The effects of atropine and chronic sympathectomy on maximal parasympathetic stimulation of parotid saliva in rats.

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Abstract
1. The effects of stimulating the postganglionic parasympathetic nerve to the parotid gland, the auriculo-temporal nerve, continuously at 40 Hz for 80 min have been assessed on the flow of saliva and its amylase content during each 10 min period and on the glandular morphology at the end of the stimulation in female Sprague-Dawley rats under chloralose anaesthesia. Adrenergic responses were blocked by prior adminstration of dihydroergotamine (1 mg/kg I.P.) and propranolol (1 mg/kg I.P.). The contralateral unstimulated parotid gland from each animal was used for morphological control purposes. 2. In normal animals there was a copious flow of salvia reaching 3 ml or more in 80 min. It was well maintained after a gradual small decline and the flow in the last 10 min period was still 60% of the in the initial period. Amylase output was relatively high in the initial period but then declined more rapidly than the flow. The acini were densely packed with granules on the control side and showed a moderate amount of degranulation on the parasympathetically stimulated side. 3. After atropine (2 mg/kg I.V.), normal animals initially showed a moderate flow of saliva, being 41% of the non-atropinized animals, but there was a rapid decline and the total flow over 80 min was only 15% of the in the non-atropinized animals. The amylase secreted was also high initially and showed a rapid decline; the total amount secreted was similar to that in non-atropinized animals. The morphology was similar to that in non-atropinized animals and showed a similar loss of acinar granules on the stimulated side. 4. Chronic bilateral postganglionic sympathetctomy (4-6 weeks duration) caused a drastic reduction in the capacity of the gland to secrete saliva in response to parasympathetic stimulation, reaching only one-third of that from normal animals. The initial output of amylase was greater than in normal animals but the total output was similar. The control unstimulated sympathectomized glands appeared similar morphologically to normal resting glands. However, on the parasympathetically stimulated side, besides the usual amount of acinar degranulation, there was also conspicuous development of acinar vacuolation, not seen in the other groups of animals. 5. After atropine, chronically sympathectomized animals produced a similar flow of saliva to that in atropinized normal animals; the initial secretion of amylase was higher but the total output was similar and the morphological appearance of the acini was similar, showing a moderate degree of acinar degranulation on the stimulated side. 6. It is concluded that some of the fluid and most of the amylase and the acinar granules secreted by normal glands in the absence of atropine is attributable to release of non-adrenergic non-cholinergic transmitters from the parasympathetic nerve terminals, when the nerve is stimulated continuously at 40 Hz. Prolonged absence of sympathetic impulses to the gland, as a result of sympathectomy, causes impaired function of the parenchymal cells that reduces their capacity to secrete fluid during parasympathetic nerve stimulation in the absence of atropine and increases their tendency to form watery vacuoles at the same time.