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I. Regeneration of rabbit endometrium following curettage
I. Regeneration of rabbit endometrium follow ,ing curettage J.
G.
SCHENKER,
M.
I.
SACKS,
W.
Z.
POLISHUK,
M.D.
M.R.C.PATH. M.D.
Jerusalem, Israel In order to establish a basis for the evaluation of the efiects of hormonal administration on endometrial regeneration, the rate of the latter was studied in rabbits after curettage. The earliest signs of regeneration were noted 3 hr. after curettage, and by 48 hr. the endometrial surface was completely lined by regenerated endometrial cells. Within 72 hr. regeneration was complete and there were no obvious differences between sections from the curetted and control horns. Mitotic activity was not evident in the early stages of regeneration but was prominent in the surface epithelial cells 48 hr. after the curettage.
vestigation. They were housed in separate cages and maintained under uniform conditions throughout the experimental period. Laparotomy was performed with the use of 5 per cent sodium pentobarbital anesthesia injected into the ear vein. The uterus and the ovaries were inspected to exclude the presence of gross pathologic changes. A small incision was then made in the upper dorsal part of the vagina, and the endometrium in one horn was curetted by a curette inserted through the cervix. Special care was taken to avoid damage to other parts of the uterus during the procedure. Groups of 5 to 9 animals were killed f/2, 3, 6, 18, 24, 48, and 72 hr. and 5: 7, 14, and 30 days after the curettage. The uterus ws removed and fixed immediately in 10 per cent formolsaline. Multiple transverse sections of the fixed uteri were made at various levels from the internal OS to the upper border of the con-ma on both the curetted and control sides. The tissue blocks were embedded in paraffin, cut at 10 p, and stained with Mayer’s hematoxylin and eosin. Selected sections were stained with colloidal iron and periodic acid-Schiff (P. A. S.) . Four or five sections taken at different levels were examined from each
THE RESISTANCE of the normal endometrium to scar formation following the denudation which occurs after parturition or after curettage rovides an almost unique situation in the % ody. I-3 We are at present investigating the effect of mechanical, chemical, and bacterial trauma on endometrial regeneration under different hormonal conditions. The aim of the present study was to determine the rate of endometrial regeneration in mature rabbits after mechanical trauma produced by curettage, so as to establish a base line for the subsequent evaluation of the effects of hormonal administration on the regenerating endometrium. Material
and
methods
A total of 77 mature virgin rabbits, of the Hebrew University strain, each weighing 3,000 to 3,500 grams, was used in this inFrom the Department of ObstetricsGynecology and the Department of Pathology, Hebrew University-Hadassah Medical School. This work Grant No. Population New York.
was supported by Research M 70.72 C from the Council, New York, 970
Volume Number
111 7
Endometrial
regeneration
after curettage
971
Fig. 1. Stellate-shaped endometrial cavity of normal mature virgin rabbit. A, The stroma of the so-called placental folds (below and to the right) is more vascular and contains fewer glands than that of the nonplacental folds. (Hematoxylin and eosin. Original magnification x42.) B, Higher magnification of 2 placental folds (on left) and 3 nonplacental folds. The surface epithelial cells vary from tall cuboidal to columnar. (Hematoxylin and eosin. Original magnification X105.)
uterine horn. The nontraumatized horn served as a control in each case and, in addition, the endometrium of 3 normal nonoperated rabbits of the same weight was examined. Results
Normal appearance of endometrium in the rabbits. No differences were seen between the endometrium of the normal nonoperated rabbits and that of the nontraumatized cornua that served as a control in the curetted animals. The endometrium was arranged in folds, and the endometrial cavity
was stellate-shaped. The number of folds seen in the sections at the various levels varied from 5 to 6 and, in each specimen, one or two of the folds (so-called placental folds) differed from the rest in that the stroma was considerably more vascular and contained very few glands (Fig. 1, A and B). The surface epithelial cells varied from tall cuboidal to columnar in type and usually showed a single layer of regularly arranged nuclei, but with occasional pseudostratification of nuclei (Fig. 2). Occasionally the surface epithelium over the placental folds was of the low cuboidal type, but flattened
972
Schenker,
Sacks, and Polishuk
Fig. 2. Normal endometrium of mature virgin rabbit showing tall columnar surface epithelium, sometimes with nseudostratification of nuclei. (Hematoxylin and eosin. Original magnification x420.) attenuated epithelium was never seen. Several layers of glands were present and lined by cells similar to those of the surface epithelium. The glands were straight and showed no obvious evidence of secretory activity in sections stained with hematoxylin and eosin. The absence of secretory activity was confirmed in sections stained with colloidal iron and P. A. S.
