Inhibition of noradrenergic neurotransmission by apomorphine and pergolide in the in situ autoperfused rat renal and superior mesenteric vascular beds
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In vitro studies have provided evidence that presynaptic dopamine receptors are present in the rat renal and superior mesenteric vascular beds. To confirm this in vivo, the effects of locally administered apomorphine and pergolide were studied in the in situ autoperfused renal and superior mesenteric vascular beds.
Local infusion of apomorphine (1 μg · kg−1 · min−1 for 5 min) or pergolide (1 μg · kg−1 · min−1 for 5 min) into either the renal or the superior mesenteric artery had no effect on perfusion pressure per se. In the renal vascular bed, the pressure response to electrical stimulation (4 Hz, 1 ms, supramaximal voltage) was reduced to 49.8±4.8% by apomorphine and to 54.8±2.7% by pergolide; in the mesenteric vascular bed, apomorphine reduced the pressure response to electrical stimulation (4 Hz, 1 ms, supramaximal voltage) to 53.8±2.9, pergolide to 52.0±1.8%. Increases of perfusion pressure in the renal and in the mesenteric vascular bed induced by locally administered noradrenaline were not modified by apomorphine or pergolide.
In both vascular beds, the inhibition of the stimulation-evoked pressure responses by apomorphine or pergolide was completely antagonized by local administration of the dopamine receptor antagonist haloperidol in a dose (1 μg · kg−1) which did not influence the inhibitory effect of the α2-adrenoceptor agonist UK-14,304; the α2-adrenoceptor antagonist rauwolscine, in a dose (100 μg · kg−1) which completely antagonized the inhibitory effect of UK-14,304, did not antagonize the inhibitory effects of apomorphine and pergolide.
Local administration of rauwolscine per se increased the pressure response to stimulation at 4 Hz in both vascular beds. In contrast, local administration of haloperidol did not influence the stimulation-evoked pressure response.
These results provide evidence for the presence of presynaptic, inhibitory dopamine receptors on sympathetic nerves in the rat renal and mesenteric vascular beds; these receptors could be involved in the blood pressure lowering effects of dopamine receptor agonists, such as apomorphine and pergolide.
Key wordsRat Presynaptic dopamine receptors Mesenteric Renal
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