Neurochemical profile in vitro of irindalone: A5-HT2-receptor antagonist

Synthesis and pharmacological evaluation of triflate-substituted analogues of clozapine: identification of a novel atypical neuroleptic

The trifluoromethanesulfonyloxy (TfO) analogues 3 and 4 of 8-chloro-11-(4-methyl-1-piperazinyl)-5H-dibenzo[b,e][1,4]diazepine (clozapine, 1) and its 2-chloro isomer (iso-clozapine, 2), respectively, were synthesized via their OMe and OH analogues with the conventional synthetic method of the tricyclic dibenzodiazepines and evaluated pharmacologically along with their parent drugs. The binding profile of the 2-OTf analogue (4) is comparable to the binding profile of 1, although the affinity for the dopamine (DA) D2 receptors is higher (IC50 values are 31 nM and 330 nM for compounds 4 and 1, respectively). Interestingly, no notable affinity for muscarinic receptors could be detected in compound 4. On the contrary, the 8-OTf analogue 3 only displayed affinity for muscarinic M1 receptors (IC50 value 35 nM) and no affinity (IC50 value > 500 nM) for the other receptors tested. The 10 mumol/kg sc dose, but not the 10 mumol/kg po dose, of compound 4 stimulated the output of DA. Increases of 80% and 35% in DOPAC output from the dorsal striatum were seen after sc and po administrations of 10 mumol/kg of compound 4, respectively. Doses up to 100 mumol/kg of compound 3 had no effect on either parameter. Doses up to 100 mumol/kg of compound 4 were not cataleptogenic, but significantly decreased apomorphine-induced locomotor activity. In conclusion, compound 4 (GMC1-169) is a new clozapine-like neuroleptic candidate, which is lacking anticholinergic properties and displays a higher potency, as compared to clozapine (1) itself.

Assessment of relative efficacies of 5-HT1A receptor ligands by means of in vivo animal models

We have evaluated the effects of ligands with varying efficacies at beta-adrenoceptors and 5-HT1A receptors in three in vivo models reflecting pre- and/or postsynaptic 5-HT1A receptor activation. Forepaw treading in rats is mediated by postsynaptic 5-HT1A receptors, 8-OH-DPAT (8-hydroxy-2-(di-n-propylamin)tetralin)-induced discriminative stimulus is predominantly mediated by postsynaptic, but presynaptic 5-HT1A receptors might also be involved, and footshock-induced ultrasonic vocalization involves predominantly presynaptic 5-HT1A receptors. In vitro receptor binding studies demonstrated high beta-adrenoceptor and 5-HT1A receptor affinity of (-)-penbutolol, high beta-adrenoceptor and 60 times lower 5-HT1A receptor affinity of (+)-penbutolol, high beta-adrenoceptor affinity and about 100 times lower 5-HT1A receptor affinity of pindolol and (-)-tertatolol, only affinity for beta-adrenoceptors of metoprolol and ICI 118,551 (erythro-D,L-1-(7-methylindan-4-yloxy)-3-isopropylamine-b utan-2-ol, and only affinity for 5-HT1A receptors of WAY 100.635 ((N-[2-[4- (2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl) cyclo-hexane-carboxamide). (-)-Penbutolol, (-)-tertatolol, pindolol and WAY 100.635 antagonized 5-MeODMT-induced (5-methoxy-N, N-dimethyltryptamine) forepaw treading in rats, and (+)-penbutolol, ICI 118,551 and metoprolol were inactive. (-)-Penbutolol, WAY 100.635 and (-)-tertatolol antagonized 8-OH-DPAT-induced discriminative stimulus in rats, pindolol and metoprolol showed a mixed antagonistic and agonistic profile. Pindolol antagonized footshock-induced ultrasonic vocalization in rats, tertatolol inhibited maximum 36% and WAY 100.635, (-)-penbutolol, (+)-penbutolol, metroprolol and ICI 118,551 were inactive. (-)-Penbutolol and WAY 100.635 reversed 8-OH-DPAT-induced inhibition of ultrasonic vocalization completely, (-)-tertatolol reversed maximum 52% and (+)-penbutolol and pindolol were inactive. It is concluded, that efficacies at 5-HT1A receptors can be estimated by applying a battery of in vivo test models that involve post- and presynaptic receptors to a variable degree. The in vivo ranking order of efficacy at 5-HT1A receptors was: WAY 100.635 = (-)-penbutolol < (-)-tertatolol < pindolol.

