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Aim: To investigate the ultrastructural changes of penile corpus cavernosum and tunica albuginea in rats treated with castration or finasteride.
Methods: Eighteen male Sprague-Dawley rats of nine weeks old were randomly divided into three groups with 6 rats each. Group A served as the control, Group B was castrated and Group C, treated with finasteride. Four weeks later, rats were anesthetized and blood samples obtained for the determination of serum testosterone (T) and dihydrotestosterone (DHT) levels; penile tissues were taken for scanning electron microscopy.
Results: The T, free T and DHT levels in Group B and the DHT level in Group C were significantly lower than those in Group A (P<0.05). The tunica albuginea was significantly thinner in Group B than that in Group A (P<0.05), but there was no significant difference between Group C and Group A (P>0.05). Elastic fibers in the tunica albuginea of Group A were very rich and arranged regularly and undulatedly, but in Group B, most of the elastic fibers were replaced by collagenous fibers. In Group C, the tunica albuginea was mainly composed of thick and irregular-arranged collagenous fibers. In Group A, there were abundant smooth muscle fibers in the trabeculae of corpus cavernosum, but they were much less in Group C and scarce or even disappeared in Group B. In Groups B and C, the diminished/disappeared smooth muscle fibers were replaced by irregularly arranged collagenous fibers.
Conclusion: In rats, androgen is essential for maintaining the normal structure of penile tunica albuginea and corpus carvenosum.
Discussion
The present study showed that in the castration animals, there were a high degree of fibrosis in the corpus cavernosum with irregularly arranged collagenous fibers and a marked decrease in smooth muscle fibers, while in the DHT-inhibited group, the corpus cavernosum contained quite an amount of thick and irregular-arranged collagenous fibers, but the degree of fibrosis was lower than that in the castration group. Results suggest that androgen is essential for the maintenance of normal ultrastructure of corpus cavernosum. Zhang et al [4] demonstrated that in mature rats, castration induced apoptosis in corpus cavernosum with the replacement of the apoptotic tissues by fibrous tissue. This may be one of the pathways through which androgen deprivation acts on corpus cavernosum. In the present study, the degree and type of corpus cavernosum fibrosis in the two groups were different, suggesting that T and DHT act on the corporal cavernosal tissues independently and differently. Finasteride can only inhibit the action of DHT, but not T on the corporal cavernosal tissue, therefore, the degree of fibrosis was less in the DHT-inhibited group than in the castration group.
The tunica albuginea of penis plays a major role in the erection mechanism. It compresses the subalbugineal venules, thus decreasing the venous outflow during erection and provides an inextensible fibrous frame for the erectile tissue of the penis [5]. In the normal control group of this study, the elastic fibers in the tunica albuginea were very rich and arranged regularly and undulatedly. In the castration group, the thickness of tunica albuginea decreased significantly and the elastic fibers were mostly replaced by collagenous fibers and in the DHT-inhibited group, the elastic fibers were replaced by disorganized and thick collagenous fibers. These results indicate that androgen is also essential for the maintenance of the normal structures of tunica albuginea.
It can be concluded that androgen is indispensable to the maintenance of normal ultrastructures of the erectile tissues. However, the interrelationship between androgen and the structure and function of the erectile tissue is not quite clear and sometimes even controversial, and further investigation is needed.
