A meta-analysis of ECG data from healthy male volunteers: diurnal and intra-subject variability, and implications for planning ECG assessments and statistical analysis in clinical pharmacology studies.

OBJECTIVE: To evaluate the innate variability in key electrocardiography (ECG) parameters from clinical pharmacology studies. METHODS: Meta-analysis of ECG data from seven clinical pharmacology studies in healthy male volunteers using model building and stepwise multiple regression analyses. RESULTS: Data from 115 male subjects provided over 2,000 observations for all key ECG parameters from baseline (Day-1) and placebo treatment periods (Day 1). Only heart rate and uncorrected QT showed clear and marked changes over the day. QTcB had greater variability compared to QTcF. 1.4% of QTcB and 0.7% QTcF observations were >430 ms and 0.1% of QTcB and 0% of QTcF observations were >450 ms. We estimated that 8.9% of subjects would have at least one out of eight post-observation QTc value in the range 430-450 ms [assuming QTc mean 385 ms, standard deviation (SD) 20 ms] due to intrinsic variability alone. Time-matched within-subjects observations demonstrated that the SD between measurements taken 1 h apart was less than seen with a longer interval, but there was little increase in variability beyond 1 h. The probability of observing an increase in QTc of 30-60 ms in a subject was estimated as 3.0% and 21.8% for one and eight post-dose observations, respectively. The greater the number of observations used to define baseline the narrower the spread; for QTcF the SD of the baseline value was 17.1 ms for a single assessment, 13.3 ms for the mean of three assessments, and 13.2 ms for the mean of all Day-1 assessments. CONCLUSIONS: The spontaneous variability in QTc measurements must be taken into account when designing studies and interpreting analyses of ECG data. The categorical analysis of QTc change of 30-60 ms is unlikely to be of any additional value to analyses of central tendency. For standard early clinical pharmacology studies, QTcF should be chosen as the primary correction method, while the mean of three measures taken in the afternoon and evening of Day-1 and pre-dose Day 1 should provide a reliable and representative baseline assessment.

Oral V2 receptor antagonist (RWJ-351647) in patients with cirrhosis and ascites: a randomized, double-blind, placebo-controlled, single ascending dose study.

BACKGROUND: RWJ-351647 is a selective V2 receptor antagonist that inhibits vasopressin-induced water reabsorption in the kidney. AIM: To investigate the safety and tolerability of RWJ-351647 compared with placebo after single oral dose administration to patients with cirrhosis and ascites, on a stable treatment with furosemide and spironolactone. METHODS: Single oral doses of 1, 2 and 5 mg of RWJ-351647 were administered to 24 patients with ascites on stable concomitant diuretic treatment. RESULTS: RWJ-351647 had a tmax of 1 to 1.1 h and mean half-life of 10.4-17.4 h. There was no affect on the pharmacokinetics of concomitant diuretics. Increases in cumulative urine volume and free water excretion, and a decrease in urine osmolality were noted in a dose-dependent manner reaching the statistical significance at the 5-mg dose. Four patients exhibited a decrease of > 2 kg in weight in the 24 h after dosing. RWJ-351647 was well tolerated, with no evidence of a dose-related increase in adverse events when compared with placebo. No changes in either serum chemistry or plasma AVP (arginine vasopressin) and renin levels were observed despite the observed aquaresis. CONCLUSION: RWJ-351647 is an effective aquaretic causing dose-dependent increases in urine output and free water clearance, when co-administered with conventional diuretics in patients with cirrhosis and ascites.

A comparison of nifedipine once daily (Adalat LA), isosorbide mononitrate once daily, and isosorbide dinitrate twice daily in patients with chronic stable angina.

