Acclimating vendor-derived animals before measuring blood pressure: how much time is needed?

B lood pressure is regulated through the complex interaction of neural, hormonal, vascular, cardiac, and renal mechanisms, and many advances in understanding this complicated process have come from research using animal models. Environmental factors such as diet, temperature, and even music can significantly alter blood pressure in research animals. Although many of these factors have been investigated experimentally, surprisingly few studies have explored the effects of transportation on blood pressure in research animals. In this issue of the Journal, Hoorn and colleagues1 show that transportation increases blood pressure in mice for >1 week after animals are received from a commercial vendor. The authors found significantly higher systolic blood pressure in BALB/c mice that were shipped overnight and allowed 1-week acclimation compared to BALB/c mice from an internal colony. After extending the acclimation period to 6 weeks, systolic blood pressure in the vendor-derived mice matched the mice bred internally. To refine the necessary acclimation period, the authors purchased a second group of BALB/c mice from the same vendor and measured systolic blood pressure after 3 weeks. In this case, systolic blood pressure was not significantly different from the internal control group. Overall, this study indicates that 1-week acclimation is insufficient for blood pressure studies and that 3–6 weeks may be required for animals to fully acclimate after transportation. One important caveat to this study is that Hoorn and colleagues used a tail-cuff method to detect elevated blood pressures after transportation, a form of stress-induced hypertension. In a recent discussion of psychogenic (i.e., stressinduced) hypertension in animal models,2 Nalivaiko presented several studies indicating that tail-cuff methods overestimate stress-induced hypertension compared to direct blood-pressure measurements. However, most of the studies discussed relied on older tail-cuff technologies, whereas Hoorn and coworkers used more current volume-pressure recording technology that mice readily acclimate to3 and that has been validated by comparison to simultaneous telemetry measurements.4 Another caveat is that the social structure was not controlled by the authors. If the animals were housed in different groups upon arrival, the altered social structure could stress the mice5 and contribute to the elevated blood pressures observed in their study. Despite the caveats mentioned, the study by Hoorn and colleagues indicates that shipping stress may have significant, long-lasting effects on blood pressure in mice. By reporting this problem observed in their studies, the authors highlight an issue that has been underappreciated in the literature and, thus, rarely studied. It is unclear how transportation stress affects blood pressure in other strains and species commonly used in blood pressure research or how related factors like the type of transportation (air vs. ground), the distance/ duration/time-zone changes involved, and seasonal differences impact the acclimation time required. Considering that short acclimation periods are common throughout the research community, transportation-induced changes represent an important confounding variable that deserves further investigation.