Endocrine roles of D-aspartic acid in the testis of lizard Podarcis s. sicula.
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 17beta-estradiol titres. In vivo experiments, consisting of i.p. injections of 2.0 micromol/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 17beta-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 17beta-estradiol concentrations were the highest. D-Asp rapidly induces a fall in 17beta-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.
Raucci
F
F
Department of Life Sciences, Second University of Naples, Via Vivaldi 43, 81100 Caserta, Italy.
D'Aniello
S
S
Di Fiore
M M
MM
D000591:Amino Acid Isomerases / Q000378:metabolism; D000818:Animals; D026603:D-Aspartic Acid / Q000096:biosynthesis / Q000502:physiology*; D004958:Estradiol / Q000032:analysis / Q000097:blood; D007150:Immunohistochemistry / Q000379:methods; D008116:Lizards / Q000033:anatomy & histology / Q000276:immunology / Q000502:physiology*; D008297:Male; D018809:Proliferating Cell Nuclear Antigen / Q000032:analysis; D012098:Reproduction; D013087:Spermatids / Q000276:immunology; D013091:Spermatogenesis / Q000502:physiology; D013093:Spermatogonia / Q000276:immunology; D013737:Testis / Q000033:anatomy & histology / Q000276:immunology / Q000502:physiology*; D013739:Testosterone / Q000032:analysis / Q000097:blood
D018809:Proliferating Cell Nuclear Antigen; D013739:Testosterone; D026603:D-Aspartic Acid; D004958:Estradiol; D000591:Amino Acid Isomerases; C019749:aspartate racemase