D-aspartic acid induces merocrine secretion in the frog harderian gland

Abstract

High levels of D-aspartic acid (D-Asp) have been found in the harderian gland (hg) of the frog,Rana esculenta. This is the first report of D-aspartate in an exocrine gland. D-aspartate content is correlated with secretory activity: it is high in July when the hg shows the highest secretory activity, lower in February, in concomitance with the low secretory activity. The harderian gland has the capacity to uptake D-Asp injected i.p. In July, gland uptake is higher than in February. Administration of 2.0 µmol/g D-Asp in frogs during both periods induces the release of secretory granules in the hg. This effect is more evident in July, when the amino acid accumulates at the apex of the cells beneath the plasma membrane. Such evidence suggests a role of D-Asp in the exocytotic mechanism.