Abstract
The effects of the cholinergic and adrenergic nerve stimulations on amylase release from the segment isolated from the rat parotid gland were investigated, employing the combined techniques of electrical field stimulation (FS) and tyramine application with automated fluorescence method for measuring amylase. The maximum amylase release in response to FS for a short period (1 min) was attained at 16 Hz frequency, 2 ms pulse width and 8 V strength stimulation in the absence of any autonomic antagonist. Periodic short-lasting FS using these parameters at intervals of about 15 min could reproduce similar sizes of amylase release for about 2 h. Continuous long-lasting FS (3 V, 2 ms, 16 Hz) caused a transient sharp increase in amylase release followed by a sustained one. The FS-evoked amylase release was completely abolished by tetrodotoxin (TTX) (10(-7) g/ml) and markedly reduced by atropine (7 X 10(-6) M) or by propranolol (10(-5) M), while it was scarcely affected by hexamethonium (3 X 10(-4) M) and phentolamine (10(-5) M). The maximum stimulus frequency of short-lasting FS for amylase release in the presence of propranolol was similar to that (16 Hz) in the control, but it was higher (32 Hz) in the presence of atropine. Reduced response in amylase release to FS by propranolol was completely restored by the superimposed addition of dibutyryl cyclic AMP (10(-4) M). Application of tyramine (5 X 10(-4) M) evoked amylase release in the presence of atropine, which was blocked mostly by propranolol and partly by phentolamine, while tyramine was ineffective in the tissue segment from rats pretreated with 6-hydroxydopamine. From these results the following were suggested; that the intrinsic cholinergic neurotransmitter activates a muscarinic receptor of the acinar cell, while the adrenergic neurotransmitter stimulates mainly a beta-adrenergic and partly an alpha-adrenergic receptor, resulting in amylase release.
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