Abstract
The effects of dopamine and noradrenaline on potassium efflux from rat parotid gland were studied in a perifusion system. Tissue specimens were preincubated with 86RbCl and the efflux of 86Rb + was used as a marker for potassium efflux. Noradrenaline induced 86Rb + efflux more effectively than dopamine. The noradrenaline-induced efflux was inhibited by α-adrenoceptor blockers, especially the α 1-antagonist prazosin. The dopamine-induced 86Rb + efflux was blocked by α-adrenoceptor antagonists, non-selective dopamine antagonists and a D-1 selective dopamine antagonist. The D-2 selectie drug, sulpiride, did not affect the dopamine-induced 86Rb + efflux. The dopamine effect was abolished when reserpinized animals were used, whereas the effect of noradrenaline was unaffected. The results suggest that dopamine has a presynaptic stimulatory effect in rat parotid gland, and that the presynaptic effect on potassium efflux seems to be mediated via the D-1 receptor subtype. Whether activation of the presynaptic D-1 receptors leads to noradrenaline release, or whether the D-1 receptor is coupled to the catecholamine transporter system remains to be studied further.
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