The nasal gland of the Montpellier snake Malpolon monspessulanus: Fine structure, secretion composition, and a possible role in reduction of dermal water loss

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Abstract
A study was made of the structure and function of the enlarged lateral nasal gland of the Montpellier snake (Malpolon monspessulanus). This unusual gland opens directly to the exterior via a duct on the nasal valve. The secretion is spread over the skin surface by a series of stroking movements with the head. An ultrastructural examination showed that the gland does not have the specialized cytological features associated with salt secretion, the only previously known function for nasal glands in reptiles. The principal tubule cells are filled with clear secretory vacuoles of various sizes, moderate numbers of mitochondria, and have few interdigitations with adjacent cells. The nuclei are basal. In one snake the cells had numerous membrane bound lamellar bodies (LB) in the basal region. These LB stained darkly with toluidine blue and strongly resembled lamellar bodies found in the mammalian lung. Although LB were not seen in nasal glands of five other snakes, membrane bound globular structures found in some might well be earlier or later stages of the same organelle, possibly a lysosome. A major portion of the gland is a system of anastomosing ducts lined with simple columnar or cuboidal epithelium. The ducts not only connect with the secretory tubules but also with blind vessels lined with squamous epithelium. The glands go through cyclic increases in size, which are externally visible as swellings posterior to the nares. Gentle pressure on the swollen glands expelled fluid through the duct on the exterior aspect of the nasal valve. At certain times the glands also responded to subcutaneous injections of the parasympathetic agent pilocarpine by pronounced swelling. The secretion was quite watery but contained a complex mixture of fatty acids, proteins, and variable amounts of sodium and potassium. The spreading of this material over the skin might be related to retardation of dermal evaporative water loss, since long chain fatty acids are known to have this effect when applied as films on an aqueous surface. In partial confirmation of this hypothesis, rates of total evaporative water loss were found to be extremely low (0.2–0.5% body weight/day for 0.2–1.0 kg snakes at 33°C). In dry air at 33°C, the dermal loss was only about 30% of the total evaporative loss.

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