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“Aging” pigments in term human placenta
''Aging'' pigments in term human placenta T. H. PARMLEY, M.D. P. K. GUPTA, M.D. M. A. WALKER, R.N .C. Baltimore, Maryland First-, second-, and third-trimester placentas were examined with fluorescent microscopy for the presence of lipofuscin pigments. Prior to 32 weeks' gestation these were not seen, but they were routinely found in the trophoblast of the term placenta. These pigments may or may not represent "aging" of the placenta. (AM. J. 0BSTET. GYNECOL. 139:760, 1981.)
LIPOFUSCINS or "aging pigments" accumulate in
fixed postmitotic cells in direct proportion to the chronologie age of the cell. 1 This relationship has been carefully quantitated by Strehler and associates 2 in the human myocardium. Using fluorescence microscopy, he demonstrated that the fraction of the myocardium occupied by pigment increased linearly at a rate of 0.6% per decade. This change was independent of the presence or type of cardiac disease. The same relationship has been observed in a wide variety of tissues across the phylogenetic spectrum. 3- 7 The ubiquity of this observation has prompted the suggestion that it is related to an inherent biologic aging process. 8 However, a biologically precise definition of such an aging process remains elusive and, therefore, relating anything else to it is currently impossible. 9 · 10 The placenta has been described as "aging" for many years, but such a statement is also plagued by the inability to define aging. 11 Thus, it seemed of interest whether or not lipofuscin pigments were present in the near-term and term human placenta. As these pigments spontaneously fluoresce, the fluorescent microscope is an available method for detecting them. Material and methods
Placental material was obtained from pregnancies in which the gestational age was known. First-trimester From the Gynecologic Pathology Laboratory of the Department of Obstetrics and Gynecology and the Division of Cytopathology of the Department of Pathology, The Johns Hopkins Hospital. Presented by invitation at the First Combined Annual Meeting of The Am.erican Associ,a.tion of Obstetricians and Gynecologists and the American Gynecological Society, Hot Springs, Virginia, September 3-6, 1980. Reprint requests: Dr. T. H. Parmley, Department of Gynecology and Obstetrics, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
760
20
15
..
"0
ii
::0
iii
10
"'0
.
c u 0
0:: 5
8-12
16-20 24-28 30-32 34-36 38-40 42-44 Gest. Age In Wks.
Fig. 1. The black portion of the bars represents those placentas that contained lipofuscin. Prior to 32 weeks none did, and after 36 weeks about half contained pigment. placentas were obtained trom suction abortions in which the pelvic examination and the stated last menstrual period were in agreement. Second-trimester placentas were obtained from ureaprostaglandin abortions in which the pelvic examination, the stated last menstrual period, and measurement of the aborted fetus were all in agreement. Third-trimester placentas were selected from pregnancies in which there were two serial sonograms confirming the gestational age or in which all of the following clinical criteria were met: ( l) two examina0002-9378/81/070760+07$ 00.70/0
©
1981 The C. V. Moshy Co.
Volume 1:19
" Aging" pigments in term placenta 761
:\umber 7
Fig. 2. Multiple. brightly fluorescent granules occupy the cytoplasm of the trophoblastic cells . The syncytial "knot" seen in th e center of the photograph is particularly prominent.
10
D
D
9 8
., c
. a: .
7
0
u
6
0
E ....
5
.....
4
D
D D
D D
DD D D ODD
3
2
DD DODD A
8
c
D
Quodronts
Fig. 3. Discrete granules are seen in the trophoblast of one villus. A closely packed cluster produced the large focus of fluorescence seen in the lower villus.
Fig. 4. All forty sections, one from each quadrant of 10 term placentas, are diagramatically illustrated here. Those in black were lipofuscin positive. Nine of the ten placentas contained pigment in at least one quadrant, but the distribution was heterogeneous.
762
Parmley, Gupta, and Walker
5
...c:cu
1/1
0
4
CJ 0
c::
~
3
:::J
0
E cu
...
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Am . .J.
