백서태자사망후(白鼠胎仔死亡後)의 태반변화

Abstract

[한글]

Placental Changes Following Fetal Death in Rats

Hyung Jin Chung

Directed by Professor Dong Sik Kim, M.D., Assoc. Prof. Yoo Bock Lee, M.D.

Department of Pathology Yonsei University College of Medicine, Seoul, Korea

Introduction

Retained secundin either following abortion or full-term pregnancy is rather

commonly observed by clinicians, and the retained placental tissue may cause

serious complications. But the studies on the fate of retained placenta are

fragmentary and no serial studies on the sequence of events might be taken place in

the placenta by the death of fetus are available.

Brews(1939), Kline(1951), Motta(1951) and Novak(1953) reported that trophoblastic

activities will recede rapidly as soon as the fetal death takes place. Russell et

al. (1957) found that urinary excretion of progesterone and estriol dropped

abruptly following the intrauterine fetal death, and the placenta underwent

infarction, although the dead fetus retained for several weeks in the uterus.

Hertig(1935) stated that cessation of fetal circulation with continuous maternal

blood flow into the placenta will cause hydropic degeneration of chorionic villi

and continuous survival of trophoblasts, and this condition may eventually lead to

the development of hydatidiform mole and possibly choriocarcinoma. But fortunately

the majority of the cases will terminate in the stage of potential mole and only a

few, one in two thousands of pregnancy, will result into true mold formation.

Anatomy and histochemistry of the normal full-term placenta of rats have been

described by Duval (1891), Jenkinson (1902) and Bridgeman (1948). However,

histologic and histochemical changes in the placenta following the fetal death

during the pregnancy have not been thoroughly investigated up to now. Therefore,

the author undertook to investigate histological and histochemical changes which

might take place following the death of fetuses during the pregnancy, with special

attention on the changes of trophoblasts.

Materials and Methods

A total of 112 female virgin albino rats, around 200 gms., were used for the

experiments. Out of them, 10 rats were used for preliminary experiments to

determine estrus cycle, to achieve successful mating, and to determine the duration

of normal pregnancy.

Remaining 102 rats were divided into 3 groups and treated as follows. Group Ⅰ of

30 rats were let proceed normal pregnancy as the control; group Ⅱ of 42 rats were

used as the group in which fetuses were killed at mid-term of pregnancy (14th day)

with electric coagulator (hyfrecator, Birtcher Co., U.S.A.); and the group Ⅲ of 30

rats were used as the group in which fetuses were surgically removed by cesarean

section at the late stage of pregnancy (18th day). Groups Ⅱ and Ⅲ were divided

again into two subgroups. Namely, the one in which all fetuses in unilateral

uterine horn were killed with continuation of pregnancy in remaining uterine horn,

and the another in which all fetuses of both uterine horns were killed or removed.

Estrus cycle was determined by vaginal smear methods of Papanicoloau (1933), and

mating was achieved by housing a male and female rat together at pre-estrus cycle

and rechecking for vaginal smear for the presence of spermatozoa. By this way, it

was found that average estrus cycle is 96 hours and the duration of normal

pregnancy is 21 days.

Specimens of the placenta were obtained by the removing of entire uterus of 3

rats at different intervals of pregnancy in each groups. In group Ⅰ, specimens

were obtained at the 5th, 7th, 9th, 11th, 13th, 15th, 17th, 19th, 20th and 21st

days of pregnancy; and in group Ⅱ at 15th, 17th, 19th, 21st, 23rd., 25th and 50th

days of pregnancy; and in group Ⅲ at 19th, 21st, 23rd, 25th and 50th days of

pregnancy. From the each removed uterus numbers of conceptuses, size of pregnant

segments, and the size of placenta were determined. Then, two sections, cross and

longitudinal, from each pregnant segments were taken and embeded into paraffin

after the fixation in 4% neutral formalin. Microsections were made in 5 to 6 μ.

thickness, and hematoxylin-eosin, periodic acid Schiff(PAS), methyl-green pyronin,

and Feulgen stainings were applied to each sections for histologic and

histochemical studies of the placenta.

Results and Summary

Stages of normal pregnancy were divided arbitrarily into early (1-10th day),

middle (11-17th day) and late (18-21st day) stages.

In early stage, formation of yolk sac, development of decidua and labyrinth were

noted, and in middle stage formation of junctional zone with further development of

labyrinth were main features, while in late stage further development of junctional

zone with formation on syncytial trophoblasts were prominent. In early stage, blood

supply to the labyrinth was dominated by maternal circulation, but as the pregnancy

proceeds fetal circulation became dominant, and at the same time erythrocytes in

fetal circulation changed from nucleated to non-nucleated red cells.

