EFFECT OF DIFFERENT PHYSICAL FORMS OF THE DIET FETO GROWING PIGS ON THE EXPRESSION OF CB1 AND CB2 IN THE MANDIBULAR GLAND

Diet-induced morphological changes of extra-enteral organs were associated with the physical forms of the diet [1]. The endocannabinoid system consists of a complexity of endogenous molecole, namely endocannabinoids ligands and receptors. There are two types of cannabinoid receptors, named type 1 receptor (CB1) and type 2 receptor (CB2). The investigation about the localization of these two receptors in the duct epithelial cells of the major salivary glands moved on the one hand from the different expression and localization of leptin and its receptor [2] and on the other hand from the decreased effect of endocannabinoids on the salivary secretion, observed in men exposed to exogenous cannabis [3]. The aim of the present study was to test whether different physical forms of diet can induce to different extents the expression of CB1 and CB2 in the mandibular glands in response to different mechanical stimulation perceived after the intake of feed differently ground (fine vs. coarse) and compacted (mash vs. pellet vs. extruded) by growing pigs. The experiment involved a total of 32 growing pigs fed ad libitum for 4 weeks with four experimental dietary treatments. One diet was differently processed to obtain different physical forms: FP - Finely ground pelleted diet (dMEAN, 0.46 mm); CM - Coarsely ground meal diet (dMEAN, 0.88 mm); CP - Coarsely ground pelleted diet (dMEAN, 0.84 mm); CE - Coarsely ground extruded (dMEAN, 0.66 mm) diet. At the end of the experimental feeding, all animals were euthanized and both mandibular glands immediately removed, weighed and fixed in buffered formaldehyde (2,5% v/v) for 24 h at room temperature. Samples were cut and automatically embedded in paraffin. The immunohistochemical reactions were visualized on 5 µm serial sections, utilising the primary goat polyclonal anti-CB1 and rabbit polyclonal anti-CB2 antibodies, the avidin-biotin-complex and the DAB as the chromogen. Sections in which the primary antibodies were omitted, represented the control of unspecific staining. A strong positivity for CB1 and CB2 in the mandibular glands of the animals fed with CP, FP and CE diets was pointed out in comparison with the animals of the CM group. In particular, the CB1 and CB2 immuno-positivity involved duct epithelial cells with a peculiar localization in the cytoplasm of some epithelial cells near or on the apical cell membrane. In the animal fed with CM diet the immuno-positivity no longer involved duct epithelial cells but in some samples as far as the serous cells in mixed acina. The connective tissue tested negative for CB1 and CB2. The CB1 and CB2 were differently espressed in the mandibular glands of pigs fed with different physical forms of the diet. These novel findings leads us to speculate on CB1 and CB2 role, as receptors involved in the control of pig salivary secretion via endocannabinoids ligands and that these molecole likely represent an important link between the physical form of the diet and salivation. However, whether they rule on amount of saliva produced or on its composition needs to be elucidated so far.