Injected monosodium glutamate increases holotryptophan pyrrolase activity and plasma corticosterone levels more in male than female rats

Monosodium glutamate [MSG] injected intra - peritoneally at doses 4 g/kg increased holotryptophan pyrrolase activity significantly by 61.6% in male rats. The increases were smaller [24%] and non- significant in females. Apotryptophan was decreased by 61% and comparably in the two sexes. Cumulative effect on total enzyme activity was a reduction of 37.5% in female rats. A decrease of 20.6% in male rats was not significant. Plasma levels of corticosterone were increased significantly in male but not in female rats. The sex differences are explained in terms of female hormones being effected by MSG administration and higher circulating MSG - induced corticosterone levels being involved in the enhancement of holotryptophan pyrrolase activity in male rats. Plasma total tryptophan levels were increased due to an inhibition of total tryptophan pyrrolase activity in female but not in male. Plasma free tryptophan concentrations were decreased in both sexes

Lack of sodium salicylate-induced enhancement of hepatic tryptophan pyrrolase in 5 day salicylate injected rats

Single administration of sodium salicylate at doses of 400 mg/kg increased hepatic holo-tryptophan pyrrolase activity but did not produce any effect an apotryptophan pyrrolase activity in rats. Repeated administration of the drug at doses of 100 mg/kg did not alter holo-enzyme activity but decreased apo and total enzyme activity in rats killed 24 hours later. Administration of 400 mg/kg sodium salicylate to 5 day, 100 mg/kg sodium salicylate injected rats did not increase holo or apo-tryptophan pyrrolase activity. Possible role of tryptophan pyrrolase in the sodium- salicylate induced changes of brain serotonin metabolism is discussed