Pineal gland free amino acids and indoles during postnatal development of the rat: correlations in individual glands.

Free amino acids and indoles were measured by HPLC in single pineal glands of 5-, 10- and 20-day-old rats sacrificed during mid-light and mid-dark at each age. Melatonin was detectable in neonates (5-day-old), but day vs night differences in indole constituents did not occur until 10 days of age. Free amino acid steady state levels were high in neonates and there was a tendency for reversal of day vs night differences coinciding with the onset of circadian rhythmicity in indole biosynthesis. High correlations (r greater than 0.85) existed for taurine vs. glutamate in individual glands regardless of age and time of sacrifice. These findings suggest that taurine and glutamate are biochemically interrelated and that developmental changes in amino acid metabolic pools reflect functional innervation of the gland.