Cardiovascular assessment in radiotelemetry-implanted pregnant rats.

OBJECTIVE: The aim of this study was to assess the potential adverse effects of the chronic use of surgically implanted radiotelemetry transmitters and femoral catheters on embryo-fetal development in rats. METHODS: Two groups of 10 female rats were implanted with femoral catheters and radiotelemetry transmitters. Ten additional rats were implanted with femoral catheters alone. The females were then time mated with male rats and pregnancy confirmed. Saline was continuously infused from gestation days 6-17. Saline infusion was replaced with 0.8 µg/ml angiotensin II in one group of animals, on gestation days 6, 9, 12, and 15 in order to demonstrate the validity of the system to detect changes in hemodynamic function by a pharmacologically active agent. Embryo-fetal development was assessed by examination of the number and location of the fetuses, early and late resorptions, and number of implantation sites. Parameters evaluated included postimplantation loss, live litter size, mean fetal body weights, and fetal sex ratios. RESULTS: Intrauterine survival was unaffected in all groups. Mean numbers of corpora lutea and implantation sites and the mean litter proportions of preimplantation loss were similar across all groups. Infusion of angiotensin II elicited the expected hemodynamic response, i.e., increased arterial blood pressure with a concomitant decrease in heart rate. CONCLUSION: Radiotelemetry can be used in combination with continuous intravenous infusion as a viable methodology for detecting test article induced changes in cardiovascular function in pregnant rats, with no effects on intrauterine growth and survival or fetal morphology.

Evaluation of respiratory function in freely moving Beagle dogs using implanted impedance technology.

INTRODUCTION: The Safety Pharmacology ICH S7A guidelines mandate the preclinical evaluation of drug effects on respiratory function. Chronic measurements of potential drug effects are commonly performed in rodents due to lack of a viable alternative in large animals. Presently, although the value and validity of these standard methods cannot be refuted, each method presents inherent limitations; such as the introduction of restraint stress (e.g. head-out rodent plethysmography and the pneumotachograph-equipped dog face mask), or sensitivity issues (e.g. whole body plethysmography). Since these approaches may limit the number of time points tested or affect respiratory parameters, new and accurate methods are needed for assessing respiratory function in conscious, freely moving animals. METHODS: We evaluated a new surgically implanted telemetry device, which adds an impedance sensor for the chronic measurement of respiratory parameters to the standard device used for safety pharmacology cardiovascular studies. The feasibility of the implantable device was assessed based on concordance of respiratory data with pneumotachograph-recorded parameters in conscious Beagle dogs following intravenous administration of a positive control (4 mg/kg doxapram). RESULTS: Linear regression analysis of data collected under restrained conditions showed a high correlation (R(2) 0.95) between impedance-derived respiratory parameters (tidal volume and respiratory frequency) and direct measurements of respiration via pneumotachograph. The correlation was reproduced when animals were challenged under the same dosing regimen. Volume changes similar to those obtained during the restrained collection were observed during the ambulatory collection following doxapram administration. Calibration of impedance-based values was adequate using both individual and population-based baseline conversion factors, both approximating actual mean respiratory variables collected with the pneumotachograph. DISCUSSION: The benefit of this model is the accurate, continuous measurement of respiratory endpoints in restrained, as well as ambulatory settings. Assessment of multiple physiological parameters collected concurrently and the use of population-based calibrations may enable the maximization of resources and shortened timelines in drug development.

Estimation of potency of HERG channel blockers: impact of voltage protocol and temperature.

INTRODUCTION: The HERG channel is widely used for the assessment of proarrhythmic risk for new drugs. HERG channel blockers obstruct channel functions through various mechanisms, which usually show time dependence, voltage dependence, and state dependence. The voltage protocol and temperature may affect the estimation of drug potency, but limited information is available in this regard. The purpose of this study was to evaluate the influence of voltage protocol and temperature on predicting the potency of HERG channel blockers, and to determine electrophysiological approaches for new drugs screening studies. METHOD: Whole-cell patch-clamp electrophysiology was carried out by utilizing different voltage step protocols to examine the potency of compounds known to preferentially block the channel in the closed (ketoconazole and BeKm-1), open, and/or inactivated states (E-4031, astemizole, and terfenadine) in HEK293 cells transfected with HERG cDNA at room temperature and near-physiological temperature. RESULTS: Drug potency determined using different voltage protocols varied dependent on the mechanisms of drug actions. For most compounds, the IC(50) values obtained with a long pulse step protocol at room temperature were close to those determined with the voltage protocols designed to disclose their intrinsic potency. Relative to room temperature, the potency of E-4031, terfenadine, and ketoconazole was not changed at approximately 35 degrees C, but potency of astemizole was reduced. DISCUSSION: The long pulse step protocol with room temperature can be selected for HERG channel safety screening studies. Alternative voltage protocols or temperatures should be considered if HERG study results are not consistent with other cardiac safety assessments.