bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of atrial natriuretic factor on cyclic nucleotides in rabbit proximal tubule.
Authors: Eitle E , Harris P J , Morgan T O
Published: June 2012

Atrial natriuretic factor induces renal sodium excretion by several mechanisms, including inhibition of angiotensin II-stimulated sodium reabsorption in the proximal tubule. In most tissues, the action of atrial natriuretic factor involves generation of the intracellular second messenger, cyclic GMP, but in the proximal tubule the presence of this signal transduction pathway has remained controversial. We used intrarenal arterial infusion of iron oxide followed by enzymatic dispersion and magnetic separation to obtain suspensions of rabbit kidney cortex enriched with either glomeruli or proximal tubules. When suspensions enriched with proximal tubules or preparations of microdissected proximal tubules were incubated with atrial natriuretic factor (1 mumol/L), cyclic GMP concentrations increased significantly. Addition of angiotensin II (1 mumol/L) together with atrial natriuretic factor had no significant effect on the stimulation of cyclic GMP accumulation observed with atrial natriuretic factor alone. Neither atrial natriuretic factor nor angiotensin II altered intracellular concentrations of cyclic AMP in tubule-enriched suspensions or microdissected tubules. We conclude that cyclic GMP acts as a second messenger for atrial natriuretic factor in rabbit proximal tubule. However, we found no evidence to support the view that alterations in intracellular cyclic AMP levels are involved in the proximal tubular actions of angiotensin II and have not been able to demonstrate that interactions between cyclic AMP and cyclic GMP underlie the antagonistic effect of atrial natriuretic factor on angiotensin II-stimulated proximal sodium transport.
Ontogeny of somatic angiotensin-converting enzyme.
Authors: Yosipiv I V , Dipp S , el-Dahr S S
Published: June 2012

Angiotensin-converting enzyme or kininase II (ACE-KII) plays a central role in the control of circulating and tissue levels of angiotensin II and kinins. Both peptides have been implicated in the regulation of renal function and growth during normal development. We tested the hypothesis that the developing rat kidney expresses ACE-KII mRNA transcripts and the active enzyme and evaluated whether the developmental expression of the ACE-KII gene is related to changes in circulating angiotensin II and tissue kallikrein. ACE-KII mRNA and enzymatic activity were low in the newborn kidney; peak expression occurred on days 15 and 20 of postnatal life (16-fold versus day 1). In extrarenal tissues, ACE-KII activity and mRNA levels were also low during the newborn period in the following order of abundance: lung > kidney > aorta > heart. The lung showed a higher age-related increase in active ACE-KII and mRNA abundance (15-fold) than heart and aorta (activity, 3- to 4-fold; mRNA, 6- to 10-fold). The developmental profile of ACE-KII correlated temporally with changes in circulating angiotensin II and tissue kallikrein. Plasma angiotensin II levels were 2.5-fold higher in newborn than adult rats, whereas renal and extrarenal kallikrein-like activity increased twofold to fivefold from birth to adulthood. These results demonstrate that the ACE-KII gene is developmentally regulated in a tissue-specific manner. Tissue kinin generation and degradation, reflected by kallikrein and ACE-KII activities, are coordinately regulated during development, whereas circulating angiotensin II and tissue ACE-KII change in a reciprocal manner.(ABSTRACT TRUNCATED AT 250 WORDS)
Dose-dependent effects of perindopril on blood pressure and small-artery structure.
Authors: Thybo N K , Korsgaard N , Eriksen S , Christensen K L , Mulvany M J
Published: June 2012

Long-term treatment of young spontaneously hypertensive rats (SHR) with angiotensin-converting enzyme (ACE) inhibitors has a persistent effect on blood pressure when treatment is withdrawn. The aim of the present study was to determine whether this effect could be mediated by the effect of treatment on resistance-artery structure. We determined the dose dependence of ACE-inhibitor therapy on blood pressure and small-artery structure during treatment and on the recovery of blood pressure when treatment was withdrawn. SHR (40 per group) were treated from age 4 to 24 weeks with one of three doses of perindopril (0.4, 0.8, or 1.5 mg/kg per day). Control groups were untreated SHR and Wistar-Kyoto rats. At 24 weeks, treatment was stopped and small arteries were taken from half of the rats from the mesenteric, femoral, cerebral, and coronary vascular beds for morphological and functional measurements. The blood pressure of the other half of the rats was followed until 36 weeks of age. During treatment, perindopril caused a dose-dependent reduction in blood pressure and in the media-lumen ratio and media area of the small arteries, whereas there was a dose-dependent increase in lumen diameter. The effect of treatment on the structure of arteries from the different vascular beds was homogeneous. Compared with values from Wistar-Kyoto rats, blood pressure normalization in SHR was not associated with full normalization of structure. After withdrawal of treatment, there was an inverse relation between perindopril dose and the persistent effect.(ABSTRACT TRUNCATED AT 250 WORDS)
Vasoconstriction with norepinephrine causes less forearm insulin resistance than a reflex sympathetic vasoconstriction.
Authors: Jamerson K A , Smith S D , Amerena J V , Grant E , Julius S
Published: June 2012

