in urinary potassium excretion of 0.8 SD above the mean in these pedigrees would be associated with high kallikrein levels in the heterozygotes similar to the high homozygotes. A decrease of 1.3 SD in urinary potassium excretion in heterozygous individuals was associated with kallikrein levels similar to the homozygous individuals with low kallikrein. Because in the steady state urinary potassium represents dietary potassium intake, this study suggests that an increase in dietary potassium intake in 50% of these pedigree members, estimated to be heterozygous at the kallikrein locus, would be associated with an increase in an underlying genetically determined low kallikrein level.(ABSTRACT TRUNCATED AT 250 WORDS)
Continuous versus intermittent angiotensin converting enzyme inhibition in renal hypertensive rats.
Authors: Battle T , Schnell C , Bunkenburg B , Heudes D , Wood J M , Ménard J
Published: June 2012

Converting enzyme inhibitors impair renal function of the kidney beyond a stenosis of the renal artery in humans and induce histological lesions in the clipped kidney of renal hypertensive rats. In two-kidney, one clip hypertensive rats, we compared the time course and magnitude of the biochemical effects of angiotensin converting enzyme inhibition on the plasma renin-angiotensin system, cardiac hypertrophy, renal lesions, and 24-hour blood pressure decrease induced by either intermittent angiotensin converting enzyme inhibition administration (benazepril PO, 10 mg/kg once a day, n = 93) or continuous administration (benazeprilat, 3 mg/kg per day via osmotic pumps, n = 92). Control rats (n = 91) received the drug vehicle intermittently or continuously. Mortality was significantly reduced by both intermittent (n = 3/93) and continuous (n = 3/92) inhibition compared with controls (n = 18/91) (P < .001). Changes in the plasma renin-angiotensin system and blood pressure were parallel. A continuous suppression of the activity of the plasma renin-angiotensin system was associated with a 24-hour decrease in blood pressure with continuous inhibition, whereas intermittent inhibition induced a similar fall in blood pressure only for the first hours after gavage.(ABSTRACT TRUNCATED AT 250 WORDS)
Possible genetic influence on the strength of human muscle nerve sympathetic activity at rest.
Authors: Wallin B G , Kunimoto M M , Sellgren J
Published: June 2012

Large reproducible interindividual differences in the strength of human muscle nerve sympathetic activity have been demonstrated previously without satisfactory explanation. We undertook the present study to investigate whether a genetic influence may be a factor of importance. Microneurographic recordings of sympathetic impulse traffic were made in the peroneal nerve in nine pairs of monozygotic male twins and eight pairs of age-matched male subjects without family relationship. The strength of the sympathetic activity was quantitated as number of sympathetic bursts per 100 heart beats and bursts per minute. Group mean values of muscle sympathetic activity, heart rate, and blood pressure were similar in the two groups. Intrapair differences (mean +/- SEM) of sympathetic activity were 5.4 +/- 1.7 bursts per 100 heart beats (1.7 +/- 0.5 bursts per minute) for the twins and 19.4 +/- 3.2 bursts per 100 heart beats (11.8 +/- 2.5 bursts per minute) for the control subjects (P < .01 for both). The degree of reproducibility between twins is similar to that reported previously between repeated recordings in the same subject. The finding may indicate that the strength of sympathetic outflow to muscle is controlled genetically. If so, we speculate that this may contribute to the heritability of blood pressure in both normotensive and hypertensive subjects.
Rested-state contractions and rest potentiation in spontaneously hypertensive rats.
Authors: Pérez G N , Petroff M V , Mattiazzi A
Published: June 2012

