Possible Involvement of β1 Receptors in Various Emetogen-Induced Increases in Salivary Amylase Activity in Rats

We investigated the inhibitory effects of β1- or β2-adrenoceptor (AR) antagonists on salivary amylase secretion produced by various emetic agents, such as cisplatin, apomorphine, and lithium chloride (LiCl), or the non-emetic agent β1/2-AR agonist isoprenaline in rats. We also determined the inhibitory effect of metoclopramide, a dopamine D2–receptor antagonist, on increases in the salivary amylase activity induced by apomorphine or granisetron, a 5-HT3–receptor antagonist, on LiCl-induced increased salivary amylase activity. Isoprenaline (0.01 mg/kg, s.c.) produced an increase in salivary amylase and the increase was inhibited by the β1/2-AR antagonist propranolol (5 mg/kg, s.c.) and β1-AR antagonist atenolol (2 mg/kg, s.c.) but not by the β2-AR antagonist butoxamine (8 mg/kg, s.c.). The increased amylase activity induced by cisplatin (15 mg/kg, i.v.), apomorphine (3 mg/kg, s.c.), or LiCl (120 mg/kg, i.p.) was inhibited significantly by atenolol (2 mg/kg, s.c.) but not by butoxamine (8 mg/kg, s.c.). In addition, increases in amylase activities induced by apomorphine and LiCl were inhibited significantly by metoclopramide (10 mg/kg, i.v.) and granisetron (3 mg/kg, i.v.), respectively. These results suggest that salivary amylase secretion induced by various emetogens is involved in β1-adrenoceptor activity and that salivary amylase activity is useful to detect emetogens with no direct β1-AR activation in rats, a species that does not exhibit vomiting.