ISSN:0263-6352    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

BackgroundThe flavonoid components of tea have been associated in epidemiological studies with a decreased risk of cardiovascular disease. Flavonoids have been shown to have antioxidant and vasodilator effectsin vitro; we therefore postulated that drinking green or black tea attenuates the well-characterized acute pressor response to caffeine and lowers blood pressure during regular consumption.ObjectiveTo determine whether green and black tea can attenuate the transient pressor effect of caffeine, or lower blood pressure during regular consumption.MethodsIn the first study, the acute effects of four hot drinks – green tea and black tea (at a dose equivalent to four standard cups), water matched to the teas for caffeine content (‘caffeine’) and water – were assessed in 20 normotensive men using a Latin-Square designed study. Clinic blood pressure was measured before and 30 and 60 min after each drink had been ingested. In the second study, the effects on blood pressure of regular green and black tea ingestion were examined in 13 subjects with high-normal systolic blood pressure and mild systolic hypertension (systolic blood pressure in the range 130–150 mmHg) using a three-period crossover study. Five cups per day of green tea, black tea and caffeine (in hot water and matched to the teas) were consumed for 7 days each, in random order. Twenty-four hour ambulatory blood pressure was measured at the end of each seven-day intervention. Results are presented as means and 95% confidence intervals (CI).ResultsAn acute pressor response to caffeine was observed. Relative to caffeine, there were further acute increases in systolic and diastolic blood pressure at 30 min among those drinking green tea [5.5 mmHg (95%CI −21.4 to 12.4) and 3.1 mmHg (95%CI −0.1 to 6.3), respectively] and black tea [10.7 mmHg (95%CI 4.0 to 17.4) and 5.1 mmHg (95%CI 1.8 to 8.4), respectively]. The changes in blood pressure at 60 min were not significant. The effect on 24-h ambulatory systolic and diastolic blood pressure of regular drinking of green tea [increases of 1.7 mmHg (95%CI −1.6 to 5.0) and 0.9 mmHg (95%CI −1.3 to 3.1), respectively] or black tea [increase of 0.7 mmHg (95%CI −2.6 to 4.0) and decrease of 0.7 mmHg (95%CI −2.9 to 1.5), respectively] was not significant relative to caffeine.ConclusionsContrary to our initial hypothesis, tea ingestion caused larger acute increases in blood pressure than caffeine alone. However, any acute effects of tea on blood pressure did not translate into significant alterations in ambulatory blood pressure during regular tea consumption.

ISSN:0263-6352    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

ObjectiveTo determine whether the prediction of target-organ damage varies according to the reproducibility of 24 h blood pressure.SettingSeventeen hypertension clinics in northeast Italy.Main outcome measuresCorrelations of left ventricular mass index and albumin excretion rate with 24 h and office blood pressures in relation to tertiles of ambulatory blood pressure reproducibility.Patients and methodsIn 716 consecutive, stage I, hypertensives enrolled in the Hypertension and Ambulatory Recording Venetia Study (HARVEST), ambulatory blood pressure monitoring was performed twice, 3 months apart. In all subjects, the albumin excretion rate was measured by radioimmunoassay, and in 567, the left ventricular mass index was assessed by echocardiography.ResultsThe subjects were divided into tertiles of ambulatory blood pressure consistency (between-monitoring differences, regardless of the sign). In the tertile of subjects with good reproducibility, correlation coefficients of systolic and diastolic ambulatory blood pressure with left ventricular mass and urinary albumin excretion were significant and higher than those of office blood pressure. In contrast, in the two tertiles with poorer reproducibility, the coefficients were barely or not significant for both pressures. The advantage of ambulatory blood pressure over office blood pressure in predicting target-organ damage was no longer present for systolic blood pressure differences greater than 3.8 mmHg and diastolic blood pressure differences greater than 3.1 mmHg.ConclusionsThese data indicate that ambulatory blood pressure is a better predictor of left ventricular mass and urinary albumin excretion than office blood pressure, but only in subjects with good pressure reproducibility. Therefore, the assessment of hypertensive patients should be based on duplicate blood pressure monitorings. Recordings with 24 h systolic and diastolic blood presssure differences greater than 4 and 3 mmHg, respectively, should be considered with caution.

