The effects of housing enrichment on cardiovascular parameters in spontaneously hypertensive rats.

By using radiotelemetry, we measured blood pressure, heart rate, and locomotor activity in adult male spontaneously hypertensive (SHR) rats during three consecutive periods in which they received various social and non-social cage enrichments. The objective was to determine whether these enriching experiences would affect cardiovascular parameters. During the first period, the readings from four individually housed males, each with a telemetry transmitter in the abdominal cavity and connected to a femoral artery catheter, were compared to those from five similarly instrumented rats that were each housed with another rat. Systolic blood pressure and activity but not diastolic blood pressure or heart rate were higher in rats housed with another rat compared to those housed alone. During the second period, each cage of animals was enriched by including a large piece of plastic drainpipe and several golf balls. In addition, the nine animals were placed together daily for two hours at the beginning of the dark phase of the photoperiod in a large, three-tiered enclosure containing a running wheel, several lengths of plastic drainpipe, and multiple golf balls. Systolic and diastolic blood pressures but not heart rate or activity were higher in the double-housed rats than those housed alone. During the last period, the rats previously housed with another rat were switched to single housing, and those previously housed alone were placed with another rat. The daily activity and cage enrichments were otherwise continued. Removal of a cage mate increased systolic blood pressure, diastolic blood pressure, and heart rate but not activity compared parameters in animals that were changed from single to double housing. During the entire experiment, activity and all cardiovascular parameters were increased during the dark phase compared to the light phase of the daily photoperiod. However, there was no statistically significant correlation between these circadian changes and the housing conditions. In summary, providing social enrichment in the form of another rat or non-social cage enrichment combined with a daily period of group housing and physical activity increased diastolic and/or systolic blood pressure of SHR rats. In addition, the loss of continuous social enrichment increased blood pressure and heart rate even when the other enrichments were continued. These changes were not always related to increased activity in the cage.