Detecting drug-induced prolongation of the QRS complex: new insights for cardiac safety assessment.

BACKGROUND: Drugs slowing the conduction of the cardiac action potential and prolonging QRS complex duration by blocking the sodium current (I(Na)) may carry pro-arrhythmic risks. Due to the frequency-dependent block of I(Na), this study assesses whether activity-related spontaneous increases in heart rate (HR) occurring during standard dog telemetry studies can be used to optimise the detection of class I antiarrhythmic-induced QRS prolongation. METHODS: Telemetered dogs were orally dosed with quinidine (class Ia), mexiletine (class Ib) or flecainide (class Ic). QRS duration was determined standardly (5 beats averaged at rest) but also prior to and at the plateau of each acute increase in HR (3 beats averaged at steady state), and averaged over 1h period from 1h pre-dose to 5h post-dose. RESULTS: Compared to time-matched vehicle, at rest, only quinidine and flecainide induced increases in QRS duration (E(max) 13% and 20% respectively, P<0.01-0.001) whereas mexiletine had no effect. Importantly, the increase in QRS duration was enhanced at peak HR with an additional effect of +0.7 ± 0.5 ms (quinidine, NS), +1.8 ± 0.8 ms (mexiletine, P<0.05) and +2.8 ± 0.8 ms (flecainide, P<0.01) (calculated as QRS at basal HR-QRS at high HR). CONCLUSION: Electrocardiogram recordings during elevated HR, not considered during routine analysis optimised for detecting QT prolongation, can be used to sensitise the detection of QRS prolongation. This could prove useful when borderline QRS effects are detected. Analysing during acute increases in HR could also be useful for detecting drug-induced effects on other aspects of cardiac function.

The prevalence of bother, acceptance, and need for help in men with erectile dysfunction.

INTRODUCTION: Apart from knowledge on the prevalence of erectile dysfunction (ED), for clinical reasons it is important to obtain information on concern or bother and need for help. However, information is lacking on men with ED who need help but do not seek medical attention. Thus, this study aimed to assess the distribution of bother, acceptance, and need for help in men with ED, and assess characteristics of patients with ED in need for help but not receiving medical attention for ED. METHODS: A total of 5,721 men aged 18 years and older and registered in 12 general practices in the middle of the Netherlands were sent a questionnaire by mail about sexual problems, ED, need for help, and medical attention. Out of 2,117 questionnaires that were returned, 1,481 were completed on ED, bother, and need for help. RESULTS: The prevalence of ED (according to World Health Organization definition) in the 1,481 men was 14.2%. Of these men 67.3% were bothered, 68.7% did not accept ED, and 85.3% wanted help. Surprisingly, 41.9% of men who denied a need for help were bothered and 19.4% did not accept ED. Only 10.4% of men with ED received any medical care. Bother in men with ED was related to increasing age (decreasing above 60 years). Compared with men who already received help for ED, men who wanted help but did not receive it more often suffered from diabetes, neurological problems, and various cardiovascular problems. On the other hand, history of myocardial infarction increased the chance of getting adequate medical attention for ED. CONCLUSIONS: The majority of men with ED are concerned or bothered and perceive a need for help. Most of them do not receive any medical attention. These men are characterized by chronic medical conditions, visiting the physician's office regularly for their medical condition.

Impact of various questionnaires on the prevalence of erectile dysfunction. The ENIGMA-study.

