V. Vulpis

Functional characterization of endothelin receptors in hypertensive resistance vessels.

OBJECTIVE The physiological and pathophysiological functions of endothelin-1 in modulating the regional blood flow of normal and spontaneously hypertensive rats (SHR) were studied in the perfused mesenteric vascular bed, a useful model for investigating resistance vessels. DESIGN AND METHODS We used 12-week-old SHR and Wistar-Kyoto (WKY) rats. Endothelin A (ETA) receptor responsiveness was evaluated by endothelin-1 (0.2-2 mumol/l) concentration-response curves, and repeated in the presence of indomethacin and the ETA and endothelin B (ETB) receptor antagonists BQ-485 and BQ-788, respectively. ETB receptor responsiveness was tested by sarafotoxin S6c concentration-response curves, obtained in the noradrenaline-precontracted mesenteric vascular bed, and repeated after treatment with BQ-788 and after endothelial denudation. RESULTS In both groups, endothelin-1 induced concentration-dependent contraction; SHR exhibited a markedly increased maximal effect compared with WKY rats (P < 0.01). BQ-485 produced a shift to the right for endothelin-1 concentration-response curves in both groups, with a higher pA2 (negative common logarithm of the antagonist that produces an agonist dose ratio of 2) value in SHR than in WKY rats (P < 0.01). The increase in the maximal effect produced by endothelin-1 in SHR was prevented by indomethacin, which also induced a significant increase in the endothelin-1 concentration producing the half-maximal response (EC50) in SHR (P < 0.05). Sarafotoxin S6c produced an ETB-dependent endothelium-mediated relaxant effect in WKY rats, which was not observed in SHR. CONCLUSIONS The higher vasoconstriction induced by endothelin-1 in SHR may be related to a greater number of available ETA receptors, due to the presence of an ETA receptor subtype. This mechanism may be linked to the production of prostanoids that add to the direct endothelin-1-evoked vasoconstriction. These results, together with the lack of relaxation in response to sarafotoxin S6c in SHR, suggest that an imbalance in the endothelin-1 ability to induce both contraction and relaxation is present in SHR with sustained hypertension, manifesting as a greater contractile effect evoked in this strain.

Influence of gender and family history of hypertension on autonomic control of heart rate, diastolic function and brain natriuretic peptide

Objective To verify in a unitary view whether autonomic control of heart rate and cardiac structure and function are modified early in offspring of hypertensive families. Methods and results We selected 87 age- and sex-matched young normotensive subjects with (n = 45) and without (n = 42) a family history of hypertension who underwent evaluations of arterial pressure, time-domain parameters of autonomic heart rate control (24-h ECG monitoring), spectral baroreflex sensitivity, left ventricular geometry and function (echo-Doppler) and plasma brain natriuretic peptide levels (BNP). The group with a family history of hypertension significantly differed from their counterparts for systolic pressure (119 ± 11 versus 114 ± 9 mmHg, P< 0.05), heart rate (RR interval, 766 ± 64 versus 810 ± 93 ms, P< 0.05), heart rate variability [the standard deviation of normal RR intervals (SDNN), 147 ± 29 versus 171 ± 33 ms, P< 0.05], diastolic function (isovolumetric relaxation time, 65 ± 9 versus 60 ± 8 ms, P< 0.05) and BNP (23 ± 13 versus 37 ± 10 pg/ml, P< 0.05). Baroreflex sensitivity values did not differ between the two groups. When gender was considered, all the above-mentioned measures, as well as baroreflex sensitivity, were significantly different between males with and without a family history of hypertension but not between females, except for BNP, which was lower in males and females with a history of hypertension (males, 24 ± 11 versus 38 ± 8 pg/ml, P< 0.01; females 21 ± 14 versus 36 ± 13 pg/ml, P< 0.05). Conclusions Male, but not female, hypertensive offspring have modified diastolic function and autonomic control of heart rate; BNP is the only parameter able to characterize hypertensive offspring independently from the influence of gender. This provides the hypothesis that the impaired production of this hormone could play a primary role in the pre-hypertensive state.

