HIGH-RESOLUTION H-1-NMR STUDY OF MEMBRANE PHOSPHOLIPIDS IN RAT PANCREAS STIMULATED BY CERULEIN

In this study, the peak observed at 3.2 +/- 0.2 ppm in the H-1 nuclear magnetic resonance (NMR) spectra recorded at 60 MHz of rat pancreas s timulated by caerulein was characterized at higher resolution (100 and 300 MHz). Whole pancreas from rats stimulated by caerulein was analyz ed ex vivo by H-1 NMR spectroscopy at 100 MHz. After suppression of th e tissue water peak (OSIRIS method), a peak at 3.2 +/- 0.2 ppm appeare d distinctly, along with two other weaker signals (2.8 and 3.5 ppm). N o signals were observed in these regions in the spectra recorded from pancreas of 48-h fasted rats. The signal at 3.2 +/- 0.2 ppm was charac terized by analysis of the high-resolution H-1 NMR (300 MHz) spectra o f lipid extracts of rat pancreas. Addition of various pure membrane ph ospholipids in extracts showed that the peak was due to the N(CH3)(3) groups of choline-containing lipids. The weaker signals (2.8 and 3.5 p pm) were attributed to the methylene protons of fatty acids and the gl ycerol of glycerophosphorylcholine (GPC). A small decrease in phosphat idylcholine (PC) concentration was observed on analysis of these lipid extracts by high-performance liquid chromatography, indicating that t he increase in intensity of the 3.2 +/- 0.2 ppm peak was not due to an y increase in PC concentration, but rather to a change in conformation of PC, allowing higher mobility of the trimethylamino protons. Lorglu mide, a specific inhibitor of caerulein, markedly reduced the intensit y of the NMR peak, and pentagastrin, which also stimulates exocytosis of zymogen granules in the pancreas, had a similar but somewhat smalle r effect than caerulein. Spectra recorded at various times after injec tion of caerulein showed that the effect was relatively short-lived oc curring over a period of 10 min following injection. The peak vanished 20 min after injection. The 3.2 +/- 0.2 ppm peak was thus regarded as an indicator of hormonal stimulation, attributed to enhanced fluidity of plasma membranes accompanying the exocytosis of zymogen granules.