ISSN:0263-6352    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

Background and aimsA single-nucleotide variant of the angiotensinogen gene (AGT 235T) has been associated with essential hypertension and increased plasma levels of angiotensinogen. This variant may also serve as a genetic marker for the increased blood pressure response to dietary salt intake, but the relationship betweenAGTgenotype and salt sensitivity has not been studied until now. We therefore examined the relationship between theAGT235T genotype and the blood pressure response to short-term dietary salt restriction in young normotensive men.Subjects and methodsA total of 187 young normotensive men were characterized for family history of hypertension, salt sensitivity, plasma parameters of the renin angiotensin system under high- and low-salt diets, and the AGT 235T genotype.ResultsWhile the T allele was significantly associated with a positive family history of hypertension (X2= 7.0;P< 0.03) and higher plasma angiotensinogen levels (P< 0.015) and renin activity (P< 0.037), blood pressure under both diets was not significantly affected by theAGTgenotype. When the subjects were classified into salt-resistant and salt-sensitive groups, genotypic distribution was nearly identical between both groups (frequency of T allele: 0.45 versus 0.46).ConclusionOur findings demonstrate that the AGT 235T allele is significantly associated with a positive family history of hypertension, but is not an important determinant of the blood pressure response to dietary salt intake in young normotensive subjects. It is therefore unlikely that the AGT 235T genotype can serve as an early genetic marker of salt sensitivity.

ISSN:0263-6352    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

ObjectiveTo study the alteration in the biomechanical properties of the thoracic aorta and its composition in young normotensive Wistar-Kyoto (WKY) rats, spontaneously hypertensive rats (SHR), and stroke-prone SHR (SHRSP).MethodsThe in-vitro biomechanical properties of the aorta in 4- and 12-week-old SHRSP were determined by means of a tensile testing machine and compared with those of the SHR and WKY rats; in addition, a biochemical analysis of collagen, elastin and advanced glycation endproducts was performed.ResultsThe aortic biomechanical properties were altered in the 4- and 12-week-old SHRSP, compared with age-matched WKY rats and SHR. The maximum stress in the 12-week-old SHRSP was reduced by 27% compared with the normotensive WKY rats, and by 26% compared with the SHR. The maximum strain values in the 4- and 12-week-old SHRSP were lower than those in the age-matched WKY rats, by 12 and 9% respectively, whereas this value in the 12-week-old SHR was significantly increased (by 26%) compared with the age-matched WKY rats. No differences were observed in the aortic contents of collagen and elastin between the SHRSP and SHR. However, the extractability of collagen by pepsin digestion in the 12-week-old SHRSP was lower than that in the age-matched SHR and WKY rats, and a significantly larger accumulation of advanced glycation endproducts was observed in the 12-week-old SHRSP than in the age-matched SHR and WKY rats, suggesting a greater formation of collagen-derived cross-links in SHRSP.ConclusionsFrom these results, we conclude that decreased aortic distensibility and mechanical strength values are partly related to the greater formation of collagen-derived cross-links in 12-week-old SHRSP, and that the mechanical properties in SHRSP may be the result not only of the larger formation of collagen-derived cross-links but also of primary defects, since the aortic mechanical strength value was decreased even in 4-week-old SHRSP.

ISSN:0263-6352    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

BackgroundChronic diabetes is associated with alterations in autonomic modulation of the cardiovascular system. Although the rat has been used extensively in studies of experimental diabetes, there have been no reports on the changes in autonomic modulation of the cardiovascular function in chronic diabetic rats.ObjectiveTo examine chronic diabetic rats to determine the autonomic modulation of arterial pressure and heart rate variabilities in the time and frequency domain.Materials and methodsDiabetes was induced in rats by a single injection of streptozotocin, and 30 min of pulsatile arterial pressure was recorded in conscious rats, 5, 10–20 days and 12–18 weeks after the streptozotocin injection. Control rats were injected with vehicle. Beat-by-beat systolic arterial pressure and heart rate were obtained from pulsatile pressure. The spectral density powers of systolic arterial pressure and heart rate were calculated using fast Fourier transformation, and integrated in low-(0.015–0.25 Hz), mid-(0.25–0.75 Hz) and high- (0.75–3.0 Hz) frequency bands. The standard deviations of systolic arterial pressure and heart rate were also calculated.ResultsBasal systolic arterial pressure and heart rate were reduced in diabetic animals studied 10-20 days and 12-18 weeks after the streptozotocin injection. The standard deviations of systolic arterial pressure and heart rate were also reduced in the chronically diabetic animals. Diabetes reduced low-and mid-frequency variability but not the high-frequency variability of systolic arterial pressure. The low-frequency variability, but not the mid-frequency variability, of the heart rate was also reduced, while the high-frequency variability of the heart rate was reduced in the more chronically diabetic rats.ConclusionOur findings that the mid-frequency band variability of arterial pressure was reduced in diabetic patients suggest that sympathetic modulation of the cardiovascular system is impaired, corroborating other studies in such patients using this and other approaches.