Extent of endometrial denudation produced by the trauma of the curettage. Examination of sections of the uterus taken at various levels immediately after the curettage and 3 hr. later showed that in almost all cases the greater part of the surface endometrium had been denuded by the trauma. In 7 of the 9 animals, it was estimated that an average of about 70 per cent of the surface was denuded, and in many sections only small foci of residual endometrium persisted (Fig. 3). In 2 animals, the effect of the trauma was less marked, and the area of denudation involved only about 20 per cent of the surface. In areas where the surface epithelium was denuded, there was usually extensive hemorrhage in the stroma and the denudation usually involved the full thickness of the endometrium with, at most, a few scattered basal glands persisting. The surface epithelium over the summits of the endometrial folds was most affected by the trauma,
whereas that in the depth of the sulci between the folds tended to persist (Fig. 3). In most cases the muscle layers were uninvolved by the trauma, but in some sections there was evidence of recent hemorrhage in the myometrium. The sections taken at various uterine levels from the same animal varied somewhat in the extent of endometrial denudation, the least marked changes being present in the section taken from the uppermost portion of the uterus close to the orifice of the Fallopian tubes.
Regeneration
of endometrium.
Three hours. The earliest signs of regeneration of the surface epithelium were seen in 2 of the 5 animals in which sections were examined after 3 hr. In each of these animals, one of the sections (from the middle level of the uterus) showed a few flattened attenuated cells covering a small portion of the denuded surface (Fig. 4). In most sections there was extensive recent hemorrhage in the stroma. Six hour,~. In the animals examined 6 hr. after the curettage, 10 to 20 per cent of the endometrial surface was occupied by residual tall cuboidal endometrial cells, apparently persisting after the curettage, and the remaining 60 to 70 per cent was denuded, as in the animals examined immediately or 3 hr. after the trauma. Definite signs of regeneration were seen in
Volume. 111 Number 7
Endometrial
regeneration
after
curettage
973
Fig. 3. Uterus of rabbit killed 3 hr. after curettage. The greater part of the endometrial surface is denuded, but foci of surface epithelium persist in the depths of the sulci. The stroma is hemorrhagic, and the endometrial cavity contains red cells and granulocytes. (Hematoxylin and eosin. Original magnification x42.)
Fig. 4. Flattened regenerated epithelial cells covering curettage. (Hematoxylin and eosin. Original magnification all sections examined from these animals. The regenerating surface epithelial cells were present in several small foci in each section, usually but not always in continuity with persisting surface endometrium or endometrial glands (Fig. 5, A). They usually occupied an estimated 15 to 20 per cent of the surface area. The regenerating cells were easily distinguished from residual surface epithelium in that they were flattened and attenuated with elongated dark nuclei (Fig. 5, B). Their cytoplasm stained more basophilically than that of the normal surface epithelial cells, and no clear cytoplasmic
part of denuded
surface 3 hr. after
x420.)
borders were evident. The residual surface endometrial cells immediately adjacent to the regenerating surface cells sometimes contained large hyperchromatic nuclei. In the denuded areas, the stroma showed extensive hemorrhage and infiltration with granulocytic leukocytes. The leukocytic infiltration was also present beneath the residual and regenerating surface cells. The endometrial cavity contained red cells, protein material, and numerous granulocytes. The myometrium showed focal areas of granulocytic infiltration. Tweloe hours. In 3 of 6 animals examined
974
Schenker,
Sacks, and Polishuk
December
hm. J. Obstrt.
