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

By using radiotelemetry, we measured blood pressure, heart rate, and locomo tor activity in adult male spontaneously hypertensive (SHR) rats during thr ee consecutive periods in which they received various social and non-social cage enrichments, The objective was to determine whether these enriching e xperiences would affect cardiovascular parameters, During the first period, the readings from four individually housed males, each with a telemetry tr ansmitter in the abdominal cavity and connected to a femoral artery cathete r, were compared to those from five similarly instrumented rats that were e ach housed with another rat. Systolic blood pressure and activity but not d iastolic blood pressure or heart rate were higher in rats housed with anoth er 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 pelf balls. In addition, the nine animals were placed together dai ly 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 h oused with another rat were switched to single housing, and those previousl y housed alone were placed with another rat. The daily activity and cage en richments were otherwise continued, Removal of a cage mate increased systol ic blood pressure, diastolic blood pressure, acid heart rate but not activi ty compared parameters in animals that were changed from single to double h ousing. During the entire experiment, activity and all cardiovascular param eters were increased during the dark phase compared to the light phase of t he daily photoperiod, However, there was no statistically significant corre lation between these circadian changes and the housing conditions. In summa ry, providing social enrichment in the form of another rat or non-social ca ge enrichment combined with a daily period of group housing and physical ac tivity increased diastolic and/or systolic blood pressure of SHR rats. In a ddition, the loss of continuous social enrichment increased blood pressure and heart rate even when the other enrichments were continued, These change s were not always related to increased activity in the cage.