Isolated epididymal duct segments and seminiferous tubules were studied by organ bath and time-lapse video microscopy to assess sperm transport and contractile activity. In all parts of the epididymis, regular contractions which elicited transport of sperm could be observed. Contraction frequency was reduced after the addition of cGMP-elevating agents sildenafil, nitric oxide (NO) or atrial natriuretic peptide (ANP) . In seminiferous tubules, slow, irregular and very fine contractions of the tubular wall were observed without clear peristalsis. Wall movements were tracked over time by recording their varying grey values in defined regions of interest. After normalisation and detrending of these data, Fourier analysis could define a frequency spectrum characterizing this irregular contractile activity. Elevating cGMP resulted in a shift of the frequency spectrum towards lower frequencies.
Western blotting, immunohistochemistry and RT-PCR using laser-dissected contractile cells confirmed expression of the corresponding cGMP pathway components. PDE5 activity was assessed using a cGMP-ELISA and sildenafil dose-dependently increased cGMP.
In a rat model of chronic sildenafil treatment, PDE5 expression, contractility and sperm transport remained unaltered.