Extracellular Matrix Gene Expression in the Left Ventricular Tissue of Spontaneously Hypertensive Rats

The aim of this study was to investigate the extracellular matrix gene expression in the hypertrophied left ventricular tissue of spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats, at early and mature ages. Interestingly, with age, a marked increase (+85% and +187% at 25 and 30 weeks of age, respectively, p < 0.01, vs 5 weeks) in matrix metalloproteinase-1 (MMP-1) mRNA levels in SHR and a progressive decrease (-50%, -70%, -78%, -70% at 10, 15, 25 and 30 weeks, respectively, p < 0.01, vs 5 weeks) in WKY were seen. Moreover, mRNA levels were significantly lower in SHR at 5 weeks. The analysis of mRNA expression for the tissue inhibitor of metalloproteinase-1 (TIMP-1) showed a significant increase in WKY (+44% and +44%, vs 15 and 25 weeks, respectively, p < 0.05), whereas there were no significant changes in SHR with development. At 30 weeks TIMP-1 mRNA levels were significantly reduced in SHR. Temporal trends of procollagen alpha1(I) and procollagen alpha1(III) mRNA levels were similar in both strains, but lower levels for procollagen alpha1(III) were found in SHR at 5 and 30 weeks. Although no significant differences were measured between the strains, mRNA levels for fibronectin were found decreased in WKY and increased in SHR with age. The results of the present study suggest an altered balance between collagen deposition and collagen degradation with development in this model of left ventricular hypertrophy and hypertension.

Mitochondrial energy metabolism in the left ventricular tissue of spontaneously hypertensive rats: abnormalities in both adeninenucleotide and phosphate translocators and enzyme adenylate-kinase and creatine-phosphokinase activities.

The aim of this study was to investigate the oxidative phosphorylation and additional adenosinetriphosphate (ATP) production mechanisms in mitochondria isolated from hypertrophied left ventricles of spontaneously hypertensive rats (SHR). Measurements of adenosinediphosphate (ADP)/ ATP and inorganic phosphate (Pi) carrier activities showed a significant reduction of Vmax values thus suggesting a general decrease of ATP supply in the hypertrophied ventricles. Investigation of mitochondrial enzyme activities showed 45% and 90% increases of adenylate-kinase and 80% and 110% increases of creatine-phosphokinase in 5- and 24-week-old SHR, before and after the development of the hypertensive state, respectively. The abnormalities found in SHR at the mitochondrial level suggest a profound rearrangement of energy production mechanisms in this model of left ventricular hypertrophy; whether the defects are determined genetically, and then worsen with the hypertensive state, remains to be determined.

Endothelin-1-receptor-mediated responses in resistance vessels of young and adult spontaneously hypertensive rats.

Objective To assess whether primary changes in endothelin-1 (ET-1) receptor responsiveness or secondary vessel functional modifications could characterize the effects evoked by ET-1 in the mesenteric vascular bed (MVB) of prehypertensive 5-week-old and 12-week-old spontaneously hypertensive rats (SHRs). Design and methods We used male 5-week-old and 12-week-old SHRs and sex- and age-matched Wistar-Kyoto (WKY) rats as controls. ET-1 receptor responsiveness was evaluated by ET-1 (0.04–2 μmol/l) concentration-response curves and repeated with indomethacin and BQ-123 (0.1–0.5 μmol/l), the latter a selective ETA receptor antagonist. ETB receptor responsiveness was tested by sarafotoxin S6c (1–100 nmol/l) and IRL-1620 (0.1–10 nmol/l) concentration-response curves, obtained in the noradrenaline-precontracted MVB. Results At 5 weeks of age, ET-1 induced a similar concentration-dependent contraction in SHRs and WKY rats, with an overlapping BQ-123 pA2 value (negative common logarithm of the antagonist that produces an agonist dose ratio of 2) in the two strains. Indomethacin was ineffective in both groups. Sarafotoxin S6c and IRL-1620 both evoked an ETB-mediated, significant relaxation, only in WKY rats. In 12-week-old SHRs, ET-1 evoked a markedly increased maximal effect compared with the response in WKY rats (P < 0.01); this was prevented by treatment with indomethacin. The BQ-123 pA2 value was higher in SHRs than in WKY rats (P < 0.01). Both sarafotoxin S6c and IRL-1620 evoked a significant concentration-dependent relaxation in WKY rats, which was not detected in SHR preparations. Conclusions Our results could suggest that the different responses evoked by ET-1 in the MVB of SHRs during the onset of hypertension may be related partially to primary alterations in the ET-1 receptorial pattern and partially to the onset of high blood pressure, leading to an impairment in the haemodynamic balance.

