Responses of cortisol and prolactin to sexual excitement and stress in stallions and geldings

Sexual stimulation induces rapid secretion of cortisol and prolactin (PRL) in stallions. Experiment 1 was designed to determine whether stallions associated location and(or) procedure with previous sexual stimulation in that location. After a control period on d 1, four stallions were exposed to an estrous mare for 5 min on d 2. On d 3, 4, 5, and 6, the same procedure was followed with no mare present. Concentrations of PRL and cortisol increased (P < .05) after mare exposure on d 2 but did not vary (P > .05) on d 1, 3, 4, 5, or 6. In Exp. 2, six stallions were used to determine the short-term effects of 1) sexual stimulation, 2) acute physical exercise, 3) restraint via a twitch (twitching), 4) epinephrine administration, and 5) no stimulation on plasma concentrations of PRL and cortisol. Stallions received one treatment per day separated by 2 d of no treatment. Concentrations of cortisol increased (P < .05) within 10 min after sexual stimulation, exercise, twitching, and epinephrine administration but not during control bleedings. Concentrations of PRL increased (P < .05) immediately after sexual stimulation, exercise, and twitching but not after epinephrine administration or during control bleeding. In Exp. 3, the same five treatments were administered to six geldings. Concentrations of cortisol increased (P < .05) after epinephrine administration, exercise, and twitching but not after sexual stimulation or during control bleedings. Concentrations of PRL increased (P < .05) after exercise and sexual stimulation. It is concluded that 1) a single episode of sexual excitement in stallions does not lead to a memory-mediated rise in either cortisol or PRL, 2) in stallions, cortisol and PRL are secreted in response to sexual stimulation, exercise, and twitching, whereas only cortisol is secreted in response to epinephrine administration, and 3) in geldings, PRL is secreted in response to exercise, and cortisol is released in response to epinephrine administration, exercise, and twitching.