We used the insulin-perfused human forearm model to assess the effects of vasoconstriction induced with norepinephrine on the extraction of glucose in the forearm in two groups of healthy young volunteers. The norepinephrine findings were compared with a previously studied group in which vasoconstriction has been caused by reflex activation of the sympathetic nervous system. The aim of the study was to determine the relative importance of hemodynamic and receptor-mediated mechanisms of insulin resistance. Plasma insulin, arterial and venous glucose samples, and forearm blood flow were measured at 10-minute intervals during a 30-minute baseline, a 60-minute intra-arterial insulin infusion, and during 30 minutes of insulin infusion plus vasoconstriction. Group 1 (n = 14) had physiological vasoconstriction induced by inflation of bilateral thigh cuffs to 40 mm Hg to cause pooling of blood in the lower extremities and reflex vasoconstriction in the forearm; group 2 (n = 8) had intra-arterial infusion of norepinephrine to achieve the same degree of vasoconstriction as seen with inflation of thigh cuffs in group 1. Subjects in group 3 (n = 7) had infusion of intra-arterial norepinephrine to achieve a twofold increase in physiological vasoconstriction. With a physiological decrease in forearm blood flow (group 1), there was a 19% decrease in forearm blood flow resulting in a 23% reduction in glucose uptake in the forearm (P < .03). The same degree of reduction in forearm blood flow with a predominantly alpha-adrenergic agonist, norepinephrine (group 2), causes much less insulin resistance (a decrease in utilization of 13%) (P < .04).(ABSTRACT TRUNCATED AT 250 WORDS)
Chronic insulin administration elevates blood pressure in rats.
Authors: Meehan W P , Buchanan T A , Hsueh W
Published: June 2012

To examine the relative contribution of dietary glucose and infused insulin on blood pressure, we administered a 4% glucose supplement (in drinking water) with and without insulin infusion (15.8 nmol [2.2 U]/d via osmotic minipump) to male Sprague-Dawley rats (n = 6). We also tested the effect of the sympatholytic agent clonidine on rats receiving glucose and insulin. Blood pressure and heart rate were recorded via a novel radio telemetry system. Experiments were performed using a crossover design with three animals receiving treatment and three receiving vehicle for 10 days. After a 10-day washout period, the groups were reversed, and the experiment was repeated. Blood samples for insulin and glucose were drawn throughout the study. Systolic and diastolic blood pressures increased (by 6.0 +/- 1.2 and 2.2 +/- 1.3 mm Hg, respectively) in the animals given glucose alone in association with an increase in plasma insulin. However, blood pressure increased more rapidly and to a greater extent, systolic by 8.6 +/- 0.7 mm Hg and diastolic by 2.9 +/- 1.1 mm Hg, during the insulin treatment that raised plasma insulin above the levels observed during glucose feeding alone. Heart rate increased equally during both treatments. The average change in blood pressure and average plasma insulin during the infusion were correlated (r = .72, P = .009). Blood pressure dropped during the week following discontinuation of the insulin infusion. On rechallenge with insulin and glucose, blood pressure again rose and then decreased after termination of the insulin and glucose administration. Clonidine prevented the rise in blood pressure and heart rate.(ABSTRACT TRUNCATED AT 250 WORDS)
Role of brain ouabainlike compound in central nervous system-mediated natriuresis in rats.
Authors: Yamada K , Goto A , Nagoshi H , Hui C , Omata M
Published: June 2012

Intracerebroventricular infusion of artificial sodium-rich cerebrospinal fluid induces increases in blood pressure and urinary sodium excretion. To examine the role of brain ouabainlike compound in these central nervous system-mediated responses, we evaluated the effects of prior intracerebroventricular injection of the Fab fragments of digoxin-specific antibody (Digibind, 10 mg/mL, 10 microL) on changes in blood pressure and urinary sodium excretion after intracerebroventricular infusion of high-sodium (323 mmol/L, 150 microL/kg per 15 minutes) cerebrospinal fluid in anesthetized rats. Antiouabain action of Digibind was revealed by the inhibition of a contractile response to ouabain in guinea pig aorta. Similar significant increases in blood pressure were found in rats that received preinjection of Digibind (n = 14) compared with control rats that received injection of saline (n = 5) or normal sheep IgG (n = 8). In rats pretreated with Digibind the natriuretic responses to central high sodium were significantly diminished by 68% (P < .05) or 82% (P < .05) compared with rats treated with saline or normal IgG, respectively. In contrast, Digibind did not affect either pressor or natriuretic responses to intracerebroventricular angiotensin II (600 ng/30 microL per 10 minutes). These data indicate that Digibind significantly inhibits increases in renal sodium excretion in response to high central sodium and suggest that brain ouabainlike compound may be involved in central nervous system-mediated natriuresis with nonpressor mechanisms.
Anteroventral third ventricle lesions abolish lumbar sympathetic responses to insulin.
Authors: Muntzel M , Beltz T , Mark A L , Johnson A K
Published: June 2012

Insulin has been shown to increase sympathetic nerve activity. Because evidence shows that insulin acts within the central nervous system, we hypothesized that lesions of the anteroventral third ventricle region, an area rich in insulin receptors, would abolish sympathetic responses to hyperinsulinemia. We measured mean arterial pressure and lumbar sympathetic nerve activity in fasted, anesthetized sham-lesioned (n = 8) and lesioned (n = 8) rats before and after intravenous insulin infusion at 0.13 U/h during euglycemic clamp. Additional sham-lesioned (n = 10) and lesioned (n = 5) rats received vehicle infusion. Insulin-infused sham-lesioned rats had substantially greater increases in lumbar sympathetic nerve activity (+83 +/- 18%) than vehicle-infused sham-lesioned rats (+27 +/- 4%). Most importantly, insulin-infused lesioned rats had increases in sympathetic activity (+32 +/- 11%) that were no greater than lesioned rats receiving vehicle (+23 +/- 16%). Blood pressure was not altered by insulin or vehicle. To test the possibility that lesions of the anteroventral third ventricle region nonspecifically suppress sympathetic excitatory responses, we evaluated reflex increases in lumbar sympathetic activity to nitroglycerin in sham-lesioned (n = 5) and lesioned (n = 8) rats. Rats with lesions and sham lesions showed comparable increases in lumbar nerve activity during nitroglycerin-induced hypotension. In summary, increases in sympathetic nerve activity to intravenous insulin infusion are abolished by anteroventral third ventricle lesions. These data indicate that the integrity of this brain region is necessary for activation of lumbar sympathetic nerve activity by systemic administration of insulin.
Glucose intolerance as a predictor of hypertension in pregnancy.
Authors: Solomon C G , Graves S W , Greene M F , Seely E W
Published: June 2012

