Nettle toxin

Histamine possesses hormone activity in animals (E 3.1) and acts as a neurotransmitter (E 3.2). It is a plant feeding deterrent present, for instance, in nettle toxin (E 5.5.3). Also the alkaloid pilocarpine has strong physiological activity in vertebrates and deters potential predators (E 5.5.3). It is used as a cholinergic drug in medicine (F 2). Urocanic acid, hydantoin propionic acid, imidazoleacetic acid riboside, 1-methylhistidine, 1-methylimidazoleacetic acid and other imidazole derivatives are involved in the removal of L-histidine and histamine residues from the organism of animals. They are found in the urine. Urocanic acid is also a constituent of sweat (E 1). It is involved in the protection of skin to UV radiation (E 2.2). 

Serotonin acts as neurotransmitter in the brain of animals (E 3.2). It is, however, also of importance as a hormone for the maintenance of normal gut mobility in the gastro-intestinal tract (E 3.1). Serotonin accumulates in the trichomal fluid of the stinging nettle (Urtica dioica) which is injected into the body of animals breaking the hairs during predation of even touching. In addition to the other constituents of the nettle toxin, e.g., acetylcholine and histamine, it provides protection against predation (E 5.5.3). 5-Hydroxy-L-tryptophan and serotonin accumulate in the seeds and fruits of several plant species, e.g., bananas, pineapples, tomatoes and walnuts. At least in walnut seeds serotonin serves in the detoxication of ammonia during maturation and abscission of the fruits (E 2.2). 

Watrous, J., and K. Thompson Chrysaora quinquecirrha (Sea Nettle) Toxin A Comparison Between a Commercial and Our Own Preparation. Toxicon 19, 319 (1981). 

Allergenic plants causing skin eruption by contact include poison ivy (Rhus radicans L.), poison oak (Rhus toxicodendron L.), poison sumac (Rhus vernix L.), and stinging nettle (Urtica dioica L.). In the United States, poison ivy and poison oak cause nearly 2 million cases of skin poisoning and skin irritation annually, for a loss of 333,000 working days. In addition, these weeds cause 3.7 million days of restricted activity among those people who are susceptible to the toxins (1). 

We first met nettle stings on p. 253, where methanoic ( formic ) acid was identified as the active toxin causing the pain. Like its... 

Fu, H.Y., S.J. Chen, R.F. Chen, et al. 2006. Identification of oxalic acid and tartaric acid as major persistent pain-inducing toxins in the stinging hairs of the nettle, Urtica thunbergiana. Ann. Bot. 98(l) 57-65. 

Kelman, S.N., G.J. Calton, and J.W. Burnett Isolation and Partial Characterization of a Lethal Sea Nettle (Chrysaora quinquecirrha) Mesenteric Toxin. Toxicon 22,139 (1984). 

Warnick, J.E., D. Weinreich, and J.W. Burnett Sea Nettle (Chrysaora quinquecirrha) Toxin on Electrogenic and Chemosensitive Properties of Nerve and Muscle. Toxicon 19, 361 (1981). 

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