M-chlorophenylpiperazine increases blood pressure and heart rate in pithed and conscious rats

Plasma catecholamine, renin activity, and ACTH responses to the serotonin receptor agonist DOI in juvenile spontaneously hypertensive rats

Mean arterial blood pressure (MAP), heart rate (HR) and arterial plasma levels of corticotropin (ACTH), renin activity (PRA) and catechols [norepinephrine (NE), epinephrine (EPI), and the intraneuronal NE metabolite dihydroxyphenylglycol (DHPG)] at baseline and in response to the serotonin-1C/2 (5-HT1C/5-HT2) agonist 1-(2,5-dimethoxy-4-iodophenyl)2-aminopropane (DOI, 1.0 mg/kg i.a.) in conscious, freely-moving, juvenile (4 week old) spontaneously hypertensive rats (SHR's) and age-matched Wistar-Kyoto (WKY) normotensive control rats were measured simultaneously. Baseline levels of MAP, NE, DHPG, and EPI all were significantly higher in the SHR's. There was a similar trend for PRA, but ACTH did not differ between the two strains. DOI produced marked increases in levels of MAP, ACTH, EPI, and also PRA but did not affect NE or DHPG concentrations. HR decreased only in the WKY group after administration of DOI. The magnitudes of the EPI and ACTH responses did not differ between the rat strains. Responses of MAP and PRA were significantly larger in SHR's. These results suggest that there is a selective hyperresponsiveness of PRA and blood pressure to 5-HT2 receptor stimulation parallel to a deficient baroreceptor reflex in juvenile SHR's.

Pharmacological characterization of serotonin receptor subtypes involved in vasopressin and plasma renin activity responses to serotonin agonists

Serotonergic drugs with 5-HT2 receptor agonist properties have been suggested to increase plasma vasopressin concentration, blood pressure (BP) and plasma renin activity (PRA). To study whether these actions are mediated by the same or different receptors, we used three potent 5-HT agonists with different structures and receptor binding profiles. All drugs were administered i.v. to conscious, unrestrained rats. The selective agonist, 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI), which has high affinity for 5-HT2 receptors, caused marked increases in BP and PRA but no change in plasma vasopressin concentrations. The 5-HT1C agonist, m-chlorophenylpiperazine (m-CPP), which also binds to other 5-HT receptors, caused moderate increases in BP and PRA and significantly elevated plasma vasopressin concentrations. The 5-HT1A agonist, 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), did not increase any of these parameters. BP and PRA elevations paralleled each other after all drugs, while vasopressin responses were clearly different. Vasopressin responses to m-CPP were entirely antagonised by the 5-HT1/5-HT2 antagonist metergoline, partially by the 5-HT2/5-HT1C antagonists ritanserin and LY 53857, but not by the 5-HT2 antagonist ketanserin. Ritanserin, LY53857 and ketanserin all very effectively blocked BP responses to m-CPP. These findings suggest that BP and PRA but not vasopressin responses are mediated by 5-HT2 receptors. Vasopressin secretion is mediated by 5-HT1 receptors, most likely by 5-HT1C receptors.

5-Hydroxytryptamine and the pathophysiology of migraine

5-Hydroxytryptamine (5-HT; serotonin) has long been implicated in the aetiology of migraine but the evidence remains circumstantial and certainly not definitive. Numerous papers have reviewed the background which is briefly outlined here. Although the continued belief in the primary involvement of 5-HT in the genesis of a migraine attack has recently been questioned, many antimigraine drugs undeniably interact potently with 5-HT receptors. It can be argued, however, that their modest clinical benefit results from their pharmacological effects, be they mediated through 5-HT receptors or otherwise, independently of any pathophysiological involvement of endogenous 5-HT. Nevertheless, there seems convincing evidence that central release of 5-HT by various drug mechanisms causes migraine-like headache in migraineurs. It remains to be seen whether these drugs mimic the pathological event initiating the spontaneous migraine attack. Regardless of these considerations, the focus of research on 5-HT and migraine has proved to be enormously profitable over several decades, culminating recently in the identification of a novel, potentially important, antimigraine drug for the treatment of the acute attack. This drug, sumatriptan, is a selective cranial vasoconstrictor which mediates this effect by specifically activating a particular 5-HT1 receptor subtype. Undoubtedly a precise understanding of its clinical mechanism of action, which is currently being studied by a number of groups, will lead to a better understanding of the pathogenesis of migraine. Perhaps this in turn will help in finally determining whether migraine is a vascular disease and whether or not a disturbance of 5-HT is just epiphenomenal or is truly the primary initiating pathological event.