DODD DODD
oo•o DODD DODD A
B
c
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Quadrants
Fig. 5. All twenty sections, one from each quadrant of five premature placentas, are diagramatically illustrated here. The one black section represents the only placental quadrant which contained lipofuscin.
tions prior to 20 weeks that were consistent with gestational age as determined by the stated last menstrual period; (2) an audible fetal heartbeat detected between 17 and 21 weeks of gestational age as determined by the stated last menstrual period; (3) an infant who, when delivered, was appropriate in size and development for the gestational age as determined by the stated last menstrual period. Initially, a single random section was taken from each placenta. It was prepared in the routine manner for paraffin block sectioning and one section was stained with hematoxylin and eosin to determine that the placenta was histologically normal. Then unstained sections were examined without knowledge of the gestational age. As light microscopic study of the morphology of the villus reveals approximate age, the initial confirmation of the presence of fluorescent pigment was made by one of us who was unfamiliar with placental morphology. T'hen the site of the fluorescence was determined by a second observer. The examination was performed as follows. The unstained section was deparaffmized in xylene. The slide was blotted dry with a paper towel and examined under oil in a Leitz Orthoplan microscope equipped with an HBO 100-watt lamp epi-illumination, a KP 500 Excitor filter, and a 515 Barrier filter. When the observations were equivocal, they were confirmed by means of a 420 Excitor filter and a 460 Barrier filter. The oil used was Cargille, type A and type B in a 50-50 mixture. Documentation was done with the use of Kodak high-speed 200 ASA Ektachrome film. As a result of the initial study, 10 additional term
April I. ltlHI ( ;nwml.
Ohst~t.
placentas and five premature placentas were cut into four quadrants and a random section was taken from each of the four quadrants; the study was repeated.
Results In the initial study, no pigment was seen in the placenta prior to 30 to 32 weeks' gestation (Fig. I). After 30 to 32 weeks. typical yellow-orange pigment granules were increasingly seen in the trophoblast (Fig. 2). They occurred as single granules or clusters (Fig.:)) . After 37 weeks, they were present in over 5Wlt of the cases (Fig. 1). We did not identify fluorescent pigment in other portions of the placental cake. We did confirm but did not study its presence in the trophoblast of the chorionic membrane. For theoretical reasons, we wondered why the pigment was not present in 100% of term placentas and suspected that heterogeneous distribution. as demonstrated by Strehler and associates.~ in the myocardium was the answer. Accordingly. we examined both term and premature placentas in four quadrants. Fourquadrant examination of the term placelltas revealed that all but one did contain pigment in at least one of its quadrants (Fig. 4), while the preterm placentas continued to show little or none (Fig. 5).
Comment The lipofuscins have been only partially characterized. However, on the basis of the available structural analyses, they are thought to be the result of peroxidation of polyunsaturated lipids by oxygen-free radicalsY- 15 These lipids are widely present in bior~embranes. On the basis of electron microscopic and histochemical studies, the membranes of several specific cell organelles have been suggested as the source of these products. 12 • 16 However, these studies are not all in agreement and they are not mutuallv exclusive. The sum of the evidence suggests that the pigments are derived from a multiplicity of sources. As these compounds are insoluble and only poorly metabolized, they accumulate in fixed postmitotic cells. This relationship is invariable over time, but it can be accelerated by a variety of environmental insults. Significant among the latter is nutritional deprivation, specifically of antioxidants such as vitamin E. 17 Vitamin E is important in the control of oxygen-free radicals, and its absence appears to be associated with more toxicity from these molecules. Further, it has been noted in primates that protein deficiency during gestation can result in increased amounts of these pigments in the central nervous system of the newborn infant. 1" Maternal disease such as hypertension, resulting in relative placental ischemia, could be the source of signiticant
"Aging" pigments in term placenta 763
Volume 13'1 '\umber 7
across-the-board nutritional deficiency and thus produce placental changes difficult to distinguish from agmg. Our observations have demonstrated the appearance of lipofuscin pigments in the human placenta as it nears term. Thus, they complement the findings of others, w. ~ 0 who found increased quantities of peroxidized lipids in the blood of pregnant women at term compared to levels seen earlier in pregnancy. These authors suggested that the pigments originated in the placenta, and our results would support their suggestion. Whether or not the placenta truly gets "old,"
REFERENCES I. Robbins, S. L., and Cotran, R. S.: Pathologic Basis of Dis-
ease, Philadelphia, 1979, W. B. Saunders Co., p. 46. 2. Strehler, B. L., Mark, D. D., Mildvan, A. S., and Gee, M. V.: Rate and magnitude of age pigment accumulation in the human myocardium,
J.
GerontaL 14:430, 1959.