Stress-induced hemodynamic responses are associated with insulin resistance in mild hypertensives

BACKGROUND High blood pressure (BP) and pulse pressure (PP) are recognized as independent risk factors for cardiovascular diseases, whereas insulin resistance (IR) is often associated with hypertension. The purpose of the study was to verify whether PP, taken at the doctors office and during laboratory stimuli, might be predictive of IR. METHODS Homeostasis model assessment insulin resistance index (HOMA) was calculated in 75 grade 1 hypertensives (148 +/- 2/92 +/- 1 mm Hg). Then, patients underwent hemodynamic reactivity study, induced by color word stroop, cold pressor, and handgrip tests. Stress response was calculated as total area (value x time) - baseline area (baseline value x time). RESULTS Patients with similar age, history of hypertension, blood lipids and office blood pressure, but different HOMA (IR-low: 36.3 +/- 1.7 v IR-medium: 62.6 +/- 1.6, P <.001; IR-high: 123.1 +/- 12.8, P <.001 v IR-low and IR-medium), were divided in tertiles. They demonstrated a significant reactivity of systolic BP (IR-low: 225 +/- 58 v IR-medium: 448 +/- 43, P <.01; IR-high: 625 +/- 55, P <.001 v IR-low and P <.01 v IR-medium), PP (IR-low: -8 +/- 19 v IR-medium: 83 +/- 13, P <.001; IR-high: 201 +/- 19, P <.001 v IR-low and IR-medium), and stroke volume (SV) (IR-low: -138 +/- 43 v IR-medium: 1 +/- 27, P <.01; IR-high: 28 +/- 24, P <.001 v IR-low), but similar arterial stiffness (PP/SV) response. Partial correlation between IR and hemodynamic measurements showed a significant association only for systolic BP (0.54, P <.001), PP (0.686, P <.001), and SV (0.384, P <.001) reactivity, but not for office and baseline values. Stepwise multiple regression showed that only PP (beta: 0.634, P <.001) and, among hemodynamic determinants, SV (beta: 0.401, P <.001) response entered into the equation. CONCLUSIONS The findings demonstrate that increased stress-induced PP, maintained by SV response, is the most predictive hemodynamic variable of reduced insulin sensitivity in mild hypertensives.

Carrier-mediated transport controls hydroxyproline catabolism in heart mitochondria from spontaneously hypertensive rat

In this study we have investigated hydroxyproline transport in rat heart mitochondria and, in particular, in heart left ventricle mitochondria isolated from both spontaneously hypertensive and Wistar‐Kyoto rats. Hydroxyproline uptake by mitochondria, where its catabolism takes place, occurs via a carrier‐mediated process as demonstrated by the occurrence of both saturation kinetics and the inhibition shown by phenylsuccinate and the thiol reagent mersalyl. In any case, hydroxyproline transport was found to limit the rate of mitochondrial hydroxyproline catabolism. A significant change in V max and K m values was found in mitochondria from hypertensive/hypertrophied rats in which the K m value decreases and the V max value increases with respect to normotensive rats, thus accounting for the increase of hydroxyproline metabolism due to its increased concentration in a hypertrophic/hypertensive state.

