Possible Compensation in Epidermal Growth Factor Production by Saliva in Rat

Abstract

In the present work, the authors investigated the effect of both main vegetative transmitters and some regulatory peptides on epidermal growth factor (EGF) secretion into whole saliva. We studied how the salivary and glandular EGF levels depend on the functional activity of salivary glands in rats. Experimental groups comprised: (a) control, (b) bilateral ablation (AB) of submandibular and sublingual salivary glands, (c) 0.5% citric acid in drinking water treatment (Cit), and (d) ablation plus citric acid combination (AB+Cit). On the 7th day under narcosis, pilocarpine-stimulated saliva was collected and the amylase activity was measured along with concentrations of EGF and the protein, both in saliva and in salivary glands. In the first study, in conscious rats adrenergic activation of EGF secretion was observed. During noradrenaline stimulation, the curve showing EGF discharge was parallel to the amylase secretory curve. Salivary amylase secretion was stimulated by adrenergic, cholinergic and VIP-ergic actions. Other regulatory peptides, such as CCK, bombesin and somatostatin, did not seem to be involved in controlling EGF or amylase secretion. In the second study, 7 days after ablation, protein concentration of salivary glands decreased in control animals 30 min after pilocarpine stimulation. There was no significant change in protein concentration after this stimulation in the other groups. EGF concentration increased about 40% in submandibular tissues of the Cit group of animals, and decreased in the parotid tissues in all treated groups. The EGF concentration decreased after pilocarpine stimulation to a great extent in all salivary tissues. Protein concentration in saliva was significantly higher than the initial level in all treated groups (AB: +240%; Cit: +80%; AB+Cit: +350%). EGF concentration of saliva was slightly decreased in the ablation group (-10%), while it increased in the other treated animals (Cit: +20%, AB+Cit: +200%). Changes in the EGF level in saliva were lower than 10% in the control group. In conclusion: 1. EGF secretion is controlled by adrenergic pathways but not by cholinergic mechanisms or by VIP, CCK, bombesin or somatostatin 2. The EGF level in saliva can be increased by enhanced activity of salivary glands 3. EGF in saliva is not exclusively produced by one type of salivary glands 4. Parotid glands can compensate the EGF secretion to saliva when functional activity of the other main gland is lost