Little evidence is available for the physiological function of D-amino acids in species other than bacteria. Here we demonstrate that naturally occurring freed -aspartate (D-Asp) is present in all magnocellular neurons of rat hypothalamus. The levels of this naturally occurring D-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 D-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 D-Asp in mammalian physiology. The findings argue against the conventional concept that only L-stereoisomers of amino acids are functional in higher species.

This article has been cited by other articles:

				G. D'Aniello, N. Grieco, M.A. Di Filippo, F. Cappiello, E. Topo, E. D'Aniello, and S. Ronsini Reproductive implication of D-aspartic acid in human pre-ovulatory follicular fluid Hum. Reprod., December 1, 2007; 22(12): 3178 - 3183. [Abstract] [Full Text] [PDF]

				A. Yamamoto, H. Tanaka, T. Ishida, and K. Horiike Functional and Structural Characterization of D-Aspartate Oxidase from Porcine Kidney: Non-Michaelis Kinetics due to Substrate Activation J. Biochem., March 1, 2007; 141(3): 363 - 376. [Abstract] [Full Text] [PDF]

				G. Noctor, G. Queval, and B. Gakiere NAD(P) synthesis and pyridine nucleotide cycling in plants and their potential importance in stress conditions J. Exp. Bot., May 1, 2006; 57(8): 1603 - 1620. [Abstract] [Full Text] [PDF]

				F Raucci, S D'Aniello, and M M Di Fiore Endocrine roles of D-aspartic acid in the testis of lizard Podarcis s. sicula J. Endocrinol., December 1, 2005; 187(3): 347 - 359. [Abstract] [Full Text] [PDF]