Histochemical studies on enzymatic activities of the human placenta
It has been established that the placenta is a large complex structure, engages in intricate biologic process and becomes senescent in a short period. It has many activities which are in part comparable to those of the gastrointestinal, respiratory, circulatory and urinary tracts. It is and active biochemical laboratory in which endocrine substance and enzymes are produced.
A number of histochemical observations have been made which shed light on certain aspects of the metabolism of the human placenta. Among these are observations on the phosphatase activities of the trophoblast; the relations between material
transport and the trophoblast; those between blood supply and enzymes; and carbohydrates and protein metabolism of the placental tissues.
However, it is known that some of the interpretations of histochemical results differ from one to another researcher.
The purpose of this study is to describe some histochemical observations on normal human placentae obtained from artificial abortions and normal deliveries, and to present interpretations of the possible functional significance of these reactions. The placentae were investigated by a variety of histochemical procedures and reactions which include observations on the occurrence and distribution of the enzymatic activities of acid phosphatase, alkaline phosphatase, adenosine diphosphatase adenosine triphosphatase, succinic dehydrogenase and glycogen, and ribonucleic acid.
Materials and Methods
The human material in this study consists of one hundred and thirty-nine well preserved placentae rangign in gestational age from 4 weeks up to term. The fresh placental tissues were obtained from artificial abortions and normal deliveries.
The pieces of the placenta were fixed or frozen immediately after removal, sectioned at 10 to 15 microns and treated according to the following methods.
The Gomori's modified method(Eranko, 1952) for acid phosphatase, the Gomori's calcium cobalt sulfide technic (Barka and Andenson, 1963) for alkaline phosphatase, the Wachstein and Meisel method(1957) for adenosine diphosphatase and adenosine triphosphatase, and the method recommended by Nachlas and his coworkers(1957) for succinic dehydrogenase were respectively applied in this study. Some piece of the placenta were fixed in cold Rossman fluid and stained by Rosa method91950) for nucleic acids.
Beside these, for contrast of enzymes, glycogen and ribonucleic acid the incubation method without substrates, and the malt diastase-digestion method were respectively used.
Summary and Conclusions
The present study concerns the enzyme activities, the glycogen and nucleic acid of the normal human placenta, with special reference to the plecental trophoblast, the villous vessels, villous stromal cells, and the decidual cells, Certain of our
findings may be summarized as follows:
1. Acid phosphatase activity: In the human plecental syncytio-trophoblast, the acid phosphatase occurred in an abundance at the first trimester(4th to 12th week) and second trimester.(13th to 28th week) and thereafter the content decreased slowly until term. In the stromal cells and decidual cells the phosphatase activity was present in slight degrees.
2. Alkaline phosphatase activity: During the first of the second trimester it tis scarce in the syncytio-trophoblast. But thereafter the activities gradually increased until term. The enzyme activity of blood vessels, stromal cells and decidual cells generally became scarce.
3. Adenosine diphosphatase and adenosine triphophatase activities; In the first trimester and a first half of the second trimester, a small amount of ADp-ase and ATP-ase appeared in the placental syncytio-trophoblast. Thereafter the enzymatic activities gradually increased towards the very end of gestation. The enzyme activities of blood vessels were little.
4. Succinic dehydrogenase activity: Large amount of the enzyme began to appear in the trophoblast in the early weeks of pregnancy and remained constant until term. The enzymatic activity of the blood vessels was hardly observed in all of the
gestational ages, but enzyme activity of the stromal cells and decidual cells were scarce.
5. Glycogen distribution: PAS positivity of the syncytio-trophoblast was very intense during the first half of the second trimester. Thereafter the intensity gradually diminshed with advancing pregnancy. In the third trimester, however, PAS positive granule were found with difficulty in the syncytial cells. Those of the blood vessels, vilous stromal cells and decidual cells revealed generally variable pale distribution.
6. Ribonucleic acid distribution: A moderate amount of pyroninophilic substances in the trophoblast was present in the first trimester. From early in the second trimester it was very definitely decreased in the epithelium. Thereafter in the second and third trimester generally the pyroninophilic substances were scarce. From the latter half of the second trimester the decidual cells began to give a remarkable positive reaction and which continued until term.
It is suggested that the enzyme activities, the contents of the glycogen and the nucleic acid of the normal human placenta are correlated with various metabolic changes of the placentae during gestation.