The prevalence estimates of erectile dysfunction (ED) vary considerably across studies. These differences may be attributed to used definitions of ED. Quantitative data on the effect of different definitions of ED on the prevalence are lacking, because precise information on the used definition and questionnaire is often absent. Aim of this study was to quantify the effect of using different questionnaires for ED on the prevalence estimates. In all, 5721 mail surveys on sexual problems and ED were sent to all men (aged >18 y) in 12 general practices in the middle of the Netherlands of which 2117 were completed. The questionnaire contained Enigma (WHO), International Index of Erectile Function (IIEF), Cologne Erectile Inventory (KEED) and one question (Boxmeer, Krimpen). The prevalence of ED based on the various questionnaires and the effect of these questionnaires on risk factor relationships was compared. IIEF gave the highest age specific and overall ED prevalence, KEED the lowest. The difference in prevalence was 16.8%. The agreement (kappa coefficient) between the various ED definitions varied from 0.52 (IIEF & KEED) to 0.95 (Enigma & Boxmeer). The number of risk factor relations were similar for the Dutch studies, reduced for the IIEF and KEED. This study provides evidence that differences in questionnaires to assess ED have a considerable effect on the (age specific) prevalence estimates and little on the risk factor relations. The number of questions of the survey appears not to be responsible for differences in the prevalence of ED and risk factor relations, however they affect the response rate. Uniform use is strongly recommended, since a 'golden standard' for ED assessment (by questionnaire) is lacking. A short questionnaire with one or two questions is recommended for example the one from the Boxmeer-study. These data may be used to adjust (age-specific) prevalence rates comparing ED prevalence in the open population across studies.

Erectile dysfunction in primary care: prevalence and patient characteristics. The ENIGMA study.

The availability of adequate treatment for erectile dysfunction (ED) triggers studies into the prevalence of ED in the general population. Yet, previous studies showed different prevalence estimates partly due to differences in patient selection, in (unclear) definitions of ED and in assessment. ENIGMA has been designed to study the prevalence of ED in the general population of The Netherlands, using the WHO definition with a description of the way of assessment. In all, 5721 mail surveys were sent to all men, aged 18 y and older in 12 general practices in The Netherlands. A total of 5601 were included in the study and 2117 (38%) were completed. A total of 38% of the men reported to have ever had some kind of erectile problem. The prevalence of ED was 17% (6% mild, 4% moderate and 7% complete). Age, diabetes, cardiovascular diseases, penile disorders, irradiation in the pelvic region, relational problems, fear for failure, surmenage, medication use and regular consumption of alcohol were independently related to ED. Men with ED were less content with their (sexual) life and had less confidence in sexual performance. Presence of ED was negatively related to affected happiness in life. ED is commonly found in men and is related to age, medication, comorbidity and lifestyle factors. Men with ED perceive a lower quality of (sex)life. Doctors should be aware of the presence of ED and its consequences in patients.

Potent cyclic peptide inhibitors of VLA-4 (alpha4beta1 integrin)-mediated cell adhesion. Discovery of compounds like cyclo(MePhe-Leu-Asp-Val-D-Arg-D-Arg) (ZD7349) compatible with depot formulation.

Additional structure-activity relationship studies on potent cyclic peptide inhibitors of very late antigen-4 (VLA-4) are reported. The new N- to C-terminal cyclic hexa-, hepta- and octapeptide inhibitors like cyclo(MeIle/MePhe-Leu-Asp-Val-X) (X = 2-4 amino acids containing hydrophobic and/or basic side chains) were synthesized using solid phase peptide synthesis methods. The peptides were evaluated in in vitro cell adhesion assays and in in vivo inflammation models. Many of the peptides like cyclo(MePhe-Leu-Asp-Val-D-Arg-D-Arg) (ZD7349) (17), cyclo(MeIle-Leu-Asp-Val-D-Arg-D-Arg-D-Phe) (20), cyclo(MeIle-Leu-Asp-Val-D-Arg-D-Arg-MePhe) (21) and cyclo(MePhe-Leu-Asp-Val-D-Arg-D-Arg-D-Ala-D-Ala) (23) were potent inhibitors of VLA-4-mediated cell adhesion and inhibited ovalbumin-induced delayed type hypersensitivity (DTH) response in mice. The more potent compounds were highly selective and did not affect U937 cell adhesion to fibronectin (VLA-5), phorbolmyristate acetate or PMA-differentiated U937 cell adhesion to intercellular cell adhesion molecule-1 (ICAM-1)-expressing Chinese hamster ovary cells (LFA-1) and adenosine diphosphate (ADP)-induced platelet aggregation (GPIIb/IIIa). In contrast to the inhibitors like Ac-cyclo(D-Lys-D-Ile-Leu-Asp-Val) and cyclo(CH2CO-Ile-Leu-Asp-Val-Pip-CH2CO-Ile-Leu-Asp-Val-Pip) described earlier, the new compounds were much more compatible with the depot formulations based on poly(DL-lactide-co-glycolide) polymers. The hexapeptide cyclo(MePhe-Leu-Asp-Val-D-Arg-D-Arg) (ZD7349) (17) inhibited MOLT-4 cell adhesion to fibronectin and vascular cell adhesion molecule-1 (VCAM-1) with IC50 values of 260 and 330 nM, respectively, and did not show any significant effect against other integrins (IC50 > 300 microM). ZD7349 inhibited ovalbumin-induced DTH response in mice when administered continuously using a mini-pump (ED50 0.01 mg/kg/day) or when given as an s.c. or i.v. bolus injection at a dose of 1-10 mg/kg. ZD7349 was also active in type II collagen-induced arthritis (CIA) and experimental autoimmune encephalomyelitis (EAE) tests at a dose of 3-10 mg/kg. The peptide was released from some formulations over a period of 10-20 days. ZD7349 is currently undergoing pre-clinical investigation.

