Retrograde and destination transfer of sex steroid hormones in the spermatic cord vessels of the mature boar (Sus scrofa) in short-daylight and long-daylight periods, as well as vernal and autumnal equinox.

The aim of this study was to examine the seasonal changes in concentration of steroid hormones in the spermatic cord vessels of the mature boar. Cytochrome P450 aromatase (P450arom) was also localized in the arteries and veins of the spermatic cord. Arterial blood was collected from the common carotid artery and from two branches of the testicular artery supplying the testis and epididymis to determine progesterone (P4), androstenedione (A2), testosterone (T2) and estradiol (E2) plasma concentrations. The greatest concentration of P4 was found in testicular artery during December (P<0.001), when compared with other periods and vessels. In contrast, the greatest A2 concentration was observed in the epididymal artery during the same season (P<0.001). Greater T2 concentrations were found in both testis and epididymal arteries than in common artery in March (P<0.001, P<0.001; respectively) and in September (P<0.01, P<0.001; respectively). The E2 concentration was weakly affected by seasonal periods, but greater E2 concentrations were found within vessels in the testis and epididymis than in the common artery. The P450arom was immunolocalized in all layers of the arteries and veins of the testicular spermatic cord. The intensity of P450arom staining was greater in December than in June (P<0.001). There were greater steroid concentrations in arterial vessels during December in comparison to June and this may explain the summer infertility in boars and may be related to the local retrograde and destination transfer into the spermatic cord area. The P450arom gene expression in this area seems to be involved in the conversion of T2 into E2 to enrich the testes and epididymis.