Amniotic fluid elicits appetitive responses in human newborns: fatty acids and appetitive responses.

In humans, maternal cues guide newborns to the maternal breast, and transitional cues may be present in maternal-fetal fluids. The aim of the present study was to determine the consistent presence of sensorial cues in three maternal-fetal fluids--amniotic fluid, colostrum, and milk--and test the ability of these cues to produce appetitive responses in newborns. In the analytical study, gas chromatography-mass spectrometry (GC-MS) detected eight fatty acids consistently present in the amniotic fluid, colostrum, and milk from 12 healthy volunteers, but we do not find a mammalian pheromone, identified in another mammalian species (rabbits), in another 30 volunteers. In the behavioral study, we explored the ability of amniotic fluid or its fatty acids to produce appetitive responses in 19 human newborns <24 hr after birth. Exposure to swabs impregnated with amniotic fluid or an artificial fatty acid mixture produced a longer duration of facial reactions that suggested appetitive (sucking) movements compared with respective vehicles (i.e., propylene glycol or centrifuged amniotic fluid with a low fatty acid content verified by GC-MS). We conclude that the fatty acids contained in amniotic fluid may constitute a transitional sensorial cue that guides newborns to the maternal breast.

Anxiolytic-like effects of human amniotic fluid and its fatty acids in Wistar rats.

Odors from amniotic fluid produce signs of calmness in mammals suggesting some anxiolytic-like properties. Experimental models, such as the defensive burying, elevated plus maze, and open field tests offer well-controlled approaches to the study of putative anxiolytic substances using rats. Using gas chromatography-mass spectrometry, we first identified eight fatty acids (lauric, myristic, palmitic, palmitoleic, stearic, oleic, elaidic, and linoleic acids) as consistently present in human amniotic fluid. We then used the defensive burying and elevated plus maze tests to compare the action of diazepam (2 mg/kg), fresh amniotic fluid, and a mixture of its fatty acids with two vehicles (i.e. propylene glycol and centrifuged amniotic fluid with a low fatty acid content). No significant differences in estradiol or progesterone content were found between fresh amniotic fluid and centrifuged amniotic fluid using the microparticle enzyme immunoassay. Compared with the vehicle, diazepam, fresh amniotic fluid, and the fatty acid mixture increased burying latency, reduced cumulative burying, and increased the time spent in the open arms of the elevated plus maze in both sexes without altering general locomotor activity. We conclude that the fatty acids contained in human amniotic fluid exert anxiolytic-like effects, with minimal or no participation of female gonadal steroids.