Tyrosine availability and brain noradrenaline synthesis in the fetus: control by maternal tyrosine ingestion.

In spite of substantial evidence that tyrosine availability modulates catecholamine synthesis, under a variety of conditions, in adult brains, its possible influence during brain development has received little attention. In the present paper, the effect of tyrosine when administered to pregnant rats on tyrosine and noradrenaline brain levels in the fetus was investigated. In the first experiment noradrenaline (NA) was detected in the fetal brain by day 13 of development. NA levels increased from days 13 to 19. Administration of tyrosine to the mother raises both tyrosine and NA levels in the fetal brain. The increase in tyrosine was similar on days 13, 15, 17 and 19 of pregnancy. However, the increase of NA was more pronounced on days 17 and 19 than on days 13 or 15. Tyrosine and NA enhancement was detected 30 min after tyrosine administration, persisted for at least 2 h and disappeared completely 6 h after its administration. Both tyrosine and NA increase are tyrosine dose-related. The present studies suggest that there are no important barriers for tyrosine transport between the maternal blood and the fetal brain. Furthermore, during prenatal life the rate of NA synthesis is regulated by tyrosine brain concentration and therefore maternal intake of tyrosine is an important factor for noradrenaline synthesis regulation in the fetal brain. The possible functional significance of noradrenaline brain increase after tyrosine administration are unknown. However, the NA modification could be the cause of the persistent behavioral modification that we have found in adult rats whose mothers were treated with tyrosine during pregnancy.