3. Braak, H.: Spindle-shapedappendagesofiiiAB-pyramids filled with lipofuscin: Striking pathological change of the senescent human isocortex, "\eta l'Jeuropathol. (Bed.) 46: 197. 1979. 4. Donato, H., Jr., Hoselton, M. A., and Sohal, R. S.:
Lipofuscin accumulation: Effects of individual variation and selective mortality on population averages, Exp. Gerontol. 14:141. 1979. 5. Rana, R. S., and Munkres, K. D.: Ageing of neurospora crassa. V. Lipid peroxidation and decay of respiratory enzymes in an inositol auxotroph, Mech. Ageing Dev. 7:241. 1978.
whether these pigments reflect nutritional deprivation, or whether they reflect some entirely unrelated process is of course not revealed by our data. Further, it must be emphasized that if "aging" does take place in the placenta, then this does not necessarily mean that "senescence" or functional deterioration occurs. The heterogeneity in the distribution of the lipofuscin may imply a corresponding heterogeneity in the rates at which various parts of the placenta age. It is well known that much cytotrophoblast, presumably "young" trophoblast, persists in the· term placenta.
11. Fox, H.: Pathology of the Placenta, Philadelphia, 1978, W. B. Saunders Co., pp. 21-22 and 203-2 !0. 12. Koobs, D. H., Schultz, R. L., andjutzy, R. V.: The origin
of lipofuscin and possible consequences to the myocardium, Arch. Pathol. Lab. Med. 102:66, 1978. · 13. Trombly, R., Tappe!, A. L., Coniglio, J. G., Grogan, W. M., Jr., and Rhamy, R. K.: Fluorescent products and polyunsaturated fatty acids of human testes, Lipids 10: 59!, 1975. 14. Taubold, R. D., Siakotos, A. N., and Perkins, E. G.:
15. 16.
-
6. Wing, G. L., Blanchard .. G. C., and Weiter,]. ].: The topography and age relationship of lipofuscin concentration in the retinal pigment epithelium, Invest. Ophthalmol. Vis. Sci. 17:601, 1978. 7. Miquel, j., Lundgren, P.R .. and Johnson, J. E., Jr.: Spectrophotofluorometric and electron microscopic study of lipofuscin accumulation in the testis of aging mice, J. Get-ontoL 33;3, 1978.
8. Kent, S.: Solving the riddle of lipofuscin origin may uncover clues to the aging process, Geriatrics 31:128, 1976. 9. Behnke, J. A., Finch, C. W., and Moment, G. B.: Biology of Aging, New York. 1978, Plenum Press. 10. Hayflick, L.: The cell biology of human aging, N. Engi.J. Med. 295:1302, 1976.
Editors' note: This manuscript was revised after these discussions were presented.
Discussion DR. RALPH WYNN, Little Rock, Arkansas. Although the placenta undergoes certain changes that appear teleologically to indicate functional aging (e.g., increased deposition of fibrinoid and calcium, thickening of basement membranes of endothelium and trophoblast, and sclerosis of vessels), other morphologic changes are consistent with maintenance or even improvement in function, such as thinning of the syncytial trophoblast, decrease in Langhans cells, increase in
17.
18.
Studies on chemical nature of lipofuscin (age pigment) isolated from normalhuman brain, Lipids 10:383, 1975. Tappe!, A. 1:.: Lipid peroxidation damage to cell components, Fed. Proc. 32:1870, 1973. Brunk, U., and Ericsson, J. L.: Electron microscopical studies on rat brain neurons. Localization of acid phosphatase and mode of formation of lipofuscin bodies, J. Ultrastruct. Res. 38:1, 1972. Freund, G.: The effects of chronic alcohol and vitamin E consumption on aging pigments and learning performance in mice, Life Sci. 24: 145, 1979. Sharma, S. P., and Manocha, S. L.: Lipofuscin formation in the developing nervous system of squirrel monkeys consequent to maternal dietary protein deficiency during gestation, Mech. Ageing Dev. 6:1, 1977. ·
19. Sekiba, K., and Yoshioka, T.: Changes of lipid peroxida-
tion and superoxide dismutase activity in the human placenta, AM. j. 0BSTET. GYNECOL. 135:368, 1979. 20. Yoshioka, T .. Kawada, K., Shimada, T., and Mori, M.: Lipid peroxidation in maternal and cord blood and protective mechanism against activated-oxygen toxicity in the blood, AM. J. OBSTET. GYNECOL. 135:372, 1979.
capillaries and their approximation to the trophoblast, an·d the surface-to-voitime ratio of the termi~al villi. 1 Estimates of at least 30% to 40% functional reserve are usually made for the term placenta. Thus, even if morphologic criteria of senescence could be defined during placental aging, a concomitant decrease in functional capacity would not necessarily follow. The electron microscope has not provided precise criteria of cellular senescence. The only ultrastructural changes that are identified fairly consistently in aged tissues are increased nuclear indentation, loss of roughsurfaced endoplasmic reticulum, and the accumulation of lipofuscin pigment. It is this pigment which Dr.
