An amplifying effect of exogenous and neurally stored 5-hydroxytryptamine on the neurogenic contraction in rat tail artery.
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 alpha 1- but not alpha 2- 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.
Szabó
C
C
Department of Medical Cell Research, University of Lund, Sweden.
Hardebo
J E
JE
Owman
C
C
D000818:Animals; D003714:Denervation; D004558:Electric Stimulation; D066298:In Vitro Techniques; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D012701:Serotonin / Q000494:pharmacology* / Q000502:physiology; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000502:physiology; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology; D014661:Vasoconstriction / Q000187:drug effects* / Q000502:physiology; D014662:Vasoconstrictor Agents / Q000494:pharmacology
D014662:Vasoconstrictor Agents; D012701:Serotonin