Cytodynamic Properties of the Human Endometrium

Original Communications CYTODYNAMIC PROPERTIES OF THE HUMAN ENDOMETRIUM V. Metabolism and the Enzymatic Activity of the Human Endometrium During the Menstrual Cycle* VIRGINIA MAE STUERMER, M.D., AND RoBERT ,J. STEIN, IowA CrTY, IowA ARBURG and his co-workers1 promoted an interest in growth and reproduction and their underlying metabolic processes which has pyramided into a voluminous literature encompassing nearly every living organ and tissue. In view of this, it is incomprehensible that the endometrium, a tissue which constitutes the very bed of mammalian reproduction, has b.een so neglected. Reynolds ' 2 classic text on uterine physiology records the known facts concerning uterine metabolism in one short chapter. Most of the work cited concerned animal material and did not differentiate myometrial and endometrial metabolism, although the morphologic and biochemical properties of the two suggest differences in physiology. The present study was undertaken to augment our knowledge of human endometrial metabolism. Weekly endometrial biopsies were taken on the same individuals, so that any changes found would reflect cyclic variations in endometrial metabolism. Some of the more important enzymatic reactions utilized in endometrial metabolism were studied. These functional changes were then correlated with morphologic alterations in an endeavor to explain logically the implications of the structural variation. Finally, the entire concept of endometrial metabolism developed in the course of the study was transposed into the clinical realm where research must ultimately find expression if it is to fulfill its most useful role. ~rhe immediate source of animal energy is glucose, but two other facts are basic to the understanding of energy transformation. First, all energy can be accounted for as being derived from the phosphorylative mechanism. Second, all biologic energy transformations revolve about the adenosine tri-phosphateadenosine mechanism. Digestion converts carbohydrates to simple sug·ars. In liver and muscle, simple sugars become glycogen (glycogenesis). Other substances besides carbohydrates-namely, glycerol, certain amino acids, lactic acid, and certain fatty acids--may be converted to glycogen (glyconeog·enesis). In glycolysis, glycogen or the simple sugars are phosphorylated and then converted to pyruvic acid by a dozen or more enzymatic reactions. Krebs3 discovered the mechanism fo1· pyruvate oxidation when he found that fumarate and pyruvate could be converted to succinate anaerobically in the presence of malanate. This led to the

W

*Parts of this paper were used in a thesis awarded second prize in the September, 1950. thesis competition sponsored by the American Association of Obstetricians, Gynecologists and Abdominal Surgeons.

359

STUI!JRMER AND S'rElN

Am. j. Obst. & (jyne~". Febru.tr:r, 1').::,:

I"Pc·og-nition of the triearboxylie ac·id (•ydP, ~whieh represents the main mpehanism for· oxidation of earbohydrates in animals. Probably phosphon·lated interlllPdiateK exist for all the steps in thi8 eyde also. The steps involved eau ht· l'onn<1 in any reeent, standard biochemical textbook. 4 Thus, the eonversion of glucose from glyrogc'll to lactie a(·icl is a proees~ aetomplished by a series of reactions whi(·h are all reversible, except for the dephosphorylation ot pyruvir ac·id. All hut two are eatalyzed by specifie enzymes and several require co-enzymes. Biologic oxidations must proceed stepwise for utilization of released energ~·. 'rh(·~- depend on the tran~Sfen'twe of h,\"(hogen to an t>nzyme. Dehydrogenases ate the' responsihle enzynH·s. If dehydrogenase is assO<·iated with a eo-enzyme, the latter i8 reduced and i hen may act as snbstrnte for a S0<'0JHl dehydrogenase to whirh hydrogen is transferred, thu:-~ reehiiming the original c·o-enzyme. Each such reaction releases energy used to regenerate high energy bonds. The cytochrorne syst.e1n operates in a shnilar 1nanner, although it transports electrons and not hydrogen. This system consists of three cytochromes, a, b, and c, and a eytoehrome oxidase." The iron atoms therein are alternately r·edneed and oxidized with the ultimate formation of water. Coupling the tricarboxylic aeid eyele to the rytochrome system affords an alternate pathwa~· for hydrogen trau~SEer. Thus the energy neeessary for maintenance of dynamic cellular equilibrium or for cellular propagation is derived from enzymatic reactions, largely of the oxidation-redu<•tion variety. These 1·eaetions arc controlled by several regulating mechanisms. With inereased differentiation, more ~Specific regulating meehanismf\ are brought into pla,,·. 'rhPsP indude hormoneH, genes, nucleoprotein;;, ele(~tr·ol,vtes, vitamins, and c·ertain oxidation-reduetion systems which act hy controlling the rate ot· the pohnity of enz,vmatic reactions. According to Re~·noldo;, the J·espil'ation of certain animal uteri, liver, ovary, and anterior pituitary varic•s with the sex eyele, heing high in proestrus and e:-;trus aJHl low in diestrus. Other fac·tor·s also point to a cyclic variation. The activity of the thyroid gland is knowu to inerease periodically and this in turn exerts some effect on the metabolism of the reproductive organs. Body temperature drops in rats, guinea pigs, and rahhits just before estrus. In human beings the drop and l'isc due to progestational cffeet form one of the presumptive indieationf:-1 of ovulation. He,vnolds sugg·ests on the basis of known reciproeal rc•lations between anterior pituitar,v a ttcl ovary on the one hand, and betwet'll onu-y and uterus on the other, that the increased metabolism of the pituitary hears a causal relationship hy way of the thyroid to the elevated metabolism observed in the uterus and elsewhere. The author found few papers on human endometrial metabolism in the literature. Raab" was able to show definite cyclic variation in metabolism in experiments carried out by the original Warburg method. Anaerobic glyeol;rsis was three times higher during the proliferative phase than during the secretory. Similarly, oxygen consumption was three times higher during the last two us compared to the first two weeks in the cycle. Adler, 7 using the same terhnique.

