RESUMEN
BACKGROUND: The post-partum blues is a transient mood alteration affecting most women a few days after delivery. Its stereotypic pattern of symptoms and time course, peaking on post-partum day 3-5, is suggestive of biological determinants superimposed on psycho-social factors. This study was designed to evaluate the possible role of the serotonin system during this period through assessment of brain tryptophan availability. METHODS: Blood samples from 50 women were collected just before (D0) and 3 days after (D3) delivery. Based on plasma concentration of tryptophan, amino acids competing with tryptophan for transport across the blood-brain barrier and on their respective affinities for this transporter, a brain tryptophan availability index (BTAI) was calculated and its variation correlated with the intensity of post-partum blues evaluated through the Kennerley and Gath score at D3. RESULTS: The BTAI showed a -15% decrease between D0 and D3 (p < 0.01, paired t-test). This decrease was not supported by a drop in plasma tryptophan since its level rather increased (+19%). There was no evidence for change in placental indoleamine-2,3-dioxygenase activity since the variation in plasma l-kynurenine (+12%) paralleled the change in tryptophan level. The decreased BTAI appeared the consequence of a dramatic increase in plasma levels of most amino acids, particularly the competitor aminoacids leucine, isoleucine, valine and tyrosine, during the early post-partum. This decrease in brain tryptophan availability was concomitant to the post-partum blues, whose intensity significantly correlated with the amplitude of BTAI variation (Pearson's coefficient -0.283, p < 0.05). CONCLUSION: This study suggests that generalized, large amplitude metabolic and/or nutritional changes occurring in the early post-partum result in a transient decrease in brain tryptophan availability, partly accounting for the mood alteration referred to as the post-partum blues, a model for the triggering of puerperal mood disorder in vulnerable women.