The storage and secretion of protein by the rat submandibular gland
The proteins secreted by the rat submandibular gland in response to various secretory stimuli have been investigated. The β-adrenergic agonist isoprenaline primarily caused the secretion of glycoproteins, although a number of other species were also present, and the saliva contained a moderate level of proteolytic activity. The ɑ-adrenergic agent phenylephrine acted very differently, causing the secretion of a considerable amount of proteolytic activity, with only a very small amount of glycoprotein present in the secretion. Stimulation of the cervical sympathetic trunk caused the secretion of fluid at all frequencies from 1-20 Hz, and this was mediated via both ɑ and β-adrenoceptors. However, at 20 Hz the proteins secreted were essentially similar to those obtained after phenylephrine, indicating that β-adrenoceptors were not involved in protein secretion. At the lower frequency of 5 Hz protein secretion appeared to be mediated via both a and β-adrenoceptors. Acetyl β-methyl choline and physalaemin were involved mainly with fluid secretion, although acetyl β-methyl choline caused the secretion of some proteolytic activity. Surprisingly this was not the case for parasympathetic nerve stimulation. The effect of reserpine upon the carbohydrate histochemistry of the rat submandibular gland was also investigated. This agent was found to cause an accumulation of carboxylated glycoproteins within the acini, which normally contain a neutral glycoprotein population. This result contrasts with the findings of previous investigations, where reserpine caused a simple accumulation of the glycoproteins normally present in the acini, with no qualitative changes.