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Migraine headache treatment with eletriptan, a second-generation serotonin receptor agonist.

Eletriptan is a member of the triptan family of selective serotonin receptor agonists. These act against migraine by inducing vasoconstriction of the meningeal arteries. In pharmacological tests, eletriptan has shown high affinity for the 5-HT(1B/1D) receptors, which have been implicated in the etiology of migraine headache attacks. Pharmacokinetic evaluations have concluded that eletriptan offers greater bioavailability than sumatriptan, the effective predecessor to eletriptan. A rapid onset of action has also been characteristic of eletriptan in clinical trials, which have likewise demonstrated eletriptan's superiority to sumatriptan in granting relief of headache pain and other symptoms associated with migraine to a greater number of migraine patients. The drug has generally been well tolerated with only mild to moderate adverse events reported. These characteristics make eletriptan an attractive alternative to sumatriptan in the treatment of migraine. (c) 2001 Prous Science. All rights reserved.

Journal Article↗

Naratriptan: a review.

Even though naratriptan and sumatriptan are both 5-HT1B/5-HT1D receptor agonists, the biological and pharmacokinetic profile of naratriptan differs significantly from that of sumatriptan. With a plasma half-life of 6 h, very high oral bioavailability of 63-74% and higher lipophilicity than sumatriptan, naratriptan exhibits a distinct clinical therapeutic profile. The similar tolerability to placebo, prolonged efficacy for 24 h or more and very low headache recurrence rate make naratriptan an attractive option in the treatment of acute migraine.

Journal Article↗

Eletriptan review.

Eletriptan is a selective, high affinity serotonin 5-HT(1B/1D)-receptor agonist which is rapidly absorbed and has a long half-life in plasma. Eletriptan has been shown to be effective and well tolerated in randomised, double-blind, placebo-controlled acute migraine trials and long-term open-label trials. Eletriptan maintains a consistency of response across three attacks and patients continue to respond to eletriptan for at least up to 1 year. Eletriptan has been compared with sumatriptan, zolmitriptan, naratriptan and ergotamine/caffeine in placebo-controlled, randomised, head-to-head trials, and has shown better efficacy with similar adverse events. In a large triptan meta-analysis, including 53 trials and > 24,000 patients, eletriptan 80 mg showed better efficacy, similar consistency but lower tolerability compared with sumatriptan 100 mg. Eletriptan has also shown efficacy in difficult-to-treat patients who were dissatisfied with their previous treatment with sumatriptan, rizatriptan, nonsteroidal anti-inflammatory drugs or Excedrin.

Clinical Trials as Topic↗

Zolmitriptan: a review of its use in migraine.

UNLABELLED: Zolmitriptan is a selective serotonin 5-HT1B/1D receptor agonist ('triptan'). Its efficacy and tolerability have been assessed in a number of randomised, placebo-controlled, double-blind trials in large numbers of adults with moderate to severe migraine attacks. Oral zolmitriptan 2.5 and 5mg has a rapid onset of action (significant headache relief is observed at 45 minutes) and efficacy is sustained in most patients who respond at 2 hours. The drug is significantly more effective than placebo as measured by a number of parameters including 2-hour headache response rates and pain-free response rates. Other symptoms of migraine, including nausea, photophobia and phonophobia are also alleviated with zolmitriptan. Zolmitriptan is effective in the treatment of migraine associated with menses and migraine with aura. There is some evidence to support the use of zolmitriptan in patients with migraine who have had a poor response to previous therapy. The efficacy of zolmitriptan appears to be maintained, with no tachyphylaxis, following repeated administration for multiple attacks of migraine over a prolonged period of time, with high headache response rates reported over all attacks. In comparison with placebo, the incidence of persistent migraine headache is reduced by zolmitriptan and recurrent migraine headache occurs less frequently with the active treatment. Zolmitriptan has also demonstrated efficacy in the treatment of persistent and/or recurrent migraine headache. For relief of migraine headache, zolmitriptan 5mg had similar efficacy to sumatriptan 100mg for a single attack, but generally was more effective than sumatriptan 25 and 50mg for multiple attacks, in single trials. The incidence of recurrent headache with zolmitriptan was similar to that with sumatriptan. Zolmitriptan is generally well tolerated with most adverse events being mild to moderate, transient and resolving without intervention or the need for treatment withdrawal. The most common adverse events with zolmitriptan therapy are asthenia, heaviness other than that of the chest or neck, dry mouth, nausea, dizziness, somnolence, paraesthesia, warm sensation, tightness, vasodilation and chest pain. CONCLUSION: Zolmitriptan is effective across a wide range of migraine subtypes, maintains efficacy when used in the long term and is generally well tolerated. Further clinical experience is necessary to define the position of zolmitriptan among other currently or soon to be available selective 5-HT1B/1D receptor agonists. However, on the basis of available data, zolmitriptan should emerge as a useful treatment option in the management of patients with moderate to severe migraine.