1, Nil Gynecol.
Fig. 5. Six
hours after curettage. A, On the right, the endometrial surface is denuded. On the left, the greater part of the surface is lined by flattened regenerating epithelium which is in continuity with persisting surface endometrium and a residual endometrial gland (lower left). (Hematexylin and eosin. Original magnification x105.) B, Part of the endometrial cavity is lined by flattened syncytial-like regenerating cells, and part is lined by residual epithelium consisting of tall cuboidal cells. (Hematoxylin and eosin. Original magnification x420.)
12 hr. after curettage, the regenerating epithelium already covered an estimated 40 to 50 per cent of the denuded surface. In the other 3 animals, the regenerated epithelium was less extensive, occupying, as in the animals killed at 6 hr., about 20 per cent of the surface area. In none of the sections from any of the animals was the surface regeneration complete. The foci of the regenerating surface epithelium were again partially distributed but were sometimes clearly in. continuity with residual surface
epithelium in depths of the sulci between the endometrial folds (Fig. 6, A and B) . Twenty-four hours. Twenty-four hours after the curettage, 40 to 60 per cent of the surface was lined by obviously regenerating cells in all animals studied, but portions of the surface were still denuded and covered by fibrinous exudate (Fig. 7, A). In most areas tbe regenerating epithelium consisted of very thin attenuated cells, but there were also areas where the regenerating cells were more cuboidal in type and the cytoplasmic
volllmc Number
Endometrial
111
7
regeneration
after
curettage
975
6. Twelve hours after curettage. The surface is partly covered by regenerating epithelial cells which are seen to be in continuity with residual surface epithelium in the depths of one of the sulci between the endometrial folds. (Hematoxylin and eosin. Original magnification Fig.
A, x105;
B, x260.)
border between them was more evident. Occasional mitotic figures were seen in these cells (Fig. 7, B) . The stroma showed severe congestion, recent hemorrhages, and, especially in the denuded areas, a mild leukocytic infiltration. Forty-eight hours. In all 7 animals, the surface was completely lined by endometrial cells, and no areas of denudation persisted. Ther,: were, however, definite variations in the a,ppearance of the regenerated endometrial lining from animal to animal and even from section to section of the same uterus. In about half of the sections, the endometrial cavity was lined by tall cuboidal or even
columnar cells (Fig. 8, A), which closely resembled the normal endometrium of the control side, except that the cell cytoplasm was a little more basophilic. At this stage, numerous mitoses were seen in the surface endometrial cells (Fig. 8, B) . In the remaining sections, at least part of the surface was lined by flattened attenuated cells similar to those seen after 12 and 24 hr. (Fig. 8, C) . The stroma was still intensely congested, showed areas of hemorrhage, and, beneath the flattened regenerating cells, sometimes contained fibrous material. Seventy-two hours. In all animals regeneration of the endometrium was complete,
976
Schenker,
Sacks,
and
Polishuk
Fig. 7. Twenty-four hours after curettage. A, More than half ot the surface is lined by regenerating epithelium, but there are still large areas of denudation. (Hematoxylin and eosin. Original magnification x42.) B, Regenerating cells are now cuboidal and cell borders are better defined than in earlier stages of reieneration (Hematoxylin and rosin. Ori$nal magnification X105.) and no difference was seen between the sections from the curetted and control horns. The stroma was equally congested on both sides, and no hemorrhage or inflammatory cell infiltration was seen. Similarly, in all animals examined 5, 7, 14, and 30 days after the curettage, the regeneration of the endometrium was complete, and no difference was seen between the sections from the curetted and control horn. Comment The process of regeneration of the endometrium was seen to occur \vith Ereat rapid-
ity. The earliest signs of regeneration were already seen 3 hr. after curettage, and within 24 hr. 40 to 60 per cent of the surface was lined by obviously regenerating cells in all animals studied. After 48 hr., the surface was completely lined by endometrial cells, but in many areas the latter were flat and cuboidal and readily distinguished from the normal endometrial lining. After 72 hr., regeneration of both the surface epithelium and the glands was complete, and no difference was seen between the sections from the curetted and control horns. An interesting histolo$c feature was that \rery few or no mitosrs wrre recognizable in
Volume Number
111 7
Fig. 8. Forty-eight hours after curettage. A, Endometrial cavity is lined by tall cuboidal or columnar cells c:losely resembling the normal endometrial lining. (Hematoxylin and eosin. Original magnification x105.) B, Mitotic activity in surface endometrial cells. (Hematoxylin and eosin. Original magnification x420.) C, Part of the endometrial cavity is lined by flattened syncytial-like cells, and part is lined by tall cuboidal or columnar cells. (Hematoxylin and eosin. Original magnification X105.)
