Estrous-related variations of blood pressure and heart rate in female rats

In female rats, several biological variables change with a 4 or 5 day estrous cycle. To clarify whether blood pressure and heart rate show estrous-related changes, we measured three variables, i.e. mean arterial pressure (MAP), heart rate (HR) and spontaneous activity (ACT), using an implantable radiotelemetry transmitter and a computerized data collecting system non-invasively and chronically for more than 2 months. Under a 12-12 light-dark cycle, the three variables revealed clear daily variations and modulations by the estrous cycle which were most pronounced in the proestrous night. During the proestrous night, ACT showed a remarkable increase and a peak in the first half of the night, whereas MAP showed a gradual increase and a peak around midnight, and HR remained low without forming a peak. All modulations by the estrous cycle disappeared following bilateral ovariectomy. It is concluded that daily variations of blood pressure and heart rate are modulated according to the estrous cycle.