Age Factors↗

Eletriptan: a review of its use in the acute treatment of migraine.

Eletriptan (Relpax) is an orally administered, lipophilic, highly selective serotonin 5-HT(1B/1D) receptor agonist ('triptan') that is effective in the acute treatment of moderate to severe migraine attacks in adults. It has a rapid onset of action and demonstrates superiority over placebo as early as 30 minutes after the administration of a single 40 or 80 mg oral dose. The efficacy of eletriptan 20 mg was similar to that of sumatriptan 100 mg, while eletriptan 40 and 80 mg displayed greater efficacy than sumatriptan 50 or 100 mg for most endpoints. Eletriptan 40 mg was generally superior to naratriptan 2.5 mg and equivalent to almotriptan 12.5 mg, rizatriptan 10 mg and zolmitriptan 2.5 mg, while eletriptan 80 mg was superior to zolmitriptan 2.5 mg for most efficacy parameters. Eletriptan 40 and 80 mg were consistently superior to ergotamine/caffeine. Eletriptan is generally well tolerated, reduces time lost from normal activities, improves patients' health-related quality of life and appears to be at least as, if not more, cost effective than sumatriptan. Eletriptan is therefore a useful addition to the triptan family and a first-line treatment option in the acute management of migraine attacks.

Animals↗

Spotlight on eletriptan in migraine.

Eletriptan (Relpax) is an orally administered, lipophilic, highly selective serotonin 5-HT(1B/1D) receptor agonist ('triptan') that is effective in the acute treatment of moderate to severe migraine attacks in adults. It has a rapid onset of action and demonstrates superiority over placebo as early as 30 minutes after the administration of a single 40 or 80 mg oral dose. The efficacy of eletriptan 20 mg was similar to that of sumatriptan 100 mg, while eletriptan 40 and 80 mg displayed greater efficacy than sumatriptan 50 or 100 mg for most endpoints. Eletriptan 40 mg was generally superior to naratriptan 2.5 mg and equivalent to almotriptan 12.5 mg, rizatriptan 10 mg and zolmitriptan 2.5 mg, while eletriptan 80 mg was superior to zolmitriptan 2.5 mg for most efficacy parameters. Eletriptan 40 and 80 mg were consistently superior to ergotamine/caffeine. Eletriptan is generally well tolerated, reduces time lost from normal activities, improves patients' health-related quality of life and appears to be at least as, if not more, cost effective than sumatriptan. Eletriptan is therefore a useful addition to the triptan family and a first-line treatment option in the acute management of migraine attacks.

Humans↗

The search for novel migraine therapies: experimental models.

