D-aspartate oxidase localisation in pituitary and pineal glands of the female pig.

Recent evidence has shown that D-aspartate modulates hormone secretion in the vertebral neuroendocrine system. Because only D-aspartate oxidase (DDO) can degrade D-aspartate, we determined DDO localisation in the pituitary and pineal glands to elucidate the control mechanisms of local D-aspartate concentration. Brain tissues and pituitary and pineal glands of the female pigs contained a similar DDO activity of 0.38-0.66 U/g protein. However, approximately ten-fold higher concentrations of D-aspartate (0.27-0.35 μmol/g protein) were found in both glands. To determine the distribution of immunoreactive DDO, we made a rabbit polyclonal antibody specific to porcine DDO using a recombinant porcine enzyme. DDO immunoreactivity was found in the cytoplasm of a subgroup of cells in the anterior and intermediate lobes, in a part of nerve processes and terminals in the posterior lobe, and in the cytoplasm of a small group of pinealocytes. We used dual-label immunocytochemistry to determine which pituitary hormones colocalise with DDO, and whether DDO and D-aspartate immunoreactivity is reciprocal. In the pituitary gland, almost all proopiomelanocortin-positive cells colocalised DDO, whereas only growth hormone-positive cells colocalised D-aspartate. D-aspartate immunoreactivity was not detected where DDO immunoreactivity was found. The present study suggests that DDO plays important roles to prevent undesirable off-target action of D-aspartate by strictly controlling local D-aspartate concentration in the pituitary and pineal glands.