The relationship between blood flow and diameter in the iliac artery of the anaesthetized dog: the role of endothelium-derived relaxing factor and shear stress.

The quantitative relationship between, increase in blood flow and arterial diameter was determined in an anaesthetized dog preparation (pentobarbitone, induction 30 mg kg-1 i.v., maintenance 3 mg kg-1 i.v. every 30 min). Changes in external iliac artery diameter were measured using piezoelectric ultrasound transducers capable of measuring diameters within the range of 2-20 mm with a resolution of +/- 0.005 mm. The diameter of the artery was measured at two sites, at one of which the endothelium was damaged using a balloon angioplasty catheter. Increases in blood flow were brought about by a combination of vasodilatation and cardiac stimulation (intra-arterial administration of acetylcholine, downstream to the sites of diameter measurement, and electrical stimulation of the left ansa subclavia), thereby preventing large changes in blood pressure. The effects of both transient and maintained increases in blood flow on mean arterial diameter in the section of artery with intact endothelium were measured. Transient increases in mean flow from 147 +/- 0.21 to 611 +/- 80.0 ml min-1 caused increases in diameter of 0.12 +/- 0.02 mm from a control of 5.42 +/- 0.19 mm. The mean delay between maximum flow and maximum diameter was 24.51 +/- 1.1 s and the half-time for the return to control diameter was 82.0 +/- 9.6 s, compared with 12.1 +/- 1.5 s for the return to control flow. Maintained (3-4 min) increases in mean blood flow (from 104.7 +/- 15.1 to 694.7 +/- 135.1 ml min-1) produced larger increases in diameter of 0.48 +/- 0.30 mm from a control diameter of 4.89 +/- 0.12 mm. These changes in diameter were abolished by N omega-nitro-L-arginine methyl ester (L-NAME. 10-100 mg kg-1 i.v.). In the section of artery with damaged endothelium, changes in diameter were relatively small and associated with small changes in blood pressure. This effect of a nearly 7-fold increase in flow on arterial diameter is dependent upon the integrity of the endothelium and the release of endothelium-derived relaxing factor and causes a 29% reduction in calculated boundary wall shear stress.

Comparative effects of anti-platelet agents as adjuncts to tissue plasminogen activator in a dog model of occlusive coronary thrombosis.

