1. Factors Affecting N-Nitrosodimethylamine Development in Germinated Barley
James Haley, Godfrey H. Palmer. J. Sci. Food Agric. 1985, 36, 471-479
Kilned malt (germinated barley) is the primary source of the low levels of volatile nitrosamines which have been found in some alcoholic drinks and beverages. Recent research has shown that appropriate levels of sulphur dioxide in the drying air during kilning effectively reduced the N-nitrosodimethylamine (NDMA) content of commercially prepared malts. The chemical mechanisms which increase or reduce the levels of volatile nitrosamines in malt are not properly understood but it has been proposed that NDMA in malt is derived from the chemical reaction between hordenine (which is found in relatively large quantities in germinated barley) and nitrogen oxides formed as a by-product of fuel combustion in the drying Since chemical nitrosation of amines in vitro is likely to show qualitative as well as quantitative differences from the nitrosation processes which occur during grain kilning, work was carried out to compare hordenine degradation and NDMA development in the presence or absence of sulphur compounds (such as sulphur dioxide and metabisulphite) during kilning of the malted grain and in model studies. In particular, the behaviour of phenolase enzymes, phenolic compounds other than hordenine and amino acids was investigated along with an assessment of the importance of the physical location of reacting species within the germinating barley grain.
2. Hordenine Content of the Marine Alga Mastocaqms stellatus and the Algal Food Product Carrageen Product Carrageen
C. J. Barwell, C. A. Canham, M. D. Guiry. PHYTOTHERAPY RESEARCH, VOL. 3, NO. 2, 1989
Mastocarpus stellatus from locations in England and Ireland has been shown to contain hordenine (N,N-dimethyltyramine), which does not occur in C. crispus (Barwell and Blunden, 1981). Hordenine is not deaminated by the A form of monoamine oxidase (monoamine: O2 oxidoreductase,deaminating) EC 220.127.116.11 (Barwell et al., 1988) which constitutes more than 90% of the monoamine oxidase activity of mammalian small intestine epithelium (Barwell and Canham, 1988). In addition, it has been shown to inhibit the uptake of the neurotransmitter noradrena- line, into sympathetic nerves (Barwell et al., 1986a).
Therefore, dietary hordenine would probably be absorbed and may exert an adverse pharmacological action, similar to that of tyramine (Youdim, 1977). In this study the seasonal hordenine content of M. stellatus, from an algal collection site in Ireland, together with the hordenine content of commercially produced Carrageen were investigated.
3. Hordenine : pharmacology, pharmacokinetics and behavioural effects in the horse
M. FRANK, T. J. WECKMAN, T. WOOD, W. E. WOODS, CHEN L. TAI, SHIH-LING CHANG, A. EWING*. Equine vet. J. (1991) 22 (6) 437-441
HORDENINE, (p-hydroxy-N,N-dimethylphenethylamine), is an alkaloid found in many plants, particularly sprouting barley (Smith 1977), and is probably present therefore at low levels in most equine diets. It has been reported in post race equine urine in England, Australia, Canada and, more recently, Kentucky.
Whether or not hordenine should be classified as a natural constituent of feedstuffs or an illegal medication is unclear. In England, it is considered part of normal feeding, and disciplinary action has not been taken when identified in equine urine. In Canada, on the other hand, it is a prohibited drug and, therefore, a prohibited medication. In Australia, the Racing Stewards have taken no action on reported positive cases, presumably because of the possibility that the drug arose from horse feed, and not from an attempt to administer an illegal drug. While the current work was in progress, the Canadian authorities have noted the possible source of hordenine in animal feed and not penalised trainers after its identification in post race samples (Beaumier 1984).
4. Deamination of hordenine by monoamine oxidase and its action on vasa deferentia of the rat
C. J. BARWELL, A. N. BASMA, M.A.K. LAFI*. J. Pharm. Pharmacol. 1989,41: 421-423
Tyramine and N,N-dimethyltyramine (hordenine) occur natur-ally. Tyramine is commonly present in cheeses, fish products and wines (Youdim 1977) and plants (Wheaton & Stewart 1970). Hordenine occurs in barley, some cacti and citrus fruit (Wheaton &Stewart 1970) and at relatively high levels, of 1-5 mg g-1, in the marine alga Mastocarpus stellatus, which is incorporated into the food product carrageen (Barwell & Blunden 1981). Tyramine is a substrate for both the A and B forms of monoamine oxidase (MAO) (amine:oxygen oxidoreductase (deaminating) (flavin- containing) EC 1.4. 3.4) (Kinemuchi et al 1984) and normally, dietary-tyramine is deaminated in the intestinal epithelium by MAO, which is predominantly MAO-A (Barwell & Canham 1988). Irreversible inhibitors of MAO-A eliminate this physiological barrier so that dietary-tyramine is absorbed and may induce hypertension, by virtue of its pharmacological action as an indirectly acting sympathomimetic amine (Patil et al 1967).
Hordenine has been shown to be deaminated by hepatic MA0 (Alles & Heegaard 1943) but it is not clear whether it is a substrate for both the A and B or only one form of the enzyme. There is apparently no reported study of its pharmacological activity. We have investigated the selectivity of hordenine, as a substrate, for MAO-A and MAO-B and its action upon the isolated vas deferens of the rat.