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CYTODYNAMIC PROPERTIES OF HUMAN

ENDO~fETRIUM

361

was unable to demonstrate any correlation between the menstrual cycle and endometrial respiration. Table I is a composite table showing range of results obtained by these two investigators. The range is so wide as to he statistically invalid. TABLE I. RESPIRATION, AEROBIC GLYCOLYSIS, ANAEROBIC GLYCOLYSIS, AND DERIVED RELATIONS OF THE ENDOMETRIUM CALCULATED FROM THE FIGURES REPOR1'ED BY RAAB,6 AND ADLER'

VALUES Respiration QO,

PROLIFERATIVE PHASE EARLY LATE

SECRETORY PHASE EARLY LATE

2.5-15.2

2.6-14.2

3.9-16.2

4.5 -23.0

3.0-10.9

3.8- 6.7

2.8- 7.1

2.6 . 4.5

13.5-18.8

10.2-16.7

8.3-17.9

5.2 -16.1

6.6-15.4

4.1-11.8

2.8-13.6

0.7 -10.2

-···--

·-

Aerobic glycolysis Qo. co. Anaerobic glycolysis QN• co.

.

inhibition

QN' co.

Q o. co,

Pe:r cent inhibition of glycolysis by air 100 (Q

(J().- Q co,)

41 -81

40.1-71

34 -85

13

-79.6

~~6. Meyerhof oxidation quotient Q N, -Qo' co, co. Q0,/3

2.2-12.6

1.4-13.8

0.5- 6.0

0.9 . 6.3

3.2-19.1

2.5-20.8

1.5· 8.9

0.85- 8.4

1.0- 6.5

1.1- 7.0

1.0- 4.0

0.5 - 1.9

~-

Anaerobic glycolysis Equivalent respiration QN' co, Q0,/3 Aerobic glycolysis Equivalent respiration

~

Dreyfuss8 studied endometrium obtained from operative cases presenting regular menstrual histories. He used a Victor modification of the Fenn differential volumeter. His range of values was much smaller (Table II). He showed no significant differencees between the proliferative and secretory phases. However, he catalogued his tissues only as either proliferative or secretory. Reynolds postulated the existence of several enzyme systems in the endometrium, but it remained for Hughes 9 to demonstrate the amylase system and for Zondek and Hestrin10 to show the existence of the phosphorylase system in human endometrium. Both of these enzyme systems were shown to have a cyclic variation. Amylase concentration increased markedly following ovulation and reached its peak just prior to menses. Phosphorylase concentration likewise soared following ovulation. Zondek felt that the activities of these

362

8'l'UERMER AND STEIN

Am .

.f.

