RAT TESTICULAR GERM-CELLS AND EPIDIDYMAL SPERM CONTAIN ACTIVE P450 AROMATASE

Although testosterone is the principal sex steroid produced by the tes tis, estrogen is known to be produced by both Leydig and Sertoli cells during different developmental periods. Additionally, evidence is unf olding to suggest that germ cells might also participate in the synthe sis of estrogen within the male reproductive tract. We have recently r eported that the messenger ribonucleic acid (mRNA) for P450 aromatase (P450arom), the enzyme that converts androgen to estrogen, is synthesi zed by rat germ cells. Therefore, the present study was conducted to d etermine which germ cell types synthesize active P450arom and to measu re the activity of this enzyme in germ cells throughout spermatogenesi s and in maturing sperm during epididymal transit. First, P450arom act ivity was measured in pachytene spermatocytes, round spermatids; and a mixture of round spermatids, elongating spermatids, and residual bodi es using the tritiated water ((H2O)-H-3) assay. Second, sperm isolated from different regions of the epididymis were assayed for P450arom ac tivity. Sperm isolated from the caput epididymis with attached efferen t ductules had the higher P450arom activity, whereas sperm isolated fr om the corpus and cauda epididymides had lower P450arom activity. The decrease in P450arom activity in cauda sperm was further confirmed by immunocytochemistry. On the basis of these observations, we conclude t hat rat testicular germ cells from pachytene spermatocytes through elo ngating spermatids and epididymal sperm contain active P450arom and th at sperm lose aromatase activity as they mature during epididymal tran sit. Therefore, both post-pachytene rat germ cells and epididymal sper m are capable of estrogen synthesis and are an additional, potentially significant, source of estrogen in the male reproductive tract.