Circulating Endothelial Cells in Renal Transplant Recipients

Circulating endothelial cells (CECs) are a marker of endothelial injury and endothelial dysfunction. We measured CECs in 95 patients with functioning renal transplants at risk of premature cardiovascular (CV) disease and in normal control subjects. We were unable to demonstrate consistent relationships between CEC levels and conventional CV risk factors in transplant recipients. However, CEC levels were increased in patients with a history of rejection. We conclude that CECs are of little use as a marker of CV risk in this population but may be a useful marker to monitor allograft rejection.

24-hour blood pressure control: its relevance to cardiovascular outcomes and the importance of long-acting antihypertensive drugs

This review article outlines the evidence that 24 h blood pressure (BP) measurements are particularly important predictors of adverse cardiovascular outcome. In turn, there is supportive evidence from a range of studies that 24 h BP control should be an integral part of the antihypertensive drug treatment strategy. Furthermore, since not all once daily antihypertensive agents can provide such 24 h control, there is a requirement for careful drug (and/or dosage) selection. Although the clinic (office) BP continues to be the standard measurement by which hypertension is diagnosed and treatment monitored, there is now clear evidence of the superiority of 24 h BP assessments. Although there are not yet prospective, outcome clinical trails which have relied upon 24 h BP values there is clear evidence that 24 h BP values correlate much more closely than conventional clinic BP values with measurements such as left ventricular hypertrophy, cerebral vascular damage (lacunar infarcts), renal damage (microalbuminuria) and vascular damage (carotid artery intima media thickness). In turn, there is evidence that during drug treatment, when achieved clinic blood pressures appear to be comparable, there is improved outcome in those patients whose 24 h BP values are significantly lower. Not all antihypertensive drugs are equivalent, however, in their abilities to reduce 24 h BP and the clinician needs to be aware of possible shortcomings when considering the choice of drug. In this respect, intrinsically long-acting agents are best equipped to provide sustained and consistent BP control throughout 24 h.

The pharmacodynamic and pharmacokinetic profiles of controlled-release formulations of felodipine and metoprolol in free and fixed combinations in elderly hypertensive patients

AIMS

The aims of this study were to study the efficacy and tolerability of felodipine extended release (ER) 5 mg and metoprolol controlled release (CR/ZOC) 50 mg given as a fixed combination (Logimax) or as a free combination in elderly (age greater than 60 years) hypertensive patients, using ambulatory blood pressure (BP) monitoring. A secondary aim was to relate the efficacy of the free and fixed combinations with pharmacokinetic profiles.

METHODS

This was a double-blind, placebo-controlled randomised three-way crossover multi-centre study. BP was measured for 26 h using ambulatory blood pressure monitoring (ABPM), which was performed on the last day of the three treatment phases.

RESULTS

Mean sitting BPs, measured during the trough period with ABPM, were significantly lower with both the free and fixed combinations of metoprolol and felodipine than placebo (141/83 mmHg free, 140/83 mmHg fixed, 156/93 mmHg placebo). The mean BPs measured over 24 h using ABPM were 143/82 mmHg, 140/82 mmHg and 158/93 mmHg for the free, fixed and placebo treatment arms, respectively. The trough-to-peak ratios (T:P) were 75% and 79% for the systolic BP and 70% and 70% for the diastolic BP for the free and fixed combinations, respectively. Pharmacokinetic evaluation revealed identical plasma concentration-time curves for felodipine given as the free or fixed combination. Comparison of the plasma concentration-time curves for metoprolol revealed a delay in the release rate from the fixed combination formulation. No significant differences in BP control between the active treatments were noted during this period. Of 26 patients entered into the study, 3 withdrew during active phase for non-drug-related reasons. No patient withdrew from active treatment due to treatment-related adverse events. The frequency of adverse event reporting for the fixed combination of felodipine and metoprolol was similar to that for placebo (60% and 58%, respectively).

CONCLUSION

The results suggest that once-daily dosing with either the free or fixed combination of felodipine 5 mg and metoprolol 50 mg produces a significant sustained reduction in systolic and diastolic BP with similar plasma concentration profiles over a 24-h period.

Endothelial dysfunction as a possible link between C-reactive protein levels and cardiovascular disease

Low-grade chronic inflammation, characterized by elevated plasma concentrations of C-reactive protein (CRP), is associated with an increased risk of atherosclerotic cardiovascular disease. Endothelial cell activation is an early event in atherogenesis, and previous studies have reported correlations between indirect markers of endothelial cell activation and CRP concentration. Therefore, in the present study, we measured CRP concentration (and leptin concentration as an index of fat mass) in nine healthy subjects (mean age 53+/-8.1 years; body mass index 27+/-3.2 kg/m(2); mean arterial blood pressure 101+/-9.0 mmHg) undergoing measurement of basal endothelial nitric oxide (NO) synthesis using intra-brachial infusions of N(G)-monomethyl-L-arginine (L-NMMA; a substrate inhibitor of endothelial NO synthase) and noradrenaline (a non-specific control vasoconstrictor). In univariate analysis, CRP concentration was correlated with (i) the percentage decrease in forearm blood flow (FBF) during L-NMMA infusion (r=0.85, P=0.004); and (ii) the serum leptin concentration (r=0.65, P=0.05). In multivariate analysis, the relationship between CRP concentration and the FBF response to L-NMMA remained significant when age and leptin (t=2.65, P=0.045), age and BMI (t=3.69, P=0.014), or age and low-density-lipoprotein-cholesterol plus high-density-lipoprotein-cholesterol (t=3.37, P=0.044), were included in regression models. In contrast, the response of FBF to noradrenaline was not significantly related to CRP concentration. These data demonstrate for the first time a relationship between low-grade chronic inflammation and basal endothelial NO synthesis (measured using an invasive method), and support the notion that endothelial dysfunction is a critical intermediate phenotype in the relationship between inflammation and cardiovascular disease.

Trandolapril does not improve insulin sensitivity in patients with hypertension and type 2 diabetes: a double-blind, placebo-controlled crossover trial

Angiotensin-converting enzyme (ACE) inhibitors are increasingly used as first-line therapy for hypertension in type 2 diabetes mellitus and are widely believed to improve insulin sensitivity (M). However, the evidence for the latter effect does not stand close scrutiny. We have assessed the effect of the ACE inhibitor trandolapril on M in 16 patients (mean +/- SD age, 58 +/- 10.6 yr) with mild-to-moderate essential hypertension (initial blood pressure, 173 +/- 14.5/93 +/- 8.0 mm Hg), obesity (body mass index, 30 +/- 5.4 kg/m2), and impaired glucose intolerance (n = 4) or type 2 diabetes (n = 12) in a double-blind, placebo-controlled crossover design. All patients underwent three 3-h euglycemic hyperinsulinemic clamp studies (soluble insulin, 1.5 mU/kg x min) after a 2-week placebo run-in and at the end of two 4-week periods of treatment with 2 mg trandolapril or placebo (2-week washout). M (mean +/- SD) did not change with trandolapril: placebo (run-in), 5.2 +/- 1.98 mg/kg x min; placebo, 5.3 +/- 1.70 mg/kg x min; trandolapril, 5.1 +/- 1.65 mg/kg x min; P = 0.58; 95% confidence intervals, -0.74, 0.43 (trandolapril vs. placebo); 95% power to exclude an 8% increase in M. In conclusion, trandolapril had no clinically relevant effect on M in patients with hypertension and type 2 diabetes. Previous reports of improved M during ACE inhibitor treatment may be attributable to suboptimal study design and/or use of surrogate measures of M.