Obst. & Gyrw< Febru,uy, 195:?

two systems were mutually complimentary. Phosphorylase aets as a synthesizing instrument, fixing diffusible sugar and keeping the latter in a nondiffusible form and hence a storable reserve stuff (glycogen). Amylase, on the other hand, mobilize~ the glycogen reserve o:f a tissue and COJJYerts the glyrogen into suga1·s (maltose, glucose) which are diffnsihl('. TABLE

II.

RESPIRA7'JOS, .\.EROlliC ULY('0LYSLS 1 Al\AEROI:llU l+J,YCOLYSL:S, AND DER!Vlm RELAT!Ol\S OF I'I!E ENDOME'fRl\JM CALCULATED FROM THE E'mL:RES REPORT~:JJ BY DREYFUSS8 L\T.rf;:-;

Re~piratilln I 13.0-~0.0)

QO,

Aerobic

( 14.7-17.~.1

glyr•oly~is

Q~o,

J.O ( 0.08-1.7)

fl.i (7.1-12.7)

( 6.2-11.1 1

8.3

7.5

85

88

l.:J

1.4

1.8

1.6

0.25

0.19

glyeoly~is

Anacrobi
('(),

Glyeoly~is

1.4 (0.07-2.1;

8.5

inhibition

(~N, -Qo' CO,

CO,

Per eent inhibition of glycolysis by air 10(1

Meyerhof oxidation quotient

Anaerobic glycolysi~ .I
::'\,

(tc<\ QO,/f Aerobic glycoly~is EquivalO:'nt respiration

This study was organized from the point of view of presenting a systematic survey of the eyclic variations of some human endometrial metab.olic mechanisms. Thus, there will be separate sections devoted to: 1. Hespiration, aerobic glycolysis, and anaerobic glycolysis

2. Activity of succinic and malic dehydrogenases 3. Cytochrome oxidase activity 4. Adenosine triphosphatase activity Each section will contain its own introduction, an outline of experimental methods, and a tabulation of results, together with a short discussion of imPlications.

CYTODYNAMIC PROPERTIES OF HUMAN ENDOMETRIUM

Volume 63 Number 2

363

The material for Section 1 was obtained by doing weekly endometrial biopsies on six regularly menstruating, physically healthy women throughout one complete menstrual cycle. Biopsies were taken with a Randall curette after the cervix had been cleansed with 1 :1,000 aqueous Zephiran. The material for the other three sections was secured from operative specimens from patients presenting regular cycles. Though menstrual histories were available from all the subjects it was felt that the results would be more valid, if so ephemeral a thing as a patient's memory could he negated. Therefore, the specimens were dated according to the technique described by Noyes. 11 Because the series is small, the specimens were grouped into early and later proliferative and early and late secretory phases. Rate of Oxygen Consumption (Q0 2 ) Because the metabolic properties of the endometrium have received scant attention, respiration and glycolysis, of the endometrium during the menstrual cycle were studied. Methods.Bndometrium, obtained by suction curette about one and one-half hours prior to the experiment, was weighed on a Roller-Smith balance. .Aliquots were taken for initial wet-dry weights and for Q02 determinations. The oxygen consumption (Q0 2 ) was measured in micro-Warburg manometers with side bulbs and gas outlets. 12 Three-tenths ml. of Krebs-Ringer phosphate solution with a 0.2 per cent concentration of added glucose was used in the manometer flasks as the substrate. The dry weights of the tissue varied from 4 to 10 mg. Results.Oxygen consumption rose during the late proliferative and late secretory phases. The differences were not pronounced and overlapping of values occurred. Statistically, there was no significant variation in oxvgen consumption--a finding consistent with that of Adler and Dreyfuss (Table III). TABLE

III.

PATIENT

1. M.D. 2.

T.

3. M. 4 .. M. 5. H. 6. R.

RESPIRATION

(QO,)

EARLY PROLIFERATIVE

3.96

R.

H. S. H.

2.91 2.98

C.

