Stimulus‐secretion coupling: role of cyclic AMP, cyclic GMP and calcium in mediating enzyme (kallikrein) secretion in the submandibular gland.

Abstract

SUMMARY1. The role of adenosine 3':5'-phosphate (cyclic AMP) and guanosine 3': 5'-phosphate (cyclic GMP) as second messengers for the enzyme secretary response evoked by the autonomic neurotransmitters, noradrenaline and acetylcholine, is examined in this in vitro study on the guinea-pig submandibular gland.2. Noradrenaline increased enzyme (kallikrein) secretion. The initial stimulation of enzyme release appeared to be dose-dependent. The time course of cumulative kallikrein secretion revealed a complex pattern. Isoprenaline and phenylephrine were almost as potent as noradrenaline in releasing kallikrein. Both propranolol and phentolamine were required to fully inhibit the noradrenaline-stimulated enzyme secretion.3. The cumulative secretion of kallikrein evoked by acetylcholine was dose-dependent. The onset of secretion showed a significantly greater time-lag than that observed with noradrenaline. Atropine effectively blocked the release of kallikrein by acetylcholine.4. Dibutyryl cyclic AMP stimulated enzyme secretion. Dibutyryl cyclic GMP caused an initial increase which was not maintained.5. The cyclic nucleotide phosphodiesterase inhibitors, theophylline and papaverine, increased basal kallikrein secretion. The action of the cyclic phosphodiesterase inhibitors on the secretary response to noradrenaline, acetylcholine, dibutyryl cyclic AMP and dibutyryl cyclic GMP was complex. In general, the increase in enzyme release produced by the secretagogues was additively enhanced by both inhibitors.6. Omission of calcium inhibited both acetylcholine and dibutyryl cyclic GMP stimulated kallikrein release, but to a lesser degree than that JANET ALBANO AND OTHERS of noradrenaline and dibutyryl cyclic AMP. High concentrations of extracellular calcium (10 mM) appeared to enhance the action of acetylcholine.7. Noradrenaline produced a rise in the intracellular level of cyclic AMP. The increase preceded the stimulated secretion of kallikrein. Of the various adrenergic agonists, noradrenaline and isoprenaline were the most potent, whereas phenylephrine was significantly less effective in raising basal cyclic AMP values. Acetylcholine was without effect, even in the presence of a cyclic phosphodiesterase inhibitor.8. Acetylcholine and noradrenaline raised intracellular levels of cyclic GMP only when the tissue incubations were performed in the presence of a cyclic phosphodiesterase inhibitor. The increase in cyclic GMP produced by acetylcholine preceded enzyme secretion.9. Morphological data substantiated the finding that the in vitro release of kallikrein evoked by the secretagogues was associated with the depletion of secretary granules and vacuolations in acinar cells of the gland slices.10. The molecular mechanisms which control enzyme secretion in the exocrine submandibular gland are discussed. Models are presented for the role of transmitter-specific cyclic nucleotides and calcium in stimulussecretion coupling.

Factors Affecting the Secretion of Submandibular Salivary Kallikrein in Cats

“…Nevertheless, such interactions are likely to occur in life (see Emmelin, 1987). Work by Albano, Bhoola, Heap & Lemon, (1976) on guinea-pig submandibular glands indicated that the pharmacological stimulation of kallikrein secretion involved fl-adrenergic mechanisms as well as a-adrenergic mechanisms.…”

Electrical coupling and dye transfer between acinar cells in rat salivary glands.

“…Procion yellow moves more irregularly in situ (Kaneko, 1971) or in vitro (Johnson & Sheridan, 1971 (Butcher, 1975;Schultz, Hardman, Shultz, Baird & Sutherland, 1973) which may play some role in determining the major differences in type of secretion elicited by the two nerve inputs. fl-Adrenoceptor agonists, which cause an increase in cyclic AMP (Bdolah & Schramm, 1965;Albano et al 1976), produce saliva with a greater protein content (Schramm, 1973). Cholinergic drugs, which cause an increase in cyclic GMP in the presence of phosphodiesterase inhibitors (Schultz et al 1973;Albano et al 1976), produce a more watery saliva (Schneyer et al 1972).…”

“…fl-Adrenoceptor agonists, which cause an increase in cyclic AMP (Bdolah & Schramm, 1965;Albano et al 1976), produce saliva with a greater protein content (Schramm, 1973). Cholinergic drugs, which cause an increase in cyclic GMP in the presence of phosphodiesterase inhibitors (Schultz et al 1973;Albano et al 1976), produce a more watery saliva (Schneyer et al 1972). In contrast to in vitro experiments, however, Muir & Templeton (1976) …”

The Role of Cyclic Nucleotides and Related Compounds in Nerve‐mediated Vasodilatation in the Cat Submandibular Gland

“…However, Diamond & Hartle (1976) have shown that cyclic GMP levels in guinea-pig taenia coli increase after the contractile response to cholinergic stimulation and not before, arguing against an involvement of the nucleotide. In the salivary gland, too, the role of cyclic GMP in secretion is not very clear (Albano et al, 1976;Durham, Butcher, Muir & Templeton, 1977) Jenkinson & Koller (1977) to explain the potentiation of an a-adrenergic response by phosphodiesterase inhibitors in guinea-pig liver slices. However, it is worth pointing out that in the present work 3 chemically distinct phosphodiesterase inhibitors have been used and while they could produce potentiation of parasympathetic vasodilatation via cyclic AMP in the manner suggested above, it seems less likely that other non-specific actions of the inhibitors are responsible.…”

“…Certainly #-receptor stimulation leads to an increase in adenylate cyclase activity (see Butcher, Goldman & Nemerovski, 1976) and cyclic AMP concentration (see Albano, Bhoola, Heap & Lemon, 1976) in the whole gland but experiments so far have been concerned with secretory activity, not the control of blood flow.…”