THE EFFECT OF SEROTONIN AND RELATED COMPOUNDS ON THE CARBOHYDRATE METABOLISM OF THE LIVER FLUKE, FASCIOLA HEPATICA

¹ Department of Pharmacology, Louisiana State University, School of Medicine, New Orleans, Louisiana

The major products of carbohydrate metabolism of the liver fluke are volatile fatty acids (propionic and acetic acids in an approximate ratio of 3:1), while only 4 to 9% of the utilized carbohydrate is converted to lactic acid. Stimulation of parasite movement under anaerobic conditions by low concentrations of serotonin or of LSD results in an increase in glucose uptake, glycogen breakdown and a 2- to 10-fold increase in lactic acid production, while there is little or no change in the production of volatile fatty acids. Bromolysergic acid diethylamide, a compound which blocks the stimulant effect of serotonin on motility, also antagonized the stimulatory effect on lactic acid production and antagonized only partially the increase in glucose uptake by these organisms. Epinephrine does not exert a significant effect on the carbohydrate metabolism of the liver fluke. It is postulated that in these parasites, lactic acid fermentation can meet increased energy requirements more efficiently than fatty acid fermentation. The possible role of serotonin on the carbohydrate metabolism of these organisms is discussed.

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