To gain further insight into the excitation-contraction coupling mechanisms in hypertrophy, we studied rested-state contractions, rest decay curves, and rest potentiation under different experimental conditions using papillary muscles of spontaneously hypertensive rats (SHR) and age-matched normotensive Wistar and Wistar-Kyoto (WKY) rats. Under constant stimulation at 1.1 Hz, contractility and relaxation were not significantly different in hypertensive when compared with normotensive animals. Rested-state contraction (the first beat after a rest interval of 15 minutes) increased to 159.2 +/- 23% and 123.5 +/- 7.5% of prerest values in Wistar and WKY rats, respectively, whereas in SHR it did not differ from prerest values (92.8 +/- 9.8%). Ryanodine, used to preferentially inhibit sarcoplasmic reticulum function, eliminated the differences in rested-state contractions observed between hypertensive and normotensive rats. Maximal rest potentiation (the first beat after a rest interval of 1 minute) was also significantly higher in Wistar and WKY rats than in SHR. These differences persisted at low extracellular Na+, when Ca2+ efflux via the Na(+)-Ca2+ exchanger was inhibited. Rest decay curves (the decay in contractility from maximal rest potentiation to rested-state contraction) showed a similar pattern in the three rat strains. The results suggest that the altered inotropic responses of the SHR arise from an alteration in calcium handling by the sarcoplasmic reticulum. Experiments on saponin-skinned trabeculae indicated that fractional calcium release induced by caffeine was significantly reduced in the SHR. We conclude that the altered inotropic response observed in SHR may reflect a diminished release of calcium from the sarcoplasmic reticulum.
Feasibility and efficacy of sodium reduction in the Trials of Hypertension Prevention, phase I. Trials of Hypertension Prevention Collaborative Research Group.
Authors: Kumanyika S K , Hebert P R , Cutler J A , Lasser V I , Sugars C P , Steffen-Batey L , Brewer A A , Cameron M , Shepek L D , Cook N R
Published: June 2012

Phase I of the Trials of Hypertension Prevention was a multicenter, randomized trial of the feasibility and efficacy of seven nonpharmacologic interventions, including sodium reduction, in lowering blood pressure in 30- to 54-year-old individuals with a diastolic blood pressure of 80 to 89 mm Hg. Six centers tested an intervention designed to reduce dietary sodium to 80 mmol (1800 mg)/24 h with a total of 327 active intervention and 417 control subjects. The intervention consisted of eight group and two one-to-one meetings during the first 3 months, followed by less-intensive counseling and support for the duration of the study. The mean net decrease in sodium excretion was 43.9 mmol/24 h at 18 months. Women had lower sodium intake at baseline and were therefore more likely to decrease to less than 80 mmol/24 h. Black subjects were less likely to decrease to less than 80 mmol/d, independent of sex or baseline sodium excretion. The mean (95% confidence interval) net decrease associated with treatment was -2.1 (-3.3, -0.8) mm Hg for systolic blood pressure and -1.2 (-2.0, -0.3) mm Hg for diastolic blood pressure at 18 months (both P < .01). Multivariate analyses indicated a larger systolic blood pressure effect in women (-4.44 versus -1.23 mm Hg in men), adjusted for age, race, baseline blood pressure, and baseline 24-hour urinary sodium excretion (P = .02). Dose-response analyses indicated an adjusted decrease of -1.4 mm Hg for systolic blood pressure and -0.9 mm Hg for diastolic blood pressure for a decrease of 100 mmol/24 h in 18-month sodium excretion. These results support the utility of sodium reduction as a population strategy for hypertension prevention and raise questions about possible differences in dose response associated with gender and initial level of sodium intake.
Developmental sensitivity to high dietary sodium chloride in borderline hypertensive rats.
Authors: Hunt R A , Tucker D C
Published: June 2012

