Cardiovascular pharmacology Pharmacological evidence that histamine H 3 receptors inhibit the vasodepressor responses by selective stimulation of the rat perivascular sensory CGRPergic outflow Guadalupe Manrique-Maldonado, Alain H. Altamirano-Espinoza, Bruno A. Marichal-Cancino, Eduardo Rivera-Mancilla, Victor Avilés-Rosas, Carlos M. Villalón n,1 Departamento de Farmacobiología, Cinvestav-Coapa, Czda. Tenorios No. 235, Col. Granjas-Coapa, Deleg. Tlalpan,14330 México D.F., Mexico article info Article history: Received 24 October 2014 Received in revised form 5 February 2015 Accepted 11 February 2015 Available online 19 February 2015 Chemical compounds studied in this article: Immepip dihydrobromide (Pubchem CID: 16078980) Ketotifen fumarate salt (Pubchem CID: 5282408) Ranitidine hydrochloride (Pubchem CID: 3033332) Thioperamide maleate salt (Pubchem CID: 16220001) JNJ7777120 (Pubchem CID: 4908365) α-CGRP (Pubchem CID: 56841902) Gallamine triethiodide (Pubchem CID: 6172) Hexamethonium chloride (Pubchem CID: 93550) Methoxamine hydrochloride (Pubchem CID: 6081) Keywords: Histamine receptors CGRP Pithed rat Sensory CGRPergic outflow abstract This study has investigated whether pharmacological activation of G i/o coupled histamine H 3 /H 4 receptors inhibits the rat vasodepressor sensory outflow. For this purpose, 100 male Wistar rats were pithed, artificially ventilated and pretreated (i.v.) with: 25 mg/kg gallamine, 2 mg/kg/min hexametho- nium and 20 μg/kg/min methoxamine, followed by i.v. continuous infusions of physiological saline (0.02ml/min) or immepip (3.1, 10 or 31 μg/kg/min; a histamine H 3 /H 4 receptor agonist). Under these conditions, electrical stimulation (0.56–5.6 Hz; 50 V and 2 ms) of the spinal cord (T 9 –T 12 ) resulted in frequency-dependent vasodepressor responses, which were: (i) unchanged during the infusions of saline or immepip (3.1 μg/kg/min); and (ii) significantly but, surprisingly, not dose-dependently inhibited by 10 and 31 μg/kg/min immepip. Moreover, the sensory-inhibition by 10 μg/kg/min immepip (which failed to inhibit the vasodepressor responses by i.v. bolus injections of α-CGRP; 0.1–1 mg/kg) was: (i) essentially unaltered after i.v. administration of saline (1 ml/kg) or blocking doses of the antagonists ketotifen (100 μg/kg; H 1 ), ranitidine (1000 μg/kg; H 2 ) or JNJ7777120 (310 μg/kg; H 4 ); and (ii) abolished after i.v. thioperamide (310 mg/kg; H 3 ). In conclusion, our results suggest that immepip-induced inhibition of the vasodepressor sensory outflow is mainly mediated by prejunctional activation of histamine H 3 receptors. & 2015 Elsevier B.V. All rights reserved. 1. Introduction Systemic vascular tone has been shown to be modulated by periva- scular sympathetic (Hoffman, 2001) and primary sensory (Kawasaki, 2002) nerves. These sensory nerves release vasodilator neuropeptides such as calcitonin gene-related peptide (CGRP), substance P and neur- okinin A (Lundberg et al., 1985; 1992; Brain and Grant, 2004), but their contribution to the control of systemic blood pressure is mainly mediated by CGRP (Shen et al., 2001; Supowit et al., 2005). Indeed, in pithed rats: (i) CGRP induces hypotensive responses at much lower doses than those of substance P (Haass and Skofitsch, 1985); and (ii) electrical spinal (T 9 –T 12 ) stimulation of the perivascular sensory CGRPergic outflow results in vasodepressor responses mainly mediated by activation of CGRP receptors (blocked by CGRP 8-37 , but not by other antagonists) (Taguchi et al., 1992). These findings established that the pithed rat model is useful to study the vasodepressor sensory CGRPergic outflow and its possible interactions with other neurotransmission Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/ejphar European Journal of Pharmacology http://dx.doi.org/10.1016/j.ejphar.2015.02.017 0014-2999/& 2015 Elsevier B.V. All rights reserved. n Corresponding author. Tel.: þ52 55 5483 2854; fax: þ52 55 5483 2863. E-mail addresses: manriquegpe@yahoo.com.mx (G. Manrique-Maldonado), alhaales@gmail.com (A.H. Altamirano-Espinoza), wachax@gmail.com (B.A. Marichal-Cancino), e.r.m_89@hotmail.com (E. Rivera-Mancilla), vectoraviles@gmail.com (V. Avilés-Rosas), cvillalon@cinvestav.mx (C.M. Villalón). 1 URL: http://farmacobiologia.cinvestav.mx/PersonalAcadémico/DrCarlosMVil- lalónHerrera.aspx. European Journal of Pharmacology 754 (2015) 25–31