PARASYMPATHETIC NONADRENERGIC, NONCHOLINERGIC REFLEX SECRETION OF PAROTID ACINAR GRANULES IN RATS PRETREATED WITH ATROPINE AND ADRENOCEPTOR ANTAGONISTS

In parotid glands of fasted rats, feeding for 60-90 min reduced numerical density of acinar secretory granules by 52% and total activity of glandular amylase by 38%. In the presence of adrenoceptor antagonists (phentolamine and propranolol, 2 mg/kg, i.p., of each) the corresponding decrease was 31% and 32%, and in combination with atropine (1 mg/kg, i.p.) 32% as to both these indices. These non-adrenergic non-cholinergic (NANC) responses depended on an intact parasympathetic auriculo-temporal nerve since they did not occur following section of this nerve. In anaesthetized animals, electrical stimulation of the sympathetic innervation (50 Hz, 1 s every 10th second) for 60 min caused secretion of parotid saliva and decreases in number of acinar granules, by 65%, and in total amylase activity, by 49%; the adrenoceptor antagonists at the above-mentioned doses completely abolished the expected responses of the parotid gland and thus showing that these antagonists at the dose level chosen achieved an effective receptor blockade. In conclusion, parasympathetic NANC mechanisms are reflexly mobilized in response to eating, and these mechanisms are potentially responsible for the whole parasympathetic response and for the major part of that response in the absence of any antagonists. Under natural reflex conditions adrenergic, cholinergic and non-adrenergic, non-cholinergic mechanisms are most likely engaged to varying extents in order to generate the most purposeful response.