The present study compared the postweaning blood pressures and body weights of borderline hypertensive rats exposed to a high (8%) sodium chloride maternal diet either from conception to weaning or only during the weaning period with borderline hypertensive rats consistently exposed to a normal (1%) sodium chloride maternal diet. Because the effects of early sodium chloride exposure may be most evident during a subsequent challenge, rats from each group were assigned to receive either an 8% sodium chloride or a 1% sodium chloride diet from 8 to 17 weeks of age. Exposure to an 8% sodium chloride diet from conception through weaning increased the adult blood pressure of borderline hypertensive rats compared with that of controls exposed to a 1% sodium chloride diet; exposure to an 8% sodium chloride diet only during weaning did not increase blood pressure. An 8% sodium chloride diet beginning at 8 weeks of age increased systolic blood pressure. The effects of perinatal and adult exposure to high dietary sodium chloride were additive. Behavioral observations and urinary electrolyte measures confirmed that pups exposed to an 8% sodium chloride diet during weaning ingested the high-sodium chloride diet. The blood pressure and heart rate response to autonomic nervous system ganglionic blockade were assessed at 17 weeks of age. Borderline hypertensive rats exposed to an 8% sodium chloride diet from conception through weaning showed an increased bradycardic response, but no difference in depressor response, to ganglionic blockade. These data suggest that the window of developmental sensitivity for modulation of blood pressure regulation by high dietary sodium chloride occurs during prenatal and early postnatal development.
Bias and variability in blood pressure measurement with ambulatory recorders.
Authors: Pannarale G , Bebb G , Clark S , Sullivan A , Foster C , Coats A J
Published: June 2012

This study sought to determine whether patient characteristics such as age, sex, blood pressure, and pulse pressure differently affect the accuracy of an oscillometric (SpaceLabs 90207) and a microphonic (TM2420 version 7) blood pressure monitor. Blood pressure recorded by two oscillometric and two microphonic ambulatory monitors was compared with simultaneous readings by two pairs of trained, blinded observers using random-zero sphygmomanometry. One hundred and eighteen subjects (53 men and 65 women, aged 17 to 94 years; systolic pressure, 89 to 211 mm Hg; diastolic, 44 to 116 mm Hg) were studied. There were no significant differences within each observer pair or between the two observer pairs as well as no correlation between interobserver differences and patient characteristics. The differences between the monitor and trained observers' readings were 2.8 +/- 9.9 mm Hg systolic and 3.9 +/- 6.8 mm Hg diastolic for the SpaceLabs and 5.0 +/- 5.2 mm Hg systolic and 3.4 +/- 6.1 mm Hg diastolic for the TM2420. Patient characteristics that predicted measurement error were defined by multiple regression. For oscillometry, systolic measurement error was highly correlated with systolic pressure, pulse pressure, and subject age. The diastolic error was significantly correlated with pulse pressure, diastolic pressure, and subject sex. For the oscillometric monitor, patient characteristics accounted for 36.6% of the variation of the systolic error and 34.7% of the variation of the diastolic error. For the microphonic monitor, only age correlated with diastolic error, and no significant correlations were seen with systolic error. Patient characteristics accounted for only 1.2% of the systolic and 8.9% of the diastolic error.(ABSTRACT TRUNCATED AT 250 WORDS)
Targeting gene expression to specific cardiovascular cell types in transgenic mice.
Authors: Hunter J J , Zhu H , Lee K J , Kubalak S , Chien K R
Published: June 2012

Transgenic techniques, which allow the introduction of exogenous genes into the genome of experimental animals, promise to bridge the gap between the in vitro observations made by molecular and cellular biologists on cardiac and vascular cells in tissue culture and the physiology and pathology of the whole organ system. One such application of these techniques is tissue targeting: by genetic manipulation to direct expression of a protein--such as a signaling peptide, a growth factor receptor, or an oncogene involved in cell growth--to a tissue where it normally would not be expressed (or where expression is tightly controlled) by fusing it to the transcriptional control sequences of another gene normally expressed in that tissue. In the cardiovascular system, regulatory sequences for cardiomyocyte-specific proteins, vascular endothelium-specific proteins, and smooth muscle-specific proteins can be used to target heterologous genes to their respective tissues in transgenic animals. The effects that such perturbations have on organ physiology and intracellular and intercellular communication can be observed by applying established physiological and molecular approaches. In this review, we highlight some tissue-specific genes from cardiac and vascular cell types whose regulatory sequences may be used to target heterologous proteins; we discuss neutral "reporter" proteins and signal transduction components as paradigms for the application of this technique; and we briefly touch on the potentials and pitfalls of transgenic approaches to molecular physiology.
Transgenic mouse models of vasopressin expression.
Authors: Grant F D , Reventos J , Kawabata S , Miller M , Gordon J W , Majzoub J A
Published: June 2012

