Effect of stallion age on the expression of LH and FSH receptors and aromatase P450 in equine male reproductive tissues.

The aim of the present study was to characterise receptors for LH and FSH (LHR and FSHR, respectively) and aromatase in epididymal and testicular tissue from stallions of different ages (prepubertal, young, mature and old). Gene and protein expression were assessed by real-time quantitative polymerase chain reaction (real-time qPCR), immunohistochemistry and multiple immunofluorescence labelling. There were no differences in LHR mRNA expression in epididymal and testicular parenchyma in stallions of different age. In contrast, expression of FSHR and CYP19A1 in caput, corpus and cauda epididymis and in testicular parenchyma increased with age (P<0.001). Immunolabelling for LHR, FSHR and aromatase was influenced by puberty. In postpubertal stallions, positive staining for LHR and aromatase was detected in Leydig cells, whereas protein expression of FSHR was present in Sertoli cells and primary spermatocytes. In prepubertal colts, staining for LHR, FSHR and aromatase was detected in seminiferous tubules. In epididymal tissue, aromatase was present in the cauda epididymis only, regardless of age. In conclusion, the results highlight the significance of gonadotropin action and oestrogen production for the maturation of male reproductive tissue in the horse. The presence of FSHR in the seminiferous tubules suggests effects of FSH on spermatogenesis in this species. The importance of oestrogen production for maintenance of testicular function in stallions was confirmed.