SECRETION OF D-ASPARTIC ACID BY THE RAT TESTIS AND ITS ROLE IN ENDOCRINOLOGY OF THE TESTIS AND SPERMATOGENESIS

The D-isomer of aspartic acid (D-Asp) has been found in rat testes. In the present study, samples of testicular venous blood plasma, rete te stis fluid, interstitial extracellular fluid, luminal fluid from the s eminiferous tubules, testicular parenchymal cells, epididymal spermato zoa and peripheral blood plasma were collected and analyzed for D-Asp by two methods, an enzymatic and a chromatographic HPLC method. The tw o methods gave very similar results for all samples. The highest conce ntrations of D-Asp (about 120 nmol/ml) were found in testicular venous blood plasma, with slightly lower concentrations in rete testis fluid (95 nmol/ml) and epididymal spermatozoa (80 nmol/g wet weight). Lower levels mere found in testicular parenchymal cells (which would compri se mostly spermatids and spermatocytes), luminal fluid from the semini ferous tubules and interstitial extracellular fluid (26, 23 and 11 nmo l/ml respectively). However, these values were all higher than those f or peripheral blood plasma (6 nmol/ml), It would appear that D-Asp is being secreted by the testis mostly into the venous blood, passing the nce into the rete testis fluid and being incorporated into the spermat ozoa at the time or after they leave the testis, The distribution of D -Asp is thus quite different from that of testosterone, and its role a nd the reason for its high concentration in the male reproductive trac t remain to be elucidated. (C) 1998 Federation of European Biochemical Societies.