Equine mandibular gland: in situ characterisation of sialoderivatives

Sialic acids modulate the metabolite transport across membranes and may be involved in protection against pathogenic agents. The presence of sialoderivatives in the equine mandibular gland requires further study.

To biochemically visualise in situ the presence of sialoderivatives, by means of mild and strong periodate oxidation and alcoholic saponification, combined with lectin histochemistry and sialidase digestion in order to hypothesise roles for detached sialoderivatives.

Mandibular glands were removed from 8 mature horses of both sexes and subjected to histochemical procedures, including periodate oxidation, saponfication and lectin staining. Controls were based upon the omission of peroxidase-conjugated lectins and respective enzyme-free buffers.

The reactivities of PNA and RCA I lectins were affected by sialidase treatment, whether preceded by saponification or not, showing that the dimer N-acetyl-sialic acid-beta-Gal was linked (1-3)GalNAc and (1-4)GlcNAc. In acinar cells the sequence sialic acid-beta-Gal(1-3)GalNAc showed sialic residues acetylated at C4 only and at C4 and C7 and/or C8 and/or C9(alpha2-6Gal) in both sexes, while in female mandibular gland also C4 and C9(alpha2-3Gal) acetylated residues were present. Sialic acid linked to beta-Gal(1-4)GlcNAc was prevalently C4 and C7 and/or C8 and/or C9(alpha2-6Gal and alpha2-3Gal) acetylated, whereas only a minor quantity showed acetyl groups at C7 and/or C8 and/or C9(alpha2-6Gal) in the acinar cells of both sexes.

The great variety of sialic acid residues expressed by equine mandibular gland could assume an important role in the defensive mechanisms towards pathogen agents and, compared with those of cattle, probably represents an example of molecular species-specificity related to different alimentary habits.