ULTRASTRUCTURAL-LOCALIZATION OF MICROLITHS IN SALIVARY-GLANDS OF CAT

Although microliths occur in normal human salivary glands and may be a n aetiological factor of sialadenitis, little is known of their natura l history. In an attempt to remedy this, we investigated a large archi val collection of normal and experimental feline parotid, submandibula r and sublingual salivary glands. In submandibular and sublingual glan ds, microliths were detected ultrastructurally in: all types of acinar secretory cells; myoepithelial cells, ductal cells; lumina; intercell ular spaces; basement membrane; stroma; macrophages; multinuclear gian t cells; and neutrophils. Microliths were not detected ultrastructural ly in parotid glands. Microliths appear to form in acinar cells during autophagy and in stagnant secretory material in lumina. Microliths ap pear to be removed by secretion in the saliva, discharge from cells la terally and basally, and engulfment by macrophages. There appears to b e a turnover of microliths, which possibly is upset by secretory inact ivity with a resulting accumulation that leads to localized obstructio n and sialadenitis.