Endometrial
regeneration
after curettage
977
the early stages of regeneration, whereas mitotic activity was prominent in the surface epithelial cells 48 hr. after the curettage. Low mitotic activity has also been noted by others4+ in studies of the renewal of the uterine mucosa after menstruation, spontaneous abortion, and normal delivery. Valuable information on the speed of cell renewal may, however, be obtained by the application of specialized techniques, such as incorporation of tritiated thymidine in vivo or in vitro? to the endometrium. There are different opinions as to the origin of the regenerating epithelium lining the denuded surface following menstruation, abortion, and curettage. The most accepted view is that the regenerating surface epithelium originates from the residual epithelium of gland stumps. Novak and Telinde4 believed that the source of the new epithelium was chiefly the epithelium of the basal stumps of the uterine glands. Sturgis and Meig9 determined that the renewal of epithelium following menstruation occurs within 48 hr., probably by migration of epithelial cells from the exposed ends of the glands. Several investigators believe that the rapidity of the new epithelialization and the lack of mitotic figures do not support the previously accepted view that the uterine epithelium regenerates from residual surface epithelium or from the epithelium of glands which have escaped destruction. In view of this, Baggish and associates9 have recently reiterated the previously expressed belief of earlier investigatorslO-l2 that the endometrial epithelium could be formed by transformation of stromal cells. Papanicolaou’sls studies showed that the tunica propria of the uterus contains a Iarge number of undifferentiated cells of mesodermal origin, which under favorable conditions may form epithelial tissue. The opinion of Singer and colleagues14 is that the origin of the new epithelial cells is by transformation of peritoneal cells after migration through the Fallopian tubes. Th e question of the origin of the regenerating endometrial cells cannot readily be answered from a study of routine histologic sections, and we did not investigate this par-
978
Schenker,
Sacks, and Polishuk
titular problem. We were not, however, impressed by an intermingling of the regenerating surface layer and underlying stromal cells as has been described by Baggish and associates.g As judged by the purely morphologic features in routine hematoxylin and eosin sections, we feel that the main source
of the regenerating surface cells was residual surface cpithelium which had escaped drstruction at the time of the curettage. We wish to thank Mr. S. Shemesh and Mrs. H. Zilberstein for their technical assistance.
REFERENCES
1. Craig, OBSTET.
J. M., GYNECOL.
and
Danliger, 86:
421,
S.:
AM.
J.
1963.
2. Schenker, J. G., and Polishuk, W. Z.: Symp. Israel Sot. Fertil. Steril. April, 1967. 3. Polishuk, W. Z., ancl Schenker, J. G.: In preparation. 4. Novak, E., and Telinde, R. W.: J. A. M. A. 83: 900, 1924. 5. Rutherford, R. N., and Mezer, J.: J. A. M. A. 119: 124, 1942. 6. Williams, J. W.: J. A. M. A. 91: 513, 1931. 7. Lachapelle, J. M., and Gillman, T.: Br. Dermatol. 81: 603, 1969. 8. Sturgis, S. H., and Meigs, J. N.: Am. J. Surg. 33: 368, 1956.