1. This study compares a cyclo-oxygenase inhibitor (aspirin), a 5-HT2 antagonist (ZM170809) and a combined thromboxane synthase inhibitor/receptor antagonist (ZD1542) as adjuncts to tissue plasminogen activator (rt-PA). 2. Application of an anodal current (332 +/- 4.1 microA) to the stenosed left circumflex coronary artery of 20 anaesthetized dogs produced a stable platelet-rich occlusive thrombus. 3. After initial i.v. administration of recombinant human tissue type plasminogen activator (rt-PA, 3 mg bolus +2 mg kg-1 h-1 for 30 min) thrombolysis occurred in 15 out of 20 dogs. All 15 dogs reoccluded. 4. The second i.v. administration of rt-PA in the presence of either aspirin, ZM170809, ZD1542 or saline resulted in thrombolysis in all 20 dogs. 5. Both the combined thromboxane synthase inhibitor/receptor antagonist (ZD1542) and 5-HT2 antagonist (ZM170809) significantly (P < 0.05) reduced the time taken to lyse the thrombus compared with the saline group. The times were 14.4 +/- 2.7 min, 18.0 +/- 3.9 min and 36.8 +/- 6.2 min for ZD1542, ZM170809 and saline respectively. 6. Aspirin did not offer any additional benefit to using rt-PA alone. The times to thrombolysis were 36.8 +/- 8.4 min for aspirin and 36.8 +/- 6.2 min for the saline group. 7. The number of dogs in which the circumflex coronary artery reoccluded within 60 min of terminating the second infusion of rt-PA were five for saline, four for aspirin, two for ZD1542 and two for ZM170809. 8. These results indicate that both ZD1542 and ZM170809 are more effective adjuncts than aspirin in thrombolysis and may provide an improvement in current clinical practice.

Redirection of arachidonic acid metabolism by ICI D1542: effects on thrombus formation in the coronary artery of the anaesthetized dog.

1. The effects of simultaneous redirection of arachidonic acid metabolism, by inhibition of thromboxane A2 (TXA2) synthase and blockade of the platelet thromboxane A2 receptor (TP-receptor), was examined on the rate of thrombus formation in a stenosed coronary artery with damaged endothelium in an anaesthetized dog. 2. Redirection of arachidonic acid metabolism was achieved by intravenous doses of ICI D1542, a selective and potent inhibitor of TXA2 synthase and the TP-receptor. 3. Redirection of arachidonic acid metabolism was demonstrated in whole blood, stimulated ex vivo by collagen. The ED50 for inhibition of TXB2 production was 7.1 micrograms kg-1, i.v.; there were corresponding increases in the production of the eicosanoids prostaglandin D2 (PGD2), PGE2 and PGF2 alpha. 4. Thrombus formation was inhibited by D1542 (ED50 0.55 micrograms kg-1, i.v.), but could be restarted by an intravenous infusion of adrenaline (0.2-38 micrograms kg-1 min-1, i.v.). In the presence of the maximum effective dose of D1542 (1 mg kg-1, i.v.) a 190 fold increase in the infusion rate of adrenaline was required to restore thrombus formation. 5. In the presence of D1542, removal of endoperoxide metabolites by inhibition of cyclo-oxygenase with aspirin (5 mg kg-1, i.v.) caused thrombus formation to restart, indicating the ability of the endoperoxide metabolites to inhibit thrombus formation in vivo. 6. These results indicate that, in the stenosed and damaged coronary artery of the dog, redirection of arachidonic acid metabolism by D1542 is more effective at preventing thrombus formation than inhibition of cyclo-oxygenase by aspirin.

Orientation selectivity and the spatial distribution of enhancement and suppression in receptive fields of cat striate cortex cells.

The relationship between orientation selectivity and spatial receptive field organization was analyzed. Receptive field maps were made with a dual stimulus technique where an optimally oriented activation slit was presented in the most responsive region to produce activity against which the effect of a test spot in various positions was determined. Both simple and complex cells had receptive fields which were subdivided into adjacent elongated and antagonistic subregions. When the two stimuli were presented in phase (both ON or OFF simultaneously) the fields had a central enhancement region with a strong suppression flank on one or both sides. Optimal slit orientation was related to the location of the suppression flank relative to the location of the central enhancement region, and the degree of orientation selectivity to the shape of the subregions and the distance between them. Estimated orientation tuning curves calculated from the receptive field maps gave satisfactory first approximations to experimental curves. The relative contribution of enhancement and suppression to orientation selectivity was studied by presenting a test slit in different orientations in phase with an optimally oriented activation slit. The orientation selectivity was produced almost exclusively by the flank suppression indicating that orientation selectivity is produced by inhibitory input. The flank suppression lacked any specific orientation selectivity, and it occurred only when both the central region and the flanks were activated in phase. Orientation selectivity in both simple and complex cells is explained by a receptive field organization where the cells have input from partially overlapping excitatory and inhibitory fields which have their centers slightly displaced from each other.