LIPOFUSCINS or "aging pigments" accumulate in
fixed postmitotic cells in direct proportion to the chronologie age of the cell. 1 This relationship has been carefully quantitated by Strehler and associates 2 in the human myocardium. Using fluorescence microscopy, he demonstrated that the fraction of the myocardium occupied by pigment increased linearly at a rate of 0.6% per decade. This change was independent of the presence or type of cardiac disease. The same relationship has been observed in a wide variety of tissues across the phylogenetic spectrum. 3- 7 The ubiquity of this observation has prompted the suggestion that it is related to an inherent biologic aging process. 8 However, a biologically precise definition of such an aging process remains elusive and, therefore, relating anything else to it is currently impossible. 9 · 10 The placenta has been described as "aging" for many years, but such a statement is also plagued by the inability to define aging. 11 Thus, it seemed of interest whether or not lipofuscin pigments were present in the near-term and term human placenta. As these pigments spontaneously fluoresce, the fluorescent microscope is an available method for detecting them. Material and methods
Placental material was obtained from pregnancies in which the gestational age was known. First-trimester From the Gynecologic Pathology Laboratory of the Department of Obstetrics and Gynecology and the Division of Cytopathology of the Department of Pathology, The Johns Hopkins Hospital. Presented by invitation at the First Combined Annual Meeting of The Am.erican Associ,a.tion of Obstetricians and Gynecologists and the American Gynecological Society, Hot Springs, Virginia, September 3-6, 1980. Reprint requests: Dr. T. H. Parmley, Department of Gynecology and Obstetrics, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
760
20
15
..
"0
ii
::0
iii
10
"'0
.
c u 0
0:: 5
8-12
16-20 24-28 30-32 34-36 38-40 42-44 Gest. Age In Wks.
Fig. 1. The black portion of the bars represents those placentas that contained lipofuscin. Prior to 32 weeks none did, and after 36 weeks about half contained pigment. placentas were obtained trom suction abortions in which the pelvic examination and the stated last menstrual period were in agreement. Second-trimester placentas were obtained from ureaprostaglandin abortions in which the pelvic examination, the stated last menstrual period, and measurement of the aborted fetus were all in agreement. Third-trimester placentas were selected from pregnancies in which there were two serial sonograms confirming the gestational age or in which all of the following clinical criteria were met: ( l) two examina0002-9378/81/070760+07$ 00.70/0
©
1981 The C. V. Moshy Co.
Volume 1:19
" Aging" pigments in term placenta 761
:\umber 7
Fig. 2. Multiple. brightly fluorescent granules occupy the cytoplasm of the trophoblastic cells . The syncytial "knot" seen in th e center of the photograph is particularly prominent.
10
D
D
9 8
., c
. a: .
7
0
u
6
0
E ....
5
.....
4
D
D D
D D
DD D D ODD
3
2
DD DODD A
8
c
D
Quodronts
Fig. 3. Discrete granules are seen in the trophoblast of one villus. A closely packed cluster produced the large focus of fluorescence seen in the lower villus.
Fig. 4. All forty sections, one from each quadrant of 10 term placentas, are diagramatically illustrated here. Those in black were lipofuscin positive. Nine of the ten placentas contained pigment in at least one quadrant, but the distribution was heterogeneous.
762
Parmley, Gupta, and Walker
5
...c:cu
1/1
0
4
CJ 0
c::
~
3
:::J
0
E cu
...
a..
2
Am . .J.
DODD DODD
oo•o DODD DODD A
B
c
D
Quadrants
Fig. 5. All twenty sections, one from each quadrant of five premature placentas, are diagramatically illustrated here. The one black section represents the only placental quadrant which contained lipofuscin.
