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.