Correlation between the affinity for [3H]mianserin-labelled receptors in brain and antagonism of the serotonin pressor response in pithed rats

Rapid down-regulation of S2 serotonin receptors by antidepressants: noradrenergic-serotonergic interactions

Mianserin stereoselectively decreases rat cortical S2 binding, the (+)enantiomer having higher potency. This and other data suggest that an alpha-2 receptor is unlikely to contribute to the mechanism of rapid S2 down-regulation by mianserin. Yohimbine, an alpha-2 antagonist which enhances desipramine-induced S2 decreases, was not dependent on NE or 5-HT release for its effect. Depletion of NE by 75% or 5-HT by 94% did not alter the ability of yohimbine and desipramine to decrease binding. These results raise previously unsuspected mechanisms involved in acute down-regulation of S2 binding by mianserin and yohimbine.

Characterization of flufylline, fluprofylline, ritanserin, butanserin and R 56413 with respect to in-vivo alpha 1-,alpha 2- and 5-HT2-receptor antagonism and in-vitro affinity for alpha 1-,alpha 2- and 5-HT2-receptors: comparison with ketanserin

The experimental drugs butanserin (R 53393), ritanserin (R 55667), R 56413, flufylline (Sgd 195/78) and fluprofylline (Sgd 144/80) were evaluated with respect to their antagonism at postjunctional alpha 1- and alpha 2-adrenoceptors and 5-HT2-receptors in pithed rats. Moreover, affinity for [3H]mianserin, [3H]prazosin and [3H]yohimbine binding sites was assessed using rat brain preparations. In all experiments ketanserin was taken as a reference compound. It is concluded that of the compounds investigated butanserin is the most potent and selective alpha 1-adrenoceptor antagonist, whereas ritanserin was found to be a potent and selective 5-HT2-antagonist. Of the other compounds, fluprofylline was a very selective though not very potent alpha 1-adrenoceptor antagonist. The other compounds were less active and less selective in this respect.

Receptor-mediated effects of serotonin and 5-methoxytryptamine on noradrenaline release in the rat vena cava and in the heart of the pithed rat

In segments of the rat inferior vena cava preincubated with 3H-noradrenaline, it was examined whether presynaptic serotonin (5-HT) receptors exist on the postganglionic sympathetic nerves of the circulatory system; for this purpose the effects of 5-HT receptor agonists and antagonists on the electrically evoked 3H overflow were studied. Furthermore, vagotomized pithed rats (treated with atropine and captopril) were used to investigate the effects of these drugs on heart rate and on the tachycardia induced by electrical stimulation of the preganglionic sympathetic nerves (C7--T1) via the pithing rod; these experiments were carried out to provide evidence that the presynaptic 5-HT receptors are operative in vivo. 5-HT and 5-methoxytryptamine (5-OCH3-T) concentration-dependently inhibited the electrically evoked 3H overflow from the vena cava. The inhibitory effect was more pronounced at 0.66 Hz than at 2 Hz. 8-Hydroxy-2-(di-n-propylamino)tetralin did not alter the evoked overflow. The inhibitory effect of 5-HT or 5-OCH3-T was antagonized by metitepin but not affected by ketanserin or rauwolscine. In pithed rats 5-HT and 5-OCH3-T by themselves dose-dependently increased heart rate. The positive chronotropic effect of 5-HT 10 mumol/kg, which was not affected by ketanserin, was considerably decreased by desipramine, indicating that 5-HT at least at this high dose acts predominantly by a tyramine-like indirect sympathomimetic effect.(ABSTRACT TRUNCATED AT 250 WORDS)

The hydroxy-hexanydronaphthoxazines: a new group of very potent and selective dopamine agonists

Replacement of the pyrrole ring system in the dopaminergic oxaergolines (e.g. RU 29717) by a phenolic OH group leads to the hydroxy-hexahydronaphthoxazines, a new group of potent dopamine agonists which exhibit increased selectivity due to their lower affinity for adrenergic and 5-HT receptors.