The effects of bitterweed (Hymenoxys odorata) on ovine carbohydrate metabolism

Abstract

The effects of bitterweed (Hymenoxys odorata) were studied on some aspects of carbohydrate metabolism in sheep. The integrity of the Embden-Meyerhof pathway was evaluated by measuring rates of glucose metabolism by red cells and blood levels of ketone bodies. Red cells were taken from sheep before and after acute intoxication with bitterweed. A comparison was made as to their in vitro ability to utilize glucose and produce the end product lactate. No differences were detected before and after the intoxications. When glucose utilization through the Embden-Meyerhof pathway is severly inhibited in body tissues, ketone levels will rise. Ovine blood concentrations of the ketones acetoacetate and D-3-hydroxybutyrate were measured before and after bitterweed intoxication. No significant differences in the blood concentrations were detected. From these experiments it does not appear that bitterweeds' mechanism of toxicity involves inhibition of carbohydrate metabolism through the Embden-Meyerhof pathway. Hymenoxon, a sesquiterpene lactone, is a major toxicant in bitterweed. It's conjugation to reduced glutathione is an important method of detoxification. Reduced glutathione levels are maintained through the activity of the pentose phosphate pathway. The pathway's ability to metabolize glucose was measured in vitro in red cells taken from sheep. No significant differences were seen before and after the sheep received bitterweed. A further test of the capacity of the pathway to replenish levels of reduced glutathione was made by introducing an oxidant challenge to glutathione in the form of ascorbate. Red cells from sheep before and after bitterweed intoxication responded to the ascorbate with a ten fold increase in glucose utilization through the pentose phosphate pathway as evidenced by carbon dioxide formation. There were no significant differences as a result of the intoxication. Bitterweed does not inhibit the cells' ability to maintain levels of reduce glutathione.