9. Baggish, M. S., Pauerstein, C. J., and Woodruff, J. D.: AM. J. OBSTET. GYNECOL. 59: 453, 1967. 10. Hirschmann, F., and Adler, L.: Monatsschr Geburtshilfe
Gynaekol.
27:
1, 1908.
Duval, M. M.: C. R. Sot. Biol. 2: 697, 1890. 12. Heape, W.: Trans. Obstet. Sot. Lond. 40: 161, 1898. 13. Papanicolaou, G.: AM. J. OBSTET. GYNECOL. 11.
14.
25: 30, Singer,
Aust. 1968.
1933.
A., Reid, B., and Copphsso, R. M., N. Z. J. Obstet. Gynaecol. 8: 163,
G.
SCHENKER,
M.
I.
SACKS,
W.
Z.
POLISHUK,
M.D.
M.R.C.PATH. M.D.
Jerusalem, Israel In order to establish a basis for the evaluation of the efiects of hormonal administration on endometrial regeneration, the rate of the latter was studied in rabbits after curettage. The earliest signs of regeneration were noted 3 hr. after curettage, and by 48 hr. the endometrial surface was completely lined by regenerated endometrial cells. Within 72 hr. regeneration was complete and there were no obvious differences between sections from the curetted and control horns. Mitotic activity was not evident in the early stages of regeneration but was prominent in the surface epithelial cells 48 hr. after the curettage.
vestigation. They were housed in separate cages and maintained under uniform conditions throughout the experimental period. Laparotomy was performed with the use of 5 per cent sodium pentobarbital anesthesia injected into the ear vein. The uterus and the ovaries were inspected to exclude the presence of gross pathologic changes. A small incision was then made in the upper dorsal part of the vagina, and the endometrium in one horn was curetted by a curette inserted through the cervix. Special care was taken to avoid damage to other parts of the uterus during the procedure. Groups of 5 to 9 animals were killed f/2, 3, 6, 18, 24, 48, and 72 hr. and 5: 7, 14, and 30 days after the curettage. The uterus ws removed and fixed immediately in 10 per cent formolsaline. Multiple transverse sections of the fixed uteri were made at various levels from the internal OS to the upper border of the con-ma on both the curetted and control sides. The tissue blocks were embedded in paraffin, cut at 10 p, and stained with Mayer’s hematoxylin and eosin. Selected sections were stained with colloidal iron and periodic acid-Schiff (P. A. S.) . Four or five sections taken at different levels were examined from each
THE RESISTANCE of the normal endometrium to scar formation following the denudation which occurs after parturition or after curettage rovides an almost unique situation in the % ody. I-3 We are at present investigating the effect of mechanical, chemical, and bacterial trauma on endometrial regeneration under different hormonal conditions. The aim of the present study was to determine the rate of endometrial regeneration in mature rabbits after mechanical trauma produced by curettage, so as to establish a base line for the subsequent evaluation of the effects of hormonal administration on the regenerating endometrium. Material
and
methods
A total of 77 mature virgin rabbits, of the Hebrew University strain, each weighing 3,000 to 3,500 grams, was used in this inFrom the Department of ObstetricsGynecology and the Department of Pathology, Hebrew University-Hadassah Medical School. This work Grant No. Population New York.
was supported by Research M 70.72 C from the Council, New York, 970
Volume Number
111 7
Endometrial
regeneration
after curettage
971
Fig. 1. Stellate-shaped endometrial cavity of normal mature virgin rabbit. A, The stroma of the so-called placental folds (below and to the right) is more vascular and contains fewer glands than that of the nonplacental folds. (Hematoxylin and eosin. Original magnification x42.) B, Higher magnification of 2 placental folds (on left) and 3 nonplacental folds. The surface epithelial cells vary from tall cuboidal to columnar. (Hematoxylin and eosin. Original magnification X105.)