The efficacy of nifedipine gastrointestinal therapeutic system (GITS), 60-90 mg o.d., isosorbide dinitrate, 40-60 mg b.d., and isosorbide mononitrate slow-release, 50-100 mg o.d. was assessed in a six week double-blind, parallel-group study in patients with stable angina on chronic beta-blocker treatment. Of 339 patients who entered the study, 229 were eligible for the valid case analysis of efficacy and 335 for the safety analysis. Nifedipine GITS was significantly better than isosorbide dinitrate (P < or = 0.025) in prolonging time to 1 mm ST-segment depression, time to maximum ST-segment depression, time to occurrence of angina and total exercise duration, in addition to reducing the number of angina attacks and glyceryl trinitrate consumption after six weeks therapy. Nifedipine GITS was also significantly better than isosorbide mononitrate (P < or = 0.025) in prolonging time to occurrence of angina and time to 1 mm ST-segment depression after six weeks therapy. The incidence of headache was considerably higher in both the isosorbide dinitrate and isosorbide mononitrate groups (40% and 41%, respectively) than in the nifedipine GITS group (9.5%, P < or = 0.001), and was the main reason for withdrawal from the study (isosorbide dinitrate 18/99, isosorbide mononitrate 17/99, nifedipine GITS 2/95). Peripheral oedema was more common in patients treated with nifedipine GITS (12.5%) compared to nitrates (2% in both groups, P < or = 0.01), but resulted in withdrawal of only one patient (treated with nifedipine GITS). This study suggests that the efficacy and tolerability of nifedipine GITS is superior to long acting nitrates as second-line therapy to beta-blockade in the treatment of chronic stable angina.

Preconditioning the human myocardium: recent advances and aspirations for the development of a new means of cardioprotection in clinical practice.

Ischemic preconditioning has been shown to be one of the most powerful means of protecting the myocardium from ischemic injury in experimental animal models, although the mechanism is incompletely understood. In this review we discuss the evidence for preconditioning occurring in ischemic syndromes in humans, whether the human myocardium can be preconditioned, and whether preconditioning would have a place as a therapeutic tool in clinical practice. Some studies evaluating patients after acute myocardial infarction have shown a better outcome in patients reporting angina before the onset of the infarction, but this is not a universal finding, and it is difficult to exclude other confounding factors, such as collateral flow, from influencing the results. More controlled prospective studies have evaluated patients undergoing percutaneous transluminal coronary angioplasty and have found less ST-segment change and less reported angina during the second balloon inflation when compared with the first. Again, it is impossible to completely exclude other causes for this effect, but the dependence on mechanisms that are known to be important for preconditioning in animal models does suggest the phenomena are the same. Further experiments using isolated human atrial muscle have shown that human myocardium can be preconditioned and that the mechanisms involved are similar to those elucidated in animal models (adenosine, protein kinase C, and ATP-dependent potassium channels). In clinical medicine preconditioning is most likely to benefit patients when it is used to protect against the ischemia induced by cardiac surgery. In this respect, a study has shown that in patients undergoing coronary artery bypass grafts, the reduction in ATP occurring during the first ischemic period is attenuated in those given an ischemic preconditioning protocol beforehand. Despite these advances, it is likely that the full potential of preconditioning in clinical practice will not be realized until the whole mechanism of protection is understood and a safe pharmacological "preconditioning" agent becomes available.

Increased endogenous catalase activity caused by heat stress does not protect the isolated rat heart against exogenous hydrogen peroxide.

