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Department of Life Sciences, Second University of Naples, Via Vivaldi 43, 81100 Caserta, Italy
¹ Department of Biochemistry and Molecular Biology, Zoological Station of Naples, Villa Comunale, 80121 Napoli, Italy

(Requests for offprints should be addressed to M M Di Fiore; Email: MariaM.DiFiore{at}unina2.it)

In the lizard Podarcis s. sicula, a substantial amount of D-aspartate (D-Asp) is endogenous to the testis and shows cyclic changes of activity connected with sex hormone profiles during the annual reproductive phases. Testicular D-Asp content shows a direct correlation with testosterone titres and a reverse correlation with 17ß-estradiol titres. In vivo experiments, consisting of i.p. injections of 2.0 µmol/g body weight of D-Asp or other amino acids, in lizards collected during the three main phases of the reproductive cycle (pre-reproductive, reproductive and post-reproductive period), revealed that the testis can specifically take up and accumulate D-Asp alone. Moreover, this amino acid influences the synthesis of testosterone and 17ß-estradiol in all phases of the cycle. This phenomenon is particularly evident during the pre- and post-reproductive period, when endogenous testosterone levels observed in both testis and plasma were the lowest and 17ß-estradiol concentrations were the highest. D-Asp rapidly induces a fall in 17ß-estradiol and a rise in testosterone at 3 h post-injection in the testis and at 6 h post-injection in the blood. In vitro experiments show that testicular tissue converted L-Asp into D-Asp through an aspartate racemase. D-Asp synthesis was measured in all phases of the cycle, but was significantly higher during the reproductive period with a peak at pH 6.0. The exogenous D-Asp also induces a significant increase in the mitotic activity of the testis at 3 h (P<0.05) and at 6 h (P<0.01). Induction of spermatogenesis by D-Asp is recognized by an intense immunoreactivity of the germinal epithelium (spermatogonia and spermatids) for proliferation cell nuclear antigen (PCNA). The effects of D-Asp on the testis appear to be specific since they were not seen in lizards injected with other D- or L-forms of amino acids with known excitatory effects on neurosecretion. Our results suggest a regulatory role for D-Asp in the steroido-genesis and spermatogenesis of the testis of the lizard Podarcis s. sicula.

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				F. Raucci and M. M. Di Fiore The Maturation of Oocyte Follicular Epithelium of Podarcis s. sicula Is Promoted by D-Aspartic Acid J. Histochem. Cytochem., February 1, 2010; 58(2): 157 - 171. [Abstract] [Full Text] [PDF]