uterine horn. The nontraumatized horn served as a control in each case and, in addition, the endometrium of 3 normal nonoperated rabbits of the same weight was examined. Results
Normal appearance of endometrium in the rabbits. No differences were seen between the endometrium of the normal nonoperated rabbits and that of the nontraumatized cornua that served as a control in the curetted animals. The endometrium was arranged in folds, and the endometrial cavity
was stellate-shaped. The number of folds seen in the sections at the various levels varied from 5 to 6 and, in each specimen, one or two of the folds (so-called placental folds) differed from the rest in that the stroma was considerably more vascular and contained very few glands (Fig. 1, A and B). The surface epithelial cells varied from tall cuboidal to columnar in type and usually showed a single layer of regularly arranged nuclei, but with occasional pseudostratification of nuclei (Fig. 2). Occasionally the surface epithelium over the placental folds was of the low cuboidal type, but flattened
972
Schenker,
Sacks, and Polishuk
Fig. 2. Normal endometrium of mature virgin rabbit showing tall columnar surface epithelium, sometimes with nseudostratification of nuclei. (Hematoxylin and eosin. Original magnification x420.) attenuated epithelium was never seen. Several layers of glands were present and lined by cells similar to those of the surface epithelium. The glands were straight and showed no obvious evidence of secretory activity in sections stained with hematoxylin and eosin. The absence of secretory activity was confirmed in sections stained with colloidal iron and P. A. S.
Extent of endometrial denudation produced by the trauma of the curettage. Examination of sections of the uterus taken at various levels immediately after the curettage and 3 hr. later showed that in almost all cases the greater part of the surface endometrium had been denuded by the trauma. In 7 of the 9 animals, it was estimated that an average of about 70 per cent of the surface was denuded, and in many sections only small foci of residual endometrium persisted (Fig. 3). In 2 animals, the effect of the trauma was less marked, and the area of denudation involved only about 20 per cent of the surface. In areas where the surface epithelium was denuded, there was usually extensive hemorrhage in the stroma and the denudation usually involved the full thickness of the endometrium with, at most, a few scattered basal glands persisting. The surface epithelium over the summits of the endometrial folds was most affected by the trauma,
whereas that in the depth of the sulci between the folds tended to persist (Fig. 3). In most cases the muscle layers were uninvolved by the trauma, but in some sections there was evidence of recent hemorrhage in the myometrium. The sections taken at various uterine levels from the same animal varied somewhat in the extent of endometrial denudation, the least marked changes being present in the section taken from the uppermost portion of the uterus close to the orifice of the Fallopian tubes.
Regeneration
of endometrium.
Three hours. The earliest signs of regeneration of the surface epithelium were seen in 2 of the 5 animals in which sections were examined after 3 hr. In each of these animals, one of the sections (from the middle level of the uterus) showed a few flattened attenuated cells covering a small portion of the denuded surface (Fig. 4). In most sections there was extensive recent hemorrhage in the stroma. Six hour,~. In the animals examined 6 hr. after the curettage, 10 to 20 per cent of the endometrial surface was occupied by residual tall cuboidal endometrial cells, apparently persisting after the curettage, and the remaining 60 to 70 per cent was denuded, as in the animals examined immediately or 3 hr. after the trauma. Definite signs of regeneration were seen in
Volume. 111 Number 7
Endometrial
regeneration
after
curettage
973
Fig. 3. Uterus of rabbit killed 3 hr. after curettage. The greater part of the endometrial surface is denuded, but foci of surface epithelium persist in the depths of the sulci. The stroma is hemorrhagic, and the endometrial cavity contains red cells and granulocytes. (Hematoxylin and eosin. Original magnification x42.)