Cardiac and vascular abnormalities in renal transplant patients: differential effects of cyclosporin and azathioprine

Renal transplant patients die prematurely of cardiovascular disease and LV hypertrophy is now recognised as an important adverse prognostic indicator. This study investigated the factors implicated in the development of echocardiographic abnormalities (including LV hypertrophy) and the possible differential effects of treatment with cyclosporin and azathioprine. A cross-sectional study was undertaken in 46 patients randomly assigned to immunosuppressant treatment with either cyclosporin or azathioprine at 1 year post-transplantation: patients were studied not less than 5 years after assignment to cyclosporin (CyA) - or azathioprine (Aza)-based treatment regimens. Although clinic blood pressure control was not different in the two treatment groups, 24 hour ambulatory BP (ABP), particularly night-time BP, was significantly higher in the CyA group. There was a trend for both left ventricular hypertrophy (61 vs. 43%) and carotid wall thickening (43 vs. 26%) to be more common in the CyA group though this failed to achieve statistical significance. Left ventricular mass was determined by ABP, rather than clinic BP, and was also associated with increased QT dispersion. Multivariate analysis identified that 24 hour ambulatory systolic blood pressure (ASBP) and time on renal replacement therapy (RRT) were the major determinants of LV mass. Thus, despite the absence of differences in clinic BP measurements, CyA treatment was associated with higher rates of cardiovascular functional and structural abnormalities. This small scale study has identified cardiovascular functional and structural abnormalities in renal transplant patients, particularly in those receiving CyA-based immunosuppressive therapy. However, rather than reflecting a direct effect of CyA they are related to increased 24 ABP (but not clinic BP). These data suggest that ABP should be used to monitor and target antihypertensive therapy in this high risk patient group. Moreover, the future use of non-calcineurin inhibitor immunosuppressant therapy may have benefits on blood pressure control and LV mass.

Insulin action is associated with endothelial function in hypertension and type 2 diabetes

A primary defect in the vascular action of insulin may be a key intermediate mechanism that links endothelial dysfunction with reduced insulin-mediated cellular glucose uptake in metabolic and cardiovascular disorders. The present study was designed to characterize more fully the relations between insulin action and endothelial function in male patients with essential hypertension (H, n=9) or type 2 diabetes (D, n=9) along with healthy control subjects (C) matched for age, body mass index, and lipid profile. They attended for measurement of whole-body insulin sensitivity (MCR) by the hyperinsulinemic clamp technique (day 1) and forearm vasoreactivity in response to intra-arterial infusions of insulin/glucose (day 2) and N(G)-monomethyl-L-arginine (L-NMMA) and norepinephrine (day 3) by bilateral venous-occlusion plethysmography. Results expressed as mean+/-SE MCR (mL/kg per minute) were 7.22+/-0. 99 (C), 6.32+/-0.78 (H), and 5.06+/-0.53 (D). Insulin/glucose-mediated vasodilation (IGMV) was 17.1+/-5.6% (C), 17. 2+/-5.5% (H), and 12.3+/-6.4% (D). L-NMMA vasoconstriction (LNV) was 37.9+/-5.1% (C), 37.5+/-2.3% (H), and 33.6+/-2.8% (D). There were no significant differences among groups for these parameters. Pooled correlation analyses revealed associations between MCR and IGMV (r=0. 46, P<0.05), MCR and LNV (r=0.44, P<0.05), and IGMV and LNV (r=0.52, P<0.01). This study supports functional coupling between insulin action (both metabolic and vascular) and basal endothelial nitric oxide production in humans.

Platelet-derived growth factor stimulation of monocyte chemoattractant protein-1 gene expression is mediated by transient activation of the phosphoinositide 3-kinase signal transduction pathway

Platelet-derived growth factor (PDGF) stimulates transcription of an immediate-early gene set in Balb/c 3T3 cells. One cohort of these genes, typified by c-fos, is induced within minutes following activation of PDGF receptors. A second cohort responds to PDGF only after a significant time delay, although induction is still a primary response to receptor activation as shown by "superinduction" in the presence of the protein synthesis inhibitor cycloheximide. PDGF-receptor activated signaling pathways for the "slow" immediate-early genes are poorly resolved. Using gain-of-function mutations together with small molecule inhibitors of kinase activity, we show that activation of PI 3-kinase is both necessary and sufficient for the induction of the prototype slow immediate-early gene, monocyte chemoattractant-1 (MCP-1). Following activation of PDGF receptors, MCP-1 mRNA does not begin to accumulate for at least 90 min. However, only a brief (10 min) interval of PI 3-kinase activity is required to trigger this delayed response. The serine/threonine protein kinase, Akt/PKB, likely functions as a downstream affector of PI 3-kinase for this induction.

ACE inhibition in chronic renal failure and in the treatment of diabetic nephropathy: focus on spirapril

The management of hypertension and nephropathy, in both diabetes and other forms of renal disease, is usually based on blood pressure reduction through an angiotensin-converting enzyme (ACE) inhibitor-based treatment regimen. With particular respect to the choice of ACE inhibitor drug, there are no definitive direct comparisons in the treatment of renal disease. In terms of blood pressure reduction, however, there is evidence that spirapril is at least as effective as the reference ACE inhibitor, enalapril. However, patients with diabetic nephropathy and/or chronic renal failure are at potential risk from drug accumulation if the preferred agent relies predominantly on glomerular filtration for its elimination. In this respect spirapril may have an advantage because it has been shown that there are no clinically relevant increases in the spirapril(at) concentrations (24 h post-dose) even in the setting of advanced renal failure (creatinine clearance <20 ml/min). Thus, there is no requirement to modify the dose and no concerns about drug accumulation or the potential for exaggerated therapeutic or adverse effects. In summary, an ACE inhibitor drug is seen as an integral component of the drug treatment regimen for patients with nephropathy. Where there is renal failure it may be prudent to administer a drug, such as spirapril, which also has alternative elimination mechanisms.

Moxonidine: pharmacology, clinical pharmacology and clinical profile

Management strategies in hypertension evolve in response to an increased understanding of underlying pathophysiological processes and developments and refinements in drug treatments. Recent research has identified the regulatory role of the imidazoline (I1) receptor in sympathetic outflow and blood pressure regulation and this has led to the development of moxonidine, a highly selective centrally acting antihypertensive agent. At a practical level, moxonidine is suitable for single daily dosing in hypertension. Furthermore, in comparative studies moxonidine has a low incidence of symptomatic adverse effects comparable, for example, to that of the ACE inhibitor drugs, captopril and enalapril. The antihypertensive efficacy of moxonidine has now been established in a series of comparative clinical trials against all other first-line antihypertensive drug classes but, in line with current concepts, it may be necessary to look beyond blood pressure reduction. For example, centrally acting agents are known to be effective for promoting the regression of LV hypertrophy and studies in hypertensive patients have shown that antihypertensive treatment with moxonidine successfully leads to significant reductions in LV mass indices. Furthermore, there is now evidence that moxonidine has a beneficial effect on insulin sensitivity such that there are likely to be improvements in the overall metabolic profile. Thus, the clinical characteristics of moxonidine indicate that it is well suited for consideration among the first-line antihypertensive treatment choices.

