Gender differences in blood pressure and heart rate in spontaneously hypertensive and Wistar-Kyoto rats

1. In general, premenopausal women are known to have lower blood pressure than men and animal models have shown a similar sexual dimorphism. However, many studies in animals have been performed using anaesthetized or restrained models. Current experiments were conducted to investigate the relationships among resting heart rate, blood pressure and gender in conscious, unrestrained normotensive Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR). 2. Biotelemetry transmitters were implanted in 6-month-old animals. Values for heart rate, diastolic blood pressure, systolic blood pressure and pulse pressure were recorded continuously at 10 min intervals after all animals recovered completely from surgery. 3. Normal circadian rhythms in heart rate were found in all rats, with no significant differences among the four groups; the circadian variation in blood pressure was evident in all groups, although much smaller. Heart rate was found to be higher in WKY female rats than in the other three groups. Male WKY rats, male SHR and female SHR had similar heart rates. Male SHR had significantly higher systolic and diastolic blood pressures than female SHR. Male and female WKY rats had similar diastolic blood pressure, but males had slightly higher systolic pressure than females. No significant difference in pulse pressure was found in WKY male and female rats. Male SHR showed significantly higher pulse pressure than female SHR at most times during the day. 4. In conclusion, these results indicate that hypertension is exacerbated in male SHR compared with females under conscious resting conditions and demonstrate that the higher heart rate observed in WKY female rats is not present in the SHR model.