Stress-like cardiovascular responses to common procedures in male versus female spontaneously hypertensive rats

We sought to determine the effects of gender on cardiovascular function of spontaneously hypertensive (SH) rats under basal conditions and after several common husbandry and experimental procedures. Heart rate (HR) and mean arterial blood pressure (NW) were monitored by radiotelemetry during undisturbed periods in the morning, at night, and after acute and chronic procedures. When undisturbed in the morning and at night, female rats had significantly (P < 0.05) higher HR than male rats, whereas male rats had significantly (P < 0.05) higher MAP. In response to all the acute procedures examined except prolonged restraint and introduction of an intruder rat of the same sex, female rats had significantly (P < 0.05) greater changes in HR or MAP than did male rats. In contrast, male rats had a greater change in MAP in response to prolonged restraint (P < 0.05) and greater HR and MAP responses (P < 0.05) in response to an intruder rat. Likewise, chronic exposure to an intruder rat increased HR and NW significantly (P < 0.05) more in males than females, and both strains partially adapted to the introduction of the unfamiliar rat after the first day. There were no significant sex-associated differences in the HR or MAP responses to transport and subcutaneous injection on four consecutive days, and neither male nor female rats adapted to the repeated procedure. We conclude that sex-associated differences in cardiovascular responses do occur in SH rats, but the direction of the difference varies with the stimulus used.