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K. Yamaji, T. Yoshitomi, S. Usui; Effects of Peptides on Monkey Iris Sphincter and Dilator Muscles . Invest. Ophthalmol. Vis. Sci. 2004;45(13):414.
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Purpose: Biologically active peptides modulate miosis and mydriasis in many non–primate mammals. Because little is known of their actions on primate iridial smooth muscles, we examined the action of seven different peptides on iris sphincter and dilator muscles of rhesus monkey. Methods: Iris sphincter and dilator muscle preparations from rhesus monkeys were mounted in an organ bath, and tension changes were recorded by an isometric transducer. Electric field stimulation (100 Hz, 0.3 msec, 10V) was applied through a pair of platinum plate electrodes. Results: Monkey iris sphincter and dilator muscles produced simple cholinergic and adrenergic excitatory responses respectively to electric field stimulation. They did not produce the inhibitory response. Substance P (SP) mediated contractions, present in rabbit iris sphincter muscles in response to strong field stimulation, did not occur in monkey iris sphincter muscle. Exogenously applied SP, calcitonin gene–related peptide (CGRP), vasoactive intestinal polypeptide (VIP) and galanin also had no effect on monkey iris sphincter. However, pituitary adenylate cyclase–activating peptide significantly enhanced the iris sphincter muscle response to field stimulation by 25.8%, while neuropeptide Y and somatostatin attenuated it by 37.7% and 14.5% respectively. In contrast to field stimulation, these three peptides did not affect the iris sphincter contractions induced by acetylcholine (0.1 mM). None of the seven peptides had an effect on monkey iris dilator muscle. Conclusions: Each of the peptides in this study can induce miosis or mydriasis in non–primate mammals. However, SP, CGRP, VIP and galanin had no effects on the sphincter or dilator muscles from rhesus eyes. The innervation of primate irides may be relatively simple compared to non–primates. Future studies will be expected on the functional significance of species differences in iridial innervation.
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