Renal effects of amlodipine in normotensive renal transplant recipients

Renal effects of amlodipine in normotensive renal transplant recipients. The use of cyclosporin A (CsA) has improved the success of renal transplantation, but is associated with hypertension and significant renal toxicity. Previous reports suggest that calcium channel blockers may be useful in opposing the adverse effects of CsA. We have evaluated the effects of amlodipine (5 mg, once daily for 8 weeks) on renal function in 27 normotensive renal transplant recipients with stable renal function, in a double-blind, placebo-controlled, multicentre, cross over study. Amlodipine significantly reduced serum creatinine concentration relative to placebo (mean+/-SD: 168+/-65 vs 177+/-66 micromol/l; P=0.002) and there was a strong trend towards an increase in effective renal plasma flow on amlodipine relative to placebo (238+/-92 vs 217+/-87 ml/min; P=0.055). Glomerular filtration rate and lithium clearance were unaffected. Trough CsA blood concentration was unaffected. Amlodipine was well tolerated, with a low incidence of adverse events, and did not affect blood pressure or heart rate. In conclusion, amlodipine reduced serum creatinine in normotensive renal transplant recipients after only 8 weeks treatment, and was well tolerated in concomitant administration with CsA.

Endothelial dysfunction in cardiovascular disease: risk factor, risk marker, or surrogate end point?

Endothelial dysfunction is a feature of the early stages of atherosclerotic cardiovascular disease. It also is almost invariably associated with recognized cardiovascular risk factors, including those that are irreversible (such as age and family history) and those that are reversible (such as hypertension and hypercholesterolemia). It remains the subject of debate whether endothelial dysfunction can be considered an independent risk factor or, perhaps more plausibly, an intermediate or surrogate end point. However, although the relevance to research into cardiovascular pathophysiology is not in dispute, there remains uncertainty about its relevance as a therapeutic target. Overall, the available evidence suggests that targeting of the conventional major risk factors remains the primary strategy, but an ancillary effect on intermediate end points, such as an improvement or reversal of endothelial dysfunction, constitutes an additional potential benefit.

Insulin-mediated vasodilation and glucose uptake are functionally linked in humans

Intra-arterial infusion of insulin in physiological doses causes forearm vasodilation which is augmented by co-infusion of D-glucose, leading us to speculate that local insulin-mediated vasodilation may depend on insulin-mediated glucose uptake. We have examined the relationship between whole-body insulin sensitivity and forearm vasodilation in response to local infusion of insulin/glucose, thus avoiding any confounding effects of sympathetic stimulation on peripheral blood flow. Eighteen healthy, normotensive male volunteers (age, 26+/-5.4 years) attended on two separate occasions for measurement of: (1) whole-body insulin sensitivity with use of the hyperinsulinemic euglycemic clamp; (2) forearm vasodilation in response to an intra-arterial infusion of insulin/glucose with use of bilateral venous occlusion plethysmography. Insulin-mediated glucose uptake (M) for the group (mean+/-SD) was 10.0+/-2.2 mg. kg-1. min-1, and the percentage change in forearm blood flow ratio (%FBFR) for the group (median, interquartile range) was 28.2% (13.6, 48.6). In univariate analysis, M was significantly correlated with %FBFR (rs=0.60, P<0.05), but not with body mass index (BMI) (rs=-0. 42), age (r=-0.39) or mean arterial pressure (r=0.13). In multiple regression analysis, %FBFR remained a significant independent predictor of M (R2 (adj)=0.48, t=3.23, P<0.01) in a model involving BMI, age, and blood pressure. These data support the concept of a significant functional relationship between insulin's metabolic and vascular actions, possibly at an endothelial level.

ACE (I/D) genotype as a predictor of the magnitude and duration of the response to an ACE inhibitor drug (enalaprilat) in humans

BACKGROUND

We have investigated the possible effects of contrasting ACE (I/D) genotypes on the responses to the ACE inhibitor enalaprilat in normotensive men.

METHODS AND RESULTS

Subjects with DD (n=12) and II (n=11) ACE genotypes received an intravenous infusion of enalaprilat or placebo. Pressor responses to stepwise, incremental doses of angiotensin I were measured at 1 and 10 hours after dosing. The dose required to raise mean blood pressure by 20 mm Hg (PD20) was calculated individually, and the ratio of PD20 during enalaprilat to that during placebo (dose ratio, DR) was used for assessment of the extent of ACE inhibition. The pressor response was significantly attenuated at 1 hour after enalaprilat in both groups, but significant attenuation was evident at 10 hours after dose only in the II subjects. The DRs at both 1 hour (median, 5.43 versus 2.82, P=0.0035) and 10 hours (2.06 versus 0.84, P=0.0008) after enalaprilat were significantly higher in II subjects than in DD subjects.

CONCLUSIONS

The effect of enalaprilat was significantly greater and lasted longer in normotensive men homozygous for the II ACE genotype. By multivariate analysis, ACE (I/D) genotype and plasma angiotensin II levels were predictive of >50% of the variation in response to ACE inhibition.

Renal and haemodynamic effects of amlodipine and nifedipine in hypertensive renal transplant recipients

BACKGROUND

Immunosuppressive treatment with cyclosporin A (CsA) improves the survival of renal allografts, but is associated with renal vasoconstriction and hypertension. Previous reports suggest that the calcium-channel blockers nifedipine and amlodipine may improve graft function in CsA-treated patients. We have compared the effects of amlodipine (5-10 mg once daily) and nifedipine retard (10-40 mg twice daily) on renal function and blood pressure in renal transplant recipients treated with CsA.

METHODS

This was a multicentre, two-way, crossover study in 27 evaluable hypertensive patients with renal insufficiency following renal transplantation, who were maintained on a stable dose of CsA. Patients received either amlodipine (5-10 mg once daily) or nifedipine retard (10-40 mg twice daily) for 8 weeks, and were then crossed over to the other treatment for a further 8 weeks.

RESULTS

Trends were seen during amlodipine treatment towards larger improvements, in serum creatinine (by 8% of baseline on amlodipine vs 4% on nifedipine), lithium clearance (13% vs 2%), and glomerular filtration rate 11% vs 7%). Effective renal plasma flow was increased by 11% of baseline on nifedipine vs 9% on amlodipine. There were no significant differences between treatments. Amlodipine and nifedipine lowered systolic blood pressure to a similar extent (21 mmHg vs 15 mmHg respectively, P=0.25), but amlodipine was more effective than nifedipine in lowering diastolic blood pressure (13 mmHg vs 8 mmHg, P=0.006). Both treatments were well tolerated.