Insulin resistance is associated with and may be causal in essential hypertension, but the relation between insulin resistance and hypertension arising de novo in pregnancy is unclear. Transient hypertension of pregnancy (new-onset nonproteinuric hypertension of late pregnancy) is associated with a high risk of later essential hypertension and thus may have similar pathophysiology. To assess the association between glucose intolerance and subsequent development of proteinuric and nonproteinuric hypertension in pregnancy in women without underlying essential hypertension or overt glucose intolerance, we performed a retrospective case-control study comparing glucose levels on routine screening for gestational diabetes mellitus among women subsequently developing hypertension. Women who developed hypertension in pregnancy (n = 97) had significantly higher glucose levels on 50-g oral glucose loading test (P < .01) and a significantly higher frequency of abnormal glucose loading tests (> or = 7.8 mmol/L) (P < .01) than women who remained normotensive (n = 77). Relative glucose intolerance was particularly common in women who developed nonproteinuric hypertension. Women who developed hypertension also had greater prepregnancy body mass index (P < or = .0001) and baseline systolic and diastolic blood pressures (P < or = .0001 for both), although all subjects were normotensive at baseline by study design. However, after adjustment for these and other potential confounders, an abnormal glucose loading test remained a significant predictor of development of hypertension (P < .05) and, specifically, nonproteinuric hypertension in pregnancy (P < .01). Among a subgroup of women in whom insulin levels were also measured (n = 80), there was a nonsignificant trend toward higher insulin levels in women developing hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)
Clonidine reverses the slowly developing hypertension produced by low doses of angiotensin II.
Authors: Gorbea-Oppliger V J , Fink G D
Published: June 2012

We used the centrally acting sympatholytic drug clonidine to evaluate neurogenic pressor activity in rats made hypertensive by chronic intravenous infusion of a low dose (4.0 ng.min-1) of angiotensin II (Ang II). Male Sprague-Dawley rats were instrumented with arterial and venous catheters and then housed in metabolic cages for the duration of the experiment. After 3 days of recovery from surgery, daily measurements were begun of mean arterial pressure, heart rate, water balance, and urinary electrolyte excretion. After 3 days of control measurements rats received either Ang II (4.0 ng.min-1 IV, n = 5) or saline vehicle (n = 4) continuously over a 15-day period. After the Ang II and vehicle infusions were ended, measurements were made during 3 days of recovery. On days 2, 7, and 12 of the experimental infusion period, clonidine hydrochloride was administered as a bolus (10.0 micrograms.kg-1 IA). The resulting changes in mean arterial pressure and heart rate were assessed over a 6-hour period. Fluid measurements were evaluated on a daily basis. In rats receiving only vehicle, clonidine produced no significant changes in any variable at any time. In rats given Ang II, mean arterial pressure increased from a control value (mean +/- SEM) of 106 +/- 1 mm Hg to 135 +/- 6, 139 +/- 6, and 148 +/- 4 mm Hg on days 2, 7, and 12, respectively. The antihypertensive response to clonidine after 6 hours on days 2, 7, and 12 of the Ang II infusion in these rats was -18 +/- 8, -16 +/- 5, and -23 +/- 9 mm Hg, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
Insulin-induced Ca2+ transport is altered in vascular smooth muscle cells of spontaneously hypertensive rats.
Authors: Touyz R M , Schiffrin E L
Published: June 2012

Intracellular calcium may be a mediator of insulin action in vascular smooth muscle cells. This study investigates effects of physiological concentrations of insulin on intracellular free calcium concentrations in primary unpassaged vascular smooth muscle cells derived from 3- and 17-week-old normotensive rats (Wistar and Wistar-Kyoto) and spontaneously, hypertensive rats (SHR). Underlying mechanisms responsible for insulin-evoked calcium responses were also studied. Basal calcium was significantly higher in 17-week SHR cells (134 +/- 8 nmol/L) compared with cells from Wistar-Kyoto (98 +/- 12 nmol/L) and Wistar (99 +/- 10 nmol/L) rats. Insulin (70 microU/mL) significantly increased calcium in all cells. Responses from 3-week rat cells were similar. The increase was amplified in 17-week SHR cells (177 +/- 7 nmol/L) compared with Wistar-Kyoto (130 +/- 14 nmol/L) and Wistar (132 +/- 16 nmol/L) cells. Genistein (0.1 mumol/L) and tyrphostin 23 (0.1 mumol/L) (tyrosine kinase inhibitors) completely abolished insulin-induced calcium effects. Stimulatory effects of insulin were significantly inhibited by 0.1 mumol/L diltiazem, staurosporine, calphostin C, and thapsigargin. The inhibitory effects of diltiazem (calcium channel antagonist) and the protein kinase C inhibitors staurosporine and calphostin C were significantly lower in cells from hypertensive compared with those from normotensive rats. Calcium recovery after insulin administration was delayed in SHR cells. In conclusion, insulin increases vascular smooth muscle cell calcium concentrations, possibly via calcium channel activation, protein kinase C-mediated mechanisms, and intracellular calcium mobilization. Alterations of these pathways as well as impaired calcium recovery to baseline may be associated with increased insulin-sensitive calcium responses in cells from SHR.(ABSTRACT TRUNCATED AT 250 WORDS)
Increased activity of the Mg2+/Na+ exchanger in red blood cells from essential hypertensive patients.
Authors: Picado M J , de la Sierra A , Aguilera M T , Coca A , Urbano-Márquez A
Published: June 2012

