Developmental changes in free D-aspartic acid in the chicken embryo and in the neonatal rat

In the lizard Podarcis s. sicula, a substantial amount of -aspartate (-Asp) is endogenous to the testis and shows cyclic changes of activity connected with sex hormone profiles during the annual reproductive phases. Testicular -Asp content shows a direct correlation with testosterone titres and a reverse correlation with 17 -estradiol titres.In vivo experiments, consisting of i.p. injections of 2·0 µmol/g body weight of -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 -Asp alone. Moreover, this amino acid influences the synthesis of testosterone and 17 -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 17 -estradiol concentrations were the highest. -Asp rapidly induces a fall in 17 -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 -Asp into -Asp through an aspartate racemase. -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 -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 -Asp is recognized by an intense immunoreactivity of the germinal epithelium (spermatogonia and spermatids) for proliferation cell nuclear antigen (PCNA). The effects of -Asp on the testis appear to be specific since they were not seen in lizards injected with other -or -forms of amino acids with known excitatory effects on neurosecretion. Our results suggest a regulatory role for -Asp in the steroidogenesis and spermatogenesis of the testis of the lizard Podarcis s. sicula.

Section: Introductionmentioning

confidence: 99%

Endocrine roles of d-aspartic acid in the testis of lizard Podarcis s. sicula

Raucci¹,

D’Aniello²,

Fiore³

2005

“…Recently, the existence of some -amino acids in some organs of higher animals has been demonstrated by several groups using HPLC techniques (D'Aniello & Giuditta 1977, Dunlop et al 1986, Neidle & Dunlop 1990, Hashimoto et al 1992, Kera et al 1995, D'Aniello et al 1995, Imai et al 1995, Hamase et al 1997. Although extensive in number, the above studies have not provided an answer to the question as to whether these -amino acids are biologically functional.…”

Section: Introductionmentioning

confidence: 99%

Regulation of rat magnocellular neurosecretory system by D-aspartate: evidence for biological role(s) of a naturally occurring free D-amino acid in mammals

Wang

Wolosker

Pevsner

et al. 2000

Little evidence is available for the physiological function of -amino acids in species other than bacteria. Here we demonstrate that naturally occurring free -aspartate (-Asp) is present in all magnocellular neurons of rat hypothalamus. The levels of this naturally occurring -amino acid were elevated during lactation and returned to normal thereafter in the magnocellular neurosecretory system, which produces oxytocin, a hormone responsible for milk ejection during lactation. Intraperitoneal injections of -Asp reproducibly increased oxytocin gene expression and decreased the concentration of circulating oxytocin in vivo. Similar changes were observed in the vasopressin system. These results provide evidence for the role(s) of naturally occurring free -Asp in mammalian physiology. The findings argue against the conventional concept that only -stereoisomers of amino acids are functional in higher species.

“…-Asp has been found in the nervous tissue of cephalopods, Octopus vulgaris, Loligo vulgaris and Sepia officinalis (D'Aniello & Giuditta 1977, 1978, D'Aniello et al 1995b, the opisthobranch mollusc, Aplysia fasciata (D'Aniello et al 1992a), and the tunicate, Ciona intestinalis (D'Aniello et al 1992b). Among vertebrates, free -Asp has been found in the nervous tissue of chickens (Neidle & Dunlop 1990), rodents (Dunlop et al 1986, D'Aniello et al 1993a, Hashimoto et al 1993b) and humans (Fisher et al 1991, 1994, Hashimoto et al 1993a. More recently, studies have shown that this enantiomer is also present in other body structures, including the endocrine glands and reproductive organs of the rat (Hashimoto et al 1993b, D'Aniello et al 1996 and in the sexual glands of Octopus vulgaris (D'Aniello et al 1995a).…”

Section: Introductionmentioning

confidence: 99%

D-aspartic acid is implicated in the control of testosterone production by the vertebrate gonad. Studies on the female green frog, Rana esculenta

Fiore¹,

Assisi²,

Botte³

et al. 1998

In the present study we report the occurrence of -aspartic acid (-Asp) in the ovary of the green frog Rana esculenta and its putative involvement in testosterone production by the gonad. In the ovary, -Asp concentrations undergo significant variations during the main phases of the sexual cycle. In spawning females (March), its concentration was low (2·5 1·1 nmol/g ovary) and during the postreproductive period ( June) it increased and reached its peak level (58·0 10·1 nmol/g) in October. In that month, vitellogenesis occurs in a new set of ovarian follicles and continues until the next spring. The concentrations of -Asp in the ovary and of testosterone in the ovary and in the plasma were inversely correlated during the reproductive cycle: when endogenous -Asp was low (March), testosterone was high (36·9 4·8 ng/g ovary; 23·1 2·76 ng/ml plasma) and, in contrast, when the -Asp concentration was high (October), the testosterone concentration was low (0·86 0·21 ng/g ovary and 5·0 1·3 ng/ml plasma). In vivo experiments, consisting of injection of -Asp (2·0 µmol/g body weight) into the dorsal lymphatic sac of adult female frogs, demonstrated that this amino acid accumulates significantly in the ovary. After 3 h, moreover, it caused a decrease in testosterone level in the plasma of about 80%. This inhibition was reversible: within 18 h after the amino acid injection, as the -Asp concentration in the ovary decreased, the testosterone titre was restored in both ovary and plasma.In vitro experiments, conducted in isolated ovarian follicles, confirmed this phenomenon and identified these gonadal components as the putative -Asp targets. Other amino acids (-Asp, -Glu, -Glu, -Ala and -Ala) used instead of -Asp were ineffective.These findings indicate that -Asp is involved in the control of androgen secretion by the ovary in this amphibian species, revealing a more complex system for control of this androgen synthesis than was previously believed to exist.