CONCLUSION

Once-daily amlodipine is at least as effective as twice-daily nifedipine retard in controlling blood pressure and does not adversely affect graft function in hypertensive renal allograft recipients.

Population pharmacokinetics of gentamicin in patients with cancer

AIMS

The purpose of this study was to describe the population pharmacokinetics of gentamicin in patients with cancer, to identify possible relationships between clinical covariates and population pharmacokinetic parameter estimates and to examine the relevance of existing dosage nomograms in light of the population model developed in these patients.

METHODS

Data were collected prospectively from 210 patients with cancer and were analysed with package NONMEM. Data were split into two sets: a population data set and an evaluation set. Creatinine clearance was estimated using measured creatinine concentrations and using 'low' creatinines set to a minimum of 60 micromol l(-1), 70 micromol l(-1) or 88.4 micromol l(-1)

RESULTS

A two compartment model was fitted to the concentration-time curve. Two best models were obtained, one that related clearance to estimated creatinine clearance (minimum creatinine value 60 micromol l(-1)) and the other that related clearance to age, creatinine concentration and body surface area. Volume of the central compartment was influenced by body surface area and albumin concentration. For both models 90% of measured concentrations lay within the 95% confidence interval of the simulated concentrations and the mean prediction errors were -7.2% and -6.6%, respectively. A final analysis performed in all patients identified the following relationship CL (1 h(-1))=0.88 x (1 + 0.043 x creatinine clearance) and central volume of distribution V1 (1)=8.59 x body surface area x (albumin/34)(-0.39). The mean population estimate of intercompartmental clearance (Q) was 1.301 h(-1) and peripheral volume of distribution (V2) was 9.801. Coefficient of variation was 18.5% on clearance and 28.2% on Q. Residual error expressed as a standard deviation was 0.36 mg l(-1) at 1.0 mg l(-1) and 1.32 mg l(-1) at 8.0 mg l(-1). The mean population estimate of clearance was 4.21 h(-1) and volume of distribution (Vss) was 24.61 (0.381 kg(-1)). The mean population estimates of half-lives were 1.8 h and 8.0 h.

CONCLUSIONS

In the context of published nomograms this analysis indicated that both the traditional approach and the new, 'once daily' approach should achieve satisfactory concentrations in cancer patients although serum concentration monitoring is required to confirm optimal dosing in individual patients.

Lacidipine: effects on vascular pressor responses throughout the dosage interval in normotensive subjects

AIMS

To assess the duration and consistency of the pharmacological activity of the dihydropyridine calcium antagonist drug, lacidipine.

METHODS

Eight healthy normotensive young males participated in a double-blind randomised crossover comparison of single and multiple doses (for 2 weeks) of lacidipine and placebo. The calcium antagonist effects were quantified at 2, 6 and 24 h post dose by the extent of the attenuation of the pressor responses to the intravenous administration of the vasoconstrictors angiotensin II and noradrenaline.

RESULTS

After 2 weeks of treatment, lacidipine consistently and significantly attenuated the pressor responses to both agents at 2 h post dose. At 6 and 24 h post dose there was a significant and progressive decline in the effectiveness of lacidipine in attenuating the pressor responses and for the response to angiotensin II there was no statistically significant effect at either 6 or 24 h post dose.

CONCLUSIONS

These results indicate that there is an obvious 'peak' in the pharmacological activity of lacidipine at about 2 h post dose and that this activity is not fully and consistently maintained throughout 24 h.

The vasodilating effect of insulin is dependent on local glucose uptake: a double blind, placebo-controlled study

During systemic hyperinsulinemia in man, skeletal muscle vasodilation has consistently been demonstrated. However, most studies that have examined the vascular effect of local hyperinsulinemia have reported either no effect or only weak vasodilation, and all of these have been open in design. The present studies were designed in a double blind, placebo-controlled manner to evaluate the direct (local) vascular effect of insulin alone and in association with physiological concentrations of D-glucose. Forearm blood flow was measured in 17 healthy male volunteers by bilateral venous occlusion forearm plethysmography. Brachial artery infusions of 1 mU/min insulin, 5 mU/min insulin, or vehicle were administered for 90 min on 3 separate study days in random order. The higher dose of insulin was associated with weak (20%) vasodilation compared with placebo (F = 5.75 and P < 0.01, by ANOVA). When this protocol was repeated with intraarterial coinfusion of D-glucose, significant augmentation of the vascular effect was demonstrated (47% vasodilation). No augmentation of insulin-mediated vasodilation was observed with coinfusion of L-glucose, the metabolically inactive stereoisomer. These data suggest that local uptake of D-glucose by insulin-sensitive tissues is an important determinant of insulin-mediated vasodilation.

Dietary sodium restriction impairs insulin sensitivity in noninsulin-dependent diabetes mellitus

Dietary sodium restriction has a variety of effects on metabolism, including activation of the renin-angiotensin system. Angiotensin II has complex metabolic and cardiovascular effects, and these may be relevant to the effects of both nonpharmacological and pharmacological interventions in noninsulin-dependent diabetes mellitus (NIDDM). We have assessed the effect of dietary sodium restriction on insulin sensitivity and endogenous glucose production in eight normotensive patients with diet-controlled NIDDM who underwent hyperinsulinemic clamp studies in a randomized, double-blind, placebo-controlled cross-over protocol after two 4-day periods on sodium replete (160 mmol/day) and sodium deplete (40 mmol/day) diets. Mean +/- SD 24-h urinary sodium was 197 +/- 76.0 mmol (replete) and 67 +/- 19.5 mmol (deplete), P = 0.03. Insulin sensitivity was 42.0 +/- 11.3 mumol/kg.min (replete) and 37.0 +/- 11.6 mumol/kg.min (deplete), P = 0.04 (a reduction of 12%). Blood pressure was 130 +/- 21/78 +/- 11 mmHg (replete) and 128 +/- 12/73 +/- 10 mmHg (deplete). Dietary sodium restriction may result in a decrease in peripheral insulin sensitivity in normotensive patients with NIDDM, possibly via an elevation in prevailing angiotensin II concentrations.

Angiotensin II antagonists: efficacy, duration of action, comparison with other drugs

The benefits of anti-hypertensive drug treatment have been established by clinical trials demonstrating significant reductions in cardiovascular morbidity and mortality. Thiazide diuretics predominated in these trials but it is reasonable to conclude that the benefits were attributable to the blood pressure (BP) reduction per se and not to specific pharmacological characteristics. Furthermore, it can be calculated that even greater benefits would probably have accrued if the magnitude of the BP reduction had been greater. On first principles, therefore, the basic requirement for any anti-hypertensive drug is confirmation of its ability to reduce BP. The angiotensin II antagonists constitute an important new class of drug, with a low incidence of adverse effects, but early studies with the prototype, losartan, have raised some doubts about its anti-hypertensive 'potency' in the clinical setting. For example, in several different comparative studies there were consistently lesser BP reductions with losartan compared to enalapril. This applied to both the trough and peak BP reductions. Furthermore, dose-response relationships have not always been clearly defined: for example, in one study diastolic BP reductions (trough) fell in the range 4.1 to 4.8 mm Hg with 50, 100 and 150 mg losartan. Although the preliminary results with newer angiotensin II antagonists suggest that they may have greater efficacy, there is only limited information about the definitive identification of the clinically relevant dose ranges for many of these drugs.