The antiaggressive potency of (-)-penbutolol involves both 5-HT1A and 5-HT1B receptors and beta-adrenoceptors

The relative importance of 5-HT1A and beta-adrenergic activities in the antiaggressive effects of (-)-penbutolol was studied in male mice. (-)-Penbutolol had high affinity for 5-HT1A receptors and beta-adrenoceptors, and antagonized the 5-methoxy-N,N-dimethyltryptamine (5-MeODMT)-induced 5-HT syndrome and the 8-hydroxy-2-(di-n-propylamin)tetralin (8-OH-DPAT)-induced discriminatory stimulus in rats. (-)-Penbutolol abolished aggressive behaviour (ED50 = 56 mumol/kg), and reversed the antiaggressive effects of 8-OH-DPAT and 1-(3-trifluoromethylphenyl)piperazine (TFMPP) (ED50 = 8.1 and 2.1 mumol/kg, respectively). (N-[2-[4-(2-Methoxyphenyl)-1-piperazinyl]ethyl-N-(2-pyridinyl) cyclohexanecarboxamide (WAY 100635) reversed the antiaggressive effects of 8-OH-DPAT (ED50 = 0.012 mumol/kg), but did not affect the antiaggressive effects of TFMPP. The antiaggressive effect of a submaximal dose of 8-OH-DPAT was markedly potentiated by beta-adrenoceptor antagonists without 5-HT1A receptor affinity, whereas (-)-penbutolol was effective at only one dose (4.5 mumol/kg). In conclusion, the 5-HT1A receptor antagonistic potency of (-)-penbutolol in aggressive mice is attenuated by beta-adrenoceptor-induced facilitation of serotonergic neurotransmission.

The role of serotonergic mechanisms in inhibition of isolation-induced aggression in male mice

The role of serotonergic (5-HT) receptor subtypes in mediation of aggressive behaviour in isolated male mice has been studied. Increase of attack latency was used as a simple measure of antiaggressive behaviour. 5-HT1A agonists (BAY R 1531, 8-OHDPAT, flesinoxan, gepirone, 5MeO DMT, buspirone, ipsapirone, BMY 14802) completely inhibit the aggressive behaviour irrespective of their intrinsic activities. Also the putative antagonists spiroxatrine and NAN 190 as well as the non-selective 5-HT1 agonists RU 24969, TFMPP, mCPP and eltoprazine have an antiaggressive effect. The mixed 5-HT1A and beta-adrenoceptor antagonists (-)-alprenolol and pindolol are ineffective and do not inhibit the effect of 8-OHDPAT. Neither does the non-selective 5-HT antagonist metergoline. The antiaggressive effect correlates with 5-HT1A receptor affinity in vitro and with generalization to the 8-OHDPAT-induced discriminative stimulus. The selective 5-HT uptake inhibitor citalopram does not inhibit aggressive behaviour. The 5-HT2 agonist DOI has an antiaggressive effect only at high doses, whereas the 5-HT2 antagonist ritanserin and the 5-HT3 antagonist ondansetron are ineffective. Prazosin (alpha 1-adrenoceptor antagonist), clonidine (alpha 2-adrenoceptor agonist), clenbuterol (beta-adrenoceptor agonist), ketanserin (5-HT2 receptor and alpha 1-adrenoceptor antagonist), clozapine and (-)-octoclothepin (dopamine (DA), 5-HT2 receptor and alpha 1-adrenoceptor antagonist) all show an antiaggressive effect. SCH 23390 (DA D1 receptor antagonist) and emonapride (DA D2 receptor antagonist) are ineffective. In conclusion, 5-HT1A receptors are involved in mediation of isolation-induced aggressive behaviour in mice. The involvement of other 5-HT receptor subtypes needs further clarification. The adrenergic system may also be involved.(ABSTRACT TRUNCATED AT 250 WORDS)

