Guy Carpenter

The influence of nerves on the secretion of immunoglobulin A into submandibular saliva in rats

1 The influence of sympathetic and parasympathetic nerve stimulations on salivary secretion of immunoglobulin A (IgA) was studied in the submandibular glands of anaesthetized rats by stimulating the nerve supplies with bipolar electrodes. 2 Although the flow of saliva from sympathetically stimulated glands was only 23 % of that from parasympathetically stimulated glands the output of IgA was over 2‐fold greater. This difference was attributable to influences of the nerves on IgA secretion through the epithelial cell polymeric immunoglobulin receptor‐mediated pathway, as Western blotting with specific antibodies to IgA and secretory component revealed that secretory IgA (SIgA) dominated in all saliva samples. 3 Study of saliva secreted in sequential periods of nerve stimulation or following rest pauses suggested that SIgA secretion occurred in the absence of stimulation but this was upregulated 2.6‐ and 6‐fold by parasympathetic and sympathetic nerve stimulations, respectively, compared with the calculated unstimulated rate. 4 The IgA content of extensively stimulated glands was 77 % of levels in unstimulated contralateral control glands despite a secretion into saliva equivalent to almost 90 % of the glandular IgA content. The IgA may be synthesized and secreted by glandular plasma cells at a rate which exceeds demand and/or such synthesis may be upregulated by nerve impulses. 5 The results indicate that salivary secretion of SIgA is upregulated by nerve impulses and that sympathetic nerves induce a greater effect than parasympathetic nerves.

Reflex secretion of proteins into submandibular saliva in conscious rats, before and after preganglionic sympathectomy

1 An indwelling catheter was placed in the left submandibular duct of rats, under pentobarbitone anaesthesia, and connected to an outflow cannula that emerged above the skull. 2 Saliva was collected from the outflow cannula in conscious rats, the same day after recovery from anaesthesia, under four different reflex conditions: grooming, heat exposure, rejection of a bitter tasting substance and feeding on softened chow, repeated in different orders. 3 Saliva flow was greatest for grooming and least for rejection. Protein concentrations were least with heat but much greater and similar for the other stimulations. Acinar peroxidase activity was high for feeding, intermediate for grooming and rejection, and again lowest with heat. Tubular tissue kallikrein activities were moderately low, being greatest with feeding and least with grooming. Secretory immunoglobulin A (SIgA) concentration was least with heat and similar for the other stimulations. 4 The next day, under pentobarbitone anaesthesia, the left preganglionic sympathetic trunk was sectioned (sympathetic decentralization) and, after recovery, the preceding stimulations were repeated. Flow of saliva showed little change, but protein and peroxidase concentrations and outputs decreased dramatically with grooming, rejection and feeding to levels similar to those with heat, which showed little change. Tissue kallikrein was lowered less dramatically, but the reductions in output were significant except with heat. Patterns of proteins resolved by electrophoresis changed for grooming, rejection and feeding and became similar to saliva from heat, which showed little change. No significant effects on SIgA concentrations occurred. 5 Gland weights from the sympathetically decentralized side were greater than from the intact side at the end of the experiments and histologically showed retention of acinar mucin. 6 Thus reflex sympathetic drive varied with the different stimulations; it was least during heat, but it had pronounced effects on acinar secretion of proteins during the other stimulations. At the same time this sympathetic drive had less impact on tissue kallikrein secretion from tubules and had little influence on flow or the concentration of SIgA secreted.

Differences in the glycosylation of rat submandibular kallikreins

The glycosylations of five different rat submandibular kallikreins, rK1, rK2, rK7, rK9 and rK10, vacuum-blotted onto nitrocellulose membranes, have been studied by means of labelled lectins using enhanced chemiluminescence detection. The results demonstrated that individual submandibular kallikreins are not heavily glycosylated in rats, but consistently show different patterns of glycosylation. Following digestion of slot-blotted enzymes with peptide-N-glycosidase F (PNGase): binding by lectin fromLens culinaris (αMan-directed) was abolished, whilst that of lectin fromMaclura pomifera (Galβ1,3GalNAc-directed) persisted (but could be abolished by periodate oxidation and endo-α-N-acetylgalactosaminidase digestion), revealing that there are O- as well as N-linked sugar chains on the kallikreins; a novel observation for this family of enzymes. The presence of GalNAc in addition to GlcNAc, Fuc, Gal and Man, in sugar chains of rK1 was confirmed by high pH anion exchange chromatography following acid hydrolysis. Different intensities of binding by lectin fromLimax flavus (NeuNAc-directed) suggest that sialylation of individual kallikreins differs, whilst sialidase and PNGase digestions suggest that sialic acid is the terminal residue of some N-linked but not O-linked structures.