As members of Western societies age, sexual function of older (elderly) individuals becomes an important issue, particularly for men. Specifically, copulatory behavior increases circulatory load, which may be related to reports of cardiac sudden death following ejaculation. To further examine this relationship, we compared heart rate (HR) before and after ejaculation in 48-week-old (aged) and 10-week-old (young) male rats. As compared with resting HR, HR after ejaculation was increased by 54.2 ± 3.5 and 41.7 ± 2.7%, respectively, among aged and young male rats. These values were significantly higher than baseline levels (P<0.01). The increases in HR at each time point during copulation were significantly higher in aged male rats than in young male rats (P<0.05 or P<0.01). We also studied decreases in HR following ejaculation and found that aged male rats had a significantly higher HR at 1 and 2 min after ejaculation than young rats (P<0.01). These results suggest that the circulatory load on the aged rat heart is greater than that on a young rat heart during copulatory behavior, especially at ejaculation. In addition, the decrease in HR in aged rats after ejaculation was more gradual than in young male rats. These results suggest that there is a higher risk of sudden cardiac death during sexual behavior in older males.

Abstract:The authors studied the physiological and behavioral responses during sexual behavior in female rats. For this purpose, electrocardiographs were recoded from conscious and unrestrained females using a radiotelemetry system. Heart rate during sexual behavior rose sharply following the introduction of a sexually active male, displayed a peak level of 425 bpm during male ejaculation, and then rapidly decreased. This pattern of heart rate in females before and after receiving ejaculation was similar to that in males before and after ejaculation. In the rate of decrease in heart rate, however, there was a significant difference between females and males. The present study is the first to show changes of heart rate during sexual behavior in female rats. Key words: female rats, heart rate, sexual behavior Activation of the hypothalamus, in particular the medial preoptic area (MPOA), and excitation of the related autonomic nerves are thought to be involved in the expression of the sexual response cycle. Blumberg et al. [2] reported that tissue temperature of the MPOA in male rats was high prior to ejaculation, and then rapidly decreased.On the other hand, it is a well-known fact that injury to the sympathetic nervous system impairs ejaculation, thus suggesting that a strong but transient excitation of the sympathetic nervous system plays an important role in ejaculation.To determine the relationship between copulatory behavior and heart rate regulated by the autonomic nervous system, Saito et al. [9] investigated the heart rate during copulatory behavior in the male rat. They dem- Kyonan-cho, Japan onstrated that heart rate during copulation rose sharply following the introduction of a receptive female, showed a peak of about 520 bpm during each ejaculation series, and then rapidly decreased.In addition, we performed a detailed investigation of sexual behavior-induced changes of heart rate in female rats, and compared it with the previous result in male rats [9]. For this purpose, electrocardiographs were recoded from conscious and unrestrained females using a radiotelemetry system. Animals: Specific-pathogen -free Iar: WistarImamichi rats of both sexes were obtained from the Imamichi Institute for Animal Reproduction (Ibaraki, Japan) at 4 weeks of age. These animals were housed in suspended wire-mesh cages (width × depth × height,