Short Communication Pharmacology 18: 276-279 (1979)

Evidence for the Histamine-Mediated Myotropic Effect of Angiotensin II in the Rabbit Aorta1 Z.S. Ercan, F.F. Ersoy, T.A. Bökesoy and R.K. Tiirker Department of Medical and Surgical Research, Faculty of Medicine, University of Hacettepe and Department of Pharmacology, Faculty of Medicine, University of Ankara, Ankara

Key Words. Angiotensin II • Induced histamine • Rabbit aorta Abstract. Histamine Hr receptor antagonist mepyrainine and Hj-receptor antagonist metiamide, respectively diminished and potentiated angiotensin II (A ID-induced myotropic responses in the rabbit aortic strips. The responses of the octapeptide were also inhibited in the presence of histidine decarboxylase inhibitor, 2-hydroxy-5-carbomethoxybenzoxyamine and restored when subcontractile quantities of histamine are added to the inhibitor-containing medium. Inhibition of histamine degradation by aminoguanidine potentiates A IDs responses. These results are taken as evidences indicating A II-induced histamine synthesis in the test preparation.

It has been stated that histamine (HA) is not involved in the myotropic action of angioten­ sin II (A II) on vascular (12) and intestinal (6, 11) smooth muscles. In guinea pig experiments intradermal injection of A II, however, pro­ duces an increase in the permeability of the capillaries which can be blocked by the HA H | -receptor blocker, mepyramine (2). In the vascular tissue HD activity is related to the non-mast cell pool of HA described by

1 This work is supported by a grant from the Turkish Scientific and Technical Research Council (TAG-350).

Schayer (14) as Induced histamine’. We recent­ ly presented evidence that the myotropic effect of clonidine in the rabbit aorta is primarily mediated through the stimulation of a-adrenergic receptors and secondarily through endoge­ nous HA (3). A II is a powerful myotropic substance acting through its specific receptors on the rabbit aorta (15). It is therefore interesting to investigate whether or not the peptide also acts to some extent through the HA synthesis stimu­ lated by A II specific receptors in the aorta. The present paper contains the results of this investigation.

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Introduction

Histamine-Mediated Vascular Effect of Angiotensin II

277

T a b l e 1. Alteration by metiamide, mepyramine, GYKI-11.121 and AG of the contractile effect of A II in the rabbit aortic strips (mean ± SEM)

Control

A 11 1 0 '8 mol/1

60.0 i 6.0 (25)

Percent of maximum response in presence of metiamide (IO '6 mol/1)

in presence of mepyramine ( 1 0 '8 mol/1)

in presence of GYKI-11.121 (1 0 'J mol/1)

in presence of GYKI-11.121 (1 0 'J mol/1) and HA (10"" mol/1)

in presence of AG (5 X 10*s mol/1)

88.0 ± 4.0 (15)

42.0 ± 4.0 (15)

35.0 ± 5.0 (12)

46.0 ± 4.0 (12)

82.0 ± 5.0 (12)

Numbers in parentheses indicate number of strips. The value for each group was found to be different (p

Evidence for the histamine-mediated myotropic effect of angiotensin II in the rabbit aorta.

Short Communication Pharmacology 18: 276-279 (1979) Evidence for the Histamine-Mediated Myotropic Effect of Angiotensin II in the Rabbit Aorta1 Z.S...
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