The identification and development of the potent 5-HT1B/1D agonist, sumatriptan has resulted in new therapeutic opportunities for the treatment of migraine and a number of chemically novel agents with a similar mechanism of action have been identified. Whilst these agents are optimised to enhance the therapeutic effect of sumatriptan, development of mechanistically novel therapies may provide new directions for the care of migraine sufferers. To develop new treatment paradigms, novel chemical entities should be evaluated in animal models which are predictive of therapeutic efficacy e.g.: in animal models where sumatriptan has shown activity, or the pathophysiological processes involved in the disease must be targeted. Therefore, investigation of mechanisms underlying cortical activity and its involvement in the activation of trigeminal vascular pathways may allow better understanding of the disease and result in the identification of new non-triptan-like therapies.

Animals↗

5-HT receptors mediating external carotid vasoconstriction in vagosympathectomized dogs.

One specific example reflecting the complexity of cardiovascular responses induced by serotonin (5-hydroxytryptamine; 5-HT) and the progress achieved in the pharmacological characterization of the receptors involved can be illustrated by the effects of 5-HT on the canine external carotid artery bed. Within this framework, it has been shown that the external carotid vasoconstrictor response to 5-HT in the dog is mediated by '5-HT1-like' receptors, which being blocked by the 5-HT1B/1D receptor antagonist GR127935, resemble 5-HT1B/1D (previously called 5-HT1D beta/1D alpha) receptors. It was proposed that these receptors could belong to the 5-HT1B, rather than the 5-HT1D, subtype on the basis of their resistance to blockade by a high dose of ritanserin (a potential 5-HT1D receptor antagonist) and the presence of mRNA for 5-HT1B(5-HT1D beta) receptors, but not for 5-HT1D(5-HT1D alpha) receptors, in vascular smooth muscle. With the advent of subtype-selective antagonists it was subsequently shown that external carotid vasoconstriction to 5-HT and sumatriptan is dose-dependently antagonized by the selective 5-HT1B receptor antagonist SB224289 (2,3,6,7-tetrahydro-1'-methyl-5-[2'-methyl-4' (5-methyl-1,2,4-oxadiazol-3-yl) biphenyl-4-carbonyl] furo [2,3-f] indole-3-spiro-4'-piperidine hydrochloride), whereas the selective 5-HT1D receptor antagonist BRL15572 (1-(3-chlorophenyl)-4-[3,3-diphenyl (2-(S,R) hydroxypropanyl) piperazine] hydrochloride) was ineffective. These findings represent the first in vivo evidence showing that vascular constriction induced by 5-HT and sumatriptan is mediated primarily via 5-HT1B, but not 5-HT1D receptors. The pharmacological profile of these receptors could be similar (isolated human temporal artery and porcine carotid arteriovenous anastomoses) to other putative 5-HT1B receptors mediating vasoconstrictor responses. In view of the putative pathophysiologic role of external carotid (and extracerebral) vasodilation in migraine, the constriction of these blood vessels by sumatriptan via 5-HT1B receptors may be, at least partly, responsible for its therapeutic efficacy in migraine.

Animals↗

Pediatric migraine: recognition and treatment.

The diagnosis of migraine headache in childhood rests on criteria similar to those used in migraine in adults. It is important, however, to appreciate several fundamental differences. These differences include the duration of attack, which is often far shorter than in an adult, and the location of the attack, which may be bilateral in many children. The treatment of children and adolescents with migraines includes treatment modalities for acute attacks, preventive medications when the attacks are frequent, and biobehavioral modes of therapy to address long-term management of the disorder. The controlled clinical trials of medications in pediatric migraine have suffered from high placebo response rates that may be related to the sites conducting the study (ie, headache specialist vs clinical research organizations). The medications have proved to be safe in the pediatric age group. Treatment modalities for acute migraine include over-the-counter nonsteroidal anti-inflammatory drugs (NSAIDs), as well as the oral triptans such as sumatriptan succinate, rizatriptan benzoate, and zolmitriptan and the nasal spray formulations of sumatriptan and zolmitriptan. Subcutaneous sumatriptan and parenteral dihydroergotamine have also been used limitedly. Preventive treatment for patients with frequent or disabling migraines (or both) includes the antidepressants amitriptyline hydrochloride and nortriptyline hydrochloride, the anticonvulsants divalproex sodium and topiramate, and the antihistaminic agent cyprohepatine hydrochloride. Biobehavioral approaches aimed at addressing the fundamental lifestyle issues and nonpharmacologic approaches to management are fundamental to long-term success.

