Expression of transforming growth factor-beta1 in penile tissue from rats with bilateral cavernosal nerve ablation

To explore the expression of transforming growth factor-beta(1) (TGF-beta1) in penile tissue from rats after bilateral cavernosal nerve (CN) ablation, mimicking patients who have had no nerve-sparing during prostatectomy.

Ten adult male rats (neurectomy group) had a bilateral CN resection aseptically under an operating microscope, with six sham-operated rats as controls. Fifteen weeks after surgery an apomorphine test was used in all rats to assess penile erection. The penile specimens were then collected and prepared for detecting the expression of TGF-beta1 by reverse transcription-polymerase chain reaction (RT-PCR), western blot and immunohistochemistry, and for quantitative analysis of the ratio of smooth muscle to collagen fibres in the corpus cavernosum with confocal microscopy.

All rats in the sham-operated group but none after neurectomy had an erectile response after subcutaneous injection with apomorphine (100 micro g/kg). Immunohistochemistry, RT-PCR and western blot analyses showed a significantly higher expression of TGF-beta1 in the penile tissues after neurectomy than after sham surgery. Smooth muscle cells (fluorescing red) and collagen fibres (green autofluorescence) after paraformaldehyde fixation, were clearly identified by confocal microscopy. The fluorescence intensity expressed as the mean (sem) ratio of smooth muscle to collagen fibres in the corpus cavernosum after neurectomy was 0.265 (0.125), significantly lower than that in the sham-operated group, at 0.760 (0.196) (P < 0.01).

An increased expression of TGF-beta1 in penile tissue which promotes the synthesis of collagen may be one of the important factors for the erectile dysfunction caused by bilateral CN ablation. Similar pathophysiological processes may occur in the corpus cavernosum of patients after radical prostatectomy.