Original articleMeasurement of hyper- and hypotension during repeated dose toxicity studies in either freely moving or physically restrained cynomolgus monkeys

IntroductionThe measurement of cardiovascular endpoints in standard toxicology studies remains a challenge as the routinely used non-invasive methods require physical restraint, causing an increase of sympathetic neural activity, leading to excitement and potentially hypertension in the experimental animals. In this study, a miniature telemetry blood pressure transmitter was used to evaluate if the acute hyper- and hypotension could be detected in free moving cynomolgus monkeys as well as physically restrained animals using positive control drugs. Furthermore, as a comparator, routine high definition oscillometry (HDO) was performed in restrained animals. Methods: Hemodynamic parameters were monitored continuously from conscious, freely moving animals following oral administration of vehicle (water) or 1 and 10 mg/kg of etilefrine, and 1 and 4 mg/kg of dihydralazine as positive control articles. A second dose session was performed to confirm the reproducibility of results and a third dose session combined with physical restraint procedures for blood collection and HDO measurements. Results: There was a dose-dependent, statistically significant increase in the systolic blood pressure following oral doses of etilefrine at all 3 dose sessions. This effect was less apparent during session 3, probably due to the physical restraint applied for the blood sampling and HDO measurement. No differences in the blood pressure were measured using HDO. On all three dose sessions following oral doses of dihydralazine the expected statistically significant decrease in the diastolic pressure could be clearly measured even when the telemetric data recordings were combined with physical restraint. Discussion: Due to the advantages of the minimally invasive telemetry technique compared to HDO and the possibility of prolonged measurement periods, it is an invaluable tool for blood pressure measurement in freely moving animals in toxicology studies.