Inhibitory 5-hydroxytryptamine receptors involved in pressor effects obtained by stimulation of sympathetic outflow from spinal cord in pithed rats.
1. A study was made of the effects of 5-hydroxytryptamine (5-HT) on pressor response induced in vivo by electrical stimulation of the sympathetic outflow from the spinal cord of pithed rats. All animals had been pretreated with atropine. Intravenous infusion of 5-hydroxytryptamine at doses of 10 and 20 micrograms kg-1 min-1 reduced the pressor effects obtained by electrical stimulation at intervals of 10 min over the 1 h of infusion. 2. This inhibitory action of 5-HT was depressed by cyproheptadine and methiothepin but was not modified by ketanserin or MDL-72222. By contrast, the inhibitory action of 5-HT was lost in pithed rats that had been pretreated with exogenous noradrenaline. 3. The 5-HT1 receptor agonist 5-carboxamidotryptamine (5-CT) caused an inhibition of the pressor response, whereas the 5-HT3 receptor agonist, 1-phenylbiguanide, produced a variable but significant increase in the pressor response. The 5-HT2 receptor agonist, m-CPP, did not modify the pressor sympathetic response. 4. Our results suggest that 5-hydroxytryptamine interferes with sympathetic neurotransmission by inhibiting pressor effects as a result of stimulation of the complete sympathetic outflow, and that this inhibition is mainly through a presynaptic 5-HT1 mechanism.
Morán
A
A
Departamento de Fisiología y Farmacología, Facultad de Farmacia, Universidad de Salamanca, Spain.
Velasco
C
C
Salvador
T
T
Martín
M L
ML
San Román
L
L
D000818:Animals; D001285:Atropine / Q000494:pharmacology; D001794:Blood Pressure / Q000187:drug effects*; D003655:Decerebrate State / Q000503:physiopathology*; D004558:Electric Stimulation; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000294:innervation; D009638:Norepinephrine / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D011985:Receptors, Serotonin / Q000187:drug effects / Q000502:physiology*; D012701:Serotonin / Q000494:pharmacology; D012702:Serotonin Antagonists / Q000494:pharmacology; D017366:Serotonin Receptor Agonists / Q000494:pharmacology; D013116:Spinal Cord / Q000502:physiology*; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000502:physiology*
D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists; D012701:Serotonin; D001285:Atropine; D009638:Norepinephrine