Evaluation of endpoints in hypertension: blood pressure

The benefits of antihypertensive therapy in reducing both cerebrovascular and cardiac events have been clearly demonstrated in the meta-analysis of randomised outcome trials. Whilst the use of diuretics and beta-blockers have tended to predominate in these trials, other agents were also included and thus it is reasonable to suggest that the benefit of treatment is not attributable to any particular class of agent but rather to a reduction in blood pressure per se. It may therefore, be reasonably argued that blood pressure itself is the only validated surrogate marker of cardiovascular outcome. In routine clinical practice evaluation has indicated that in treated hypertensives not only is blood pressure not lowered to normotensive levels but also that control of pressure was not consistent over a 24 hour period. Finally epidemiological evidence suggests that blood pressure control should be based upon treatment strategies that lower blood pressure to normotensive levels in a smooth and consistent fashion.

Insulin as a vascular hormone: implications for the pathophysiology of cardiovascular disease

1. Metabolic disorders, such as obesity and non-insulin-dependent diabetes mellitus, and cardiovascular disorders, such as essential hypertension, congestive cardiac failure and atherosclerosis, have two features in common, namely relative resistance to insulin-mediated glucose uptake and vascular endothelial dysfunction. 2. Significant increases in limb blood flow occur in response to systemic hyperinsulinaemia, although there is marked variation in the results due to a number of confounding factors, including activation of the sympathetic nervous system. Local hyperinsulinaemia has a less marked vasodilator action despite similar plasma concentrations, but this can be augmented by co-infusing D-glucose. 3. Insulin may stimulate endothelial nitric oxide production or may act directly on vascular smooth muscle via stimulation of the Na+-H+ exchanger and Na+/K+-ATPase, leading to hyperpolarization of the cell membrane and consequent closure of voltage-gated Ca2+ channels. 4. There is evidence both for and against the existence of a functional relationship between insulin-mediated glucose uptake (insulin sensitivity) and insulin-mediated vasodilation (which can be regarded as a surrogate measure for endothelial function). 5. If substrate delivery is the rate-limiting step for insulin-mediated glucose uptake (in other words, if skeletal muscle blood flow is a determinant of glucose uptake), then endothelial dysfunction, resulting in a relative inability of mediators, including insulin, to stimulate muscle blood flow, may be the underlying mechanism accounting for the association of atherosclerosis and other cardiovascular disorders with insulin resistance. 6. Glucose uptake may determine peripheral blood flow via stimulation of ATP-dependent ion pumps with consequent vasorelaxation. 7. A 'third factor' may cause both insulin resistance and endothelial dysfunction in cardiovascular disease. Candidates include skeletal muscle fibre type and capillary density, distribution of adiposity and endogenous corticosteroid production. 8. A complex interaction between endothelial dysfunction, abnormal skeletal muscle blood flow and reduced insulin-mediated glucose uptake may be central to the link between insulin resistance, blood pressure, impaired glucose tolerance and the risk of cardiovascular disease. An understanding of the primary mechanisms resulting in these phenotypes may reveal new therapeutic targets in metabolic and cardiovascular disease.

How reproducible is bilateral forearm plethysmography?

AIMS

In studies using strain-gauge forearm plethysmography to measure changes in forearm blood flow (FBF) during intra-arterial infusions of vasoactive substances, measurements are often made in both arms simultaneously and the change in ratio of the infused and control arms used to express responses. However, the reproducibility of bilateral plethysmography in this setting has not been addressed in published studies. The unilateral technique remains in use, and forearm vascular resistance (FVR), an alternative method of expressing responses, is used by some investigators. We have assessed: (a) the intra-subject variability of bilateral FBF measurements (FBF ratios) at rest, after unilateral forearm exercise, and during intra-arterial infusions of vasoconstrictor substances; (b) whether bilateral plethysmography is more reproducible than unilateral plethysmography; and (c) the reproducibility of FVR (unilateral and bilateral).

METHODS

Study 1 Nine healthy subjects attended 3 study days, 1 week apart. FBF was measured at rest and after 2 min of standardized unilateral forearm exercise; between-day intra-subject variability was expressed as coefficients of variation (CV) calculated using two-way analysis of variance (ANOVA). Study 2 Five healthy subjects attended 2 study days when FBF was measured during incremental infusions of noradrenaline (15, 30, 150, 300 pmol min[-1]) and angiotensin II (1, 5, 10, 50 pmol min[-1]); for each individual subject at each dose intra-subject variability was assessed using the difference between responses (percentage change from baseline) on days 1 and 2.

RESULTS

Study 1 At rest, intra-subject variability (CV) of baseline FBF ratios was 19% compared with 31% (left) and 39% (right) for unilateral FBF measurements. After ipsilateral exercise, unilateral FBF measurements were more reproducible (32 vs 17%) than FBF ratios; by 20 min after exercise, the previous pattern had been re-established (19 vs 27%). Intra-subject variability (CV) of baseline FVR ratio and post-exercise FVR was 14%. Study 2 Inter-quartile ranges of the differences between responses on days 1 and 2 (FBF ratios vs FBF) were: angiotensin II 14 vs 18%; noradrenaline 16 vs 27%.

CONCLUSIONS

FBF ratios are more reproducible than unilateral FBF measurements at rest (CV 19% vs 39%) and for measuring responses to intra-arterial infusions of vasoconstrictor substances. FVR may have a small reproducibility advantage. Non-experimental stimuli can cause significant and misleading changes in measured responses if unilateral measurements are used; it is therefore recommended that responses to intra-arterial infusions should be measured using bilateral forearm plethysmography with the results expressed as FBF ratios.

Clinical pharmacokinetics of nifedipine. Implications for the care of the elderly

Nifedipine, the prototype for the dihydropyridine class of calcium antagonists, has been available for 20 years and its efficacy as a vasodilator and an antihypertensive agent is well recognised. The development of the so-called nifedipine gastrointestinal therapeutic system (GITS), which allows once-daily administration, has modified and improved the overall therapeutic profile of nifedipine to such a significant extent that it might almost be considered a new drug entity. The nifedipine GITS is associated with distinct improvements in terms of patient compliance and convenience, and a reduced incidence of adverse effects. With regard to the care of the elderly, this 'new' drug offers the prospect of a well tolerated and effective treatment without major cost implications.

