Table of Contents
ISRN Pharmacology
Volume 2013, Article ID 717529, 8 pages
http://dx.doi.org/10.1155/2013/717529
Research Article

Hypotensive and Vasorelaxant Effects of Sericin-Derived Oligopeptides in Rats

1Department of Biochemistry, Faculty of Medical Science, Naresuan University, Phitsanulok 65000, Thailand
2Department of Physiology, Faculty of Medicine, Chiang Mai University, Chiang Mai 50200, Thailand
3School of Food Technology, Institute of Agricultural Technology, Suranaree University of Technology, Nakhon Ratchasima 30000, Thailand
4Department of Anatomy, Faculty of Medicine, Chiang Mai University, Chiang Mai 50200, Thailand

Received 30 August 2013; Accepted 22 September 2013

Academic Editors: R. Couture, S. Tsuruoka, and R. Villalobos-Molina

Copyright © 2013 Amnart Onsa-ard et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Sericin-derived oligopeptides obtained from silk cocoons were investigated for the in vivo hypotensive effect and investigated for the underlying mechanism involved in vasodilation in isolated rat thoracic aorta. In normotensive anesthetized rats, oligopeptides induced an immediate and transient hypotensive activity. In rat aortic rings, oligopeptides induced a concentration-dependent vasorelaxation in vessels precontracted with both KCl and phenylephrine (PE) with endothelium-intact or endothelium-denuded rings. In endothelium-intact rings, pretreatment with Nω-Nitro-L-arginine methyl ester hydrochloride (L-NAME, 100 µM), an inhibitor of the NO synthase (NOS) or 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 1 µM), a selective inhibitor of the guanylyl cyclase enzyme, significantly reduced the relaxant effect of oligopeptides. However, indomethacin, an inhibitor of the cyclooxygenase, had no effect on oligopeptides-induced relaxation. In addition, pretreatment with tetraethylammonium (TEA, 5 mM) reduced the maximal relaxant effect induced by oligopeptides. By contrast, relaxation was not affected by 4-aminopyridine (4-AP, 1 mM), glibenclamide (10 µM), or barium chloride (BaCl2, 1 mM). In depolarization Ca2+-free solution, oligopeptides inhibited calcium chloride- (CaCl2-) induced contraction in endothelium-denuded rings in a concentration-dependent manner. Nevertheless, oligopeptides attenuated transient contractions in Ca2+-free medium containing EGTA (1 mM) induced by 1 µM PE, but they were not affected by 20 mM caffeine. It is obvious that potent vasodilation effect of oligopeptides is mediated through both the endothelium and the vascular smooth muscle.