Immunohistochemical localization of melatonin in the rat Harderian gland

Using fluorescence and double antibody techniques, melatonin was localized immunohistologically in the secretory cells of the Harderian gland of mature male rats. The presence and quantity of melatonin in the acinar cells seem to correlate with the amount of porphyrins inside the lumen. The specificity was proven by disappearance of yellow fluorescence after saturation of antibody with melatonin or after use of nonspecific antibody only.