Arginine vasopressin is a nine-amino acid neuropeptide hormone important in the regulation of water metabolism. It also may have a role in other physiological functions, such as blood pressure regulation and the response to stress. Whole animal studies have provided a good understanding of vasopressin physiology and regulation of the normal vasopressin gene, and in vitro cell culture studies have demonstrated important features of the intracellular regulation of vasopressin gene expression. Transgenic mice provide useful models for the study of the in vivo regulation of gene expression. Previously reported mouse lines transgenic with vasopressin gene constructs have not expressed the transgene in a tissue distribution similar to that detected for the endogenous mouse vasopressin gene. An 8.2-kb genomic construct of the rat vasopressin gene, including 3 kb each of 5' and 3' flanking sequences, has been used to develop a line of transgenic mice. These animals express the transgene in a tissue-specific manner, demonstrate appropriate osmotic regulation of transgenic vasopressin mRNA, and have normal water metabolism. Animals homozygous for the 8.2-kb transgene have increased basal plasma levels of vasopressin peptide but have no apparent change in basal water metabolism. The findings with this and other previously reported mouse lines transgenic for vasopressin constructs provide a basis for developing future transgenic lines to study the in vivo regulation of the vasopressin gene.
Double knockouts. Production of mutant cell lines in cardiovascular research.
Authors: Mortensen R M
Published: June 2012

Double knockouts by homologous recombination is a method for producing cell lines with an inactivating mutation in any desired gene. The biochemical analysis of genetically altered cell lines has been important in determining the function of specific proteins. Until recently, mutant cell lines have been produced by random mutagenesis and then selection for a particular phenotypic change. Recent technological advances in gene targeting by homologous recombination now enable the production of mutants in any desired gene. Diploid cells contain two copies or alleles of each gene encoded on an autosome (nonsex) chromosome. In most cases, both alleles must be inactivated to produce a phenotypic change in a mutant cell line, hence the term "double knockout." We and others have described the production of mutationally altered cell lines by inactivating both alleles by the production of two targeting vectors, two separate homologous recombination events, and selection. A simpler procedure, involving considerably less effort and time, has been used to inactivate several alpha-subunits of G proteins and other genes. This method facilitates the inactivation of more than one gene in a single cell line.
Coarctation induces alterations in basement membranes in the cardiovascular system.
Authors: Lipke D W , McCarthy K J , Elton T S , Arcot S S , Oparil S , Couchman J R
Published: June 2012

A coarctation hypertensive rat model was used to examine the effects of elevated blood pressure on basement membrane component synthesis by cardiac myocytes and aorta using immunohistochemistry and Northern blot analysis. Carotid arterial pressure increased immediately on coarctation, and left ventricular hypertrophy was maximal within 5 days. In immunohistochemical studies, fibronectin and laminin were increased and the basement membrane chondroitin sulfate proteoglycan decreased in both the subendothelial space and smooth muscle cell basement membranes of the aorta above the clip compared with controls, whereas only fibronectin was elevated in the aorta below the clip. No change in basement membrane staining intensity for the cardiac myocytes was observed. Alterations in steady-state mRNA levels for fibronectin and laminin in the aorta paralleled those observed by immunohistochemical analysis with regard to protein and tissue type affected as well as intensity of the changes. However, changes in mRNA levels (but not protein deposition) for perlecan and type IV collagen were also observed in aortas from hypertensive rats compared with controls. Increases in steady-state mRNA levels for all basement membrane components in the heart and vasculature peaked before maximal cardiac hypertrophy (5 days). These studies indicate that alterations in basement membrane component deposition in the hypertrophied vasculature occur at both transcriptional and translational levels and suggest that the cell attachment glycoproteins fibronectin and laminin may be important factors in the vascular response to elevated transmural pressure.
Antihypertensive therapy and adaptive mechanisms in peripheral ischemia.
Authors: Nelissen-Vrancken H J , Boudier H A , Daemen M J , Smits J F
Published: June 2012

