In this study significant reduction in

In this study, significant reduction in the HCO3− content in sham-operated and testosterone-treated rats following bafilomycin A1 administration suggested that V-ATPase could be involved in mediating the decrease in vas deferens fluid HCO3− content, most probably due to the increase in H+ secretion that neutralizes the HCO3−. It is generally known that besides increased in H+ content, HCO3− content of the luminal fluid can also be affected by intracellular pH, CO2 partial pressure as well as glucose [[30], [31], [32], [33], [34]]. Besides its ability to stimulate proton secretion, testosterone was also reported able to modulate the transport of ions across the vas deferens epithelium [35], which might also affect the luminal HCO3− content. Other possibilities were that testosterone could modulate the HCO3−trsnporters such as Cystic Fibrosis transmembrane regulator (CFTR), Na+/HCO3− co-transporters (NBC) and Cl−/HCO3− exchanger. The possible role of anion transporter/exchanger in mediating changes to vas deferens fluid pH was supported by a report which indicated a concerted action between V-ATPase and Na+−HCO3– cotransporter in regulating acidification and/or HCO3− reabsorption of the excurrent ductal fluid of the testis [36]. Besides, the presence of Na+−HCO3– cotransporter (SLC4A4) has also been reported in the vas deferens in mice [37]. Nevertheless, the physical and functional relationship between these transporters in pH regulation in vas deferens have yet to be identified. In the meantime, this study has shown the direct involvement of androgen receptor (AR) and dihydrotestosterone (DHT) in mediating testosterone effect on vas deferens fluid secretion, its pH and HCO3− content. Higher pH and HCO3− content were observed following concomitant administration of testosterone with flutamide and finasteride, indicating that blocking testosterone action or DHT action/formation could have reversal effect on the studied parameters. AR has a direct role in the up-regulation of V-ATPase A1 and B1/2 Zoniporide dihydrochloride synthesis by testosterone. Besides, the observed testosterone effects were most probably mediated via DHT as V-ATPase expression decreased following administration of 5α-reductase inhibitor which inhibits testosterone conversion to DHT [38]. The involvement of AR suggests that genomic mechanism is likely to be involved, where upon binding of the ligand to AR, transcription factor will be activated which results in transcription of androgen-responsive genes [39]. The role of AR in the male reproductive organs have been reported. Cultured vas deferens epithelial cells have been found to contain high levels of AR, which expression can be induced by androgen [40]. There were evidences which showed that DHT can bind directly to AR in vas deferens of humans [41]. Further, Jean Faucher et al. [42] reported that the proximal region of vas deferens contains higher amounts of androgens (testosterone + DHT) as compared to caput epididymidis. Besides, the important role of DHT is reflected by high levels of 5α-reductase in vas deferens and other male accessory reproductive organs such as epididymis, where this enzyme is involve in DHT synthesis from testosterone [43,44]. Distribution of V-ATPase further confimed its role in vas deferens fluid acidification. V-ATPases is present at the apical membrane of vas deferens and its relatively higher distribution under testosterone influence suggested its direct involvement in establishing the acidic vas deferens fluid pH. We have also shown that V-ATPase was also distributed in the smooth muscle of vas deferens, however its role is unknown. Kurauchi-Mito, Ichihara [45] suggested that there might be interaction between smooth muscle cell specific pro (renin) receptor (PRR) and V-ATPase which is required for V-ATPase-dependent autophagy, a process essential for smooth muscle survival [[46], [47], [48]].
Conflicts of interest
Acknowledgement This study was supported by Fundamental Research Grant Scheme, FP025-2014A, Ministry of Education, Putrajaya, Malaysia and PPP grant (PG230-2015B), University of Malaya, Kuala Lumpur, Malaysia.