The objective of this study was to investigate PJ secretion in growing pigs of Polish synthetic line 990, Pietrain and Duroc breeds. The 990 and Pietrain pigs strongly responded with protein secretion to a meal, whereas the Duroc breed showed much weaker kinetics of postprandial pancreatic juice flow. No significant differences in plasma leptin were found, just a slight tendency towards a lower leptin ratio in synthetic line 990. The observed trends may involve the inhibitory effect of plasma leptin on the exocrine pancreas resulting in a reduced ability to inhibit the exocrine pancreas. The presented data suggest that the insulo-acinar axis may play an important role in the regulation of exocrine pancreas secretion in pigs.