Multicenter, double-blind clinical trial with different doses of pinacidil in patients with mild-to-moderate essential hypertension☆

Abstract The antihypertensive efficacy and therapeutic safety of pinacidil, 12.5 or 25 mg twice daily (BID), were assessed in a multicenter, double-blind, crossover trial. Seventy-seven patients (mean age, 47.3 years) with mild-to-moderate essential hypertension were enrolled in the study and randomly assigned to one of the following schedules: sequence A: pinacidil 12.5 mg BID for 3 weeks; 1-week washout period (two placebo capsules per day); pinacidil 25 mg BID for 3 weeks. Sequence B: pinacidil 25 mg BID for 3 weeks; 1-week washout (two placebo capsules per day); pinacidil 12.5 mg BID for 3 weeks. Both drug doses (25 or 50 mg/d) were equally effective, producing a similar and significant reduction in systolic and diastolic blood pressures in the sitting and standing positions. Systolic blood pressure was reduced by approximately 7% to 8% from baseline in both sequences A and B. Diastolic blood pressure, measured in both positions, was reduced by 8% to 9% from baseline. Heart rate did not appear to be influenced by either dose. Analysis of variance showed no significant differences between the sequences; the only highly significant difference was between the times ( P

Antihypertensive and Metabolic Effects of Amlodipine in Patients with Non-Insulin-Dependent Diabetes Mellitus

SummaryThe aim of this study was to evaluate the antihypertensive efficacy and possible effects on metabolic control of amlodipine in hypertensive diabetic patients. After a washout period of 4 weeks, 28 ambulatory patients with mild essential hypertension and non-insulin-dependent diabetes mellitus received amlodipine 10mg once daily for 12 weeks. Blood pressure was significantly decreased after 2,4,8 and 12 weeks of treatment when compared with basal values. No significant changes in heart rate occurred. A significant decrease in fasting plasma glucose was evident after 12 weeks. A slight but not significant decrease in pre- and postprandial plasma glucose, glycosuria and fructosamine concentrations occurred after 4 and 12 weeks of treatment. Microalbuminuria decreased significantly at the end of the study. No correlation was found between the reduction in microalbuminuria and the reduction in systolic or diastolic blood pressure. Cholesterol concentrations and triglycerides decreased, although only the latter was significant. The results of this study confirm the antihypertensive efficacy of amlodipine in hypertensive diabetic patients, and suggest a favourable influence of this drug on glycaemic and lipid control. The favourable changes in microalbuminuria observed after treatment need further studies to elucidate both the exact mechanisms behind increased microalbuminuria in the hypertensive diabetic state and the factors involved in the reduction.

Non-invasive haemodynamic study in hypertensive subjects after treatment with verapamil slow release

Aim of this study is to investigate the haemodynamic effects, after the short and long-term antihypertensive treatment. After a wash-out period and a placebo treatment period, 30 hypertensive patients received verapamil SR (slow release, 240 mg o.d.) for 30 days. A significant decrease in systolic and diastolic blood pressure was obtained already 4 h after the first administration of verapamil; it was more evident and persistent throughout the study. No significant changes of heart rate or PR interval in ECG were observed. A significant decrease in total vascular resistances, both supine and upright, was evident already 4 h after the drug intake and observed throughout the study. The major effect was obtained after one month. No significant changes of cardiac output, cardiac index and stroke volume were recorded. Furthermore, plasma verapamil levels were measured to confirm that the haemodynamic effects are obtained by low drug concentrations. The present study provides evidence that the antihypertensive effect of verapamil, whose mechanism is the reduction of total vascular resistances, is progressive, long acting and achieved by low plasma levels, when slow release formulation is considered.