In the present experiments the effect of long-term peripheral ischemia on the capillary of two hind limb skeletal muscles was investigated in spontaneously hypertensive rats. Furthermore, the effect of antihypertensive therapy on changes in capillarity and on the previously observed hyperreactivity of the ischemic vascular bed to vasoconstrictors was investigated in perfused hind limbs of rats after long-term treatment with the angiotensin I converting enzyme inhibitors captopril (0.5 mg/kg.h) or zabiciprilate (0.025 mg/kg.h), the angiotensin II type 1 receptor antagonist losartan (0.625 mg/kg.h), or the calcium antagonist felodipine (0.042 or 0.42 mg/kg.h). Skeletal muscle ischemia in the left hind limb was induced by partial ligation of the left common iliac artery. Long-term (4 weeks) ischemia increased significantly the capillary-to-fiber ratio in the soleus muscle, composed predominantly of type I fibers in spontaneously hypertensive rats, of the ischemic hind limb, whereas capillarity in the contralateral muscle was not affected. Furthermore, capillarity in the gastrocnemius muscle (type II muscle fiber part) of both the ischemic and contralateral hind limb did not change. Long-term treatment with the angiotensin I converting enzyme inhibitors during ischemia abolished the increase in the capillary-to-fiber ratio in the soleus muscle, whereas a comparable antihypertensive dose of felodipine had no effect. Greater blood pressure reductions by both losartan and felodipine prevented increases in capillarization in skeletal muscle ischemia. With respect to vascular hyperreactivity during ischemia, only treatment with losartan normalized reactivity of the ischemic vascular bed to vasoconstrictors.(ABSTRACT TRUNCATED AT 250 WORDS)
Caffeine attenuates the renal vascular response to angiotensin II infusion.
Authors: Brown N J , Ryder D , Nadeau J
Published: June 2012

Non-modulation has been proposed as an intermediate phenotype in human essential hypertension. The trait is characterized by blunted aldosterone and renal plasma flow responses to short-term angiotensin II (Ang II) infusion. Elevated tissue Ang II levels or decreased tissue adenosine levels could account for this decreased sensitivity to Ang II. In support of the latter possibility, endogenous adenosine has been shown to contribute to the renal vasoconstrictive response to Ang II in animals. We therefore tested the hypothesis that endogenous adenosine contributes to modulation of renal plasma flow in sodium-replete humans. We examined the effect of long-term administration of the adenosine receptor antagonist caffeine on baseline renal plasma flow and on the renal plasma flow response to short-term Ang II infusion in six salt-replete normotensive subjects in a single-blind, placebo-controlled study. para-Aminohippurate clearance was used to assess renal plasma flow. Ang II was infused in graded doses (0.3 to 3 ng/kg per minute) in the presence and absence of caffeine (250 mg PO TID for 7 days). Blood pressure, plasma renin activity, Ang II, electrolytes, and para-aminohippurate clearance were measured before and after each dose of Ang II. Caffeine did not alter either baseline blood pressure or the blood pressure response to Ang II but did increase baseline plasma renin activity from 0.72 +/- 0.09 to 1.42 +/- 0.26 ng angiotensin I/mL per hour (P = .01).(ABSTRACT TRUNCATED AT 250 WORDS)
Altered cardiorespiratory transfer in hypertension.
Authors: Novak V , Novak P , de Champlain J , Nadeau R
Published: June 2012

