Molecular imaging of adrenal gland by desorption electrospray ionization mass spectrometry

Abstract

Subtle differences in the spatial distributions of closely related compounds including norepinephrine and epinephrine as well multiple lipids are easily distinguished in adult porcine (17 × 8 mm) and rabbit (7 × 4 mm) adrenal glands in a DESI-MS imaging experiment at atmospheric pressure with a spatial resolution of ∼200 µm. Sensitive and specific detection in the course of DESI imaging discloses details of catecholamine distribution in porcine adrenal medulla and cortex; the average mass of epinephrine interrogated in each pixel is estimated to be about 150 pg. The distribution of ascorbic acid was revealed in the negative ion mode. In addition, the distribution of cholesterol, which cannot be observed using conventional DESI, was obtained using in situ reaction with betaine aldehyde added to the DESI spray while imaging the porcine adrenal gland tissue. Four characteristic types of distributions were observed, with major amounts of the components in the medulla, the cortex, the reticular zone or in the fourth case, being homogeneously distributed. The results agree with and extend information available from histological studies.