A preliminary study of the effects of intravenous m-chlorophenylpiperazine, a serotonin agonist, in elderly subjects

m-Chlorophenylpiperazine (m-CPP), a serotonin receptor agonist, is currently being investigated as a probe of serotonergic responsivity in various neuropsychiatric disorders. The safety of m-CPP in elderly populations and its potential usefulness in exploring possible serotonergic dysfunction in Alzheimer's disease and normal aging were assessed by examining the behavioral, neuroendocrine, and physiological effects of this agent in 15 elderly subjects (mean age 69 +/- 2 years): 9 Alzheimer patients and 6 healthy normal volunteers. Intravenous m-CPP (0.08 mg/kg) was well tolerated in all subjects and produced no serious adverse effects. The behavioral effects were modest; in particular, minimal anxiety was observed, a finding that contrasted to results from an earlier study reporting that intravenous m-CPP at a slightly higher dose induced marked anxiety and panic attacks in younger subjects. m-CPP produced significant increases in plasma cortisol and prolactin, and significant changes in blood pressure and temperature in these elderly subjects. The results of this preliminary study suggest that intravenous m-CPP is safe and well-tolerated in elderly subjects. Future studies at higher doses can now proceed to study more definitively the question of possible age- and disorder-related reductions in central nervous system (CNS) serotonergic responsivity.

Comparative anxiogenic, neuroendocrine, and other physiologic effects of m-chlorophenylpiperazine given intravenously or orally to healthy volunteers

The serotonin agonist m-chlorophenylpiperazine (m-CPP) had greater anxiogenic and other mood and cognitive effects when administered intravenously (0.1 mg/kg) rather than orally (0.5 mg/kg) to healthy subjects. Nonetheless, similar elevations in peak plasma cortisol and prolactin concentrations were obtained with the two dosage regimens, and temperature elevations were greater after oral m-CPP. Plateau phase plasma concentrations of m-CPP at the times of the maximum neuroendocrine responses to intravenous and oral m-CPP were similar. Since all rodent and nonhuman primate studies have used parenterally administered m-CPP, and previous clinical investigations using intravenous rather than oral m-CPP have yielded somewhat discrepant results, our normative data should be useful for comparing results across different human studies and across species.

Hyperthermia induced by m-CPP in the rat and its modification by antidepressant treatments

Administration of the serotonin agonist m-chlorophenylpiperazine to rats produced a dose-related hyperthermia. Pretreatment with the serotonin receptor antagonist metergoline totally abolished this response, whereas similar treatment with haloperidol, phenoxybenzamine, naloxone, clonidine, pindolol, propranolol, methiotepin, and ritanserin was ineffective. In studies investigating the modification of the response by antidepressant treatments both acute (3 day) and chronic (22 day) administration of the MAO inhibitor clorgyline, as well as the tricyclics clomipramine and imipramine, attenuated the hyperthermic response to m-CPP. These findings are discussed with regard to the specificity of m-CPP-induced hyperthermia and its subsequent modification by antidepressant treatments, in order to evaluate this model's use as a probe for assessment of the serotonergic system.

Effects of fenfluramine, m-chlorophenylpiperazine, and other serotonin-related agonists and antagonists on penile erections in nonhuman primates

Fenfluramine, m-chlorophenylpiperazine (m-CPP), 1-phenylpiperazine, and the buspirone metabolite, 1-(2-pyrimidyl)piperazine given intravenously to adult rhesus monkeys regularly elicited penile erections. In contrast, serotonin (5-HT) agonists with 5-HT1A site specificity (8-OH-DPAT, buspirone) as well as trazodone, ritanserin, and metergoline were no different from saline in producing penile erections. Fenfluramine's effects were blocked by the 5-HT2 antagonists, ritanserin and metergoline, while m-CPP's effects were not blocked by the peripheral 5-HT antagonist, xylamidine, indicating that tumescence can be elicited by serotonergic agents which act at non-5-HT1A sites in the central nervous system.