Rats were allowed to drink a solution of sodium D Asp for 12 days and after that the concentration of D Asp that accumulated in tissues was determined along with the concentration of LH and testosterone. In rat as in humans, D Asp also actively induced LH and tes tosterone release. In fact, when rats were treated with D bated in several a medium containing 0. 1 mM of sodium D Asp demonstrated that this amino acid is capable of inducing the synthesis of testosterone and that this event is mediated by cAMP, which acts as the mole cule involved in the signal transduction for testosterone synthesis from rat Leydig cells. Also, this last result is in agreement with previous studies by other investigators in which it was demonstrated that the increase of testosterone synthesized by Leydig cells occurs under Inhibitors,Modulators,Libraries the intervention of the cAMP.

The final con cern of this study was to examine the biosynthesis of D Asp in the pituitary and testis. The results demonstrated that Inhibitors,Modulators,Libraries rat tissues contain a racemase activity that is Inhibitors,Modulators,Libraries capable of converting L Asp into D Asp. We have termed this enzyme D aspartate racemase and it is present in all the rat tissues we analyzed. The pituitary and the testis are the tissues with higher concentrations. These data thus indicate that a relationship exists between the endog enous concentration of D Asp and the concentration of the D aspartate racemase in the tissues. Asp, a significant increase in LH and testosterone was observed after the 12 days of treatment, coincid ing with the increased levels of D Asp in the pituitary and testis respectively.

Thus, these data indicate that D Asp is involved in the regulation of the above hor mones. In vitro experiments conducted on an isolated rat pituitary Inhibitors,Modulators,Libraries incubated with D Asp demonstrated that D Asp at the concentration of 0. 1 mM in the medium is capable of inducing the synthesis of LH and testo sterone. In addition, when the pituitary gland was incubated with 0. 1 mM D Asp, a significant increase of cGMP occurred in the assay mixture thus indicating that the release and synthesis of LH occurred under the Inhibitors,Modulators,Libraries intervention of the cGMP. These data are in agreement with previous results obtained by other investigators, who demonstrated that the molecule involved in the signal transduction for other metabolites in the rat pituitary was cGMP.

Similarly, in vitro experiments conducted on isolated Leydig cells incu In this study, we also investigated the action of L Asp on hormone release in rats. A group of 10 male rats were treated necessary with L Asp instead of D Asp at the same time and at the same concentration and then levels of LH and tes tosterone in the blood were determined. The results of this investigation indicated that the L Asp does not induce any significant increase of serum LH or testosterone, thus indicating thus that only the stereo chemical form of D Asp is active in the hormone release.