OBJECTIVE: The aim was to investigate the potential for the enhancement of endogenous catalase activity after heat stress to protect the isolated rat myocardium from the injurious effects of exogenous hydrogen peroxide. METHODS: Male Sprague-Dawley rats were randomised to either heat stress or sham treatment. At 24 and 48 h after treatment hearts were retrogradely perfused at a constant flow rate of 10 ml.min-1. After a 15 min stabilisation period hearts were perfused with 75 microM hydrogen peroxide for 85 min. Mechanical function was measured by an intraventricular isovolumic latex balloon while coronary perfusate was collected for measurement of lactate dehydrogenase activity. At the end of the perfusion period the glutathione status of the hearts was determined. In separate experiments baseline cardiac catalase activity and glutathione state were measured 24 and 48 h after heat stress or sham treatment. RESULTS: Cardiac catalase activity was increased by 49% at both 24 and 48 h after heat stress in comparison with sham controls. Glutathione concentrations were reduced by 12% 24 h after heat stress but had recovered by 48 h. Perfusion of sham hearts with 75 microM hydrogen peroxide resulted in a progressive decline in mechanical function as evident by a fall in developed pressure and rise in diastolic pressure. Coronary resistance also rose during the perfusion period as shown by a progressive increase of coronary perfusion pressure. Coronary effluent lactate dehydrogenase release was only increased above basal concentrations at the end of the perfusion period, whereas cardiac glutathione concentrations were severely depleted. Hearts taken 24 h after heat stress showed a reduced resistance to the effect of 75 microM hydrogen peroxide on mechanical activity, although there was no difference in the pattern of lactate dehydrogenase release or depletion of glutathione. Perfusion of hearts taken 48 h after heat stress with 75 microM hydrogen peroxide resulted in the same effect on mechanical dysfunction, coronary resistance, lactate dehydrogenase release, and cardiac glutathione depletion as sham controls. CONCLUSIONS: The increase in endogenous cardiac catalase activity caused by prior heat stress is insufficient to protect the isolated rat heart from injury induced by exogenous hydrogen peroxide.

The protective effect of heat stress against reperfusion arrhythmias in the rat.

Heat stress provides protection against mechanical dysfunction and myocardial necrosis after prolonged ischemia. We have investigated whether this protection extends to reperfusion arrhythmias occurring after a short (non-lethal) ischemic insult. Anaesthetized open chest rats were subjected to a 5-min occlusion of the left coronary artery. The incidence and duration of reperfusion arrhythmias and the duration of sinus rhythm were assessed in the first 5 min of reperfusion. Prior heat stress led to a reduction in the incidence (100-63%, P < or = 0.05) and duration (66.2 +/- 15.8 to 9.4 +/- 2.9 s, P < or = 0.05) of ventricular tachycardia and a non-significant reduction in the incidence (76-50%) and duration (74.3 +/- 23.4 to 42.9 +/- 24.4 s, P = 0.09) of ventricular fibrillation. This resulted in a significant increase in the duration of sinus rhythm (142.1 +/- 27.6 to 216.7 +/- 24.8 s, P < or = 0.05) and reduction in arrhythmia score (P < or = 0.05) in heat stressed rats compared with controls. This protection against reperfusion arrhythmias was associated with a two-fold increase in endogenous catalase activity and expression of the inducible heat stress protein HSP 70. Inhibition of catalase with pre-administered 3-amino triazole resulted in a paradoxical protection in both sham and heat stress hearts. We conclude that heat stress leads to protection against reperfusion arrhythmias; however, we have been unable to resolve whether the changes in catalase activity or HSP expression are the mediators of the demonstrated cardioprotection.

Heat stress attenuates free radical release in the isolated perfused rat heart.

Prior heat stress leads to an enhancement of postischemic mechanical function and improvement in biochemical indices of injury in the rat heart, associated with an elevation in endogenous catalase activity. We have examined the effect of heat stress on free radical release during reperfusion in the isolated rat heart using electron spin resonance (ESR). Twenty four hours after heat stress or sham treatment, hearts were perfused in the Langendorff mode and subjected to 10 min of no-flow global ischemia followed by 10 min of reperfusion. Coronary effluent was collected at specific time points in PBN for ESR measurement. A PBN adduct was identified with characteristics consistent with an alkoxyl radical: PBN-LO. In sham hearts there was a rapid rise in adduct release to a maximum (228 +/- 15% of stabilization values, p < .05) occurring 1 min into reperfusion. In heat stress hearts there was no significant rise in adduct release during the reperfusion period. Pretreatment of hearts with 3-amino triazole, an inhibitor of catalase, failed to clarify whether the protection seen in heat stress hearts was a result of the elevation in catalase activity. These results suggest that heat stress protects the myocardium against the oxidative stress of ischemia-reperfusion.

Subclinical cardiomyopathy in Becker muscular dystrophy.