The effect of continuously slowing respiration (from 0.46 to 0.05 Hz, eg, from 30 to 3 breaths per minute) on cardiovascular variables was studied in 14 hypertensive patients and 16 normotensive subjects. Beat-to-beat time-frequency (Wigner) distributions were used for dynamic analysis of RR interval and systolic and diastolic pressures. Dominant breathing frequency at rest did not differ in hypertensive patients from the control group (0.21 versus 0.19 Hz). However, in the hypertensive group it was disturbed 34.4% of the time by slow breathing and apneas, which evoked transient blood pressure instability and increased spectral powers at low frequencies (range, 0.01 to 0.1 Hz). The nonrespiratory fluctuations (NONRFs) and respiratory fluctuations (RFs) in RR interval and NONRFs in systolic pressure were smaller in hypertensive patients (P < .001). In both groups, slowing of respiratory frequency from 0.46 to 0.05 Hz entrained RFs in the RR interval and systolic and diastolic pressures. RFs in the RR interval remained diminished in hypertensive patients (P < .001), but RFs in systolic pressure increased higher at maximum, corresponding to breathing frequencies from 0.07 to 0.09 Hz (P < .001). A dynamic cardiorespiratory index (ratio of RFs in RR interval and systolic pressure) was smaller (P < .01) in hypertensive patients than in normotensive subjects. Irregular breathing at rest was found in hypertensive patients. The transfer from respiration into RR interval was diminished, suggesting an impaired parasympathetic responsiveness in mild hypertension.
Effects of fludrocortisone on sympathetic nerve activity in humans.
Authors: Mion D , Rea R F , Anderson E A , Kahn D , Sinkey C A , Mark A L
Published: June 2012

Fludrocortisone reduces plasma norepinephrine in healthy humans, but forearm vascular and pressor responses to norepinephrine are potentiated. The effects of fludrocortisone on sympathetic nerve activity in healthy humans are not known. To investigate these effects we evaluated muscle sympathetic nerve activity, heart rate, and arterial pressure in 11 healthy volunteers during three protocols: (1) before and on day 7 of fludrocortisone (0.4 mg/d) treatment with ad libitum diet (n = 6); (2) before and on day 7 of fludrocortisone (0.4 mg/d) or placebo with a 150 mmol/24 h (mEq/24 h) sodium diet (n = 7); and (3) before and on day 2 of fludrocortisone (0.4 mg/d) or placebo with a 150 mmol/24 h (mEq/24 h) sodium diet (n = 4). Placebo did not alter any parameter.(ABSTRACT TRUNCATED AT 250 WORDS)
Glucocorticoid increases angiotensin II type 1 receptor and its gene expression.
Authors: Sato A , Suzuki H , Murakami M , Nakazato Y , Iwaita Y , Saruta T
Published: June 2012

Recently, we demonstrated that glucocorticoid potentiates inositol triphosphate production evoked by angiotensin II in vascular smooth muscle cells. To clarify this mechanism, we investigated the effects of dexamethasone on the modulation of angiotensin II type 1 receptor and on postreceptor mechanisms in vascular smooth muscle cells. The number of angiotensin II type 1 receptors began to increase after 12 hours' incubation with dexamethasone. After 48 hours, the Bmax value reached 27 +/- 3 fmol/mg protein in dexamethasone-treated cells and 15 +/- 3 fmol/mg protein in control cells. However, binding affinity did not change. A glucocorticoid antagonist, RU 38486, completely blocked these effects of dexamethasone. Also, to elucidate the effects of dexamethasone on postreceptor mechanisms, GTP analogue-induced inositol trisphosphate production in permeabilized cells was examined. Pretreatment with 1 mumol/L dexamethasone for 48 hours did not affect these inositol trisphosphate productions. Moreover, dexamethasone had no effect on the level of Gq alpha protein. Furthermore, steady-state levels of angiotensin II type 1 receptor messenger RNA were increased 2.2 +/- 0.3-fold after 30 minutes' exposure to 1 mumol/L dexamethasone and 7.8 +/- 0.4-fold after 24 hours. We conclude that glucocorticoid induced expression of the angiotensin II type 1 receptor gene and resulted in an increase in the number of angiotensin II type 1 receptors through the glucocorticoid-specific receptor, without significant effect on postreceptor systems in vascular smooth muscle cells.
C-type natriuretic peptide neuromodulates independently of guanylyl cyclase activation.
Authors: Trachte G J , Drewett J G
Published: June 2012

