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Takeshi Yoshitomi, Kazutsuna Yamaji, Hitoshi Ishikawa, Yoshitaka Ohnishi; Effect of Pituitary Adenylate Cyclase–Activating Peptide on Isolated Rabbit Iris Sphincter and Dilator Muscles. Invest. Ophthalmol. Vis. Sci. 2002;43(3):780-783.
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purpose. Pituitary adenylate cyclase–activating peptide (PACAP) is a sensory
neuropeptide in the eye that is released by noxious stimuli and
considered to be a mediator of the neurogenic ocular injury response,
including miosis. The purpose of this study was to clarify the
functional role of PACAP in iris sphincter and dilator muscles.
methods. Iris sphincter and dilator muscles were isolated from rabbit eyes, and
the effect of PACAP on mechanical responses of these muscles using
isometric tension-recording methods was investigated.
results. The iris sphincter responded to electric field stimulation with
contractions composed of fast twitch and subsequent slow components.
Both PACAP 27 and PACAP 38 enhanced the twitch response, but neither
had an effect on the slow response. The effect of both PACAPs on the
twitch response was dose dependent. Neither PACAP had an effect on the
amplitude of contraction evoked by exogenously applied Ach. For the
iris dilator muscle, PACAP 27 inhibited the contractions induced by
field stimulation or phenylephrine, whereas PACAP 38 had no effect.
conclusions. Both PACAP 27 and PACAP 38 enhance cholinergic transmission in
sphincter muscle. The PACAP 27 induces relaxation of the dilator muscle
by a direct effect on the muscle itself. The PACAP released during an
ocular inflammatory response may induce miosis by the enhancement of
cholinergic stimulation of the iris sphincter and by direct relaxation
of the dilator muscles.
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