STUDIES ON EXOCRINE SECRETIONS - HISTOCHEMICAL INVESTIGATIONS ON MAJOR SALIVARY GLANDS OF EXOTIC ANIMALS

The present work attempts to throw further light on the field of exocrine secretion in general and on the salivary gland function in particular. Special attention has been paid to the synthetic products of the mucous-secreting and protein-producing cells making up the submaxillary and the parotid glands. To this end, several exotic animals have been utilized for these experiments, among which tapirs, giant and small ant eaters, two-toed sloths, skunks, racoons, neonatal and adult opossums, armadillos, flying squirrels and South American porcupines. The data reported in this paper concerns the tapirs, ant eaters, opossums, two-toed sloths, skunks and racoons. The histochemical experiments carried out endeavored to identify the chemical products elaborated by the salivary gland cells. In general terms it was found that serous-producing structures synthesize, along with the enzymatic proteins, different amounts of glycoprotein material. These carbohydrate-protein molecules are both of the neutral and acidic type. The parotid glands of ant bears, sloths and skunks secreted an acid mucin identified as a sialoglycoprotein; the parotids of the opossums, racoons and tapirs did not elaborate histochemically detectable acidic polyanions. All the parotid glands produced high amounts of neutral glycoproteins and the zymogen granules were strongly stained by PAS. The parotid glycoproteins were very resistant to enzymatic degradation as noticed after proteolytic digestion with papain and pepsin. With the exception of the basophilia in the parotid of the ant bears (only slightly affected) neuraminidase did not modify the PAS and AB stainings in any of the serous-producing structures. Conversely, the mucin of the submaxillary glands was quite susceptible to proteolysis and the histochemical approach indicated that it was composed primarily of a sialoglyco-protein. The only exception was represented by the opossum submaxillary whose mucin showed strong chemical affinity with the parotid secretion. The basophilic staining of the submaxillary glands in general was very susceptible to neuraminidase. Of interest was the fact that the PAS reaction was also drastically abolished in several animal glands. This data further confirmed that 1) the glycoprotein present in these glands was primarily represented by sialic acid and indicated that 2) this acid is, per se, PAS-positive. The excretory system in some animal glands was highly secreting. The type of material elaborated by the cells making up the ducts was almost exclusively represented by neutral glycoproteins indicating, thus, that the type of secretion produced by the ductal cells was chemically similar to that of the parotid. These results indicate clearly that the old classification which considers these glands serous or mucous is erroneous. There is no purely protein-secreting gland since all, even though in different measure, elaborate and synthesize glycoprotein material. © 1969 Springer-Verlag.