Orthostatic hypotension is one of the most frequent cardiovascularadverse effects reported during Phase I clinical trials. According toBioPrint™ (clinical database covering 31100 compounds), syncope isreported for 248 drugs (22%) and identified as a frequent finding (i.e.,incidence >1%) for 39 (3.5%). However, syncope risk is not routinelyaddressed during pre-clinical studies defined by the ICHS7A. In thisstudy, we investigated the orthostatic response (OR) using a tilt modelin dogs during a telemetry study.

Four dogs equipped with DSI telemetry transmitters were orallydosed with Verapamil (VER: 1, 5 and 15 mg/kg) or vehicle (VEH) andthe signals recorded for 6 h post-dose. In addition to ECG (PR, QRSand QT durations), arterial pressure (AP) and left ventricular function(dP/dTmax), OR was evaluated using the tilt procedure each time ablood sample was taken to measure plasma exposure (predose, 1, 2and 6 h post-dose). Apart from the dose-related expected effects onPR (+7%, +13% and +41% after the different doses of VER vs. +1.5%after VEH), systolic AP (−1%, −8% and −13% vs. −3%) and dP/dTmax (−6%, −12% and −13% vs. −4%), VER also affected the OR at15 mg/kg when compared to VEH (−30% vs. −18%).

These results demonstrate that OR defects can be identified duringstandard telemetry studies, taking benefit of the limited butnecessary sampling procedures used to correlate the effects withplasma exposure. According to the clinical incidence of OR deficits,the tilt procedure could be used more extensively in pre-clinicalstudies.

doi:10.1016/j.vascn.2009.04.182

Cardiovascular collapse caused by a potent TRPV4 channel agonist

Haisong Ju⁎, Weike Bao, Robert Willette, Dennis MurphyGlaxoSmithKline Pharmaceuticals, King of Prussia, PA, United States

The TRPV4 channel, a member of the transient receptor potential(TRP) family, is an osmo/mechano-sensitive ligand-gated, non-selective cationic channel. A potent and selective TRPV4 agonist(compound X) caused mortality in mice and rats during an intra-venous infusion (iv) of 33 µg/kg/min. The cardiovascular effects ofcompound X were evaluated in the anesthetized rat. An infusion rateof 3.3 µg/kg/min produced a moderate to marked decrease insystolic blood pressure and a mild to moderate decrease in diastolicblood pressure. Circulatory collapse occurred between 1 and 11 minafter the start of iv infusion of 7–10 µg/kg/min. Early decreases insystolic blood pressure during the 7 µg/kg/min infusion occurredwith absence of changes in diastolic blood pressure, +dP/dt,contractility index and LVEDP. The selective decrease in systolicblood pressure and the absence of a change in cardiac contractilitysuggest that a decrease in stroke volume may have occurred. Therapid and marked decreases in both systolic and diastolic bloodpressures at the time of circulatory collapse suggest that circulatorycollapse involved dilation of both arteries and veins and/or loss ofblood volume. Compound X did not produce any ECG waveformabnormalities or arrhythmias in rat. In follow up studies in rat,compound X was associated with profound vascular leakage andtissue hemorrhage in the lung, intestine and kidney. In addition,compound X produced potent endothelial-dependent relaxation ofisolated vascular ring segments and had no effect on cardiaccontractility in the isolated rat heart. Taken together, these datasuggest that the cardiovascular collapse induced by compound Xwas due to a combination of blood volume reduction and vesseldilation.

doi:10.1016/j.vascn.2009.04.183

Non-invasive monitoring of in situ pO2 during engraftment ofstem cells in the infarct heart

Mahmood Khan⁎, Periannan Kuppusamy, Robert L. HamlinThe Ohio State University, Columbus, OH, United States

Cardiovascular disease is the leading cause of deaths in the UnitedStates. One of the major limitations of cell-based therapies for thetreatment of ischemic heart disease has been the inability to monitorthe distribution of the implanted cells and their effect on the localtissue oxygen concentration (pO2) over a long term. The goal of thisstudy was to use an EPR (electron paramagnetic resonance)-detectable oxygen-sensing nanoparticulate probe (LiNc-BuO) to labelskeletal myoblasts (SM) and to monitor the cell migration as well asin situ pO2 in the infarct myocardium for several weeks post-implantation.

Methods:Myocardial infarction was created by ligation of the LADartery in mice. Mouse SM (75% purity, CD56+ cells by FACS) werelabeled with the probe by incubating in culture for 72 h. A singleintra-myocardial injection of the labeled SM (10 µL, 1×105 cells) wasgiven using a 29 1/2-guage needle in the infarct region. The retentionand redistribution of the injected cells and in situ myocardial pO2were monitored by EPR. Immuno-histological studies of the skeletalmuscle specific marker, MY-32, were used at different time periodsduring engraftment.

Results: The EPR signals obtained in mouse hearts implanted withthe labeled SM cells clearly established the retention of the probe atthe site of implantation for up to 4 weeks. The differentiation of theSM into skeletal muscle cells were confirmed by MY-32 stainingstarting 1 week after implantation. The baseline myocardial pO2 was15.8±1.2 mmHg (n=6). Immediately after permanent LAD ligation,the tissue pO2 in the ischemic region decreased to 1.7±0.75 mmHg.The myocardial pO2 immediately after the cell therapy was 2.5±1.0 mmHg. The pO2 was significantly higher at 1, 2, and 3 weeks(Table 1) after SM cell therapy.

Conclusion: The studies clearly established our ability to track theSM cell engraftment, in vivo and showed increased pO2 levels at thetherapeutic site.

doi:10.1016/j.vascn.2009.04.184

Assessing autonomic status in beagle dogs by means of heartrate variability

Rikard PehrsonAstraZeneca R&D, Södertälje, Sweden

Heart rate variability (HRV) is reported to reflect changes in theautonomic nervous system.We tested if HRV couldmirror physiologicaland/or pharmacological autonomic changes in telemeterised beagledogs. In four dogs the voluntary behaviour (sitting, resting, andstanding) was investigated. Saline and atropine was given at separateoccasions. Contribution to HRV from different frequencies, i.e. low (LF%,0.04–0.15 Hz), high (HF%, 0.15–0.4 Hz) and LHF% (LF%+HF%) wascalculated. Putatively, LF% and HF% reflect sympathetic and parasympa-thetic input respectively. Correlation of HRV to autonomic status andblood pressures was made.

LF%, HF% and LHF% were not heart rate dependent up toapproximately 70 bpm. In the absence of atropine HF% was generallyhigher than LF%, but during low heart rate LF% was higher than HF%due to shift in peak HRV frequency. Atropine treatment decreasedboth LF% and HF%, even after return to normal heart rate. Decrease inHF% was more pronounced than decrease in LF%, implying both a

Abstracts / Journal of Pharmacological and Toxicological Methods 60 (2009) 210–258 255