ISSN:0263-6352    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

ObjectiveTo investigate the cardiovascular effects of micro-injection into the hippocampus of selective μ, δ and κ opioid receptor agonists in anesthetized spontaneously hypertensive rats, isolation-induced hypertensive rats and their normotensive Wistar-Kyoto and group-housed Sprague-Dawley controls.Methods and resultsThe microinjection of a selective κ agonist, spiradoline mesylate, (±)-(5α,7α,8β)-3,4-dichloro-N-methyl-N-[7-(1-pyrrolidinyl)-1-oxaspiro[4.5]dec-8-yl]-benzeneacetamide mesylate) (5 nmol) into the dorsal region of hippocampus, where injection of control saline failed to affect cardiovascular activities, induced centrally mediated decreases in mean blood pressure and heart rate in both hypertensive and normotensive rats. The effects were blocked by prior treatment of the hippocampus with nor-binaltorphimine dihydrochloride, a selective κ opioid receptor antagonist. The hypotensive and bradycardic effects were quantitatively similar between spontaneously hypertensive rats and Wistar-Kyoto rats and between isolated hypertensive rats and normotensive group-housed rats. The sequential administration of increasing doses (5, 10, 50 nmol) of the selective μ agonist [D-Ala2, N-Me-Phe4, Gly5-ol]-enkephalin and δ agonists [D-Ala2, D-Leu5]-enkephalin or [D-Pen2, D-Pen5]-enkephalin into the same areas of the hippocampus as used for the κ agonist had no significant effects on mean blood pressure and heart rate in either hypertensive or normotensive rats.ConclusionThe present results extend our previous findings of a hippocampally mediated hypotensive effect of κ agonists in the spontaneously hypertensive rat to the isolated rat model of hypertension and they establish that μ and δ opioid receptor agonists similarly applied are ineffective. Hippocampal κ receptors may have a greater role in cardiovascular control than μ and δ receptors.

ISSN:0263-6352    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

ObjectiveWe measured changes in heart rate and lumbar sympathetic nerve activity in conscious, spontaneously hypertensive and Wistar-Kyoto rats during acute blood pressure lowering with nicardipine, enalaprilat and concomitant nicardipine/enalaprilat administration. In a second experiment, we determined the effect of these drugs on arterial baroreflex control of lumbar sympathetic nerve activity.MethodsMale spontaneously hypertensive and WistarKyoto rats were instrumented for continuous heart rate, blood pressure and lumbar sympathetic nerve activity recordings. Twenty-four hours later in conscious rats, nicardipine, enalaprilat and enalaprilat/nicardipine were infused at sufficient doses to reduce mean arterial pressure by 20 mmHg over 30 min. In a second experiment with the same drugs, baroreflex curves relating lumbar sympathetic nerve activity to mean arterial pressure were analyzed using a logistic curve-fitting program.ResultsBlood pressure reductions induced by the three infusion protocols were similar in magnitude and profile. In both spontaneously hypertensive and Wistar-Kyoto rats, nicardipine induced greater reflexive increases in lumbar sympathetic nerve activity than enalaprilat. Pretreatment with a reduced dose of enalaprilat blunted subsequent nicardipine-induced sympathetic activation. Nicardipine tended to induce greater increases in the heart rate than enalaprilat, but overall, the difference was not significant. Baroreflex sensitivity was similar regardless of drug class. Nicardipine significantly increased minimum nerve activity compared with enalaprilat in spontaneously hypertensive rats (similar trends were observed in Wistar-Kyoto rats). This increase in minimum nerve activity was blunted by enalaprilat.ConclusionsThese results indicate that pretreatment with an angiotensin converting enzyme inhibitor minimizes dihydropyridine-induced increases in sympathetic activity. This beneficial effect is attributable to suppression of minimum sympathetic activity. These data suggest that coadministration of an angiotensin converting enzyme inhibitor may improve the long-term cardiovascular benefit of dihydropyridine calcium channel blockers.

