Compensatory proliferative response of the rat submandibular salivary gland to unilateral extirpation

Summary

The present experiment was conducted in order to identify the progenitor compartment of the submandibular salivary gland (SSG) and to explore the proliferative activity of this gland in response to unilateral extirpation. Left submandibular and retrolingual glands were extirpated in 30 rats (B.W. 200 ± 12 g). The rats were killed 0, 1, 2, 3, 5 and 7 days after surgery. Five intact rats served as controls. The animals were given intraperitoneal injections of³HTdR (0.5 μCi/grB.W) 1 h before they were killed. The contralateral SSG’s were subjected to routine histological procedures and embedded in glycol methacrylate. Selected sections (2 μm thickness) were processed for autoradiography. In each gland, labelled and unlabelled nuclei were counted in 50 random microscopic fields and sorted according to their parenchymal histomorphological features and “nuclear class” (number of nuclei/cross section/ feature). In the control glands the total labelling index (LI) was 0.18%; during acute compensatory stimulation, however, the total LI reached a maximum of 0.86% on day 3 after surgery. suggesting that the SSG, which normally undergoes a slow turnover, is capable of elevated proliferation in response to a stimulus. In both normal and stimulated glands, the LI was higher in the intercalated ducts (1.1%–5.85%) than in the granular ducts (0.17%–0.93%) and acini (0.05%–0.36%). This consistency of LI ratio between the various histomorphological features in the normal and experimental glands indicates that the glandular progenitor compartment is located in the intercalated ducts, which supply cells to both the ductal system and acini. The junctions between the intercalated and granular ducts and between the intercalated ducts and acini are located at the site of the histomorphological features of nuclear class 6, which also displayed the highest LI in both control and stimulated animals. Hence, it is concluded that progenitor compartment is not limited to the intercalated ducts, but extends, to some degree, towards both acini and granular ducts.