3.10

OF THE ENDOMETRIUM DURING THE MENSTRUAL CYCLE

·---·····-······-···--

LATE PROUFERATIVE

F--ARLY SECRETORY

LATE SECRETORY

3.92 3.83 4.18 5.58 4.64 4.21

2.59 ·1.36 3.21 3.34 4.9 4.85

4.36 5.48 5.5 4.36 4.53 5.08

Although the proliferative and secretory endometriums differ morphologically, failure to demonstrate cyclic variation in the Q02 was not surprising. Lyman and Barron13 showed that the over-all Q02 values of a pathologic tissue could be identical with its normal counterpart. They found average Q02 values of 17.6 ± 0.4 for both normal and nephritic kidneys. However, oxidation of pyruvate was reduced from 8.2 to 0.5 in normal kidneys while the lactate Q02 was reduced from 7.7 to 1.0 in nephritic kidneys, showing that fundamental changes in the enzymatic constitution of a tissue can take place without affecting the resting oxygen consumption. This concept can be applled to the endometrium as will be shown in subsequent experiments in this report.

S'l'UERMER

364

A~D

,\m. j. Ob;t. & Gyne<.

S'l'EIN

Febru"'y, 1912

Aerobic Glycolysis 'l'hough the differences found in total respil'ation of endometrium during different phases of the menstrual cycle were small, acting on Lyman's principle stated before, we determined aerobic glycolysis ( Q0 2 acid). Methods.The 1nethod of Dickens and SimerJ.l was used. The medium was KrebsRinger-bicarb.onate'"; the gas mixture, % per cent oxygen and 5 per cent carbon dioxide. Results.Highest values for aerobic glycolysis oeeurred during the secretory phase, an effect opposite to that in anaerobic glycolysis (Table IV). The values obtained for anaerobic and aerobic glycolysis of endometrium indicated that in the former glucose is transformed into lartic acid (anaerobically) and in the latter pyruvic acid is oxidized to carbon dioxide and water (aerobically). The phosphorylated intermediates as well as the citric acid cycle and the eyclophol'a.se system will have to he investigated in detail to explain the exact enzymatic changes taking place in the endometrium. 'l'Am,E

IV.

)~.:t:J:OilW

Cli.YCOT.Yi:>Ifl \ Q

~~II>)

lW 'l'Hf; };NJ>OME'rRIUM DuRING

TH~;

M;;l\'s'l'IWAL CYm,r~

PROLIFERATIVE

0.68 0.50 0.60 0.44 0.51

0.63

0.79 0.88 0.84

1.92 2.0 :!.05

0.92 0.84

1.77 1.48

0.7?.

3.0 2.98 3.40 3.05 2.96

].64

Anaerobic Glycolysis As previously stated, Raah" aemonstrated that the rate of anaerobic glycolysis was three times higher during the proliferative phase; Adler 7 found no change; Dreyfuss8 a slight Yariation. Because anaerobic glycolysis is an important source of cellular energy, activities of certain enzymes necessary for anaerobic glycolysis in endometrium were reinvestigated dming the different phases of the menstrual cycle. Method.The weighed tissue was homogenized in 0.2 ml. of cold triple glass-distilled water. Sufficient cold water was added to make a 5 per cent suspension. Fol' the assay, 0.3 ml. of the homogenate was added to each working flask. 'l'he method of Novikoff, Potter, and LePage' 6 modified by Copenhaver, Meyer, and MeShan 17 was employed. Resttlts.~-

Anaerobic g·lycolysis decreased markedly during the secretory phase. The highest activity in the early proliferative phase (Q gradually to the lowest in the late secretory ( 6.8).

gOz

18.2) dropped N., The over-all Q ('() was 2

Volume 63 Number 2

365

CYTODYNAMIC PROPERTIES OF HUMAN ENDOMETRIUM

higher during the proliferative phase (Table V). Explanations for these differences may be numerous. Rapid growth of the glands during the proliferative phase together with a relatively small vascular supply forces the tissue to function in a state of partial anaerobiosis. Therefore, until adequate vascularization occurs the endometrium may acquire its energy through anaerobic means. TABLE

V. ANAEROBIC GI,YCOLYTIC AcTIVITY

N (QCO.)

