Pre- and postsynaptic effects of brimonidine on isolated rabbit iris dilator muscles

Sonoko Tatsui,1 Hitoshi Ishikawa,2 Kimiya Shimizu,1 Kimiyo Mashimo1 1Department of Ophthalmology, School of Medicine, Kitasato University, 2Department of Orthoptics and Visual Sciences, School of Allied Health Sciences, Kitasato University, Sagamihara, Japan Purpose: Brimonidine is an imidazoline...

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Autores principales:	Tatsui S, Ishikawa H, Shimizu K, Mashimo K
Formato:	article
Lenguaje:	EN
Publicado:	Dove Medical Press 2016
Materias:	brimonidine rabbit iris dilator electrical field stimulation pre-synaptic-adrenoceptor post-synaptic-adrenoceptor imidazolin Ophthalmology RE1-994
Acceso en línea:	https://doaj.org/article/0ddfd459ba3e4c3eab297dbf7b271bf2
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spelling	oai:doaj.org-article:0ddfd459ba3e4c3eab297dbf7b271bf22021-12-02T00:30:48ZPre- and postsynaptic effects of brimonidine on isolated rabbit iris dilator muscles1177-5483https://doaj.org/article/0ddfd459ba3e4c3eab297dbf7b271bf22016-05-01T00:00:00Zhttps://www.dovepress.com/pre--and-postsynaptic-effects-of-brimonidine-on-isolated-rabbit-iris-d-peer-reviewed-article-OPTHhttps://doaj.org/toc/1177-5483Sonoko Tatsui,1 Hitoshi Ishikawa,2 Kimiya Shimizu,1 Kimiyo Mashimo1 1Department of Ophthalmology, School of Medicine, Kitasato University, 2Department of Orthoptics and Visual Sciences, School of Allied Health Sciences, Kitasato University, Sagamihara, Japan Purpose: Brimonidine is an imidazoline compound used for the treatment of glaucoma, but having very little effect on pupil diameter. Like para-aminoclonidine, most imidazoline compounds interact with postsynaptic α-adrenoceptors and cause pupil dilatation. Therefore, as part of an investigation of the mechanism of action of brimonidine on pupil diameter, the present study was initiated to measure, in vitro, the relative potency of brimonidine on the pre- and postsynaptic α-adrenoceptors of rabbit iris dilator muscle. Methods: The contractile activity of brimonidine and its effect on twitch contraction evoked by electrical field stimulation were studied in isolated rabbit iris dilator muscles by isometric tension recording. Results: Brimonidine significantly inhibited the twitch contraction of the dilator muscle caused by field stimulation, without affecting the response to exogenously applied phenylephrine. Compared to phenylephrine, brimonidine caused only a small contractile response with % maximum contraction values of<10%. Conclusion: These results suggest that brimonidine may act on nerve endings to inhibit adrenergic neurotransmission with very little effect on postsynaptic α-adrenoceptors. This may indicate that brimonidine reduced the pupil diameter just a little, thus improving night vision. Keywords: brimonidine, rabbit iris dilator, electrical field stimulation, presynaptic α2-adrenoceptor, postsynaptic α1-adrenoceptor, imidazolinTatsui SIshikawa HShimizu KMashimo KDove Medical Pressarticlebrimonidinerabbit iris dilatorelectrical field stimulationpre-synaptic-adrenoceptorpost-synaptic-adrenoceptorimidazolinOphthalmologyRE1-994ENClinical Ophthalmology, Vol 2016, Iss Issue 1, Pp 845-849 (2016)
institution	DOAJ
collection	DOAJ
language	EN
topic	brimonidine rabbit iris dilator electrical field stimulation pre-synaptic-adrenoceptor post-synaptic-adrenoceptor imidazolin Ophthalmology RE1-994
spellingShingle	brimonidine rabbit iris dilator electrical field stimulation pre-synaptic-adrenoceptor post-synaptic-adrenoceptor imidazolin Ophthalmology RE1-994 Tatsui S Ishikawa H Shimizu K Mashimo K Pre- and postsynaptic effects of brimonidine on isolated rabbit iris dilator muscles
description	Sonoko Tatsui,1 Hitoshi Ishikawa,2 Kimiya Shimizu,1 Kimiyo Mashimo1 1Department of Ophthalmology, School of Medicine, Kitasato University, 2Department of Orthoptics and Visual Sciences, School of Allied Health Sciences, Kitasato University, Sagamihara, Japan Purpose: Brimonidine is an imidazoline compound used for the treatment of glaucoma, but having very little effect on pupil diameter. Like para-aminoclonidine, most imidazoline compounds interact with postsynaptic α-adrenoceptors and cause pupil dilatation. Therefore, as part of an investigation of the mechanism of action of brimonidine on pupil diameter, the present study was initiated to measure, in vitro, the relative potency of brimonidine on the pre- and postsynaptic α-adrenoceptors of rabbit iris dilator muscle. Methods: The contractile activity of brimonidine and its effect on twitch contraction evoked by electrical field stimulation were studied in isolated rabbit iris dilator muscles by isometric tension recording. Results: Brimonidine significantly inhibited the twitch contraction of the dilator muscle caused by field stimulation, without affecting the response to exogenously applied phenylephrine. Compared to phenylephrine, brimonidine caused only a small contractile response with % maximum contraction values of<10%. Conclusion: These results suggest that brimonidine may act on nerve endings to inhibit adrenergic neurotransmission with very little effect on postsynaptic α-adrenoceptors. This may indicate that brimonidine reduced the pupil diameter just a little, thus improving night vision. Keywords: brimonidine, rabbit iris dilator, electrical field stimulation, presynaptic α2-adrenoceptor, postsynaptic α1-adrenoceptor, imidazolin
format	article
author	Tatsui S Ishikawa H Shimizu K Mashimo K
author_facet	Tatsui S Ishikawa H Shimizu K Mashimo K
author_sort	Tatsui S
title	Pre- and postsynaptic effects of brimonidine on isolated rabbit iris dilator muscles
title_short	Pre- and postsynaptic effects of brimonidine on isolated rabbit iris dilator muscles
title_full	Pre- and postsynaptic effects of brimonidine on isolated rabbit iris dilator muscles
title_fullStr	Pre- and postsynaptic effects of brimonidine on isolated rabbit iris dilator muscles
title_full_unstemmed	Pre- and postsynaptic effects of brimonidine on isolated rabbit iris dilator muscles
title_sort	pre- and postsynaptic effects of brimonidine on isolated rabbit iris dilator muscles
publisher	Dove Medical Press
publishDate	2016
url	https://doaj.org/article/0ddfd459ba3e4c3eab297dbf7b271bf2
work_keys_str_mv	AT tatsuis preandpostsynapticeffectsofbrimonidineonisolatedrabbitirisdilatormuscles AT ishikawah preandpostsynapticeffectsofbrimonidineonisolatedrabbitirisdilatormuscles AT shimizuk preandpostsynapticeffectsofbrimonidineonisolatedrabbitirisdilatormuscles AT mashimok preandpostsynapticeffectsofbrimonidineonisolatedrabbitirisdilatormuscles
_version_	1718403659192074240

Pre- and postsynaptic effects of brimonidine on isolated rabbit iris dilator muscles

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