tions prior to 20 weeks that were consistent with gestational age as determined by the stated last menstrual period; (2) an audible fetal heartbeat detected between 17 and 21 weeks of gestational age as determined by the stated last menstrual period; (3) an infant who, when delivered, was appropriate in size and development for the gestational age as determined by the stated last menstrual period. Initially, a single random section was taken from each placenta. It was prepared in the routine manner for paraffin block sectioning and one section was stained with hematoxylin and eosin to determine that the placenta was histologically normal. Then unstained sections were examined without knowledge of the gestational age. As light microscopic study of the morphology of the villus reveals approximate age, the initial confirmation of the presence of fluorescent pigment was made by one of us who was unfamiliar with placental morphology. T'hen the site of the fluorescence was determined by a second observer. The examination was performed as follows. The unstained section was deparaffmized in xylene. The slide was blotted dry with a paper towel and examined under oil in a Leitz Orthoplan microscope equipped with an HBO 100-watt lamp epi-illumination, a KP 500 Excitor filter, and a 515 Barrier filter. When the observations were equivocal, they were confirmed by means of a 420 Excitor filter and a 460 Barrier filter. The oil used was Cargille, type A and type B in a 50-50 mixture. Documentation was done with the use of Kodak high-speed 200 ASA Ektachrome film. As a result of the initial study, 10 additional term
April I. ltlHI ( ;nwml.
Ohst~t.
placentas and five premature placentas were cut into four quadrants and a random section was taken from each of the four quadrants; the study was repeated.
Results In the initial study, no pigment was seen in the placenta prior to 30 to 32 weeks' gestation (Fig. I). After 30 to 32 weeks. typical yellow-orange pigment granules were increasingly seen in the trophoblast (Fig. 2). They occurred as single granules or clusters (Fig.:)) . After 37 weeks, they were present in over 5Wlt of the cases (Fig. 1). We did not identify fluorescent pigment in other portions of the placental cake. We did confirm but did not study its presence in the trophoblast of the chorionic membrane. For theoretical reasons, we wondered why the pigment was not present in 100% of term placentas and suspected that heterogeneous distribution. as demonstrated by Strehler and associates.~ in the myocardium was the answer. Accordingly. we examined both term and premature placentas in four quadrants. Fourquadrant examination of the term placelltas revealed that all but one did contain pigment in at least one of its quadrants (Fig. 4), while the preterm placentas continued to show little or none (Fig. 5).
Comment The lipofuscins have been only partially characterized. However, on the basis of the available structural analyses, they are thought to be the result of peroxidation of polyunsaturated lipids by oxygen-free radicalsY- 15 These lipids are widely present in bior~embranes. On the basis of electron microscopic and histochemical studies, the membranes of several specific cell organelles have been suggested as the source of these products. 12 • 16 However, these studies are not all in agreement and they are not mutuallv exclusive. The sum of the evidence suggests that the pigments are derived from a multiplicity of sources. As these compounds are insoluble and only poorly metabolized, they accumulate in fixed postmitotic cells. This relationship is invariable over time, but it can be accelerated by a variety of environmental insults. Significant among the latter is nutritional deprivation, specifically of antioxidants such as vitamin E. 17 Vitamin E is important in the control of oxygen-free radicals, and its absence appears to be associated with more toxicity from these molecules. Further, it has been noted in primates that protein deficiency during gestation can result in increased amounts of these pigments in the central nervous system of the newborn infant. 1" Maternal disease such as hypertension, resulting in relative placental ischemia, could be the source of signiticant
"Aging" pigments in term placenta 763
Volume 13'1 '\umber 7
across-the-board nutritional deficiency and thus produce placental changes difficult to distinguish from agmg. Our observations have demonstrated the appearance of lipofuscin pigments in the human placenta as it nears term. Thus, they complement the findings of others, w. ~ 0 who found increased quantities of peroxidized lipids in the blood of pregnant women at term compared to levels seen earlier in pregnancy. These authors suggested that the pigments originated in the placenta, and our results would support their suggestion. Whether or not the placenta truly gets "old,"
REFERENCES I. Robbins, S. L., and Cotran, R. S.: Pathologic Basis of Dis-
ease, Philadelphia, 1979, W. B. Saunders Co., p. 46. 2. Strehler, B. L., Mark, D. D., Mildvan, A. S., and Gee, M. V.: Rate and magnitude of age pigment accumulation in the human myocardium,
J.
GerontaL 14:430, 1959.
3. Braak, H.: Spindle-shapedappendagesofiiiAB-pyramids filled with lipofuscin: Striking pathological change of the senescent human isocortex, "\eta l'Jeuropathol. (Bed.) 46: 197. 1979. 4. Donato, H., Jr., Hoselton, M. A., and Sohal, R. S.:
Lipofuscin accumulation: Effects of individual variation and selective mortality on population averages, Exp. Gerontol. 14:141. 1979. 5. Rana, R. S., and Munkres, K. D.: Ageing of neurospora crassa. V. Lipid peroxidation and decay of respiratory enzymes in an inositol auxotroph, Mech. Ageing Dev. 7:241. 1978.
whether these pigments reflect nutritional deprivation, or whether they reflect some entirely unrelated process is of course not revealed by our data. Further, it must be emphasized that if "aging" does take place in the placenta, then this does not necessarily mean that "senescence" or functional deterioration occurs. The heterogeneity in the distribution of the lipofuscin may imply a corresponding heterogeneity in the rates at which various parts of the placenta age. It is well known that much cytotrophoblast, presumably "young" trophoblast, persists in the· term placenta.
