CELL-PROLIFERATION AND APOPTOSIS IN ISOPRENALINE-INDUCED SIALOSIS IN THE RAT SUBMANDIBULAR GLANDS

Regression of submandibular acinar cell hyperplasia after withdrawal o f the mitogenic stimulus induced by isoprenaline was studied in male W istar rats. Intraperitoneal administration of 39 mg of isoprenaline, i n divided doses over a 9-day period, resulted in a marked increase in gland size and weight. The proportional volume occupied by acinar cell s increased. These changes were associated with acinar cell proliferat ion and an increase in the mitotic index and cytoplasmic:nuclear ratio . Thus, both hyperplasia and hypertrophy clearly contributed to gland enlargement. Granular and other duct cells appeared to be unaffected b y isoprenaline administration. Following cessation of the drug, the mi totic index reached a peak value by the second day but thereafter decl ined rapidly. This change was matched by a marked rise in the apoptoti c cell index, the latter reaching a maximum by the fourth day. By the end of the second week, glands had returned to normal with respect to size and weight and neither hyperplasia nor apoptosis could be detecte d histologically. These results confirm that apoptosis is involved in the regulation of submandibular salivary gland size.