Analgesics↗

Comparison of the serotonin receptors that mediate smooth muscle contraction in canine and porcine coronary artery.

Serotonin (5-HT) is one important mediator of the coronary vasospasm and occlusion associated with thrombosis and atherosclerosis. 5-HT concentration-dependently contracted both canine and porcine coronary artery rings in vitro. In the dog, 5-HT-induced contraction was not blocked by either LY53857 (1 microM) or ketanserin (1 microM), but was blocked by the nonselective 5-HT receptor antagonist 1-naphthylpiperazine (1-NP) (100 nM), indicating 5-HT receptor involvement. Unlike the dog, both LY53857 (1 microM) and ketanserin (30 nM) antagonized 5-HT-induced contraction in pig arteries. Dissociation constants for LY53857 and ketanserin in porcine arteries were compared with those in rat jugular vein, a tissue possessing a well characterized 5-HT2 receptor. Both LY53857 (3 nM) and ketanserin (3 nM) antagonized 5-HT-induced contraction in rat jugular vein; however, the affinities of LY53857 and ketanserin in the rat jugular vein were significantly higher than those in the pig coronary. The rank order contractile potency for 5-HT, (alpha Me-5-HT) and sumatriptan in porcine coronary artery was consistent with that established for a 5-HT2 receptor, whereas the rank order potency in canine coronary artery indicated non-5-HT2 receptor involvement. Sumatriptan, a 5-HT1D receptor-selective agonist, was equieffective to 5-HT in contracting the canine coronary artery, a response inhibited by 1-NP (100 nM). Sumatriptan failed to contract either the pig coronary or rat jugular vein. In summary, significant differences exist in the 5-HT receptors that mediate contraction between the canine and porcine coronary artery.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

Evidence for presynaptic location of inhibitory 5-HT1D beta-like autoreceptors in the guinea-pig brain cortex.

The effects of 5-hydroxytryptamine (5-HT) receptor agonists and antagonists on tritium overflow evoked by high K+ were determined in superfused synaptosomes and slices, preincubated with [3H]5-HT, from guinea-pig brain cortex. In addition, we estimated the potencies of 5-HT receptor ligands in inhibiting specific [3H]5-HT binding (in the presence of 8-hydroxy-2(di-n-propylamino)tetralin and mesulergine to prevent binding to 5-HT1A and 5-HT2C sites) to guinea-pig cortical synaptosomes and membranes. 5-HT receptor agonists inhibited the K(+)-evoked tritium overflow from synaptosomes and slices. In synaptosomes the rank order of potencies was 2-[5-[3-(4-methylsulphonylamino)benzyl-1,2,4-oxadiazol-5-yl] -1H-indole-3-yl] ethylamine (L-694,247) > 5-carboxamidotryptamine (5-CT) > oxymetazoline (in the presence of idazoxan) > or = 5-HT > sumatriptan > or = 5-methoxy-3(1,2,3,6-tetrahydropyridin-4-yl)-1H-indole (RU 24969). The potencies of the agonists in inhibiting tritium overflow from slices correlated with those in synaptosomes, suggesting that the same site of action is involved in both preparations. In synaptosomes the nonselective antagonist at cloned human 5-HT1D alpha and 5-HT1D beta receptors, methiothepin, shifted the concentration-response curve for 5-CT to the right (apparent pA2: 7.87). In contrast, ketanserin at a concentration which should block the 5-HT1D alpha, but not the 5-HT1D beta, receptor did not alter the inhibitory effect of 5-CT on tritium overflow. In cortical synaptosomes and membranes, [3H]5-HT bound to a single site with high affinity. In competition experiments, 5-HT receptor agonists and antagonists inhibited specific [3H]5-HT binding. In synaptosomes the rank order was L-694,247 > methiothepin > 5-CT > 5-methoxytryptamine > 5-HT > or = sumatriptan > or = oxymetazoline > RU 24969 > ketanserin > ritanserin. A very similar rank order was obtained in cerebral cortical membranes. The potencies of the 5-HT receptor agonists in inhibiting tritium overflow from synaptosomes and slices correlated with their potencies in inhibiting [3H]5-HT binding to synaptosomes and membranes. In conclusion, the 5-HT receptors mediating inhibition of 5-HT release in the guinea-pig cortex are located on the serotoninergic axon terminals and, hence, represent presynaptic inhibitory autoreceptors. The [3H]5-HT binding sites in cerebral cortical synaptosomes and membranes exhibit the pharmacological properties of 5-HT1D receptors. The correlation between the functional responses and the binding data confirms the 5-HT1D character of the presynaptic 5-HT autoreceptors. According to the results of the interaction experiment of ketanserin and methiothepin with 5-CT on 5-HT release, the presynaptic 5-HT autoreceptors can be subclassified as 5-HT1D beta-like.

