Occurrence of D-aspartic acid in rat brain pineal gland.

We found a high concentration (1030 pmol per pineal gland) of D-aspartic acid (D-Asp) in the pineal gland of 6-week-old Sprague-Dawley (SD) rats. The content of D-Asp decreased with age, being 210 and 33 pmol per pineal gland in 28- and 45-week-old rats respectively. The proportion of D-Asp [(D-Asp/total Asp) x 100] also decreased with age, declining from 66% to 10% between 6 and 45 weeks after birth. The proportion of D-Asp did not differ between the sexes. The concentration of D-Asp was higher at night (at 2.00 a.m. 2830 +/- 485 pmol per pineal gland) than during the day (at 10.00 a.m. 1030 +/- 200 and at 3:00 p.m. 682 +/- 194 pmol per pineal gland), suggesting that biosynthesis of D-Asp in the pineal gland occurs at night. D-Asp was found to be distributed in the cytosol of pinealocytes, but its biological role remains unclear.