Of the four endogenous members of the natriuretic peptide family, only atrial natriuretic peptide has been demonstrated to have neuromodulatory effects. This study compares the neuromodulatory effects of atrial natriuretic peptide and a recently identified natriuretic peptide, C-type natriuretic peptide, in the rabbit isolated vas deferens. The ability of these peptides to alter cyclic nucleotide concentrations was assessed to determine the potential contribution of either cyclic AMP or cyclic GMP to the observed responses. The central hypothesis tested was that C-type natriuretic peptide modulates neurotransmission via an interaction with a guanylyl cyclase. C-type natriuretic peptide inhibited both purinergic and adrenergic neurotransmission in a concentration-dependent manner but failed to alter either cyclic GMP or cyclic AMP concentrations. Maximal inhibitory effects of C-type natriuretic peptide averaged 35 +/- 4% for purinergic and 49 +/- 7% for adrenergic neurotransmission. Atrial natriuretic peptide not only attenuated both purinergic and adrenergic neurotransmission but also increased cyclic GMP concentrations. C-type natriuretic peptide probably inhibited the release of the neurotransmitters because it failed to alter contractions to exogenously administered norepinephrine or ATP, the two putative neurotransmitters. These results suggest that the C-type natriuretic peptide receptor, guanylyl cyclase B, is not present in rabbit vas deferens and that C-type natriuretic peptide suppresses peripheral sympathetic neurotransmission independently of guanylyl cyclase activation.
Combined antihypertensive and lipid-lowering therapy in experimental glomerulonephritis.
Authors: Rubin R , Silbiger S , Sablay L , Neugarten J
Published: June 2012

We examined the interrelation between systemic hypertension, hyperlipidemia, and progressive renal injury in experimental glomerulonephritis. Induction of nephrotoxic serum nephritis in Sprague-Dawley rats led to systemic hypertension and hyperlipidemia. Four groups of rats were studied over a 16-week period: (1) untreated nephritic rats; (2) nephritic rats treated with hydralazine, reserpine, and lasix (AH); (3) nephritic rats treated with lovastatin (4 mg/kg) (Lova); and (4) nephritic rats treated with combined antihypertensive/lipid-lowering therapy (AH/Lova). Systolic blood pressure rose progressively in untreated rats (152 +/- 4 mm Hg at 16 weeks). Blood pressure was reduced by antihypertensive therapy (P < .001) (108 +/- 2 mm Hg in the AH group and 111 +/- 3 mm Hg in the AH/Lova group) but remained elevated in animals treated with lovastatin alone (P > .05) (156 +/- 3 mm Hg in the Lova group). Serum cholesterol rose progressively in untreated rats (3.70 +/- 0.85 mmol/L [143 +/- 33 mg/dL] at 16 weeks). The rise in serum cholesterol was prevented by lovastatin therapy (P < .001) (2.22 +/- 0.41 mmol/L [86 +/- 16 mg/dL] in the Lova group and 2.09 +/- 0.52 mmol/L [81 +/- 2 mg/dL] in the AH/Lova group) but not antihypertensive therapy (P > .05) (2.92 +/- 0.65 mmol/L [113 +/- 25 mg/dL] in the AH group). Proteinuria was reduced by antihypertensive therapy (P < .001) and lipid-lowering therapy (P < .05) (16-week values: 1.069 +/- 0.167 g/d in untreated rats, 0.663 +/- 0.164 g/d in the Lova group, 0.392 +/- 0.051 g/d in the AH group, and 0.176 +/- 0.035 g/d in the AH/Lova group).(ABSTRACT TRUNCATED AT 250 WORDS)
Dose-related effects of magnesium on myocardial function in the neonate.
Authors: Caspi J , Coles J G , Benson L N , Herman S L , Augustine J , Wilson G J
Published: June 2012

