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Stimulating effect of alpha-adrenoceptor agonists on isoproterenol-induced amylase release in rat parotid tissue
Abstract:
Isoproterenol (ISO)-induced amylase release from rat parotid slices was increased by the addition of methoxamine to either a normal or a calcium (Ca)-free medium. The potentiating effect of methoxamine was completely blocked by the addition of phentolamine, irrespective of whether the slices were incubated in the normal or the Ca-free medium; and the effect also disappeared after prolonged preincubation (60 min) of the slices in the Ca-free medium. Both verapamil and procaine reduced methoxamine-induced amylase release, but only verapamil blocked the stimulating effect of methoxamine in the normal medium. ISO-induced accumulation of cyclic AMP in the slices was unaffected by methoxamine or phenylephrine. The results suggest a possibility that the potentiating effect of methoxamine on ISO-induced amylase release may be independent of the presence of extracellular Ca and the increased accumulation of cyclic AMP in the tissue is unnecessary.
Insights
Methoxamine enhances isoproterenol-induced amylase release from rat parotid slices, an effect independent of extracellular calcium and cyclic AMP accumulation. This finding suggests a novel signaling pathway for amylase secretion.
Area of Science:
- Pharmacology
- Cell Biology
- Biochemistry
Background:
- Isoproterenol (ISO) is known to stimulate amylase release from rat parotid glands.
- Methoxamine's role in potentiating ISO-induced amylase release requires further investigation, particularly concerning its dependence on calcium and cyclic AMP.
Purpose of the Study:
- To investigate the effect of methoxamine on isoproterenol-induced amylase release from rat parotid slices.
- To determine the role of extracellular calcium and cyclic AMP in methoxamine's potentiating effect.
Main Methods:
- Rat parotid slices were incubated in normal or calcium-free media.
- Amylase release was measured following stimulation with isoproterenol and methoxamine.
- The effects of phentolamine, verapamil, and procaine were assessed.
- Cyclic AMP accumulation was measured in response to methoxamine and phenylephrine.
Main Results:
- Methoxamine potentiated isoproterenol-induced amylase release in both normal and calcium-free media.
- This potentiation was blocked by phentolamine and diminished after prolonged incubation in calcium-free medium.
- Verapamil and procaine reduced methoxamine-induced amylase release, with verapamil blocking the effect in normal medium.
- Methoxamine did not affect ISO-induced cyclic AMP accumulation.
Conclusions:
- Methoxamine potentiates isoproterenol-induced amylase release via a mechanism likely independent of extracellular calcium.
- The observed potentiation does not appear to involve increased cyclic AMP accumulation.
- These findings suggest a distinct signaling pathway for methoxamine's modulatory effect on amylase secretion.