11. Fox, H.: Pathology of the Placenta, Philadelphia, 1978, W. B. Saunders Co., pp. 21-22 and 203-2 !0. 12. Koobs, D. H., Schultz, R. L., andjutzy, R. V.: The origin
of lipofuscin and possible consequences to the myocardium, Arch. Pathol. Lab. Med. 102:66, 1978. · 13. Trombly, R., Tappe!, A. L., Coniglio, J. G., Grogan, W. M., Jr., and Rhamy, R. K.: Fluorescent products and polyunsaturated fatty acids of human testes, Lipids 10: 59!, 1975. 14. Taubold, R. D., Siakotos, A. N., and Perkins, E. G.:
15. 16.
-
6. Wing, G. L., Blanchard .. G. C., and Weiter,]. ].: The topography and age relationship of lipofuscin concentration in the retinal pigment epithelium, Invest. Ophthalmol. Vis. Sci. 17:601, 1978. 7. Miquel, j., Lundgren, P.R .. and Johnson, J. E., Jr.: Spectrophotofluorometric and electron microscopic study of lipofuscin accumulation in the testis of aging mice, J. Get-ontoL 33;3, 1978.
8. Kent, S.: Solving the riddle of lipofuscin origin may uncover clues to the aging process, Geriatrics 31:128, 1976. 9. Behnke, J. A., Finch, C. W., and Moment, G. B.: Biology of Aging, New York. 1978, Plenum Press. 10. Hayflick, L.: The cell biology of human aging, N. Engi.J. Med. 295:1302, 1976.
Editors' note: This manuscript was revised after these discussions were presented.
Discussion DR. RALPH WYNN, Little Rock, Arkansas. Although the placenta undergoes certain changes that appear teleologically to indicate functional aging (e.g., increased deposition of fibrinoid and calcium, thickening of basement membranes of endothelium and trophoblast, and sclerosis of vessels), other morphologic changes are consistent with maintenance or even improvement in function, such as thinning of the syncytial trophoblast, decrease in Langhans cells, increase in
17.
18.
Studies on chemical nature of lipofuscin (age pigment) isolated from normalhuman brain, Lipids 10:383, 1975. Tappe!, A. 1:.: Lipid peroxidation damage to cell components, Fed. Proc. 32:1870, 1973. Brunk, U., and Ericsson, J. L.: Electron microscopical studies on rat brain neurons. Localization of acid phosphatase and mode of formation of lipofuscin bodies, J. Ultrastruct. Res. 38:1, 1972. Freund, G.: The effects of chronic alcohol and vitamin E consumption on aging pigments and learning performance in mice, Life Sci. 24: 145, 1979. Sharma, S. P., and Manocha, S. L.: Lipofuscin formation in the developing nervous system of squirrel monkeys consequent to maternal dietary protein deficiency during gestation, Mech. Ageing Dev. 6:1, 1977. ·
19. Sekiba, K., and Yoshioka, T.: Changes of lipid peroxida-
tion and superoxide dismutase activity in the human placenta, AM. j. 0BSTET. GYNECOL. 135:368, 1979. 20. Yoshioka, T .. Kawada, K., Shimada, T., and Mori, M.: Lipid peroxidation in maternal and cord blood and protective mechanism against activated-oxygen toxicity in the blood, AM. J. OBSTET. GYNECOL. 135:372, 1979.
capillaries and their approximation to the trophoblast, an·d the surface-to-voitime ratio of the termi~al villi. 1 Estimates of at least 30% to 40% functional reserve are usually made for the term placenta. Thus, even if morphologic criteria of senescence could be defined during placental aging, a concomitant decrease in functional capacity would not necessarily follow. The electron microscope has not provided precise criteria of cellular senescence. The only ultrastructural changes that are identified fairly consistently in aged tissues are increased nuclear indentation, loss of roughsurfaced endoplasmic reticulum, and the accumulation of lipofuscin pigment. It is this pigment which Dr.