OBJECTIVE: To investigate the prevalence, age distribution, and spectrum of cardiac involvement in a cohort of patients with Becker muscular dystrophy. DESIGN: A prospective non-invasive study with clinical, electrocardiographic, and echocardiographic assessment. PATIENTS: 19 patients (age range 16-41 years) with Becker muscular dystrophy attending the Muscle Clinic at Hammersmith Hospital and 22 healthy controls (age range 22-36 years). RESULTS: 17 patients (89%) were symptom free; two had exertional dyspnoea. Three had a past history of acute pericarditis. The electrocardiogram was abnormal in 14 patients (74%). Intraventricular conduction delay or right bundle branch block was present in eight (42%). Three (16%) had tall R waves (R/S > 1) in lead V1 in the absence of right bundle branch block and eight (42%) had Q waves in the lateral and inferolateral leads. The PQ interval was significantly shorter in patients with Becker muscular dystrophy (p < 0.01). Echocardiography showed left ventricular dilatation in seven patients (37%) and 12 (63%) had subnormal systolic function caused by global hypokinesia (fractional shortening < 27%). Six of these patients were under the age of 22 years. Patients with Becker muscular dystrophy had significant reduction of both fractional shortening and corrected mean velocity of circumferential shortening compared with controls. No correlation was found between fractional shortening and age. The third filling fraction was significantly reduced in patients with Becker muscular dystrophy (p < 0.05), although other indices of diastolic function (isovolumic relaxation time and E/A ratios) were not significantly different. CONCLUSIONS: Though most patients with Becker muscular dystrophy were symptom free, a high percentage had evidence of a subclinical cardiomyopathy. Electrocardiography showed that the inferolateral and posterior segments of the left ventricle tended to be affected and may show evidence for conduction tissue disease. Echocardiography showed that most patients had left ventricular dilation and global hypokinesia. The severity of left ventricular disease was unrelated to age; some younger patients had severe left ventricular dysfunction. All patients with Becker muscular dystrophy should have echocardiographic assessment of left ventricular function.

Is the direct effect of naloxone on liver cell metabolism an artifact?

Proprietary naloxone hydrochloride (Narcan) acts on isolated hepatocytes from 24-h starved rats to increase 14CO2 production from [1-14C]oleate and to reverse in part the inhibitory effect of ethanol on the oxidation of [1-14C]oleate to 14CO2. The effects are attributable not to naloxone itself, but to the methyl p-hydroxybenzoate present in Narcan as a preservative. The question is posed as to whether methyl p-hydroxybenzoate and p-hydroxybenzoate contribute to the reported antagonism by proprietary naloxone of acute ethanol intoxication in vivo.

Interactions between insulin and thyroid hormone in the control of lipogenesis.

1. The effects of intragastric glucose feeding and L-tri-iodothyronine (T3) administration on rates of hepatic and brown-fat lipogenesis in vivo were examined in fed and 48 h-starved rats. 2. T3 treatment increased hepatic lipogenesis in the fed but not the starved animals. Brown-fat lipogenesis was unaffected or slightly decreased by T3 treatment of fed or starved rats. 3. Intragastric glucose feeding increased hepatic lipogenesis in control or T3-treated fed rats, but did not increase hepatic lipogenesis in starved control rats. Glucose feeding increased hepatic lipogenesis if the starved rats were treated with T3. Glucose feeding increased rates of brown-fat lipogenesis in all experimental groups. The effects of glucose feeding on liver and brown-fat lipogenesis were mimicked by insulin injection. 4. The increase in hepatic lipogenesis in T3-treated 48 h-starved rats after intragastric glucose feeding was prevented by short-term insulin deficiency, but not by (-)-hydroxycitrate, an inhibitor of ATP citrate lyase. The increase in lipogenesis in brown adipose tissue in response to glucose feeding was inhibited by both short-term insulin deficiency and (-)-hydroxycitrate. 5. The results tend to preclude pyruvate kinase and acetyl-CoA carboxylase as the sites of interaction of insulin and T3 in the regulation of hepatic lipogenesis in 48 h-starved rats. Other potential sites of interaction are discussed.