Developmental changes of trypsin-like protease activity in the submandibular glands of male and female young growing rats.

The changes during infancy of trypsin-like protease activity in the submandibular glands of male and female rats (4-20 weeks of age) were observed. Activity was low at 4 weeks of age, then increased markedly at 8-10 weeks of age. Seven peaks (I-VII) with isoelectric points of 4.0, 4.3, 4.5, 5.0, 5.4, 5.7 and 6.4 of protease activity were observed in the glands of adult rats by isoelectric focusing. Only peaks I and II were detected in the glands at 4 weeks of age in both sexes. After 8 weeks, all 7 peaks appeared in the glands of males and females. Repeated injection of isoprenaline into rats of 7 weeks of age elevated markedly the weight of submandibular glands; the elevation of protease activity and of inhibitory activity against dopa-decarboxylase was not found. These results indicate that proteases in peaks I and II appear at an age close to that of development of acini; protease activity in peaks III-VII increases is close to the time of development of the granular ducts.