Animals↗

Interactions of GR127935, a 5-HT(1B/D) receptor ligand, with functional 5-HT receptors.

GR127935 (N-[methoxy-3-(4-methyl-1-piperazinyl)phenyl]-2'-methyl-4'-(5-methyl-1,2 ,4-oxadiazol-3-yl) [1, 1-biphenyl]-4-carboxamide hydrochloride) has been recently introduced as an experimental tool to antagonize 5-HT(1B/D) receptor-mediated functional responses. The compound indeed exhibits a very high affinity and selectivity for 5-HT(1B/D) binding sites and it antagonizes a number of 5-HT(1B/D) receptor-mediated responses. The present experiments were performed to investigate the selectivity of GR127935 against functional responses mediated by 5-HT1-like, 'orphan' 5-HT1-like (5-ht7?), 5-HT2, 5-HT3 or 5-HT4 receptors in several in vivo preparations. Intravenous (i.v.) treatment with GR127935 (300 microg x kg(-1)) potently antagonized decreases in total carotid blood flow as well as hypotensive responses induced by the 5-HT1-like receptor agonist sumatriptan in rabbits. I.v. bolus injections of GR127935 (up to 500 and/or 1500 microg x kg(-1)) did not significantly modify 5-HT-induced: (i) tachycardia in the pig (5-HT4 receptor-mediated) and cat ('orphan' 5-HT1-like or, perhaps, 5-ht7 receptor-mediated); (ii) depressor effects in the rat and cat ('orphan' 5-HT1-like or 5-ht7 receptor-mediated); (iii) von Bezold-Jarisch reflex in the rat or the early phase of the urinary bladder contraction in the cat (both 5-HT3 receptor-mediated). In contrast, high doses (500-1500 microg x kg(-1)) of GR127935 suppressed 5-HT-induced pressor responses in the rat and cat and urinary bladder contractions (secondary phase) in the cat as well as the DOI ((+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane hydrochloride)-induced pressor responses in the rat, which are all mediated by 5-HT2A receptors. In conclusion, the present study demonstrates that GR127935 is a selective 5-HT(1B/D) receptor antagonist devoid of interactions at 'orphan' 5-HT1-like (5-ht7?), 5-HT3 and 5-HT4 receptors. However, GR127935 possesses a moderate 5-HT2A receptor blocking property, which is consistent with its binding profile (pKi: 7.4). Lastly, in view of the potent antagonist action of GR127935, the sumatriptan-induced hypotension in rabbits seems to be mediated by 5-HT(1B/D) receptors.

Animals↗

Involvement of 5-HT1B receptors in triptan-induced contractile responses in guinea-pig isolated iliac artery.