The antagonistic effects of magnesium ion as a calcium ion blocker may decrease calcium influx associated with ischemia. However, the effect of magnesium on the preischemic neonatal myocardium has not been investigated previously. The purpose of this study was to investigate the effects of the administration of increasing doses of magnesium on left ventricular performance in the neonate. We assessed left ventricular function (pressure-volume data obtained by the conductance catheter/micromanometer technique) in three groups (n = 6 in each) of newborn pigs (3 to 5 days old) differing with respect to magnesium concentrations. End-systolic elastance did not change during infusion in group A (magnesium = 1.2 mmol/L), whereas in groups B (magnesium = 8 mmol/L) and C (magnesium = 16 mmol/L) it decreased significantly (P < .05) to 67 +/- 6% and 44 +/- 8% of baseline, respectively. The decrease in end-systolic elastance was associated with a significant reduction in cardiac output (P < .05) and stroke work (P < .05) in group C. After administration of magnesium, end-systolic elastance returned to baseline in group B in contrast to group C (78 +/- 3% of baseline value, P < .05). The slope constant of the end-diastolic pressure-volume relation decreased significantly (P < .05) from the preinfusion baseline values of 0.42 +/- 0.08 mL-1 in group B and 0.46 +/- 0.05 mL-1 in group C to 0.3 +/- 0.04 and 0.26 +/- 0.03 mL-1, respectively, versus no change in group A.(ABSTRACT TRUNCATED AT 250 WORDS)
Pressure-flow curves reflect arteriolar responses in perfused rat hindquarters.
Authors: Prewitt R L , Reilly C K , Wang D H
Published: June 2012

Results from studies using pump-perfused rat hindquarters are consistent with increased wall-to-lumen ratios in resistance vessels of spontaneously hypertensive rats (SHR). However, in vivo measurements of cremaster arterioles have not shown increased wall-to-lumen ratios in SHR. To investigate this discrepancy, we studied three groups of male SHR and Wistar-Kyoto rats at 12 weeks of age. In the first two groups, the cremaster muscle was prepared to allow microscopic observation while the hindquarters were pump-perfused with increasing concentrations of norepinephrine in oxygenated Tyrode's solution. Both groups of SHR showed an increase in vasodilated resistance and elevated maximal vasoconstrictor response. In the first group, arterioles showed dose-dependent constriction that was greater in smaller arterioles but did not differ between hypertensive and normotensive rats. Vasodilated diameters of second-order arterioles were significantly smaller in the hypertensive rats. In the second group, servo-null pressures in the first-order arteriole showed that the microvessels contributed proportionally to the elevation in resistance in both SHR and normotensive rats. In the third group, first- and second-order arterioles were measured in vivo and histologically. Arteriolar diameters did not differ between SHR and normotensive rats with either method. In fixed sections the cross-sectional area of the media-intima was greater in the SHR. Therefore, data from the pump-perfused rat hindquarters accurately reflect vasoconstrictor responses of the arterioles, and in deference to in vivo measurements on arteriolar walls that include the adventitia, the increased response in the SHR can be explained by hypertrophy of the arteriolar medial-intimal area.
Potential problems with the random-zero sphygmomanometer.
Authors: Birkett N J
Published: June 2012

The random-zero sphygmomanometer is frequently used in epidemiologic and clinical research to increase the reliability and validity of blood pressure readings. However, recent reports have suggested that there is a correlation between the zero values of a random-zero sphygmomanometer and the zero-corrected blood pressure readings obtained. The design of the random-zero sphygmomanometer would suggest that the zero values and zero-corrected blood pressures should be uncorrelated. Hence, residual correlation might be of importance in determining the utility of this device. We have explored this relation in the Middlesex County Blood Pressure Survey, which collected data on 2725 randomly selected adults. Each person had three blood pressure readings taken with a random-zero sphygmomanometer operated by trained interviewers. There was a very weak but statistically significant correlation between the zero values and zero-corrected systolic blood pressure (r = .034, regression slope = -.10), but there was no statistically significant relation with zero-corrected diastolic blood pressure (r = .0003, slope = .0006). Both the correlations and regression slopes were higher for subjects over age 65 years. These data fail to confirm the observed correlations found by Kronmal et al. This discrepancy might be explained by differences in measurement technique, which could introduce a blood pressure-dependent skewing of the range of zero values. If confirmed, this effect would have no effect on the validity of the final blood pressure readings and hence would not need to be considered in decisions about the use of the random-zero sphygmomanometer.