Blockade of 5-HT2 receptors with sarpogrelate uncovers 5-HT7 receptors inhibiting the tachycardic sympathetic drive in pithed rats.

Our group has previously shown in pithed rats that the cardiac sympathetic drive, which produces tachycardic responses, is inhibited by 5-HT via the activation of prejunctional 5-HT1B/1D/5 receptors. Interestingly, when 5-HT2 receptors are chronically blocked with sarpogrelate, the additional role of cardiac sympatho-inhibitory 5-HT1F receptors is unmasked. Although 5-HT2 receptors mediate tachycardia in rats, and the chronic blockade of 5-HT2 receptors unmasked 5-HT7 receptors mediating cardiac vagal inhibition, the role of 5-HT7 receptors in the modulation of the cardiac sympathetic tone remains virtually unexplored. On this basis, male Wistar rats were pretreated during 14 days with sarpogrelate (a 5-HT2 receptor antagonist) in drinking water (30 mg/kg/day; sarpogrelate-pretreated group) or equivalent volumes of drinking water (control group). Subsequently, the rats were pithed to produce increases in heart rate by either electrical preganglionic spinal (C7 -T1 ) stimulation of the cardiac sympathetic drive or iv administration of exogenous noradrenaline. The iv continuous infusion of AS-19 (a 5-HT7 receptor agonist; 10 µg/kg/min) (i) inhibited the tachycardic responses to sympathetic stimulation, but not those to exogenous noradrenaline only in sarpogrelate-pretreated rats. This inhibition was completely reversed by SB258719 (a selective 5-HT7 receptor antagonist; 1 mg/kg, iv) or glibenclamide (an ATP-sensitive K+ channel blocker; 20 mg/kg, iv). These results suggest that chronic 5-HT2 receptor blockade uncovers a cardiac sympatho-inhibitory mechanism mediated by 5-HT7 receptors, involving a hyperpolarization due to the opening of ATP-sensitive K+ channels. Thus, these findings support the role of 5-HT7 receptors in the modulation of the cardiac sympathetic neurotransmission.

Pharmacokinetics and Pharmacodynamics of Lurasidone Hydrochloride, a Second-Generation Antipsychotic: A Systematic Review of the Published Literature.

Lurasidone hydrochloride, a benzisothiazol derivative, is a second-generation (atypical) antipsychotic agent that has received regulatory approval for the treatment of schizophrenia in the US, Canada, the EU, Switzerland, and Australia, and also for bipolar depression in the US and Canada. In addition to its principal antagonist activity at dopamine D2 and serotonin 5-HT2A receptors, lurasidone has distinctive 5-HT7 antagonistic activity, and displays partial agonism at 5-HT1A receptors, as well as modest antagonism at noradrenergic α2A and α2C receptors. Lurasidone is devoid of antihistaminic and anticholinergic activities. It is administered once daily within the range of 40-160 mg/day for schizophrenia and 20-120 mg/day for bipolar depression, and its pharmacokinetic profile requires administration with food. In adult healthy subjects and patients, a 40 mg dose results in peak plasma concentrations in 1-3 h, a mean elimination half-life of 18 h (mostly eliminated in the feces), and apparent volume of distribution of 6173 L; it is approximately 99 % bound to serum plasma proteins. Lurasidone's pharmacokinetics are approximately dose proportional in healthy adults and clinical populations within the approved dosing range, and this was also found in a clinical study of children and adolescents. Lurasidone is principally metabolized by cytochrome P450 (CYP) 3A4 with minor metabolites and should not be coadministered with strong CYP3A4 inducers or inhibitors. Lurasidone does not significantly inhibit or induce CYP450 hepatic enzymes.

Is circadian rhythm disruption important in obsessive-compulsive disorder (OCD)? A case of successful augmentation with agomelatine for the treatment of OCD.

The main augmentation strategy in the treatment of obsessive-compulsive disorder (OCD) is the addition of low-dose dopamine antagonists, such as risperidone. However, the development of additional pharmacological therapeutics is necessary because some patients remain refractory to these strategies. In the present report, we describe an adult male patient with clomipramine treatment-resistant OCD who did not respond to augmentation with risperidone and aripiprazole but who showed clinical improvement with agomelatine. The effect of agomelatine in resynchronizing circadian rhythms may demonstrate the importance of the circadian rhythm disruption observed in OCD. Moreover, the regulation of the serotoninergic system is circadian in nature, and the resynchronization of the serotoninergic system may regulate serotoninergic dysfunction, a major factor in OCD.