The euglycaemic hyperinsulinaemic clamp: an evaluation of current methodology

1. The recognition of the role of insulin resistance in disease states and the recent development of new drugs that modify insulin-dependent metabolism has led to increased use of the euglycaemic hyperinsulinaemic clamp to measure in vivo insulin sensitivity, but several key aspects of the technique are poorly documented in the literature. 2. We have evaluated the reproducibility and intersubject variation of measurements of insulin sensitivity in groups of insulin-sensitive and insulin-resistant subjects and assessed the effects of hand warning on haemodynamic and metabolic responses. 3. Subjects participated in one of two protocols: (i) 18 healthy male volunteers and 18 patients with hypertension and glucose intolerance were clamped on two occasions, 1 week apart with measurements of insulin sensitivity (M) derived after 120 and 180 min of hyperinsulinaemia; and (ii) six healthy volunteers were clamped on one occasion with simultaneous sampling of antecubital and 'arterialized' (dorsal hand) venous blood for comparison of plasma glucose concentrations and oxygen saturation and a further six volunteers were clamped on two occasions with and without the use of hand warming. 4. Measurements of M derived after 120 min (M120) and 180 min (M180) of hyperinsulinaemia were reproducible: the coefficients of repeatability (mg/kg per min) of M120 and M180 were 1.0 and 0.9 for volunteers and 1.0 and 1.0 for the patient group, respectively. The intersubject variation in insulin stimulus was high: coefficients of variation for M180 were 22% for volunteers compared with 38% for the patient group. In volunteers compared with the patient group, hand warming significantly increased venous oxygen saturations (95 +/- 2 vs 79 +/- 18%, respectively) and glucose concentrations (5.2 +/- 0.2 vs 4.5 +/- 0.4 mmol/L, respectively) and measurements of M were significantly higher using arterialized compared with antecubital venous blood. However, local hand warming was associated with systemic vasodilatation: blood pressure decreased (e.g. 6 mmHg diastolic; P < 0.05) with a compensatory increase in heart rate (8 b.p.m.). 5. In conclusion, clamps of 120 and 180 min duration yielded measurements of M that were reproducible. The technique is much more robust when used in the context of a crossover design because of the significant (20-40%) intersubject variation in M, even among apparently homogeneous male volunteers. Hand warming effectively arterializes venous blood and gives significantly higher M values, but induces systemic vasodilation, which may confound measurements of M.

Benefits of twenty-four-hour blood pressure control

BACKGROUND

Despite the clear recognition that blood pressure does not remain at the same level over a 24-h period, normally falling during sleep and rising during times of physical or mental activity, a single blood pressure measurement gained during the working day is conventionally used to classify a patient as normotensive or hypertensive. ANTIHYPERTENSIVE TREATMENT AND 24-H BLOOD PRESSURE CONTROL: There is still no definitive proof that antihypertensive drugs providing full 24-h blood pressure control will lead to improved outcomes compared with drugs that provide incomplete 24-h blood pressure control. However, there is a large body of evidence showing that cardiovascular target-organ damage is correlated with 24-h blood pressure measurements and supportive evidence that a fall in these 24-h measurements can predict a likely reduction in cardiovascular target-organ damage.

CONCLUSIONS

In deciding which antihypertensive agent to use, physicians should select, where possible, those agents that provide blood pressure control through the 24-h period.

White-coat hypertension as a cause of cardiovascular dysfunction

BACKGROUND

The increasing use of 24 h ambulatory blood pressure monitoring has allowed diagnosis of white-coat hypertension, in which blood pressures are higher on clinic measurements than on ambulatory monitoring. Treatment is not generally thought to be necessary for this disorder. However, there is evidence that patients with white-coat hypertension develop renal impairment and left ventricular hypertrophy. We undertook this study to assess whether white-coat hypertension, in the absence of cardiovascular structural abnormalities, is associated with cardiovascular functional abnormalities.

METHODS

Cardiovascular function was assessed by ultrasonography in three groups of patients classified as normotensive, persistently hypertensive, or white-coat hypertensive (23, 20, and 22 patients, respectively) on the basis of ambulatory blood pressure monitoring, carried out for 28 h with recordings taken every 15 min during the day and every 20 min during the night, and clinic measurements, made with a semi-automatic oscillometric device.

RESULTS

Similar abnormalities of diastolic left ventricular function were identified in the patients with persistent hypertension and those with white-coat hypertension; both groups differed in these indices from the normotensive group (E/A ratios 0.94 [SD 0.23], 1.06 [0.21], and 1.24 [0.31] respectively; ANOVA p < 0.005). In addition, the white-coat and persistently hypertensive groups, when compared with the normotensive group, showed similar abnormalities of elasticity, compliance, and stiffness (stiffness index 4.32 [1.90], 4.53 [1.38], and 3.27 [0.95] respectively; ANOVA p < 0.05) of the large arteries.

INTERPRETATION

Functional cardiovascular abnormalities were identified in white-coat hypertensive patients who had no identifiable structural abnormalities. Such functional abnormalities can be reversed by antihypertensive treatment. We propose that patients with white-coat hypertension might benefit from antihypertensive treatment as well as those with persistent hypertension. This hypothesis should be addressed in prospective clinical trials.

Concentration-effect relationships and implications for trough-to-peak ratio

The guidelines on trough-to-peak ratio identified an index of the duration of action of an antihypertensive drug (relative to its dosage interval) to prevent the use of inappropriately large doses of drug simply to extend the apparent duration of action. In some instances, however, trough-to-peak ratio may be dose-dependent and this analysis examines the contribution that the underlying concentration-antihypertensive effect relationship makes to the dose dependency of trough-to-peak ratio. Where this concentration-effect relationship is essentially linear the trough-to-peak ratio is almost invariably dose-independent. In contrast, where the relationship is identified as being of a sigmoid-Emax type the trough-to-peak ratio is likely to be dose-dependent. The nature of the concentration-effect relationship also influences the duration of action beyond the dosage interval whereby "linear" drugs are superior to "Emax" drugs by virtue of the greater persistence of the antihypertensive effect.

Calculation of trough-to-peak ratio in the research unit setting. Advantages and disadvantages

The trough-to-peak ratio for the response to an antihypertensive drug is a clinically meaningful parameter but only when the calculation has been derived from an appropriate and scientifically robust study. Since the methodological details have not been defined by any regulatory authority, several possible approaches have developed. The major apparent advantages of the intensive study of individual patients in the research unit setting are that the conditions of measurement can be standardized and an accurate account can be taken of the circadian variations in the responses to placebo and active drug treatment. The principal disadvantage is that it is an "artificial" environment that may, or may not, be directly relevant to routine clinical circumstances. Nevertheless, the values obtained with this approach to date are directly comparable to values obtained by the alternative approaches, such as ambulatory blood pressure measurements (provided that those are also well-conducted studies). Thus, using the trough-to-peak ratio not only appears valid but also permits the detailed study of individual patients and also lends itself to the incorporation of additional and confirmatory clinical pharmacological assessments.

White-coat hypertension as a cause of cardiovascular dysfunction

BACKGROUND

The increasing use of 24 h ambulatory blood pressure monitoring has allowed diagnosis of white-coat hypertension, in which blood pressures are higher on clinic measurements than on ambulatory monitoring. Treatment is not generally thought to be necessary for this disorder. However, there is evidence that patients with white-coat hypertension develop renal impairment and left ventricular hypertrophy. We undertook this study to assess whether white-coat hypertension, in the absence of cardiovascular structural abnormalities, is associated with cardiovascular functional abnormalities.