Responses of single units in the monkey superior colliculus to stationary flashing stimuli.

1. Responses of pan-directional cells in the superficial layers of the superior colliculus in paralysed anaesthetized rhesus monkeys to stationary flashing stimuli have been studied. 2. The receptive field centre response is always of the transient excitatory on-off type, while the surround response is transient inhibitory both at light-on and at light-off. The receptive field centres are circular or slightly elliptical. The average size of the receptive field centres is much larger than that of retinal ganglion cells. All units except those in the far temporal periphery receive binocular input. In each unit the on and off responses have the same latency times. With increasing stimulus area, the latency time at light-on and at light-off first decreases and then remains constant. In most units the number of spikes in the burst at light-on and at light-off first increases, reaches a maximum and then decreases with increasing stimulus area. This decrease demonstrates the presence of an inhibitory surround. 3. A model of spatial and temporal properties of centre and surround mechanisms is tested. Addition of excitatory centre input and inhibitory surround input, which have different spatial and temporal properties, determines the output of the neurone. The centre mechanism gets excitatory input from retinal ganglion cells and shows saturation. The inhibitory surround mechanism is made by an inhibitory interneurone. It could not be decided whether the excitatory input for this interneurone comes from retinal axon collaterals (forward inhibition) or from axon collaterals of "principal" cells in the superior colliculus (backward inhibition).

Responses of single units in the monkey superior colliculus to moving stimuli.

1. Single unit responses of pan-directional cells to moving and stationary flashing stimuli were studied in the superficial layers of the superior colliculus in paralysed, anaesthetized rhesus monkeys. The aim of this study was to see how far cell responses to moving stimuli fit in with what would be expected from their responses to stationary flashing stimuli. 2. Both the leading and the trailing edge of a moving stimulus evoke a transient response. If the diameter of moving light spots is increased the strength of the leading edge response increases, reaches a maximum and decreases to a constant value which is similar to the behaviour of the on response when the diameter of flashing spots is increased. The strength of the trailing edge response increases and reaches the same strength as that of the leading edge response. If the width of a long moving slit is increased, the strength of the leading edge response is the same at all slit widths, while the strength of the trailing edge response shows a course similar to that of the trailing edge response if the spot diameter is increased. If the length of a wide moving slit is increased both the leading and the trailing edge responses decrease. These results indicate that the strength of both leading and trailing edge responses is dependent on the degree the inhibitory surround is activated. 3. The leading and the trailing edge of a stimulus evoke their responses at the same position in the receptive field independent of the direction of movement. 4. Increasing the velocity of a moving stimulus shows that in general the leading edge response is present up to higher velocities than the trailing edge response independent of the sign of contrast. The burst duration to moving stimuli decreases with increasing stimulus velocity and appears to be determined by the time a moving edge is present in the receptive field centre. When this time becomes shorter than 10--20 ms, the burst duration for moving stimuli is constant and about the same as for flashing stimuli. This indicates that, although spatial receptive field properties can vary considerably, temporal receptive field properties show a strong similarity among different units. 5. The response latencies to light and dark moving edges are the same, which in turn are about equal to the response latencies to stationary flashing stimuli. 6. Stimulation experiments show that the general response characteristics to moving stimuli can be predicted by using a set of receptive field parameters derived from responses to stationary flashing stimuli. The most important variable of moving stimuli appears to be the period of time a moving contour is present within the receptive field centre, besides the degree of activation of the inhibitory surround.