This histamine-like effects of Phallusia nigra extract: evidences for direct activity at H1 receptors

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Costa, L.V. and Malpezzi, E.L.A. and Berlinck, R.G.S. and Rowan, E.G. and deFreitas, J.C. (1997) This histamine-like effects of Phallusia nigra extract: evidences for direct activity at H1 receptors. Comparative biochemistry and physiology. Part C, Pharmacology, toxicology & endocrinology, 117 (1). pp. 111-115. ISSN 1367-8280 (http://dx.doi.org/10.1016/S0742-8413(96)00228-9)

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Abstract

The methanol extract (mol. wt lower than 3,000 Da) of the sea squirt Phallusia nigra has stimulatory activity on guinea-pig ileum preparations. This effect was inhibited by cyproheptadine and mepyramine, but not by atropine. Mepyramine antagonized competitively the extract activity with a pA2 of 10.09 ± 1.12, suggesting a direct activity on H1 histamine receptors. The extract was also assayed on guinea-pig right atria, however, only a mild increase in spontaneous contractions was observed compared to histamine, showing that the extract was a rather poor activator of cardiac H2 receptors. Histamine was not detected upon TLC analysis of the extract by comparison with an authentic standard.

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