0~' THE ENDOMETRIVM

DURING THE MENSTRUAL CYt~I.E ANAEROB:C GLYCOLYTIC AC1'IVITY ENDOMETRIUM EARLY PROLH'ERATIVE

18.2 17.6 18.8 18.3 17.2 19.4

LATE PROLIF·ERATIVE

EARLY SECRETORY

LATE SECRETORY

14.8 15.2 13.4 13.9 13.4 13.3 14.9

8.9 10.0 8.8 9.0 9.2 8.8 9.4 8.7

6.3 7.0 6.0 6.8 7.2 7.7

The Ensymes McShan and his co-workers 18 have shown that the activity of adenosine triphosphatase, succinic and malic dehydrogenases, and cytochrome oxidaS(' in the ovary of rats during the different phases of reproduction varies directly with growth and development of the corpus luteum. Endometrial changes are monitored by ovarian hormones but no data are available regarding enzymatic activity in human endometrium. Therefore, we tried to demonstrate certain enzymes in the endometrium together with evidence of their cyclic variation in order to develop probable relations between ovarian hormones and endometrial metabolism. Succinic dehydrogenase, malic dehydrogenase, and cytochrome oxidase were used as representative aerobic enzymes, and adenosine triphosphatase as a representative energy-depleting type enzyme.

Succinic Dehydrogenase

Results.Activity increased markedly from early proliferative to early secretory and attained its maximum activity during the latter phase. A fall in succinic dehydrogenase activity occurred during the late secretory phase. Values were relatively higher than in the early proliferative ('l'able VI).

Malic Dehydrogenase l\Ialic dehydrogenase requires the presence of diphosphopyridine nucleotide in ordel' to react with the cytochrome system, but this factor is not necessary for succinic dehydrogenase. Therefore, determinations were made to see if MDH-ase activity would parallel SDH-ase activity. Results.Malic dehydrogenase activity increased from the minimum in early proliferative to the maximum in the early secretory phase (Table VII). These values paralleled the succinic dehydrogenase activity except that no drop in malic dehydrogenase activity occurred during the late secretory phase. The values found in early proliferative and late secretory phases were approximately the same.

STUERMER AND S'l'EIN

366 TABLE

VI.

Am.

J.

()b,t, & Gyncc.

Febru;uy, 1952

SUCCINIC DEHYDROGE:-!ASt: ACTIVI'l'Y OF THE BNIJOME'l'RI1.'~1 DURING THE MENSTRt:AL CYCLE

-------------------------- -·- ··------S l'CCINTO DEHYDROGEN ASf1 ACTIVITY ( QO,) ·-·-~---~-

-----~

-~---------

EN!>OME~'P.Il:M

EARLY

...

LA1'E

IO:AIO.Y

LATE

,.;ECRETORY

St:CRETOHY

41.-t

!2H.l

20.5 20.0

28.0

20J)

::!9.(i

21.:-l

28.7

25.5

~})..1

21..1

~4 ..'l :.;;ul 2ti.O

~QO

25.8

20.7 :!9 ..1 A,--e-ra_g_e------cc20.7______ - - - - ! - - - !:!8.S --~-ang~_Q9Jl:~l.4) 'l'Asr.~:

(28.fJ-:30.0 1

vn.

MALrc DJ<:JtvvRoGEKAst: .\.("nvrTv or· THt: ENDOMt:-rRit'M DntrNG •rHE Jl.ft:KH~'RrAr. Cvrr.r: MALIC I>EH YllRO(JE:NASE ACTIVIT'i ( Q0 2 )

·-------~~·---~----------~~··-----

EARLY l'ROJ,JFERATIVE

· I

-~~-~OLH'ER.ATIYE

27.1 28.0 27.4 26.9 21.2 25.9 Average

ENDOME~'RIT:M

· r."A-l•r;· -------

:~::

Range (25.9·28.3) ___

I

I I

29.0

:34.o

i I i

33.1

1

1- --- !~H-

46.R +9.0 44.9 48.3 42.9 45.5

1

I

:n.1

__ \ ____ ----~~:~

__j___ ._.. (29:~:~1-~:QL. _

I_

LATE

HECRF:TORY

_____ 1

:)2.5 il2.2

... - -

r:ARL v

1

_

28.4 28.8 26.2 28.1 28.5

:::~ ~~2.9-~~0) ............. l. ___C?6.2-2~:~~-- .... .

Cytochrome Oxidase Since both malic and succinic dehydrogenaHe require the presence of the cytochrome cytochrome-oxidase system for artivity, a study of the cyclic· activity of cytoeh1·ome-oxidase was made. }fethods.-

The assay for ('ytochrome oxidase adivity was carried out on the same 1issue samples as the assay for succinic dehydrogenase. The substrate consisted of 0.3 ml. 9 x 10- 4 M cytochr·ome c. 22 Activity of this enzyme was expressed in terms of the Q0 2 of the endometrium during the different phases of the menstrual cycle (Table VIII). The lowest average Q02 value of 207.8 occurred in the early pt'Oliferative phase and increased to 463.9 in the early sem·etory phase. 'fhe values dropped sharply during the late secretory phasr and approximated the lowest values.

