Demonstration of a new resonance peak by proton NMR in rat pancreas stimulated with caerulein.

Low-resolution proton nuclear magnetic resonance (1H NMR) analysis of the pancreas of rats stimulated with caerulein, a cholecystokinin analog, was found to differ from that of control rats either fed ad libitum or fasted for two days. The hormonal stimulation induced (a) an increase in the longitudinal relaxation time T1; (b) a 1H NMR peak situated at 1.8 +/- 0.2 ppm from the resonance peak of tissular water. This resonance peak was not observed in the pancreas of fasted rats, although it could just be detected in the pancreas of rats fed ad libitum. These features were not observed after injection of lorglumide, an antagonist of cholecystokinin, followed by caerulein stimulation. On the other hand, stimulation with secretin induced a slight increase in T1 but did not lead to the appearance of the 1.8 +/- 0.2 ppm peak. The 1.8 +/- 0.2 ppm resonance peak thus appears to be related to the hormone-stimulated state of the exocrine pancreas and might be a useful indicator of the physiological state of exocrine pancreatic tissue. From ultrastructural examination of pancreatic cells and 1H NMR studies of solutions of the major membrane phospholipids in rat plasma, we concluded that the 1.8 +/- 0.2 ppm resonance peak stemmed from an alteration in the metabolism of membrane phospholipids and/or an increase in membrane fluidity after stimulation of acinar cells by caerulein.