Deamination of hordenine by monoamine oxidase and its action on vasa deferentia of the rat

Abstract

The selectivity of the naturally occurring amine, N,N-dimethyltyramine (hordenine) for monoamine oxidase (MAO) and its action upon isolated vasa deferentia of the rat was investigated. Hordenine was deaminated by rat liver MAO with a Michaelis constant of 479 microM and maximum velocity of 128 nmol (mg protein)-1 h-1 compared with 144 microM and 482 nmol (mg protein)-1 h-1 for tyramine. Studies, with selective irreversible inhibitors of MAO, showed that hordenine was a highly selective substrate for MAO-B of liver and that it was not deaminated by the MAO-A of intestinal epithelium. In contrast to tyramine, hordenine did not produce contractions of isolated vasa deferentia. However, 25 microM hordenine potentiated contractile responses of vasa, from control animals, to submaximal doses of noradrenaline and inhibited responses to tyramine. It did not alter responses, to noradrenaline, of vasa denervated by chronic pretreatment of rats with guanethidine. Therefore, it appears that hordenine acted as an inhibitor of noradrenaline uptake, in isolated vasa deferentia. These results indicate that dietary-hordenine is unlikely to be deaminated by intestinal MAO as this is predominantly MAO-A. Consequently, it is likely to be absorbed and could affect the sympathetic nervous system, by virtue of its action as an inhibitor of noradrenaline uptake.

Label-free target identification using in-gel fluorescence difference via thermal stability shift

“…4a), is an alkaloid found in several plants, particularly sprouting barley. 17 Hordenine has several bioactivities such as the stimulation of gastrin release in rats, 18 the inhibition of norepinephrine uptake in isolated vasa deferentia, 19 and the increases in respiratory and heart rates when intravenously injected into horses. 20 From screening of small-molecule libraries to identify compounds affecting in vitro protein translation, hordenine was found to increase the translation of the luciferase reporter gene (Fig.…”

Changes in the Functional Components of Barley Produced from Different Cultivars and Germination Periods

“…It has been shown that hordenine is biosynthesized by the stepwise N ‐methylation of tyramine, which is first converted to N ‐methyltyramine and then further methylated to hordenine (Lovett et al 1994). It has been reported to exert various effects, including the inhibition of monoamine oxidase (Barwell et al 1989), as well as antibacterial and antibiotic properties (Rao 1970). Recently, Kim et al (2013) conducted a study to inhibit melanogenesis in human melanocytes.…”

Hordenine content of the marine alga Mastocarpus stellatus and the algal food product Carrageen

“…However, its low rate of metabolism and hence inactivation by both microsomal N-demethylation (Barwell et a[., 1986b) and deamination by monoamine oxidase (Barwell et al, 1988) suggest it would be absorbed from the intestine and reach the nervous system. Because of its action as a noradrenalineuptake blocker (Barwell et al, 1986a) it may be expected to act adversely if ingested either alone or in combination with drugs which modify the action of noradrenergic neurones.…”

“…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).…”