Parasympathetic non-adrenergic, non-cholinergic mechanisms in reflex secretion of parotid acinar granules in conscious rats.

1. Female adult rats were subjected to sympathetic denervation of the parotid glands by bilateral removal of the superior cervical ganglion 10-12 days before acute experiments. The sympathectomy was in some of the experimental groups combined with either bilateral adrenal medullectomy, treatment with the sensory neurotoxin capsaicin or parasympathetic denervation of the gland by cutting the auriculotemporal nerve. 2. Food but not water was withheld for 29-32 h before acute experiments. All animals were given an intraperitoneal injection of phentolamine (2 mg kg-1) and propranolol (1 mg kg-1) and, when appropriate, also atropine (1 mg kg-1). Then the experimental animals were fed their ordinary food of hard chow for 60-90 min. Thereafter, these animals and their non-fed controls were killed, and the parotid glands were removed and used for either morphometric assessment or measurement of amylase activity. 3. In the atropinized rats subjected to sympathectomy alone, eating reduced the numerical density of acinar secretory granules by 50% and the total activity of amylase by 55%; the corresponding figures were, when sympathectomy was combined with adrenal medullectomy, 51 and 63%. Also, in atropinized animals subjected to sympathectomy and capsaicin pretreatment, eating reduced the numerical density of acinar granules and the total amylase activity, in this case by 45 and 35%, respectively. 4. In the atropinized rats subjected to sympathectomy and parasympathectomy, eating caused no change in the numerical density of acinar granules but reduced the total amylase activity by 35%. 5. In the non-atropinized rats subjected to sympathectomy alone, eating reduced the numerical density of acinar granules by 22%, while there was no change in the total amylase activity. 6. In conclusion, eating evoked a reflex activation of the sympathectomized parotid gland that engaged non-adrenergic non-cholinergic receptors of the acinar cells. The present results give weight to a physiological role for non-adrenergic non-cholinergic parasympathetic mechanisms in salivary secretion under reflex conditions.