Superfused strips of the human saphenous vein preincubated with
3H-noradrenaline were used to investigate the influences of serotonin (5-HT) receptor agonists and antagonists on the electrically evoked tritium overflow.
| 1. |
5-HT and the preferential 5-HT1A receptor agonist 8-OH-DPAT [8-hydroxy-2-(di-n-propylamino)tetralin] concentration-dependently inhibited the evoked 3H overflow.
|
| 2. |
The evoked 3H overflow was not affected by 0.1 or 1  mol/l TVX Q 7821 (2-{4-[4-(2-pyrimidinyl)-1-piperazinyl]-butyl}-1,2-benzisothiazol-3(2H)one-1,1-dioxide), which selectively binds to 5-HT1A sites; TVX Q 7821 10 mol/l produced an increase in overflow.
|
| 3. |
The inhibitory effect of 5-HT on the impulse-evoked 3H overflow was abolished by the nonselective 5-HT receptor antagonist metitepin, but was not attenuated by propranolol.
|
| 4. |
Metitepin also abolished the inhibitory effect of 8-OH-DPAT on evoked 3H overflow, whereas the 5-HT2 receptor antagonist ketanserin was inactive in this respect. There was also no antagonism of the effect of 8-OH-DPAT by the  2-adrenoceptor antagonist rauwolscine or the dopamine receptor antagonist flupenthixol.
|
These results suggest that both 5-HT and 8-OH-DPAT inhibit noradrenaline release by activating inhibitory 5-HT receptors on the sympathetic nerves of the human saphenous vein. These receptors possess similarities to 5-HT1 recognition sites, but a further subclassification is not yet possible on the basis of the available data.
Key words Noradrenaline release - Presynaptic receptors - Serotonin receptors - 5-HT1 receptors - Human saphenous vein
This study was supported by a grant of the Deutsche Forschungsgemeinschaft