Epidemiological, clinical, and experimental evidence suggests a relation between Mg2+ metabolism and essential hypertension. The aim of the present study was the detection of abnormalities of the erythrocyte Mg2+/Na+ exchanger in essential hypertensive patients. We studied 66 untreated essential hypertensive patients and 36 normotensive control subjects. Maximal efflux rates of total Mg2+ efflux and the Na(+)-dependent and Na(+)-independent components of Mg2+ efflux were determined in Mg(2+)-loaded red blood cells. Mg2+/Na+ exchanger was calculated as the Na(+)-dependent component of the Mg2+ efflux. Mean values of Mg2+/Na+ exchanger were clearly elevated in hypertensive subjects with respect to normotensive control subjects [184.7 +/- 15.7 versus 84.4 +/- 6 mumol(L.cell.h)-1; P < .001]. This elevation was due primarily to the increased total Mg2+ efflux [324.2 +/- 21.9 versus 257.9 +/- 17.3 mumol(L.cell.h)-1; P < .05], whereas the Na(+)-independent component was not significantly different between the groups [154.5 +/- 11.8 versus 173.4 +/- 15.5 mumol(L.cell.h)-1; P = NS]. Moreover, total erythrocyte Mg2+ content was slightly reduced in hypertensive patients with respect to normotensive control subjects (1.84 +/- 0.04 versus 2.07 +/- 0.04 mmol/L.cell; P < .001). Using the 99% confidence limits of the normotensive population as the normal range, 30 (45.5%) hypertensive subjects showed values of Mg2+/Na+ exchanger higher than 160 mumol(L.cell.h)-1. The Mg2+/Na+ exchanger was inversely correlated with basal intraerythrocyte Mg2+ content (r = -.323; P = .001). From a clinical point of view, we found a positive correlation between diastolic blood pressure values and Mg2+/Na+ exchanger (r = .246; P < .05) in the sample of essential hypertensive patients.(ABSTRACT TRUNCATED AT 250 WORDS)
Hypertension induced by a nonpressor dose of angiotensin II in kininogen-deficient rats.
Authors: Majima M , Mizogami S , Kuribayashi Y , Katori M , Oh-ishi S
Published: June 2012

Brown Norway Katholiek rats with very low levels of plasma kininogens excreted a much smaller amount of kinin in the urine than normal rats of the same strain. The systolic blood pressure of 7-week-old kininogen-deficient rats (132 +/- 2 mmHg, n = 7) was not different from that of normal rats. Angiotensin II (Ang II) (20 micrograms/d SC) from 7 weeks of age for 2 weeks with a micro-osmotic pump caused significant increases in blood pressure (181 +/- 5 mm Hg, n = 7, 9 weeks old) in the deficient rats, although the same treatment induced no blood pressure increase in the normal rats. Also during this period, the deficient rats had significantly higher heart rates, tended to excrete less urinary sodium, and showed significantly higher sodium levels in serum, erythrocytes, and cerebrospinal fluid compared with the normal rats. Ang II increased urinary excretion of aldosterone in both deficient and normal rats (P < .05). Spironolactone treatment (50 mg/kg per day) for 7 days in deficient rats restored blood pressure and heart rate to normal levels and significantly reduced sodium levels in erythrocytes and cerebrospinal fluid. Subcutaneous infusion of bovine low-molecular-weight kininogen with an osmotic pump in Ang II-treated deficient rats induced significant reductions in blood pressure, heart rate, and erythrocyte sodium levels. By contrast, subcutaneous infusion of the bradykinin antagonist Hoe 140 in Ang II-treated normal rats induced a hypertensive response in parallel with significant increases in heart rate and erythrocyte sodium level. These results suggest that the lack of kinin generation observed in the kininogen-deficient rats may cause the hypertensive response during the administration of a nonpressor dose of Ang II mainly through sodium retention probably caused by aldosterone release.
Differential regional hemodynamic effects of corticotropin in conscious sheep.
Authors: Bednarik J A , May C N
Published: June 2012

The regional hemodynamic effects of 5 days of intravenous infusion of corticotropin (ACTH) (5 micrograms/kg per day) were examined in conscious sheep (n = 8). Mean arterial pressure increased from 81 +/- 2 to 93 +/- 3 mm Hg (P < .001) on day 2 of ACTH and remained at this level during the infusion. Cardiac output increased from 5.13 +/- 0.19 to 6.06 +/- 0.33 L/min (P < .01) because of an increase in stroke volume from 65 +/- 4 to 79 +/- 8 mL per beat (P < .01); heart rate remained unchanged. ACTH did not alter total peripheral conductance but had differential effects on regional conductances. Mesenteric conductance fell from 5.8 +/- 0.2 to a minimum of 4.9 +/- 0.3 (mL/min)/mm Hg (P < .05), and renal conductance increased from 3.5 +/- 0.3 to 4.6 +/- 0.3 (mL/min)/mm Hg (P < .001). There was a small increase in iliac conductance (P < .05) and no change in coronary conductance. Mesenteric and iliac conductances fell progressively over 24 to 48 hours, whereas renal conductance increased rapidly after 3 hours of ACTH, reaching a maximum after 6 hours. Renal blood flow was increased during ACTH infusion from 278 +/- 18 to 403 +/- 23 mL/min (P < .001); mesenteric blood flow was unchanged; there was a small increase in iliac blood flow (P < .01); and coronary blood flow increased (P < .05), paralleling the change in cardiac output.(ABSTRACT TRUNCATED AT 250 WORDS)
How should diastolic blood pressure be defined during pregnancy?
Authors: Blank S G , Helseth G , Pickering T G , West J E , August P
Published: June 2012

