The pharmacological actions of 5-hydroxytryptamine,FMRF-amide and substance P and their possible occurrence in the heart of the snail Helix aspersa L. |
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| Authors: | Paul J. Boyd Neville N. Osborne Robert J. Walker |
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| Affiliation: | 1. Department of Neurophysiology, School of Biochemical and Physiological Sciences, University Southampton, Southampton SO9 3TU, U.K.;2. Nuffield Laboratory of Ophthalmology, University of Oxford, Walton Street, Oxford OX2 6AW, U.K. |
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| Abstract: | The actions of 5-hydroxytryptamine (5-HT), FMRF-amide and substance P were tested on the isolated heart of Helix aspersa. All three compounds were found to produce positive inotropic and chronotropic effects, the order of potency being 5-HT > substance P > FMRF-amide. However, whereas the responses to 5-HT and FMRF-amide were maximal within a few seconds, the response to substance P had a longer latency. Two other similar undecapeptides, eledoisin and physalaemin, were also tested and were found to have very similar actions to those of substance P. The effects of 5-HT and FMRF-amide could be separated using the 5-HT blockers methysergide and ketanserin, which had relatively little effect on the response to FMRF-amide.Immunohistochemical staining was carried out on sections through the Helix auricle and ventricle for 5-HT, FMRF-amide and substance P. Substantial 5-HT-like and substance P-like immunoreactivity was observed, apparently concentrated in nerve endings, but the level of FMRF-amide-like immunoreactivity was considerably lower. The fluorescence produced by all three compounds was evenly distributed throughout the heart tissue. HPLC analysis of heart tissue extract demonstrated a high level of 5-HT (about 8 μg/g wet weight) but a negligible catecholamine content. |
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| Keywords: | To whom correspondence should be addressed |
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