High-Resolution 1H NMR Study of Membrane Phospholipids in Rat Pancreas Stimulated by Caerulein

Abstract

In this study, the peak observed at 3.2 +/- 0.2 ppm in the 1H nuclear magnetic resonance (NMR) spectra recorded at 60 MHz of rat pancreas stimulated by caerulein was characterized at higher resolution (100 and 300 MHz). Whole pancreas from rats stimulated by caerulein was analyzed ex vivo by 1H NMR spectroscopy at 100 MHz. After suppression of the tissue water peak (OSIRIS method), a peak at 3.2 +/- 0.2 ppm appeared distinctly, along with two other weaker signals (2.8 and 3.5 ppm). No 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 characterized by analysis of the high-resolution 1H NMR (300 MHz) spectra of lipid extracts of rat pancreas. Addition of various pure membrane phospholipids 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 ppm) were attributed to the methylene protons of fatty acids and the glycerol of glycerophosphorylcholine (GPC). A small decrease in phosphatidylcholine (PC) concentration was observed on analysis of these lipid extracts by high-performance liquid chromatography, indicating that the increase in intensity of the 3.2 +/- 0.2 ppm peak was not due to any increase in PC concentration, but rather to a change in conformation of PC, allowing higher mobility of the trimethylamino protons. Lorglumide, a specific inhibitor of caerulein, markedly reduced the intensity of the NMR peak, and pentagastrin, which also stimulates exocytosis of zymogen granules in the pancreas, had a similar but somewhat smaller effect than caerulein.(ABSTRACT TRUNCATED AT 250 WORDS)