Adenosine Triphosphatase Cells contain reservoirs of energy such as adenosine triphosphate, glycogen, phosphocreatine, and fat, as well as enzymes essential for the liberation of the energy. In normal growth or differentiation and in cellular specialization these energy reservoirs vascillnte betwcen periods of marked aetivi1y and periods of relative quiescence. The content of adenosine triphosphatase. in I' at muscle, lungs, kidney, spleen, liver, brain, and ovary has been reported. 22 • 23 Evidence indicates

Volume 63 Numbet· 2

CYTODYK AMIC PROPERTIES OE' TABLE

VIII.

EARLY PROLIFERATIVE

219.3 200.0 216.4 210.5 197.8 203.1

HUMA~

367

ENDOMETRIUM

CYTOCHROJ\IE OXIDASE ACTIVITY OF THE ENDOMETRIUM DURING THE MENSTRVAL CYCLE

PROUFERA TIVE

l';ECRETORY

LATE SECRETORY

296.4 305.9 300.0 298.4 305.2 296.3 308.3

428.0 492.0 500.5 483.6 477.4 435.0 440.0

274.0 255.5 240.2 268.8 270.5 258.5 238.7

that the adenosine triphosphate system may store within its structure the energy liberated by the process of anaerobic 24 and aerobic 25 metabolism. ·This system also links the energy-consuming to the energy-producing reactions. 26 There are no reports concerning ATP-ase activity of human endometrium. Since energy changes in other tissue may be mediated through the AT·P system, studies were made on the ATP-ase activity of the endometrium during the menstrual cycle. Jllethod.The method of DuBois and Potter 27 in which the quantity of ATP-ase determines the velocity of the liberation of inorganic phosphorus from ATP was used. Restdts.Greatest ATP-ase activity was found in the· early secretory phase and least in the early proliferative and late secretory phases. The rise of ATP-ase activity throughout the proliferative and early secretory phases parallels the rise in succinic and malic dehydrogenases (Table IX). 'fABLE

lX.

ADENOSINE TRIPHOSPHATASE ACTIVITY OF THE ENDOMETRIUM DVRING THE l\:IE-"'STRUAI, CYCLE

ENDOMETRJUM EARLY PROUFERATIVE

8.3 9.4 9.8

8.1 7.5 7.8 8.8

PROLIFERATIVE

SECRETORY

I..ATE SECRETORY

12.4 14.9 12.3 14.1 13.8

20.0 24.9 20.6 22.8 21.0 23.4 22.5

5.8 7.2 7.5 7.9 6.9 6.7

From the data presented it can be seen that the concentrations of all four enzymes studied varied with the menstrual cycle. The highest values were obtained during the late proliferative and early secretory phases. Whether this high enzymatic content can be correlated with the functional activity of the endometrium is nnknown.

868

S'l'UERMER AND STEIN

Am.

J.

()b,t. & Gynec.

February, 1952

Hormonal control of the Pndometrium has IH•t•n fail'lv well drfined. Bstrogen reaches its grratt>st coneentration during the Jatt> p.roliferatiw and early secretory phases,zn, :'"progesterone, dming the em·ly se<~r·etor·y phase·.'<~, 1'hus enzymatic activity and thP <·mwentrations of <'sh·og·<·n aiHl p!·ogestet'OlW parallel each othrr. \Vhethrr this llleans that fmwtion is gTeatet· when enzyme activity is high is not clear. However, otw approac·h to this wohlem would ht> to detet!lline the r·elationship of enzymE• cont·eutt·atinns to H]weific functiom; of th<· tissue and to other enqme :;;ystems.

