PURPOSE: We evaluated the changes of the erectile function and histology of the corpus cavernosum in a rat model of metabolic syndrome. MATERIALS AND METHODS: We used male spontaneous hypertensive rats (SHRs) as an experimental group (n=6) and Wistar-Kyoto rats as a control group (n=6). The SHRs were fed with a high fat diet, but the Wistar-Kyoto rats were fed with a normal fat diet for 12 weeks. All the groups were then checked for body weight and various biochemiclal parameters. To investigate penile erection, the intracavernosal pressure (ICP), mean arterial pressure (MAP) and cGMP level of the corpus cavernosum were recorded for all the groups. Serial sections of the penis were used to perform Masson's trichrome staining and immunohistochemistry for determining the TGF-beta 1 expression. RESULTS: We confirmed that metabolic syndrome was induced in the experimental group by the significant difference of the various biochemical parameters. (ED note: For the results of erectile function? This wasn't clear.)As a result of erectile function, the ICP/MAP ratios were checked as 51.0+/-7.5% and 31.0+/-5.5%, respectively, for the control and experimental groups. So the ICP/MAP ratio of the latter was markedly decreased compared with the former and the cGMP level of the corpus cavernosum was the same for both groups. On Masson's trichrome staining, the number of smooth muscle cell was decreased and the collagen fibers with an irregular, distorted arrangement were increased in the experimental group. The immunoreactivity for TGF-beta 1 tended to increase in the experimental group. These histological findings revealed that fibrosis of the corpus cavernosum occurred in the experimental group. CONCLUSIONS: Our results demonstrate that metabolic syndrome is harmful to erectile function and it leads to histological changes of the corpus cavernosum according to a rat model of metabolic syndrome.