Controversy exists concerning the most accurate method for defining diastolic blood pressure in pregnancy. Both disappearance (phase V) and muffling (phase IV) of Korotkoff sounds have been advocated. We previously reported an objective noninvasive method for measuring blood pressure, called K2 analysis, which in nonpregnant subjects was not different from intra-arterial diastolic blood pressure and was more accurate than the auscultatory technique. For determination of the relation of diastolic blood pressure (using K2) in pregnancy with muffling and disappearance of Korotkoff sounds, 58 women (42 hypertensive, 16 normotensive) underwent 556 blood pressure evaluations in the supine position at various stages of pregnancy. K2 analysis was compared with simultaneous auscultation by two observers, A1 (n = 461 observations; 364 hypertensive, 97 normotensive) and A2 (n = 415; 316 hypertensive, 99 normotensive). Overall, muffling was detected by observer A1 52.9% (244/461) and by observer A2 44.3% (184/415) of the time. When evaluated by clinical classification, muffling was found by both observers to be present less often in the hypertensive group (A1: 47.5%; A2: 37.3%) compared with the normotensive group (A1: 73.2%; A2: 66.7%) (P < .0001). When both observers were present (n = 348), they agreed that muffling was present only 112 times. Disappearance of sound was detected by both observers 98.3% (A1: 453/461; A2: 408/415) of the time. Muffling overestimated K2 diastolic pressure by 7 to 10 mm Hg, whereas there was no statistically significant difference between disappearance and K2 diastolic pressure for hypertensive subjects and a 2.5-mm Hg underestimation of K2 diastolic pressure for normotensive subjects.(ABSTRACT TRUNCATED AT 250 WORDS)
Confirmation of mutant alpha 1 Na,K-ATPase gene and transcript in Dahl salt-sensitive/JR rats.
Authors: Ruiz-Opazo N , Barany F , Hirayama K , Herrera V L
Published: June 2012

As the sole renal Na,K-ATPase isozyme, the alpha 1 Na,K-ATPase accounts for all active transport of Na+ throughout the nephron. This role in renal Na+ reabsorption and the primacy of the kidney in hypertension pathogenesis make it a logical candidate gene for salt-sensitive genetic hypertension. An adenine (A)1079-->thymine (T) transversion, resulting in the substitution of glutamine276 with leucine and associated with decreased net 86Rb+ (K+) influx, was identified in Dahl salt-sensitive/JR rat kidney alpha 1 Na,K-ATPase cDNA. However, because a Taq polymerase chain reaction amplification-based reanalysis did not detect the mutant T1079 but rather only the wild-type A1079 alpha 1 Na,K-ATPase allele in Dahl salt-sensitive rat genomic DNA, we reexamined alpha 1 Na,K-ATPase sequences using Taq polymerase error-independent amplification-based analyses of genomic DNA (by polymerase allele-specific amplification and ligase chain reaction analysis) and kidney RNA (by mRNA-specific thermostable reverse transcriptase-polymerase chain reaction analysis). We also performed modified 3' mismatched correction analysis of genomic DNA using an exonuclease-positive thermostable DNA polymerase. All the confirmatory test results were concordant, confirming the A1079-->T transversion in the Dahl salt-sensitive alpha 1 Na,K-ATPase allele and its transcript, as well as the wild-type A1079 sequence in the Dahl salt-resistant alpha 1 Na,K-ATPase allele and its transcript. Documentation of a consistent Taq polymerase error that selectively substituted A at T1079 (sense strand) was obtained from Taq polymerase chain reaction amplification and subsequent cycle sequencing of reconfirmed known Dahl salt-sensitive/JR rat mutant T1079 alpha 1 cDNA M13 subclones. This Taq polymerase error results in the reversion of mutant sequence back to the wild-type alpha 1 Na,K-ATPase sequence. This identifies a site- and nucleotide-specific Taq polymerase misincorporation, suggesting that a structural basis might underlie a predisposition to nonrandom Taq polymerase errors.
Acute and chronic calcium antagonist treatment elevates sympathetic activity in primary hypertension.
Authors: Lindqvist M , Kahan T , Melcher A , Hjemdahl P
Published: June 2012

Eleven men with mild to moderate primary hypertension were studied at rest and during mental stress before and during intravenous infusion of the calcium antagonist felodipine. Eight of them were restudied during long-term treatment (extended-release felodipine, 10 mg daily). For comparison, 10 normotensive control subjects were studied with the short-term protocol. Heart rate, cardiac output, central cardiovascular pressures, and forearm blood flow were registered. Arterial and venous sampling was performed. Norepinephrine spillovers to arterial plasma and from the forearm were assessed with the use of radiotracer methodology. In the hypertensive patients, felodipine lowered mean arterial blood pressure acutely by 8% (P < .01). Systemic vascular resistance decreased by 22% (P < .001), cardiac output increased by 20% (P < .01), and norepinephrine spillover to arterial plasma increased by 61% (P < .001). Forearm vascular resistance fell by 30% (P < .001), but norepinephrine overflow from the forearm increased by 115% (P < .001). These forearm responses were not seen in normotensive subjects despite similar systemic responses to felodipine infusion. After 8 weeks of treatment, mean arterial pressure decreased to 15% below baseline (P < .001), cardiac output returned toward pretreatment levels, and systemic vascular resistance remained low. Forearm blood flow returned toward basal levels, but forearm vascular resistance remained lowered. Total body and forearm norepinephrine spillover values were as elevated as in the acute situation. The hemodynamic "defense reaction" and the sympathoadrenal response to mental stress were essentially unaffected by felodipine. Stress-induced small elevations of neuropeptide Y-like immunoreactivity persisted during felodipine. Thus, the vasodilatation induced by felodipine elicits sympathetic counterregulation, which persists in the long term with respect to peripheral and total sympathetic activities, despite resetting of the baroreflex control of heart rate.
Endogenous angiotensin II enhances phenylephrine-induced tone in hypertensive rats.
Authors: Qiu H Y , Henrion D , Levy B I
Published: June 2012

