Visualizing NO-mediated effects on wall movements in seminiferous tubules of the testis

Contractile function of peritubular smooth muscle cells (PTCs) surrounding seminiferous tubules (STs) in the testis is pivotal for male reproduction. PTCs encompass the germinal epithelium hosting proliferation and maturation of male germ cells to become spermatozoa. Once shed from the epithelium (spermiatio), spermatozoa are still immobile and require PTC contractions to propel them towards the rete testis. In the rat, spermatogenic stages are arranged sequentially along the tubules can be distinguished by transillumination microscopy.A custom Fiji-based code was built to characterize spontaneous superficial wall movements in isolated rat ST before and after spermiatio and in response to nitric oxide (NO) treatment.Spontaneous contractions were visible at the ST wall and showed an irregular and undulating pattern. Significant differences in contractility of the ST wall before and after spermiatio were found. Treatment with NO donors significantly reduced wall contractions independent of the respective spermatogenic stage.In STs of human patients, spontaneous contractions and NO-induced effects could also be visualized by the same ex vivo approach.In agreement, isolated human PTCs revealed an increase of relaxation-mediating cGMP by NO and showed a reduced calcium increase in response to noradrenaline when inhibiting cGMP hydrolysis with sildenafil.Different spontaneous contraction patterns associated with different spermatogenic stages (before and after spermiatio) could be detected and visualized. These findings suggest region-specific, localized functions of PTCs in the ST. Susceptibility of spontaneous and noradrenaline-induced contractions to NO-related signaling points to a yet underexplored role of cGMP signaling in the regulation of PTC contractile activity.