The effects of pregnancy and lactation on the activities of trypsin and alpha-chymotrypsin in the rat pancreas.

1. The food intake, pancreas weight and trypsin (EC 3.4.21.4) and alpha-chymotrypsin (EC 3.4.21.1) activities in the pancreas were measured in rats during pregnancy and lactation and after the young were weaned. 2. All the quantities measured increased significantly during lactation and had returned to their original values by 4 weeks after weaning. Food intake and pancreas weight were highest after the second week of lactation. Total trypsin and alpha-chymotrypsin activity, and the activity per g tissue, fell during pregnancy and rose during lactation, reaching a maximum 1 week after weaning. 3. From these and other results it is suggested that the hypertrophy and hypersecretion of pregnancy and lactation are initiated by changes insulin secretion and mediated by the trophic effects of gut hormones, and that differences in the nature and timing of the response may be controlled by nutrient availability.