Subthreshold concentrations of angiotensin II (Ang II) potentiate agonist-induced tone in a variety of blood vessels. We measured in vivo the mesenteric artery diameter and blood flow in 12-week-old normotensive Wistar-Kyoto (WKY) rats (n = 20) and spontaneously hypertensive rats (SHR, n = 20); systemic blood pressure was monitored continuously. Phenylephrine (10 mumol/L) superfused on the exteriorized mesentery reduced arterial diameter from 480 +/- 40 to 256 +/- 18 microns (P < .05) in WKY rats and from 562 +/- 26 to 273 +/- 7 microns (P < .05) in SHR, whereas blood flow was lowered by 77% in WKY rats and 76% in SHR (P < .05 in both strains). Topical superfusion of an angiotensin-converting enzyme inhibitor (perindoprilat, 10 and 100 mumol/L) attenuated the phenylephrine-induced decrease in diameter and blood flow in both strains (P < .05). The Ang II type 1 receptor blocker losartan (10 mumol/L) attenuated the phenylephrine-induced decrease in diameter and blood flow in both strains (P < .05). The relaxing effect of losartan was significantly accentuated by the addition of perindoprilat (10 mumol/L) to the superfusate (P < .05 in both strains). Systemic blood pressure was unaffected by the topical application of phenylephrine (10 mumol/L), perindoprilat (10 or 100 mumol/L), or losartan (10 mumol/L). We conclude that phenylephrine-induced tone impairment by angiotensin-converting enzyme inhibition and Ang II type 1 receptor blockade in vivo probably reflects the role of endogenous Ang II in the potentiation of the adrenergic response during the control of vascular tone. This role is identical in both normotensive and hypertensive rats.
Mechanism of vasoconstriction induced by chronic inhibition of nitric oxide in rats.
Authors: Bank N , Aynedjian H S , Khan G A
Published: June 2012

Either acute or chronic inhibition of nitric oxide synthesis by L-arginine analogues results in increases in mean arterial pressure and reductions in renal blood flow. The role of endogenous vasoconstrictors in mediating these effects is not entirely clear. In the present study, nitric oxide was inhibited in male Sprague-Dawley rats by oral administration of nitro-L-arginine for 3 weeks. At the end of this time, mean arterial pressure was 30 to 40 mm Hg higher than in normal controls, renal blood flow and glomerular filtration rate were 25% to 30% lower, and renal vascular resistance was markedly increased. Intravenous infusion of receptor antagonists for angiotensin II, thromboxane, epinephrine, and endothelin-1 had no significant effect on the hypertension. Inhibition of prostaglandin synthesis and furosemide-induced diuresis in the presence of angiotensin blockade also had no effect on blood pressure. Renal vascular resistance was also unaffected by these interventions, except that saralasin did reduce renal resistance in both control and nitric oxide-inhibited groups. However, the absolute level of renal vascular resistance remained higher in the latter group. Calcium channel blockade partially corrected blood pressure and renal resistance, but the levels remained significantly higher than in control animals. The findings are consistent with the view that the increase in vascular smooth muscle tone caused by inhibition of nitric oxide synthesis cannot be accounted for by overexpression of common endogenous vasoconstrictors. Rather, the generalized increase in vascular smooth muscle tone appears to be due to a direct effect of reduced nitric oxide availability, which may lead to an increase in intracellular calcium concentration or sensitivity.
Alterations in flow-dependent vasomotor tone in spontaneously hypertensive rats.
Authors: Qiu H Y , Henrion D , Levy B I
Published: June 2012

We studied the effect of endothelium on the flow-induced response of conductance arteries and the resistance arteriolar network in an in situ model of perfused mesenteric artery in normotensive Wistar-Kyoto and spontaneously hypertensive rats. The mesenteric network was perfused with a Tyrode's albumin solution. The diameter of a conductance mesenteric artery was measured using a video camera system, and mesenteric pressure was recorded in a collateral artery. The preparation was perfused at 0.2, 2, and 4 mL/min, and flow-diameter-pressure relations were established (1) under control conditions, (2) during local inhibition of nitric oxide synthesis by topical application of N omega-nitro-L-arginine methyl ester (L-NAME) (1 mmol/L), and (3) after endothelium removal (CO2 drying). In normotensive rats, L-NAME decreased conductance artery diameter by 12 +/- 2% (P < .01) at 0.2 mL/min and 3.3 +/- 1.9% (P < .05) at 2 mL/min. In hypertensive rats, L-NAME did not modify mesenteric diameter. Endothelium removal markedly increased arterial resistance in both strains and decreased conductance artery diameter in normotensive rats (10.3 +/- 3%, P < .05 at 0.2 mL/min and 4.2 +/- 2%, P < .05 at 2 mL/min) but not in hypertensive rats. The present study suggests that the endothelium plays a similar role in the control of mesenteric resistance in both strains and that there is a significant diameter-flow dependency affected by both endothelium removal and inhibition of nitric oxide synthesis in conductance mesenteric arteries from normotensive but not from hypertensive rats.
Agonist-induced phosphorylation of the vascular type 1 angiotensin II receptor.
Authors: Kai H , Griendling K K , Lassègue B , Ollerenshaw J D , Runge M S , Alexander R W
Published: June 2012