Fig. 4. Flattened regenerated epithelial cells covering curettage. (Hematoxylin and eosin. Original magnification all sections examined from these animals. The regenerating surface epithelial cells were present in several small foci in each section, usually but not always in continuity with persisting surface endometrium or endometrial glands (Fig. 5, A). They usually occupied an estimated 15 to 20 per cent of the surface area. The regenerating cells were easily distinguished from residual surface epithelium in that they were flattened and attenuated with elongated dark nuclei (Fig. 5, B). Their cytoplasm stained more basophilically than that of the normal surface epithelial cells, and no clear cytoplasmic
part of denuded
surface 3 hr. after
x420.)
borders were evident. The residual surface endometrial cells immediately adjacent to the regenerating surface cells sometimes contained large hyperchromatic nuclei. In the denuded areas, the stroma showed extensive hemorrhage and infiltration with granulocytic leukocytes. The leukocytic infiltration was also present beneath the residual and regenerating surface cells. The endometrial cavity contained red cells, protein material, and numerous granulocytes. The myometrium showed focal areas of granulocytic infiltration. Tweloe hours. In 3 of 6 animals examined
974
Schenker,
Sacks, and Polishuk
December
hm. J. Obstrt.
1, Nil Gynecol.
Fig. 5. Six
hours after curettage. A, On the right, the endometrial surface is denuded. On the left, the greater part of the surface is lined by flattened regenerating epithelium which is in continuity with persisting surface endometrium and a residual endometrial gland (lower left). (Hematexylin and eosin. Original magnification x105.) B, Part of the endometrial cavity is lined by flattened syncytial-like regenerating cells, and part is lined by residual epithelium consisting of tall cuboidal cells. (Hematoxylin and eosin. Original magnification x420.)
12 hr. after curettage, the regenerating epithelium already covered an estimated 40 to 50 per cent of the denuded surface. In the other 3 animals, the regenerated epithelium was less extensive, occupying, as in the animals killed at 6 hr., about 20 per cent of the surface area. In none of the sections from any of the animals was the surface regeneration complete. The foci of the regenerating surface epithelium were again partially distributed but were sometimes clearly in. continuity with residual surface
epithelium in depths of the sulci between the endometrial folds (Fig. 6, A and B) . Twenty-four hours. Twenty-four hours after the curettage, 40 to 60 per cent of the surface was lined by obviously regenerating cells in all animals studied, but portions of the surface were still denuded and covered by fibrinous exudate (Fig. 7, A). In most areas tbe regenerating epithelium consisted of very thin attenuated cells, but there were also areas where the regenerating cells were more cuboidal in type and the cytoplasmic
volllmc Number
Endometrial
111
7
regeneration
after
curettage
975
6. Twelve hours after curettage. The surface is partly covered by regenerating epithelial cells which are seen to be in continuity with residual surface epithelium in the depths of one of the sulci between the endometrial folds. (Hematoxylin and eosin. Original magnification Fig.
A, x105;
B, x260.)
border between them was more evident. Occasional mitotic figures were seen in these cells (Fig. 7, B) . The stroma showed severe congestion, recent hemorrhages, and, especially in the denuded areas, a mild leukocytic infiltration. Forty-eight hours. In all 7 animals, the surface was completely lined by endometrial cells, and no areas of denudation persisted. Ther,: were, however, definite variations in the a,ppearance of the regenerated endometrial lining from animal to animal and even from section to section of the same uterus. In about half of the sections, the endometrial cavity was lined by tall cuboidal or even
columnar cells (Fig. 8, A), which closely resembled the normal endometrium of the control side, except that the cell cytoplasm was a little more basophilic. At this stage, numerous mitoses were seen in the surface endometrial cells (Fig. 8, B) . In the remaining sections, at least part of the surface was lined by flattened attenuated cells similar to those seen after 12 and 24 hr. (Fig. 8, C) . The stroma was still intensely congested, showed areas of hemorrhage, and, beneath the flattened regenerating cells, sometimes contained fibrous material. Seventy-two hours. In all animals regeneration of the endometrium was complete,
976
Schenker,
Sacks,
and
Polishuk