ISSN:0263-6352    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

ObjectiveTo define the changes in variability of heart rate and of blood pressure during vasodilation in a group of hypertensive patients treated with an angiotensin II type I (AT1) receptor inhibitor.DesignLosartan (50 mg/day at 0800 h) or placebo were administered for 3 weeks according to a single blind, crossover, randomized protocol, to 18 hypertensive patients (16 men and two women, mean age 42 6 3.6 years). Continuous ECG recording and beat-to-beat blood pressure monitoring were carried out with subjects in the supine position and during a head-up tilt test, as well as after sublingual administration of trinitroglycerine. The elaboration of ECG traces in the frequency domain, was carried out using an autoregressive method and measured using the autoregressive moving average technique.ResultsOrthostatic stimulus, both during treatment with losartan and with placebo, caused a significant decrease in the heart rate high frequency power; on the other hand, the low frequency power appeared unchanged after placebo and was significantly reduced with losartan. Five minutes after the administration of trinitroglycerine, the low frequency power with placebo showed a significant increase (817 ± 221 versus 465 ± 101 ms2,P< 0.03). No change was recorded in total power nor in low frequency or high frequency power during losartan therapy. The ratio of low frequency to high frequency powers showed a sympathetic prevalence during vasodilation only during placebo treatment, whereas a mainly unchanged balance was maintained during losartan treatment. Blood pressure variability showed a sympathetic prevalence after upright and trinitroglycerine stimulation only in placebo-treated subjects.ConclusionsOur study demonstrated that vasodilation is not able to evoke an unbalancing of the autonomic modulation in hypertensive patients treated with an AT1 receptor inhibitor, but permits the maintenance of a significant vagal component, thus highlighting the favorable profile of this drug in the autonomic control of circulation.

ISSN:0263-6352    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

ObjectiveAn exaggerated blood pressure response to mental stress in postmenopausal women has been reported but the underlying mechanism is not clear. In the present study, we examined the role of estrogen in the blood pressure response to mental stress.Subjects and methodsHemodynamic responses to mental stress and constrictor responses to norepinephrine were compared in 18 premenopausal (mean ± SD age 33 ± 5 years), 22 postmenopausal women (62 ± 7 years) and 13 postmenopausal women with estrogen replacement therapy (58 ± 8 years). Premarin was infused in 10 postmenopausal women to determine whether estrogen attenuates norepinephrine-induced vasoconstriction. The hemodynamic responses to a standard mental arithmetic test were measured. Norepinephrine (12.5, 25, 50, 100 ng/min) was infused at 0.5 ml/min for 5 min via the dorsal hand vein. Norepinephrine (100 ng/min) combined with premarin (200 μg/min) was infused into the dorsal hand vein of postmenopausal women. Changes in venous diameter were measured by ultrasonography using a 7.5 MHz transducer.ResultsAll study subjects were healthy, normotensive and had normal lipid profiles. The postmenopausal women showed a significantly greater blood pressure response to the mental arithmetic test than the premenopausal women or those taking estrogen replacement therapy (P< 0.01). Norepinephrine induced significant dose-dependent vasoconstriction in all three groups (P< 0.001). The postmenopausal women showed significantly greater constriction in response to norepinephrine than the premenopausal women and those taking estrogen replacement therapy (P< 0.02). Premarin significantly attenuated the norepinephrine-induced vasoconstriction in the postmenopausal women (P< 0.001).ConclusionHealthy, normotensive postmenopausal women showed an exaggerated blood pressure response to mental stress. An increased vasoconstriction in response to norepinephrine and loss of estrogenmediated vasodilation may contribute to the increased blood pressure response to stress in postmenopausal women without estrogen replacement therapy.

ISSN:0263-6352    

出版商:OVID    

年代:1999

数据来源: OVID