Release of tonin by rat submaxillary gland slices in vitro.

The effects of isoproterenol, dibutyryl cyclic AMP, theophylline, and angiotensin II upon tonin release were examined by incubation of rat submaximllary gland slices. Isoproterenol, dibutyryl cyclic AMP, and theophylline stimulated tonin release. Propranolol inhibited the effect of isoproterenol. Angiotensin II by itself did not inhibit tonin release, but it suppressed the increase in tonin release produced by isoproterenol. These results suggest that the tonin stimulating effect of isoproterenol is due, at least in part, to a direct stimulation of beta-receptor upon the submaxillary glands and that cyclic AMP system may play a role as an intracellular mediator of this action. Angiotensin II, which is formed directly from a natural protein substrate by tonin, is suggested to inhibit tonin sectetion in some situations.