Plasma free tryptophan variation during oestrous cycle of the rat

The concentration of plasma free tryptophan was shown to undergo a regular and statistically significant fluctuation through the four phases of the oestrous cycle of the rat. The highest concentration of plasma free tryptophan was observed during oestrus. During metoestrus the concentration of plasma free tryptophan decreased by 25% to the lowest observed level; thereafter it gradually increased during dioestrus and pro-oestrus. The concentration of plasma total tryptophan was found to be unchanged during the oestrous cycle of the rat.