Dopamine‐induced amylase secretion from rat parotid salivary gland in vitro: an effect mediated via noradrenergic and cholinergic nerves.

Abstract

1 The effect of dopamine on amylase secretion by rat parotid tissue was examined in vitro.2 Dopamine induced marked amylase secretion from the tissue in a dose-dependent manner. Its EC50 value was about 4 gM and the maximal response was obtained at a concentration of 100 AM.3 The dopamine-induced secretion was inhibited by the dopamine-antagonists haloperidol, (+)-butaclamol and spiroperidol. 4 Atropine reduced the dopamine-induced secretion significantly, and physostigmine enhanced the secretion. 5 Parasympathectomy of the gland resulted in a significant decrease in the dopamine-induced secretion, but did not reduce the secretion induced by dopamine with atropine. 6 Dopamine-induced ACh release from parasympathetic nerve terminals in the tissue was studied in tissue preparations that had been loaded with [3H]-choline. Dopamine elicited Ca2+-sensitive tritium release, and dopamine antagonists or parasympathectomy prevented this release. 7 Sympathectomy or reserpine treatment of rats resulted in significant decrease in the dopamineinduced secretion, but increase in noradrenaline (NA)-or isoprenaline-induced secretion. 8 Dopamine-induced NA release was studied by preloading the parotid tissue with [3H]-NA. Dopamine induced Ca2"-sensitive tritium release, and dopamine antagonists or sympathectomy prevented the release. 9 Several lines of circumstantial evidence strongly suggested that dopamine has a specific site for action in the parotid tissue that is independent of NA receptors. 10 In sympathectomized or reserpine-treated glands, atropine completely inhibited the dopamineinduced amylase secretion, suggesting that dopamine did not have a direct effect on postsynapses. 11 These findings indicate that dopamine induces amylase secretion in two indirect ways mediated through ACh and NA released from parasympathetic and sympathetic nerve terminals, respectively.

Mechanism underlying histamine‐induced desensitization of amylase secretion in rat parotid glands

“…The tissue slices (0.4 mm thick) prepared from the parotid glands with a McIlwain Tissue Chopper (The Mickle Laboratory Engineering Co., Surrey, U.K.) were equilibrated with the solution for 15 min at 37°C with shaking. The slices were treated with 1 mM histamine under the conditions described previously (Hata et al , 1983; 1986). In brief, the slices (50 mg wet weight) were incubated for 10 min at 37°C in 10 ml of KRT solution with 1 mM histamine(hereinafter referred to as the first incubation or histamine treatment).…”

Effects of amphetamine on salivary secretion

“…No inhibitory effect by the drug was thus exerted peripherally in the gland. The peripheral effect of amphetamine is most likely to have been exerted via noradrenaline because dopamine has no direct effect on fluid secretion in the rat parotid gland, even though it may induce secretion indirectly by inducing the release of noradrenaline (26, 27). Furthermore, the data seem to contradict the assumption that amphetamine would cause hyposalivation by noradrenergic vasoconstriction.…”

Dopamine actions in vitro on enzyme and electrolyte secretion from normal and sympathectomized rat parotid glands.

“…Salivary gland responses to stimulation with dopamine include enzyme release both in the guinea-pig submandibular gland (Bloom, Carlsoo & Danielsson, 1975) and in the rat parotid gland (Sundstrom, Carls66, Danielsson & Henriksson, 1985a;Hata, Ishida, & Kondo, 1986). Dopamine also induces potassium release in intact rat parotid gland (Sundstrom, Henriksson & Lindstr6m, 1985b;Sundstr6m, Danielsson, Henriksson & Lindstrom, 1988).…”

“…Dopamine also induces potassium release in intact rat parotid gland (Sundstrom, Henriksson & Lindstr6m, 1985b;Sundstr6m, Danielsson, Henriksson & Lindstrom, 1988). In both processes dopamine has been suggested to be at least partially involved in the presynaptic regulation of transmitter release (Sundstr6m et al 1985a,b;Hata et al 1986). The present study was designed to inves gate pre-and postsynaptic dopamine interactions in salivary glands with special reference to the effect of sympathetic denervation on adult animals.…”