1. The interactions between sympathetic neuroeffector transmission and 5-hydroxytryptamine (5-HT) were investigated in segments of rat isolated tail artery. 2. Contractile responses to field stimulation of the artery segments were abolished by tetrodotoxin (3 x 10-7 M). A subthreshold concentration of acutely applied exogenous 5-HT (10-8 M) markedly enhanced the contractions induced by sympathetic nerve stimulation, through an action on postjunctional 5-HT2-receptors. 3. The amplifying effect of 5-HT involved an enhanced influx of extracellular calcium into the smooth muscle cells. In contrast, the neurogenic contractions in vessels not exposed to 5-HT were not dependent on extracellular calcium. 4. The adrenergic component of the amplified response involved postjunctional α1- but not α2- adrenoceptor activation. 5. Exposure of the vessels to 5-HT (5 x 10-7 M) for 30 min resulted in uptake of the amine into the perivascular sympathetic nerves, as demonstrated by immunohistochemistry. After chemical sympathectomy with 6-hydroxydopamine in vitro or in vivo, or surgical sympathectomy, there was little or no uptake. 6. Exposure to 5-HT followed by repeated washing resulted in an enhancement of the neurogenic contraction, which was still fully tetrodotoxin-sensitive. The enhanced response was blocked by ketanserin (10-8 M) and prevented by the presence of the 5-HT uptake blocker, paroxetine (3 x 10-8 M), during the period of exposure to 5-HT.
|Original language||English (US)|
|Number of pages||7|
|Journal||British Journal of Pharmacology|
|State||Published - Jan 1 1991|
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