To investigate the relation of testosterone-induced relaxation with smooth muscle K⁺ channels in human internal spermatic veins. Testosterone induces relaxation in human isolated internal spermatic veins, and this effect decreases in high-grade varicocele (recently reported).

The responses of isolated internal spermatic veins from patients with varicocele were recorded isometrically using a force displacement transducer. After contracting the venous rings with 45 mM KCl, relaxation with testosterone (0.1-300 μM) was recorded in the absence or presence of large conductance calcium-activated K⁺ channel and the voltage-sensitive K⁺ channel inhibitor tetraethylammonium, adenosine triphosphate-sensitive K⁺ channel inhibitor glibenclamide, voltage-dependent inward rectifier K⁺ channel inhibitor barium chloride, and voltage-sensitive K⁺ channel inhibitor 4-aminopyridine.

Testosterone induced relaxation in human isolated internal spermatic veins in the absence of inhibitors (maximal effect 52.88 ± 6.72, n = 24). Although tetraethylammonium, barium chloride, and 4-aminopyridine did not alter the testosterone-induced relaxant responses, GLI inhibited these responses.

These results have demonstrated that testosterone induces relaxation in human isolated internal spermatic veins of patients with varicocele by way of adenosine triphosphate-sensitive K⁺ channels.