Using a series of triptans we characterized in vitro the 5-hydroxytryptamine (5-HT) receptor that mediates the contraction in guinea-pig iliac arteries moderately precontracted by prostaglandin F2alpha (PGF2alpha). Additionally, we investigated by reverse-transcriptase polymerase chain reaction (RT-PCR) which triptan-sensitive receptor is present in this tissue. Frovatriptan, zolmitriptan, rizatriptan, naratriptan, sumatriptan, and almotriptan contracted guinea-pig iliac arteries with pD2 values of 7.52+/-0.04, 6.72+/-0.03, 6.38+/-0.06, 6.22+/-0.05, 5.86+/-0.05 and 5.26+/-0.04 respectively. For comparison, the pD2 values for 5-HT and 5-carboxamidotryptamine (5-CT) were 7.52+/-0.02 and 7.55+/-0.03 respectively. In contrast to all other triptans tested, the concentration-response curve for eletriptan was biphasic (first phase: 0.01-3 microM, pD2 approximately 6.6; second phase: > or = 10 microM). Contractions to 5-HT, 5-CT, frovatriptan, zolmitriptan, rizatriptan, naratriptan, sumatriptan, almotriptan, and eletriptan (first phase) were antagonized by the 5-HT1B/1D receptor antagonist GR127935 (10 nM) and the 5-HT1B receptor antagonist SB216641 (10 nM). RT-PCR studies in guinea-pig iliac arteries showed a strong signal for the 5-HT1B receptor while expression of 5-HT1D and 5-HT1F receptors was not detected in any sample. The present results demonstrate that triptan-induced contraction in guinea-pig iliac arteries is mediated by the 5-HT1B receptor. The guinea-pig iliac artery may be used as a convenient in vitro model to study the (cardio)vascular side-effect potential of anti-migraine drugs of the triptan family.

Animals↗

Uncertainty analysis in pharmacokinetics and pharmacodynamics: application to naratriptan.

PURPOSE: The aim of the study was to predict pain relief of migraine in patients following naratriptan oral (tablet) administration by using uncertainty analysis. The analysis was based on phase I pharmacokinetic naratriptan data, sumatriptan pharmacodynamic data, and naratriptan preclinical (animal) potency information, together with general knowledge as to how migraine affects oral absorption. METHODS: A previously developed pharmacokinetic (PK)/pharmacodynamic (PD) model for naratriptan disposition and effect was used. The uncertain parameters in the model, which were associated with absorption and scaling between first-in-class compound sumatriptan and naratriptan, were modeled using fuzzy sets theory. Global sensitivity analysis was then used to investigate the impact of each PK/PD parameter on the responses. RESULTS: Acknowledging parametric uncertainty did not improve prediction of the probability of pain relief. Global sensitivity analysis demonstrated that predictions were heavily influenced by interindividual variability in pharmacodynamics, as the dose response relationship was relatively insensitive to the pharmacokinetics. CONCLUSIONS: To predict the probability of pain relief following oral (tablet) administration of naratriptan, a simple dose response, instead of the PK/PD model, would have yielded very similar predictions. The naratriptan PK/PD model may be improved by either refining the PD model or better still by specifying the interindividual error by additional data collecting with an improved design.

Algorithms↗

Triptans: do they differ?

Headache care specialists agree that the introduction of sumatriptan constitutes a major advance in headache therapy, but they differ about whether other triptans offer clinically significant advantages over sumatriptan. This article examines this issue by considering the similarities and differences among triptans.

Clinical Trials as Topic↗

Pharmacological characterisation of postjunctional 5-HT receptors in cerebral arteries from the sheep.