PAS positive materials (neutral mucopolysaccharides) began to appear at mid-stage

of pregnancy, particularly at Reichert's membrane, yolk sac, and junctional zone.

Methyl-green pyronin positive substances (RNA) appeared in relatively large amount

from the 9th day of pregnancy in the cells of yolk sac, labyrinth, junctional zone,

and decidua, and the amount decreased somewhat in late stage of pregnancy. Feulgen

staining gave similar results as to methyl-green pyronin staining, but the largest

amount of Feulgen positive materials was observed in the nuclei of syncytial

trophoblasts in junctional zone.

Fetal death in the middle-stage of pregnancy (14th day) brought various

degenerative changes in the yolk sa, Reichert's membrane, labyrinth, junctional

zone and decidua. The most significant changes were atrophy and collapse of fetal

circulation in the labyrinth, necrosis of yolk sac, cystic changes in the

junctional zone, and thrombosis at demarcation line between decidua and junctional

zone. As the time passes, the all elements of placental tissue underwent

coagulation necrosis, but the trophoblasts in the junctional zone and labyrinth

survived longer than any other elements. PAS positive materials deposited in

somewhat larger amount at the junctional zone in comparison with normal pregnancy

group, but somewhat diminished at the remaining part of the placenta. And the same

was true with methyl-green pyronin and Feulgen stainings.

Surgical removal of the fetuses in the late stage of pregnancy (18th day) also

brought the most prominent changes to the yolk sac and labyrinth, which resulted in

complete coagulation necrosis later. And the other changes as well as the results

of PAS, methyl-green pyronin and Feuigen stainings were similar to those seen in

group Ⅱ.

Regardless, either the fetuses were killed at middle stage or late stage of

pregnancy and fetuses in unilateral or bilateral uterine horn, the placenta

retained until the 21st day of pregnancy and some of them were spontaneously

evacuated during the 21st and 23rd days of pregnancy. The placentas which remained

longer period of time were totally necrotic.

Therefore, continuous survival of trophoblasts beyond normal pregnancy period,

pathologic proliferation of trophoblasts or mole formation could not be observed by

the method applied in this experiment, although frequently cystic changes were

observed in the junctional zone. The reason of prompt degeneration of placenta and

unsuccessful survival of trophoblasts is probably due to the fact that when the

fetus dies before full-term gestation thrombosis is taken place at demarcation

between decidua and junctional zone of placenta serving blood circulation from both

fetal and maternal side resulting in coagulation necrosis of the placenta.

[영문]

Introduction

Retained secundin either following abortion or full-term pregnancy is rather commonly observed by clinicians, and the retained placental tissue may cause serious complications. But the studies on the fate of retained placenta are fragmentary and no serial studies on the sequence of events might be taken place in the placenta by the death of fetus are available.

Brews(1939), Kline(1951), Motta(1951) and Novak(1953) reported that trophoblastic activities will recede rapidly as soon as the fetal death takes place. Russell et al. (1957) found that urinary excretion of progesterone and estriol dropped abruptly following the intrauterine fetal death, and the placenta underwent

infarction, although the dead fetus retained for several weeks in the uterus.

Hertig(1935) stated that cessation of fetal circulation with continuous maternal blood flow into the placenta will cause hydropic degeneration of chorionic villi and continuous survival of trophoblasts, and this condition may eventually lead to

the development of hydatidiform mole and possibly choriocarcinoma. But fortunately the majority of the cases will terminate in the stage of potential mole and only a few, one in two thousands of pregnancy, will result into true mold formation.

Anatomy and histochemistry of the normal full-term placenta of rats have been described by Duval (1891), Jenkinson (1902) and Bridgeman (1948). However, histologic and histochemical changes in the placenta following the fetal death during the pregnancy have not been thoroughly investigated up to now. Therefore,

the author undertook to investigate histological and histochemical changes which might take place following the death of fetuses during the pregnancy, with special attention on the changes of trophoblasts.

Materials and Methods

A total of 112 female virgin albino rats, around 200 gms., were used for the experiments. Out of them, 10 rats were used for preliminary experiments to determine estrus cycle, to achieve successful mating, and to determine the duration of normal pregnancy.

Remaining 102 rats were divided into 3 groups and treated as follows. Group Ⅰ of 30 rats were let proceed normal pregnancy as the control; group Ⅱ of 42 rats were used as the group in which fetuses were killed at mid-term of pregnancy (14th day)

with electric coagulator (hyfrecator, Birtcher Co., U.S.A.); and the group Ⅲ of 30 rats were used as the group in which fetuses were surgically removed by cesarean section at the late stage of pregnancy (18th day). Groups Ⅱ and Ⅲ were divided again into two subgroups. Namely, the one in which all fetuses in unilateral uterine horn were killed with continuation of pregnancy in remaining uterine horn, and the another in which all fetuses of both uterine horns were killed or removed.

