Hormonal responses to different sexually related conditions in male rats H. Bonilla-Jaime ⁎ , G. Vázquez-Palacios, M. Arteaga-Silva, S. Retana-Márquez Department of Reproductive Biology, Universidad Autonoma Metropolitana-Iztapalapa, Mexico City, C.P. 09340, Mexico Received 15 April 2005; revised 25 August 2005; accepted 26 August 2005 Available online 30 September 2005 Abstract Plasma levels of corticosterone (C) and testosterone (T) increase after sexual activity in males of several species. However, the physiological significance of these increases has not been elucidated. In the present study, hormonal response to different conditions linked to sexual activity was assessed. In the first experiment, plasma levels of C and T were assessed both in sexually experienced and naive male rats after the following conditions: (A) control group, without sexual stimulation; (B) males exposed to ovariectomized females; (C) males exposed to intact, non-receptive females; (D) males exposed to receptive females with the vagina obstructed, to avoid intromission; (E) males exposed to receptive females: but separated by a grid that prevents physical contact; (F) males exposed to receptive females during 30 min. In a second experiment, experienced male rats were allowed to repeatedly copulate until reaching the criteria for sexual exhaustion, and 24 h later, they were allowed to copulate. Once sexually related conditions ended, males were killed and their blood was obtained. C and T plasma levels were assessed by HPLC with ultraviolet (UV) detection. Results indicate that T did not increase significantly in naive male in any sexual condition, while in the experienced males, significant increases were observed with the mere presence of a receptive female and also after ejaculation. These increases were significantly larger in experienced males. On the other hand, C also increased in all sexual conditions, both in experienced and naive rats; however, the increase observed was larger in experienced males. Regarding sexual satiety, both C and T increased after copulating ad libitum to satiety. T increased almost three-fold compared to control, while C increased two-fold. No significant changes were observed in either one of the steroids 24 h after sexual exhaustion, even though males remained with a receptive female during an hour. These results show that sexual experience has an important influence on the hormonal response to sexual activity. C rises could be directly related to sexual arousal involved in the different sexual conditions, while T rises seem to have a direct relationship with both the motivation and execution aspects of masculine sexual behavior. © 2005 Elsevier Inc. All rights reserved. Keywords: Corticosterone; Testosterone; Sexual behavior; Sexual satiety; Male rat Introduction The hormonal influence on the regulation of sexual behavior is well known. However, the importance of mating behavior in triggering an endocrine response has been poorly analyzed. Several reports show that plasma levels of corticosterone (C) and testosterone (T) increase after sexual activity in males of many species. In male rats, increases in luteinizing hormone (LH), prolactin (Prl) and T have been reported when subjects reach ejaculation (Kamel and Frankel, 1978; Kamel et al., 1977). A similar hormonal response has been observed in pigs (Borg et al., 1991) and rabbits (Agmo, 1976). In contrast, in stallions and bulls, the increase of T after sexual behavior was not observed after sexual stimulation followed by ejaculation (Borg et al., 1991; Rabb et al., 1989). In rats, the increase of T has been observed only in sexually experienced males, but not in naive males (Kamel et al., 1975). Furthermore, the only presence of a receptive female rat increases the levels of luteinizing hormone and T (Graham and Desjardins, 1980). On the other hand, it has been reported that, in sexual satiety, which consists of a prolonged sexual inhibition in response to copula ad libitum (Beach, 1956; Larsson, 1956), the motivational component of reproductive behavior is diminished (Rodriguez-Manzo and Fernández-Guasti, 1995). It has been suggested that T is involved in motivational aspects of sexual behavior (Alexander et al., 1994; Stoleru et al., 1993), hence, the modifications in plasma levels of this steroid after sexual satiety were also analyzed in this study. Hormones and Behavior 49 (2006) 376 – 382 www.elsevier.com/locate/yhbeh ⁎ Corresponding author. Departamento de Biología de la Reproducción, Universidad Autónoma Metropolitana-Iztapalapa, C.P. 09340, Iztapalapa, D.F. Mexico. Fax: +1 5255 5804 4930. E-mail address: bjh@xanum.uam.mx (H. Bonilla-Jaime). 0018-506X/$ - see front matter © 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.yhbeh.2005.08.005