OBSERVATIONS ON THE ORIGIN OF AMNIOTIC FLUID ENZYMES

Summary

An enquiry has been made into the origins of a group of amniotic fluid enzymes which have complex specific activity patterns during gestation. Between 13 and 18 weeks of gestation, the specific activities of hexosaminidase, α-l, 4-glucosidase, and the placental and heat-labile alkaline phosphatases in amniotic fluid were in excess of those expected on the hypothesis of a serum origin. In contrast, a significant fraction of the acid phosphatase activity during this period could be attributed to its influx from maternal serum. In amniotic fluid at term, hexosaminidase, heat-labile alkaline phosphatase and acid phosphatase appeared to originate from the surrounding tissues, although fetal urine was found to be an additional source of acid phosphatase. The placental alkaline phosphatase in amniotic fluid at term had a mean specific activity which was the closest to that expected on the hypothesis of a serum origin. It is probable that tissue protein is released into the amniotic fluid at term, and possibly also between 13 and 18 weeks of gestation. The methods used to draw these conclusions may be of general use for examining the origins of individual proteins in amniotic fluid.