Plasma corticosterone levels during sexual behavior in male rats

The activity of the pituitary-adrenal (p-a) system, as reflected in plasma levels of corticosterone, was determined in 14 male Long Evans rats during copulation, exposure to an open field and in control conditions. Plasma corticosterone concentration during copulation was higher than in control conditions (13.3 ± 1.2 vs 9.4 ± 1.2 μm%, p < .01), but well below mean levels obtained in the open field (21.2 ± 0.8 μm%). Individual data indicated that some males gave no evidence of p-a activation during sexual activity. Furthermore, animals which showed increased steroid levels during copulation tended to have longer latencies to reinitiate copulation after ejaculation and were behaviorally less active in a subsequent open field test. It was suggested that neither sexual arousal nor copulatory performance necessarily activates the p-a system. Males showing p-a activation may be slow to habituate to a novel stimulus and thus the elevated steroid levels may reflect an insufficient number of habituation trials with the receptive female.