Agonist-induced receptor phosphorylation plays a role in transmembrane signal transduction systems. Although the cDNA for the rat vascular type 1 angiotensin II receptor (AT1AR) encodes a G protein-coupled receptor with several potential phosphorylation sites for serine/threonine and tyrosine kinases, little is known about the phosphorylation of this receptor. The aim of this study was to determine the effects of angiotensin II (Ang II) on phosphorylation of the AT1AR in rat aortic vascular smooth muscle cells. Using [32P]orthophosphate-labeled cells, immunoprecipitates with anti-AT1AR antibody revealed a labeled band of molecular weight 52 kD, corresponding to the Ang II receptor. Ang II induced a rapid and significant increase in phosphorylation of the Ang II receptor, with a peak at 20 minutes. Phosphoamino acid analysis showed that the major phosphoamino acid is serine, in both the basal and Ang II-stimulated states. Constitutive and agonist-stimulated tyrosine phosphorylation is also observed to a lesser extent. Immunoblotting of anti-phosphotyrosine immunoprecipitates with anti-AT1AR antibody showed that Ang II caused a delayed tyrosine phosphorylation of the receptor with a peak at 20 minutes in a dose-dependent manner. Forskolin increased total phosphorylation of AT1AR but had no effect on tyrosine phosphorylation. Neither phorbol 12-myristate-13-acetate nor ionomycin altered receptor phosphorylation. These findings suggest that Ang II induces the phosphorylation of its own G protein-coupled receptor through both serine and tyrosine kinases and raise the possibility that phosphorylation of the AT1AR is an important regulator of receptor function.
Impaired cardiovascular reflexes precede deoxycorticosterone acetate-salt hypertension.
Authors: Veelken R , Hilgers K F , Ditting T , Leonard M , Mann J F , Geiger H , Luft F C
Published: June 2012

We hypothesized that impaired cardiopulmonary reflexes but not altered baroreceptor reflexes precede deoxycorticosterone acetate (DOCA)-salt hypertension. Uninephrectomized rats were given either DOCA and 0.9% NaCl as drinking water, 0.9% NaCl alone, or tap water. We measured mean blood pressure, heart rate, and renal sympathetic nerve activity. After 8 days, mean blood pressure was not different in DOCA-salt and control rats. Volume-sensitive cardiopulmonary reflexes were tested by intravenous volume loading with saline (10% body weight in 15 minutes), which decreased renal sympathetic nerve activity without changing mean blood pressure or heart rate. This response was blunted in DOCA-salt rats. Chemosensitive cardiopulmonary reflexes were tested by 15-minute infusions of the serotonin 5-HT3 agonist phenylbiguanide, which decreased renal sympathetic nerve activity without changing mean blood pressure or heart rate. Sustained decreases in renal sympathetic nerve activity occurred during phenylbiguanide infusion in controls but were blunted over time in DOCA-salt rats. The arterial baroreflex responses to graded infusions of methoxamine and nitroprusside were analyzed by sigmoidal curve fitting. There were no differences in gain of renal sympathetic nerve activity or heart rate between the groups. Thus, DOCA-salt rats exhibit impaired cardiopulmonary reflexes before the onset of hypertension; the volume-sensitive reflexes are more severely affected than chemosensitive reflexes. The arterial baroreceptor reflex is unaltered. The decreased sensitivity of cardiopulmonary reflexes may contribute to DOCA-salt hypertension.
Chronic administration of aldosterone depresses baroreceptor reflex function in the dog.
Authors: Wang W
Published: June 2012

In a previous study it was shown that acute perfusion of aldosterone into the isolated carotid sinus decreased baroreceptor activity. The aim of the present study was to determine whether chronic, systemic administration of aldosterone also depresses baroreflex function. In six conscious dogs, the baroreflex was determined before and 10 days after an osmotic minipump containing aldosterone (100 micrograms/kg in 2 mL) was implanted. The slope of the relation between systolic arterial pressure and heart rate was significantly blunted after aldosterone administration (9.1 +/- 0.7 versus 13.3 +/- 1.2 for nitroglycerin, P < .01; 23.4 +/- 5.0 versus 40.1 +/- 5.0 for phenylephrine, P < .01). Baroreflex slopes did not change in a sham group (minipump with saline) and an aldosterone plus spironolactone (600 mg/d) group. Plasma aldosterone levels were significantly elevated after the aldosterone minipump was implanted (443 +/- 72 versus 37 +/- 11 pg/mL, P < .001). Mean arterial pressure was not significantly increased after aldosterone (106.5 +/- 3.8 versus 100.4 +/- 2.6 mm Hg, P = .2). On the 10th day after aldosterone or saline infusion, an acute experiment was carried out. Single baroreceptor fibers were recorded from the carotid sinus nerve. Compared with the sham group, the threshold was significantly elevated in the aldosterone group (111.3 +/- 2.1 versus 85.8 +/- 2.8 mm Hg), and the peak discharge rate was markedly decreased (32.5 +/- 1.5 versus 54.7 +/- 2.5 spikes per second, P < .01). The depressed baroreceptor function could be partially restored after a bolus injection of the Na+,K(+)-ATPase inhibitor ouabain (5 micrograms/kg i.v.).(ABSTRACT TRUNCATED AT 250 WORDS)
Beta-adrenergic neuroeffector mechanisms in cardiac hypertrophy of renin transgenic rats.
Authors: Böhm M , Moll M , Schmid B , Paul M , Ganten D , Castellano M , Erdmann E
Published: June 2012