METHODS

Cardiovascular function was assessed by ultrasonography in three groups of patients classified as normotensive, persistently hypertensive, or white-coat hypertensive (23, 20, and 22 patients, respectively) on the basis of ambulatory blood pressure monitoring, carried out for 28 h with recordings taken every 15 min during the day and every 20 min during the night, and clinic measurements, made with a semi-automatic oscillometric device.

RESULTS

Similar abnormalities of diastolic left ventricular function were identified in the patients with persistent hypertension and those with white-coat hypertension; both groups differed in these indices from the normotensive group (E/A ratios 0.94 [SD 0.23], 1.06 [0.21], and 1.24 [0.31] respectively; ANOVA p < 0.005). In addition, the white-coat and persistently hypertensive groups, when compared with the normotensive group, showed similar abnormalities of elasticity, compliance, and stiffness (stiffness index 4.32 [1.90], 4.53 [1.38], and 3.27 [0.95] respectively; ANOVA p < 0.05) of the large arteries.

INTERPRETATION

Functional cardiovascular abnormalities were identified in white-coat hypertensive patients who had no identifiable structural abnormalities. Such functional abnormalities can be reversed by antihypertensive treatment. We propose that patients with white-coat hypertension might benefit from antihypertensive treatment as well as those with persistent hypertension. This hypothesis should be addressed in prospective clinical trials.

Post hoc analysis: use and dangers in perspective

DANGERS AND ADVANTAGES OF POST HOC ANALYSIS: Post hoc analysis is of major importance in the generation of hypotheses. However, the hypothesis is created by the analysis and has not been proved by any "experiment'. In some circumstances the conclusion derived from a post hoc analysis is entirely appropriate. For example, it was the only method used by Crick and Watson for determining the structure of DNA. In other circumstances, however, the results will be misleading. NEED FOR CAUTION WITH INTERPRETATION: The results of a post hoc analysis should be viewed with considerable scepticism and, in advance of confirmation by other appropriately designed prospective studies, should not be regarded as definitive proof.

Mistyping of the human angiotensin-converting enzyme gene polymorphism: frequency, causes and possible methods to avoid errors in typing

A polymorphism of the gene encoding the human angiotensin I-converting enzyme (ACE), which is defined by an insertion/deletion polymorphism in intron 16, has been identified as a candidate genetic locus in the development of cardiovascular and renal disease. We have demonstrated that the accuracy of ACE genotyping is critically dependent on the strategy of the PCR used in typing. Of 1238 individuals genotyped by a standard method, 335 were typed as DD, 645 as DI and 258 as II. However, when DD individuals were retyped using modified methods (including either 5% dimethyl sulphoxide, or a 'hot start') 35 of the original 335 samples (10.5%) were retyped as DI. In approximately half of these mistyped samples, PCR amplification was assessed as inefficient by the absence of a third faint heteroduplex band in a control ID sample: when the assay was repeated without any modifications, the mistyped samples were correctly genotyped. In the remainder, mistyping persisted. In these cases, the use of a third 'nested' PCR primer specific for the I allele was required for successful genotyping, providing a more reliable strategy without the need for further modification to the PCR technique. Our results suggest that the triple primer approach is the method of choice for accurate ACE genotyping.

Potential confounding effect of hand-warming on the measurement of insulin sensitivity

1. Hand-warming is employed during metabolic studies to "arterialize' venous blood, but also has systemic haemodynamic effects. Study 1 aimed to determine if hand-warming affects the value for whole-body insulin sensitivity derived from the hyperinsulinaemic euglycaemic clamp technique. Study 2 was designed to assess the effect of hand-warming on contralateral forearm blood flow. 2. In study 1, eight healthy male subjects attended for four modified euglycaemic clamp studies, during which the right hand was placed in a heated-air hand box (55 degrees C), and the glucose infusion rate was adjusted according to blood samples from a cannula in either an ipsilateral dorsal hand vein or a contralateral antecubital vein with the box switched either on or off. In study 2, five healthy subjects attended two study days when the effect of 2 h of hand-warming (or control) on contralateral forewarm blood flow was measured. 3. Study 1; when clamps were performed according to samples taken from the contralateral antecubital vein, insulin sensitivity values were significantly lower during box-on versus box-off clamps (mean +/- SD 10.2 +/- 3.0 versus 13.0 +/- 3.8 mg min-1 kg-1, P < 0.05, 95% confidence interval -0.2, -5.3). When clamps were performed according to samples taken from the ipsilateral hand, there was no difference in insulin sensitivity during box-on versus box-off clamps (9.2 +/- 2.1 versus 9.0 +/- 1.7 mg min-1 kg-1, P not significant, 95% confidence interval -0.5, +0.9). There was a mean increase in heart rate of 6 beats/min in the box-on conditions (P < 0.05, analysis of variance). Study 2; forearm blood flow in the contralateral arm during hand-warming was significantly higher than in the control condition (P < 0.05, analysis of variance), although heart rate was similar on both study days. 4. Hand-warming had a detectable effect on insulin sensitivity when clamps were performed according to samples withdrawn from the contralateral arm, but no measurable effect when clamps were performed in the conventional manner. In addition, hand-warming increased heart rate during hyperinsulinaemia and contralateral FBF under basal conditions. These findings raise concern about unwanted (potentially confounding) systemic haemodynamic effects of hand-warming on the measurement of insulin sensitivity and insulin-mediated vasodilation.

Endothelial nitric oxide production and insulin sensitivity. A physiological link with implications for pathogenesis of cardiovascular disease

BACKGROUND

Insulin sensitivity varies up to threefold in apparently healthy individuals, but the mechanism for this is unknown. We have examined the hypothesis that vascular endothelial nitric oxide production and insulin sensitivity are directly related in humans.

METHODS AND RESULTS

Nineteen healthy male subjects were studied on 3 separate days 1 week apart during which time they underwent measurement of insulin sensitivity by the euglycemic hyperinsulinemic clamp technique (soluble insulin 1.5 mU . kg-1 . min-1) and measurement of in vivo basal and stimulated endothelial nitric oxide production by forearm venous occlusion plethysmography. There was a correlation between insulin sensitivity and forearm vasoconstrictor responses to NG-monomethyl-L-arginine, the substrate inhibitor of nitric oxide synthase (r = .52, P < .05). No correlations were observed between insulin sensitivity and noradrenaline, acetylcholine, or sodium nitroprusside responses.

CONCLUSIONS

Endothelial nitric oxide synthesis and insulin sensitivity are positively related in healthy humans, which suggests a direct physiological link.

Review: the central role of calcium in the pathogenesis of cardiovascular disease

Calcium-dependent processes play a central role in several different cells of the cardiovascular system including vascular smooth muscle and endothelial cells and also in monocytes, macrophages and platelets. In response to extracellular stimuli cytosolic calcium concentration increases. The increase is composed of two distinct phases. Firstly, calcium is released from intracellular stores via IP3. In the second phase calcium influx across the cell membrane is mostly responsible for the sustained rise in intracellular calcium concentration. This phase of the peak increase in cytosolic calcium is a prerequisite for sustained activation of the cell and the processes of vascular smooth muscle contraction and the activation of nuclear transcription factors for protein biosynthesis. Under ischemic conditions the regulatory systems which control the intracellular free calcium concentration consume a major portion of the cell's physiological energy supply (90%) and a decreased oxygen supply under ischemic conditions rapidly reduces the cell's capacity for intracellular calcium storage or outward transport across its membrane. Calcium antagonist drugs principally act on L-type calcium channels to reduce the influx of calcium into the the cells of the body. Since calcium antagonist drugs are able to influence a wide range of cellular processes which have been implicated in atherosclerosis, glomeruloscierosis, left ventricular hypertrophy and insulin resistance there are strong grounds for their use in a range of clinical disease states.

