***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: Background D-aspartic acid is an amino acid present in neuroendocrine tissues of invertebrates and vertebrates , including rats and humans . Here we investigated the effect of this amino acid on the release of LH and testosterone in the serum of humans and rats . Furthermore , we investigated the role of D-aspartate in the synthesis of LH and testosterone in the pituitary and testes of rats , and the molecular mechanisms by which this amino acid triggers its action . Methods For humans : A group of 23 men were given a daily dose of D-aspartate ( DADAVIT ® ) for 12 days , whereas another group of 20 men were given a placebo . For rats : A group of 10 rats drank a solution of either 20 mM D-aspartate or a placebo for 12 days . Then LH and testosterone accumulation was determined in the serum and D-aspartate accumulation in tissues . The effects of D-aspartate on the synthesis of LH and testosterone were gauged on isolated rat pituitary and Leydig cells . Tissues were incubated with D-aspartate , and then the concentration ( synthesis ) of LH and cGMP in the pituitary and of testosterone and cAMP in the Leydig cells was determined . Results In humans and rats , sodium D-aspartate induces an enhancement of LH and testosterone release . In the rat pituitary , sodium D-aspartate increases the release and synthesis of LH through the involvement of cGMP as a second messenger , whereas in rat testis Leydig cells , it increases the synthesis and release of testosterone and cAMP is implicated as second messenger . In the pituitary and in testes D-Asp is synthesized by a D-aspartate racemase which convert L-Asp into D-Asp . The pituitary and testes possesses a high capacity to trapping circulating D-Asp from hexogen or endogen sources . Conclusion D-aspartic acid is a physiological amino acid occurring principally in the pituitary gl and and testes and has a role in the regulation of the release and synthesis of LH and testosterone in humans and rats Background Although abundant research has investigated the hormonal effects of d-aspartic acid in rat models , to date there is limited research on humans . Previous research has demonstrated increased total testosterone levels in sedentary men and no significant changes in hormonal levels in resistance trained men . It was hypothesised that a higher dosage may be required for experienced lifters , thus this study investigated the effects of two different dosages of d-aspartic acid on basal hormonal levels in resistance trained men and explored responsiveness to d-aspartic acid based on initial testosterone levels . Methods Twenty-four males , with a minimum of two years ’ experience in resistance training , ( age , 24.5 ± 3.2 y ; training experience , 3.4 ± 1.4 y ; height , 178.5 ± 6.5 cm ; weight , 84.7 ± 7.2 kg ; bench press 1-RM , 105.3 ± 15.2 kg ) were r and omised into one of three groups : 6 g.d−1 plain flour ( D0 ) ; 3 g.d−1 of d-aspartic acid ( D3 ) ; and 6 g.d−1 of d-aspartic acid ( D6 ) . Participants performed a two-week washout period , training four days per week . This continued through the experimental period ( 14 days ) , with participants consuming the supplement in the morning . Serum was analysed for levels of testosterone , estradiol , sex hormone binding globulin , albumin and free testosterone was determined by calculation . Results D-aspartic acid supplementation revealed no main effect for group in : estradiol ; sex-hormone-binding-globulin ; and albumin . Total testosterone was significantly reduced in D6 ( P = 0.03 ) . Analysis of free testosterone showed that D6 was significantly reduced as compared to D0 ( P = 0.005 ) , but not significantly different to D3 . Analysis did not reveal any significant differences between D3 and D0 . No significant correlation between initial total testosterone levels and responsiveness to d-aspartic acid was observed ( r = 0.10 , P = 0.70 ) . Conclusions The present study demonstrated that a daily dose of six grams of d-aspartic acid  decreased levels of total testosterone and free testosterone ( D6 ) , without any concurrent change in other hormones measured . Three grams of d-aspartic acid had no significant effect on either testosterone markers . It is currently unknown what effect this reduction in testosterone will have on strength and hypertrophy gains Abstract d-Aspartic acid ( d-Asp ) is an endogenous amino acid present in neuroendocrine systems . Here , we report evidence that d-Asp in the rat is involved in learning and memory processes . Oral administration of sodium d-aspartate ( 40 mM ) for 12–16 days improved the rats ’ cognitive capability to find a hidden platform in the Morris water maze system . Two sessions per day for three consecutive days were performed in two groups of 12 rats . One group was treated with Na-d-aspartate and the other with control . A significant increase in the cognitive effect was observed in the treated group compared to controls ( two-way ANOVA with repeated measurements : F(2 , 105 ) = 57.29 ; P value < 0.001 ) . Five further sessions of repeated training , involving a change in platform location , also displayed a significant treatment effect [ F(2 , 84 ) = 27.62 ; P value < 0.001 ] . In the hippocampus of treated rats , d-Asp increased by about 2.7-fold compared to controls ( 82.5 ± 10.0 vs. the 30.6 ± 5.4 ng/g tissue ; P < 0.0001 ) . Moreover , 20 r and omly selected rats possessing relatively high endogenous concentrations of d-Asp in the hippocampus were much faster in reaching the hidden platform , an event suggesting that their enhanced cognitive capability was functionally related to the high levels of d-Asp . The correlation coefficient calculated in the 20 rats was R = −0.916 with a df of 18 ; P < 0.001 . In conclusion , this study provides corroborating evidence that d-aspartic acid plays an important role in the modulation of learning and memory 
    Output:
    
Our results showed that exogenous D-Asp enhances testosterone levels in male animal 's studies , whereas studies in human yielded inconsistent results .