We studied neuroeffector defects in hypertrophied myocardium of hypertensive transgenic rats harboring the mouse Ren-2d gene. In transgenic rats, epinephrine and neuropeptide Y concentrations were reduced. A heterologous desensitization of adenylyl cyclase was observed, which was accompanied by a downregulation of beta 1-adrenergic receptors, an increase of inhibitory G protein alpha-subunits, and a mildly depressed catalyst activity of adenylyl cyclase, whereas the bioactivity of stimulatory G protein alpha-subunits and beta 2-adrenergic receptors was unchanged. Desensitization of adenylyl cyclase was accompanied by a reduced positive inotropic response to isoproterenol, whereas the effect of Ca2+ was unchanged. We conclude that sympathetic neuroeffector defects occur in transgenic rats similar to those observed in human failing myocardium. These alterations occur in the stage of hypertrophy and could contribute to contractile dysfunction in later stages.
Calcium current in smooth muscle cells from normotensive and genetically hypertensive rats.
Authors: Wilde D W , Furspan P B , Szocik J F
Published: June 2012

Genetic hypertension results from numerous phenotypic expressions. We hypothesized that increased calcium current in vascular smooth muscle of genetically hypertensive animals is partly responsible for observed increases in agonist sensitivity, contractility, and calcium influx. Using adult, spontaneously hypertensive stroke-prone rats (SHRSP) and normotensive Wistar-Kyoto (WKY) controls from an inbred colony, we characterized calcium current in smooth muscle cells isolated from cerebral arteries. Calcium current in WKY cells reached a maximum of -27.7 +/- 2.7 pA (n = 32) at +20 mV. Peak inward current at +20 mV in SHRSP cells had a mean amplitude of -44.4 +/- 3.0 pA (n = 72, P < .05). SHRSP cells exhibited a higher calcium current density. Maximal inward current normalized to cell capacitance yielded mean values of 2.07 +/- 0.11 pA/pF for WKY (n = 32) and 2.80 +/- 0.12 pA/pF (n = 79) for SHRSP (P < .05) cells. Transient-type Ca2+ channel current had the same magnitude and current-voltage relation in both cell types, giving an L-type/T-type ratio of 3.85 for WKY and 6.25 for SHRSP cells. The voltage-dependent inactivation curve for SHRSP calcium current was shifted to the right only over the range of -50 to -30 mV, but the half-maximal inactivation voltages and Boltzmann coefficients were not significantly different between cell types. Increased calcium inward current in this model of genetic hypertension could account in part for altered calcium homeostasis and increased vascular reactivity, contributing to hypertension and vasospasm.
Alcohol abolishes the hypotensive effect of clonidine in spontaneously hypertensive rats.
Authors: Abdel-Rahman A A
Published: June 2012

This study tested the hypothesis that concurrent ethanol administration attenuates the hypotensive effect of clonidine. Four groups of spontaneously hypertensive rats matched for baseline systolic pressure and body weight were randomly assigned the following treatments: (1) water (control), (2) ethanol, (3) clonidine, and (4) ethanol plus clonidine for 13 weeks. Ethanol was provided in the drinking water as 5% for 1 week, 10% for the next 2 weeks, and 20% from week 4 to 13. Starting from similar baseline systolic blood pressures, the blood pressure of the control group increased 10 to 15 mm Hg over the 13-week treatment period. A similar rise in systolic blood pressure occurred in ethanol-treated rats despite a drastic (40% to 50%, P < .05) reduction in fluid intake. Clonidine (300 micrograms/kg per day) caused a smaller and shorter reduction in fluid intake. The fluid intake of the combined treatment group was similar to that of the ethanol group. Either treatment caused a significant and additive reduction in body weight gain. Treatment-related mortality (20%) occurred only in the combined treatment group by the 12th week. Clonidine elicited a slowly developing hypotensive response (P < .05) that started 2 to 3 weeks after treatment was initiated and lasted throughout the treatment period. Ethanol abolished the hypotensive effect of clonidine and resulted in blood pressure values that were not significantly different from those of the control or the ethanol group. Blood ethanol concentration was similar in the presence or absence of clonidine (5.5 +/- 1.9 versus 6.5 +/- 3 mmol/L).(ABSTRACT TRUNCATED AT 250 WORDS)
Hypertrophy and Hyperplasia of Smooth Muscle Cells of Small Intramyocardial Arteries in Spontaneously Hypertensive Rats
Authors: Amann Kerstin , Gharehbaghi Hassan , Stephan Sybille , Mall Gerhard
Published: June 2012

Abstract
Hearts of stroke-prone spontaneously hypertensive rats (SHR) were investigated by means of stereology and were compared with those of normotensive Wistar-Kyoto controls. At the age of 9 months, hypertensive rats showed cardiac hypertrophy, marked myocardial fibrosis, activation of nonvascular interstitium, focal myocytial degeneration, reduction of capillarization, and microarteriopathy of small intramyocardial arteries. Stereologically, a significant increase in the total left ventricular arterial wall volume (+180% versus controls) was found in SHR hearts. By using new stereological techniques, the orientator and the nucleator, we investigated whether this significant increase in total left ventricular arterial wall volume was due to hyperplasia of smooth muscle cells in addition to the process of vascular smooth muscle cell hypertrophy that is common in SHR. Additionally, the nuclear size and ratio of cell volume to nuclear volume were determined using another new stereological technique, the selector. The stereological data indicate a significant increase in mean cell and nuclear volumes as well as in the total number of left ventricular arterial smooth muscle cells of SHR. Additionally, the total length of intramyocardial arteries was also significantly increased in hypertensive rats. The volume and number of arterial smooth muscle cells per arterial length were significantly (
P
<.001 and
P
<.05, respectively) higher in SHR than in normotensive controls. Thus, we conclude that hypertrophy and hyperplasia of smooth muscle cells are involved in intramyocardial arterial growth processes in hypertensive heart remodeling. Hyperplasia may be responsible for the realization of physiological growth processes, eg, length increase in the intramyocardial arterial tree, whereas hypertrophy predominantly causes the remarkable increase in the total wall volume of left ventricular intramyocardial arteries in stroke-prone SHR.