The hormone oxytocin (OT) is important for evoking smooth muscle contraction in the uterus. The OT receptor (OTR), whose signaling cascade includes increased intracellular calcium, can be activated by both OT and the related peptide vasopressin (VP). In human testis the wall of seminiferous tubules are formed by several layers of smooth muscle-like peritubular myoid cells, which might also be targeted by OT and/or VP. Using testicular sections and cultured primary cells (HTPCs from men with normal spermatogenesis) immunohistochemistry showed slightly positive reactions for OTR and VP receptor V1a. RT-PCR analysis showed presence of OTR in all tested cells (n=5 patients). In HTPCs VP receptors V1a and V1b were present in only 1 out of 5 samples, while V2 was absent. When OT (10nM) or VP (10 mM) were added a transient rise in intracellular calcium occurred in 85% or 84% of all cells, respectively. The specific OTR blocker tocinoic acid (20 mM) reduced the percentage of responsive cells to 21% (OT) and 29% (VP). Thus OT and VP act mainly via OTR. The calcium-actived BK_Ca channel is expressed by HTPCs and as we found OTR signaling involves BK_Ca. Thus, using the membrane potential dye DiBAC₄(3), we found that OT caused hyperpolarization. Blockage of BK_Ca (with iberiotoxin) abolished this event. The data identify OT as a hormone also of relevance to the human testis. It targets peritubular cells and affects the membrane potential. Whether it stimulates contraction is currently being studied.

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