Antihypertensive effects of chronic 5-hydroxytryptamine (5-HT2) receptor blockade with irindalone in the spontaneously hypertensive rat

The present study was conducted to evaluate the antihypertensive effects of irindalone, a potent 5-HT2-receptor blocking agent with weak alpha 1-adrenoceptorblocking properties. Young spontaneously hypertensive rats (SHR) received irindalone in the food (daily intake estimated to 10 mg/kg) for 10 weeks and older SHR received irindalone subcutaneously for 2 weeks (3 mg/kg/day by osmotic pump). The indirect systolic blood pressure was measured each week (tail plethysmography) and at the end of the intervention periods the direct intraarterial blood pressure was measured in conscious rats. Subsequently a dose-response curve of pressor responses to phenylephrine was constructed in pithed rats. Chronic oral treatment with irindalone reduced the development of hypertension but influenced neither body weight nor heart weight. The subcutaneous treatment with irindalone reduced the blood pressure in relatively older SHR compared with controls. Pressor responses to phenylephrine were antagonized in rats receiving oral treatment. However, during subcutaneous treatment with irindalone the dose-response curve to phenylephrine was not influenced, suggesting that the blood pressure reduction was not directly related to a concomitant alpha 1-adrenoceptor blockade. These results demonstrate that irindalone effectively reduces the blood pressure in SHR and that no tolerance develops to its antihypertensive effects. Since the blood pressure reduction, at least following subcutaneous treatment, was not directly related to a concomitant alpha 1-blockade, it is suggested that the 5-HT2-receptor blockade may be of relevance for the antihypertensive effect.

Cardiovascular effects of irindalone, a new S2-serotonergic antagonist, in the rat

Irindalone is a new antihypertensive agent with affinity to serotonin (5-HT2) receptors and at higher concentrations also to alpha 1-adrenoceptors. The present study was designed to evaluate the relative importance of the antagonism of central and peripheral alpha 1- and 5-HT2-receptors in the blood pressure lowering properties or irindalone after acute administration. In conscious Sprague-Dawley rats intravenous irindalone (0.05-1.5 mg/kg) dose-dependently reduced the blood pressure. In the same dose-range irindalone antagonized pressor responses to phenylephrine and electrical stimulation of the spinal sympathetic outflow (SNS) in the pithed rats, indicating that the acute blood pressure lowering effect is primarily related to the blockade of alpha 1-adrenoceptors. However, the concomitant 5-HT2-receptor blockade may contribute since irindalone in a dose (0.15 mg/kg) where it had no alpha-adrenoceptor blocking properties enhanced the hypotensive response to selective alpha 1-adrenoceptor blockade by prazosin (1 micrograms/kg). We found no evidence that central mechanisms contributed to the blood pressure lowering effect of irindalone. In anaesthetized rats irindalone (1 mg/kg) did not reduce the directly recorded sympathetic nerve activity. Intracerebroventricular administration of irindalone in conscious rats (10-100 micrograms) had no consistent effects on the blood pressure and did not enhance the hypotensive response to intracerebroventricularly administered prazosin (10 micrograms). Finally, the hypotensive response to irindalone was not influenced by depletion of central serotonin stores (by PCPA). It is concluded that the blood pressure lowering effect of irindalone following acute administration is related primarily to blockade of peripheral alpha-adrenoceptors but that the concomitant blockade of 5-HT2-receptors may contribute.