Short- and long-term effects of glycyrrhizic acid in repetitive stress

1. This study was carried out to determine the effect of shortterm and long -term ingestion of glycyrrhizic acid on the response to 2 h of restraint st ress by measuring locomotor activity and plasma corticosterone levels, 2, Male Sprague-Dawley rats were randomly assigned into four groups, each g roup having eight rats. Group 1 (control) was given ordinary tap water, whi le groups 2 (short term), 3 and 1 (both long term) were given tap water con taining 1 mg/mL glycyrrhizic acid to drink for 10 days, 4 weeks and 9 weeks , respectively. All the rats were subjected to 2 h of restraint stress and the locomotor activity assessed using an activity test in an open field are na followed by blood sampling to determine the plasma corticosterone level. These procedures were repeated daily for 14 days, 3. The basal locomotor activity scores for rats given glycyrrhizic acid for 10 days or 4 weeks were similar to those of controls; however, that of the rats treated long term with glycyrrhizic acid was significantly lower (21. 0+/-3.0 squares crossed; P < 0.0005), Following the first period of restrai nt stress there was a highly significant decrease in locomotor activity, wh ich remained significantly lower until the seventh and subsequent periods, indicating an adaptation to the repeated stress had occurred, Although the decrease in locomotor activity was partially blocked and adaptation to repe titive stress was enhanced in the rats given glycyrrhizic acid for 10 days, this was not seen in rats treated with glycyrrhizic acid for 3 or 9 weeks, The corticosterone levels in control rats were significantly elevated for 4-5 days following the exposure to repetitive stress but decreased graduall y from day 7 onwards. However, both short- and long-term glycyrrhizic acid- treated rats had higher plasma corticosterone levels than the controls (P < 0.05), 4, In conclusion, repetitive restraint stress caused decreased locomotor ac tivity associated with increased plasma corticosterone levels, both of whic h, in normal rats, decreased with adaptation to stress. The stress response was partially blocked and adaptation enhanced in rats given glycyrrhizic a cid for 10 days, but not in rats given glycyrrhizic acid for 4 and 9 weeks. Glycyrrhizic acid ingestion caused high plasma corticosterone.