Estrus cycle was determined by vaginal smear methods of Papanicoloau (1933), and mating was achieved by housing a male and female rat together at pre-estrus cycle and rechecking for vaginal smear for the presence of spermatozoa. By this way, it

was found that average estrus cycle is 96 hours and the duration of normal pregnancy is 21 days.

Specimens of the placenta were obtained by the removing of entire uterus of 3 rats at different intervals of pregnancy in each groups. In group Ⅰ, specimens were obtained at the 5th, 7th, 9th, 11th, 13th, 15th, 17th, 19th, 20th and 21st days of pregnancy; and in group Ⅱ at 15th, 17th, 19th, 21st, 23rd., 25th and 50th days of pregnancy; and in group Ⅲ at 19th, 21st, 23rd, 25th and 50th days of pregnancy. From the each removed uterus numbers of conceptuses, size of pregnant segments, and the size of placenta were determined. Then, two sections, cross and

longitudinal, from each pregnant segments were taken and embeded into paraffin after the fixation in 4% neutral formalin. Microsections were made in 5 to 6 μ. thickness, and hematoxylin-eosin, periodic acid Schiff(PAS), methyl-green pyronin, and Feulgen stainings were applied to each sections for histologic and histochemical studies of the placenta.

Results and Summary

Stages of normal pregnancy were divided arbitrarily into early (1-10th day), middle (11-17th day) and late (18-21st day) stages.

In early stage, formation of yolk sac, development of decidua and labyrinth were noted, and in middle stage formation of junctional zone with further development of labyrinth were main features, while in late stage further development of junctional

zone with formation on syncytial trophoblasts were prominent. In early stage, blood supply to the labyrinth was dominated by maternal circulation, but as the pregnancy proceeds fetal circulation became dominant, and at the same time erythrocytes in

fetal circulation changed from nucleated to non-nucleated red cells.

PAS positive materials (neutral mucopolysaccharides) began to appear at mid-stage of pregnancy, particularly at Reichert's membrane, yolk sac, and junctional zone.

Methyl-green pyronin positive substances (RNA) appeared in relatively large amount from the 9th day of pregnancy in the cells of yolk sac, labyrinth, junctional zone, and decidua, and the amount decreased somewhat in late stage of pregnancy. Feulgen

staining gave similar results as to methyl-green pyronin staining, but the largest amount of Feulgen positive materials was observed in the nuclei of syncytial trophoblasts in junctional zone.

Fetal death in the middle-stage of pregnancy (14th day) brought various degenerative changes in the yolk sa, Reichert's membrane, labyrinth, junctional zone and decidua. The most significant changes were atrophy and collapse of fetal circulation in the labyrinth, necrosis of yolk sac, cystic changes in the

junctional zone, and thrombosis at demarcation line between decidua and junctional zone. As the time passes, the all elements of placental tissue underwent coagulation necrosis, but the trophoblasts in the junctional zone and labyrinth survived longer than any other elements. PAS positive materials deposited in

somewhat larger amount at the junctional zone in comparison with normal pregnancy group, but somewhat diminished at the remaining part of the placenta. And the same was true with methyl-green pyronin and Feulgen stainings.

Surgical removal of the fetuses in the late stage of pregnancy (18th day) also brought the most prominent changes to the yolk sac and labyrinth, which resulted in complete coagulation necrosis later. And the other changes as well as the results

of PAS, methyl-green pyronin and Feuigen stainings were similar to those seen in group Ⅱ.

Regardless, either the fetuses were killed at middle stage or late stage of pregnancy and fetuses in unilateral or bilateral uterine horn, the placenta retained until the 21st day of pregnancy and some of them were spontaneously

evacuated during the 21st and 23rd days of pregnancy. The placentas which remained longer period of time were totally necrotic.

Therefore, continuous survival of trophoblasts beyond normal pregnancy period, pathologic proliferation of trophoblasts or mole formation could not be observed by the method applied in this experiment, although frequently cystic changes were

observed in the junctional zone. The reason of prompt degeneration of placenta and unsuccessful survival of trophoblasts is probably due to the fact that when the

fetus dies before full-term gestation thrombosis is taken place at demarcation between decidua and junctional zone of placenta serving blood circulation from both fetal and maternal side resulting in coagulation necrosis of the placenta.