In the sheep cerebral vasculature 5-hydroxytryptamine (5-HT) caused a contraction of which ketanserin was found to be an effective antagonist (Basilar artery, pA2 = 9.33 +/- 0.16; middle cerebral artery, pA2 = 9.19 +/- 0.16; pial artery, pA2 = 9.47 +/- 0.12). Sumatriptan (GR 43175), a selective 5-HT1-like receptor agonist, was also found to have a small contractile effect on the sheep cerebral vasculature (Basilar artery, pD2 = 6.26 +/- 0.11; middle cerebral artery, pD2 = 6.25 +/- 0.10; pial artery, pD2 = 6.13 +/- 0.15). The contractile effect of sumatriptan was not antagonised by either ketanserin (1 microM) or MDL 72222 (1 microM). 5-HT therefore appears to cause contraction by stimulation of a mixed receptor population of 5-HT1-like and 5-HT2 receptors. In the sheep middle cerebral artery the addition of haemolysate was found to cause a contractile response and also to augment the contractile effects of both noradrenaline and 5-HT but only in the presence of a functional endothelium. However, 5-HT was never found to relax precontracted rings of the middle cerebral artery in either the presence or absence of a functional endothelium. These results indicate a basal release of EDRF in cerebral arteries that attenuates the effects of various constrictor agents.

Animals↗

GR127935 is a potent antagonist of the 5-HT1-like receptor mediating contraction in the canine coronary artery.

The effects of the recently developed 5-HT1D receptor antagonist, GR127935 (N-[4-methoxy-3-(4-methyl-1-piperazinyl) phenyl]-2'-methyl-4'-(5-methyl-1,2,4-oxadiazol-3-yl) [1,1,-biphenyl]-4-carboxamide), and those of the preferential human 5-HT1D alpha receptor antagonist, ketanserin, on the isometric contraction induced by 5-hydroxytryptamine (5-HT) and sumatriptan in endothelium-denuded ring segments of canine coronary artery were analyzed. Sumatriptan mimicked 5-HT with lower potency but similar efficacy. GR127935 (1,3 and 10 nM) concentration dependently antagonized the contractions elicited by both agonists; only the 5-HT maximum was reduced. Ketanserin and mianserin (both at 1 microM) were inactive. These data strongly suggest that a 5-HT1D receptor mediates contraction in the dog coronary artery. The possibility that this 5-HT1D receptor resembles the cloned human 5-HT1D beta subtype is discussed.

Animals↗

5-HT1D as well as 5-HT1A autoreceptors modulate 5-HT release in the guinea-pig dorsal raphé nucleus.

5-Hydroxytryptamine (5-HT) release was measured by fast cyclic voltammetry in guinea-pig dorsal raphé nucleus slices. Release was reproducibly evoked by a single 0.1 msec pulse of electrical stimulation. The 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH DPAT) produced a concentration-related inhibition of the stimulated 5-HT release, with 50% inhibition at 47 nM. This inhibition was competitively antagonized by N-tert-butyl 3-4-(2-methoxypheny)piperazin-1-yl-2- phenylpropanamide dihydrochloride [(+/-)WAY 100135], a selective 5-HT1A receptor antagonist (pA2 = 7.9). The 5-HT1D receptor agonist sumatriptan also produced a concentration-related inhibition of 5-HT release, with 50% inhibition at 40 nM. The effect of sumatriptan on 5-HT release was antagonized by the 5-HT1D receptor antagonist 2'-methyl-4'-(5-methyl-[1,2,4]oxadiazol-3-yl)-biphenyl-4-carboxyli c acid [4-methoxy-3-(4-methyl-piperazin-1-yl)-phenyl]-amide (GR127935) (pA2 = 8.7). Both (+/-)WAY 100135 and GR127935 increased the 5-HT release evoked by a train of 5 pulses at 1 Hz, suggesting that they were antagonizing the feedback of endogenously released 5-HT onto its autoreceptors. These findings demonstrate for the first time the presence of functional 5-HT1D as well as 5-HT1A autoreceptors in the guinea-pig dorsal raphé nucleus.

8-Hydroxy-2-(di-n-propylamino)tetralin↗