Fig. 7. Twenty-four hours after curettage. A, More than half ot the surface is lined by regenerating epithelium, but there are still large areas of denudation. (Hematoxylin and eosin. Original magnification x42.) B, Regenerating cells are now cuboidal and cell borders are better defined than in earlier stages of reieneration (Hematoxylin and rosin. Ori$nal magnification X105.) and no difference was seen between the sections from the curetted and control horns. The stroma was equally congested on both sides, and no hemorrhage or inflammatory cell infiltration was seen. Similarly, in all animals examined 5, 7, 14, and 30 days after the curettage, the regeneration of the endometrium was complete, and no difference was seen between the sections from the curetted and control horn. Comment The process of regeneration of the endometrium was seen to occur \vith Ereat rapid-
ity. The earliest signs of regeneration were already seen 3 hr. after curettage, and within 24 hr. 40 to 60 per cent of the surface was lined by obviously regenerating cells in all animals studied. After 48 hr., the surface was completely lined by endometrial cells, but in many areas the latter were flat and cuboidal and readily distinguished from the normal endometrial lining. After 72 hr., regeneration of both the surface epithelium and the glands was complete, and no difference was seen between the sections from the curetted and control horns. An interesting histolo$c feature was that \rery few or no mitosrs wrre recognizable in
Volume Number
111 7
Fig. 8. Forty-eight hours after curettage. A, Endometrial cavity is lined by tall cuboidal or columnar cells c:losely resembling the normal endometrial lining. (Hematoxylin and eosin. Original magnification x105.) B, Mitotic activity in surface endometrial cells. (Hematoxylin and eosin. Original magnification x420.) C, Part of the endometrial cavity is lined by flattened syncytial-like cells, and part is lined by tall cuboidal or columnar cells. (Hematoxylin and eosin. Original magnification X105.)
Endometrial
regeneration
after curettage
977
the early stages of regeneration, whereas mitotic activity was prominent in the surface epithelial cells 48 hr. after the curettage. Low mitotic activity has also been noted by others4+ in studies of the renewal of the uterine mucosa after menstruation, spontaneous abortion, and normal delivery. Valuable information on the speed of cell renewal may, however, be obtained by the application of specialized techniques, such as incorporation of tritiated thymidine in vivo or in vitro? to the endometrium. There are different opinions as to the origin of the regenerating epithelium lining the denuded surface following menstruation, abortion, and curettage. The most accepted view is that the regenerating surface epithelium originates from the residual epithelium of gland stumps. Novak and Telinde4 believed that the source of the new epithelium was chiefly the epithelium of the basal stumps of the uterine glands. Sturgis and Meig9 determined that the renewal of epithelium following menstruation occurs within 48 hr., probably by migration of epithelial cells from the exposed ends of the glands. Several investigators believe that the rapidity of the new epithelialization and the lack of mitotic figures do not support the previously accepted view that the uterine epithelium regenerates from residual surface epithelium or from the epithelium of glands which have escaped destruction. In view of this, Baggish and associates9 have recently reiterated the previously expressed belief of earlier investigatorslO-l2 that the endometrial epithelium could be formed by transformation of stromal cells. Papanicolaou’sls studies showed that the tunica propria of the uterus contains a Iarge number of undifferentiated cells of mesodermal origin, which under favorable conditions may form epithelial tissue. The opinion of Singer and colleagues14 is that the origin of the new epithelial cells is by transformation of peritoneal cells after migration through the Fallopian tubes. Th e question of the origin of the regenerating endometrial cells cannot readily be answered from a study of routine histologic sections, and we did not investigate this par-
978
Schenker,
Sacks, and Polishuk
titular problem. We were not, however, impressed by an intermingling of the regenerating surface layer and underlying stromal cells as has been described by Baggish and associates.g As judged by the purely morphologic features in routine hematoxylin and eosin sections, we feel that the main source
of the regenerating surface cells was residual surface cpithelium which had escaped drstruction at the time of the curettage. We wish to thank Mr. S. Shemesh and Mrs. H. Zilberstein for their technical assistance.
REFERENCES
1. Craig, OBSTET.
J. M., GYNECOL.
and
Danliger, 86:
421,
S.:
AM.
J.
1963.
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