Localization, Transport, and Uptake of d-Aspartate in the Rat Adrenal and Pituitary Glands

Large amounts of d-aspartate (d-Asp) are present in the rat adrenal and pituitary glands. d-Asp is thought to be synthesized in the mammalian body and also accumulates in various tissues following intraperitoneal or intravenous administration. This report examines the origins of d-Asp in the adrenal and pituitary glands. We administered d-Asp to male rats intraperitoneally and immunolocalized this exogenous d-Asp in adrenal and pituitary tissue, using an anti-d-Asp antiserum which was previously developed in our laboratory. d-Asp levels in the rat adrenal gland have been shown to undergo a transient increase at 3 weeks of age and to decrease rapidly thereafter. We found that in the adrenal gland, exogenous d-Asp administered intraperitoneally was incorporated into the same region of the adrenal cortex in which endogenous d-Asp was present. By Northern and Western blot analysis and immunohistochemistry of glutamate (Glu) transporter, we also found that expression of the Glu transporter (GLAST), which has an affinity for d-Asp, transiently increased at 3 weeks of age and that localization patterns of the Glu transporter within the tissue were almost coincident with those of endogenous d-Asp. These observations suggest that d-Asp in the adrenal cortex of 3-week-old male rats is primarily acquired by uptake from the vascular system. We have previously shown that d-Asp is specifically localized in prolactin (PRL)-containing cells in the anterior lobe of the adult rat pituitary gland. Here we report that in the pituitary gland, exogenous d-Asp accumulated in endothelial cells, but not in PRL-containing cells. Northern and Western blot analysis and immunohistochemistry of Glu transporter revealed that developmental changes in the Glu transporter (GLAST) expression did not correlate with tissue levels of d-Asp and that the Glu transporter was not expressed in PRL-containing cells. These observations suggest that, in contrast to the adrenal gland, most of the d-Asp in the pituitary gland of adult male rats originates inside the gland itself.