Haemodynamics, cardiac conduction and pharmacokinetics of mibefradil (Ro 40-5967), a novel calcium antagonist

OBJECTIVES

Mibefradil (Ro40-5967) is a chemically novel non-dihydropyridine calcium antagonist. In this phase II study we compared its acute and chronic effects on blood pressure, heart rate and atrioventricular conduction (electrocardiographic PQ interval) with those of verapamil and diltiazem.

PATIENTS AND METHODS

After a 4-week placebo run-in, 18 patients with mild to moderate essential hypertension were given single doses of mibefradil (150 mg), slow-release (SR) verapamil (240 mg), diltiazem (240 mg) and placebo at weekly intervals; pharmacokinetics and the effects on blood pressure, heart rate and PQ interval were studied on four 10-h study days. Seventeen of the same patients subsequently underwent 4 weeks of treatment with either mibefradil (100 mg daily; n = 10) or verapamil SR (240 mg daily; n = 7), and on the last day, they attended a further 10-h study day. Two studies were conducted: an acute, single-dose, double-blind, randomly allocated, placebo-controlled, crossover study and a chronic, open-label, randomly allocated, parallel-group study.

RESULTS

Mibefradil was well tolerated. In the acute study, the antihypertensive effect (difference from placebo) of mibefradil 150 mg was of slower onset than that of verapamil or diltiazem, but comparable blood pressure reductions had been achieved by 6 h. The mean +/- SD maximal PQ prolongation (difference from placebo) was 15.6 +/- 16.1 ms, compared with 44.0 +/- 22.6 ms for verapamil and 56.0 +/- 48.9 ms for diltiazem (P<0.05 mibefradil versus verapamil; P<0.01 mibefradil versus diltiazem). In the chronic study there were no significant differences during steady-state conditions between mibefradil at 100 mg and verapamil SR at 240 mg in their effects on blood pressure, PQ and heart rate. The mean +/- SD elimination half-life (t1/2) of mibefradil under steady-state conditions was 26.8 +/- 5.5 h (versus an apparent t1/2 of 16.9 +/- 11.1 h for verapamil SR, P<0.05).

CONCLUSIONS

Mibefradil is a well-tolerated and efficacious antihypertensive agent well suited to single daily dosing because of its intrinsic long plasma half-life. The effects on both blood pressure and PQ interval are of more gradual onset than those of unmodified verapamil and diltiazem after single doses.

Clinical pharmacology of drugs acting on imidazoline and adrenergic receptors. Studies with clonidine, moxonidine, rilmenidine, and atenolol

Centrally acting antihypertensive drugs are recognized to be safe and effective treatment for high blood pressure. Centrally mediated side effects, such as sedation, are commonly dose- and treatment-limiting events. Imidazoline-preferring receptors, while functionally similar to alpha 2 adrenoceptors, are distinguishable not only on the basis of in vitro radioligand binding but also in vivo in terms of side effects. Drugs with an imidazoline structure lower blood pressure but are less likely to impair psychomotor function. A placebo-controlled study compared moxonidine 0.1 mg with clonidine 0.1 mg orally in nine normal subjects. Both active drugs lowered blood pressure compared to placebo (clonidine more than moxonidine). However, psychomotor function and self-scored sedation and dry mouth were significantly affected only by clonidine. In a long-term (4 weeks) double-blind cross-over study in essential hypertension, rilmenidine was well tolerated and had similar effects to those of atenolol on erect and supine blood pressure. Rilmenidine had no effect on a wide range of autonomic and psychomotor tests or on responses to mental or physical stress. Atenolol, by contrast, had the predicted effects of a beta adrenoceptor antagonist on heart rate during exercise and the Valsalva maneuver. Imidazoline-preferring drugs offer a new and realistic approach to antihypertensive therapy with blood pressure reduction not limited by marked sedation within the therapeutic dose range.

Analysis of trough:peak ratio and the assessment of anti-hypertensive drug action

The conventional blood pressure (BP) measurement is essentially a 'snapshot' at a single time point in any given 24 h period. In the clinical management of the hypertensive patient, however, it is assumed that this snapshot is representative of the BP throughout 24 h and indicative of the consistency of the control produced by anti-hypertensive drug treatment. However, anti-hypertensive drugs vary in the duration and consistency of their anti-hypertensive effect and a single measurement of BP can only be reliably indicative if the drug effect is known to be consistently maintained throughout the 24 h. Following the deliberations of the Food and Drug Administration in the USA, the calculation of a trough:peak ratio has been proposed as an index of the consistency of the anti-hypertensive response and the suitability of an anti-hypertensive drug for its chosen dose and dose interval. In brief, to confirm that the magnitude of the BP is relatively consistent throughout 24 h it is recommended that the magnitude of the BP reduction at the end of the dose interval (at trough) should be at least 50% of the BP reduction measured at peak, namely a trough:peak of 50%. The trough:peak ratio provides a clinically relevant index for assessing whether an anti-hypertensive drug is likely to provide a consistent anti-hypertensive effect throughout the 24 h.

Enhanced pressor response to angiotensin I in normotensive men with the deletion genotype (DD) for angiotensin-converting enzyme

The insertion (I)/deletion (D) polymorphism of the human angiotensin-converting enzyme gene has emerged as a genetic risk factor for ischemic heart disease. However, the functional consequences of this polymorphism in humans are not known. Ten normotensive men with the DD genotype and 10 with the II genotype participated in a study in which pressor responses to stepwise infusions of incremental doses of angiotensin I (Ang I) and Ang II and Ang II production during Ang I infusion were measured. Pressor responses were expressed as PD20, which reflects the angiotensin dose required to raise mean blood pressure by 20 mm Hg. The PD20 for Ang I in subjects with the DD genotype was significantly lower than that in II genotype subjects (8.8 versus 14.8 ng/kg per minute, P = .0091), whereas the PD20 for Ang II between the two groups did not differ significantly. The ratio of PD20 for Ang I and Ang II in DD subjects was significantly lower than that in II subjects (0.85 versus 0.96, P = .0452), and the venous levels of Ang II during Ang I infusion in DD subjects were significantly higher than those in II subjects (P < .01). Our study has shown increased pressor responsiveness to Ang I, probably as a consequence of the generation of increased Ang II levels, in subjects homozygous for the DD allele of the angiotensin-converting enzyme gene. This result may be relevant to the reported adverse cardiovascular risk conferred by the D allele, as it provides a mechanistic rationale for the association between this polymorphism and cardiovascular disease.