Comment 'l'he reHtllts presented indicate that metabolic and enzymatic activity of the endometrium val'ieH with the different phases of the menstrual eycl('. Changes in the aPtivity of enzymes at'(' t·elated to the processes concNned with growth, differentiation, and funetion. In the liver, the actions of adenosine triphosphatase. succiniP dehydrogenase. and cytochrome ox:idas('a 1 increase during late embryonic life and reach adult levels two weeks afte1· birth. These enzymes represent both energy-yielding and Pnergy-depleting types. 'l'he potentially mobilized ener·gy becomes greater in both types of enzymes during the period of inereased differentiation and function. In early fetal life, 34 the succinic dehydrogenase of the eerebl'al cortex is approximately :3G JWI' cent of that of tlw adult. Th(' aetivity of succinic dehydrogenase is SO to 100 per· C('llt higher in pulp taken from trained muscle than in that from fatigued muscle.'1·' Raskaan foulld a significant increase in the activities of eytochrome oxidase and succinic dehydrogenaRe and in the conef'ntration of eytochrome a in the kidneys of clogs after unilateral nephrectomy; tho~e increases preceded hypet'trophy of the remaining kidney. The activities of these enzymes and the concentration of cytochrome c were decreased in slices and suspensions of kidneys ft·om hypertemdve dogs. Malic and succinie dehydrogenases, adenosine triphosphatase, and cytochrome oxidase reach high levelH during the development and growth of the eorpus luteum. 37 ln endometrial growth or differentiation (the proliferative phase) and. specialization (the St>erdory phast•), a relatimtHhip S('ems to exist between t'nzymatie activity and functional activity such as has been shown for other tissue:-;. During· the proliferative phaHe of the endomet1·ium, malie and sueeini•~ dehydrogena:;;es, cytochrome oxidase, and adeuosin(' triphosphataHe incr·ease in activity. The activity reaches its maximum during the early RN'l'Ptory phase and declines during the Ia te Rt'cretory. 'rhc relation of hormonal activity to the metabolic and enzymatie change;; in the endometrium is a faseinating, eontroversial, and highly fertile field for· t•esearch. Khayyal and Seott 38 found that oxygen consumption by rat or mouse uteri in vitro showed eyelie val'iations, being almost constant during estrus and the first part of diestrus and nearly doubling during the lattH part of diestrus. After spaying, no such variations took place. Subcutaneous injections of fresh bovine follicular fluid <'aused a rise in oxygen consumption of the rat ut('rus. Conversely, DavicF' reported that oxygen consumption did not increaRe during natural estrus or when estrns was induced by hormones in the spayed animal. Kerly•o found that the rate of anaerobic glycolysis varied in uteri of control rats. Injection of estradiol increased the rate. 'fhough the oxygen consumption was also increased, this effect was less marked than the rise in anaerobic glycolysis. Carrol 41 reported that injeetions of fifty gamma of estradiol into rats caused inereased uterine respiration, and augmented .aerobic and anaerobic glycolysis. 'fhis investigation made no attempt to determine the effect of hormone~-> on the respiration, aerobic or anaerobic glycolysis, nor on enzymatic activity

Volume 63 Number 2

CYTODYN AMIC PROPERTIES OF HUMAN ENDOMETRIUM

369

of endometrium. However, if one accepts the view that the endometrium during the proliferative phase is under the influence of estrogen and during the secretory, under both progesterone and estrogen, certain obvious deductions can be made. The problem of the immediate future is to determine mechanisms by which hormones, on the one hand, and changes in the external environment, on the other, affect the activity of the specific enzymes. Next, the reciprocal relations between the metabolic and endocrine systems must be clarified. The recent investigations by Cori and his co-workers 42 of the effect of the anterior pituitary and adrenal cortex on glycolytic enzymes in animal tissues opens an avenue of approach which should stimulate much work in the field of female endocrinology. The balance between aerobic and anaerobic glycolysis in the endometrium is determined by the functional state of the tissue. This makes the relationship of glycopenia of the uterus to sterility more comprehensible. It also suggests a whole new approach to persistent sterility in the woman who has no apparent abnormality according to present methods of investigation. The habitual aborter may well demonstrate an enzymatic deficiency incompatible with continued pregnancy. Faulty placental development may be a reflection of imperfect enzymatic function. Not only the pregnancy cycle but also the menstrual cycle depends upon proper enzyme-endocrine reciprocity. The increasing numbers of functional bleeders should be reduced through the complete understanding of the cyclic variations of enzyme activity. Enzymatic failure might well account for the picture of poorly developed seeretory endometrium seen in a portion of patients with abnormal bleeding. Hyperplastic endometrial changes could be enhanced by changes in endocrine-enzyme balance, thus placing the etiology of cystic hyperplasia, pseudomalignant endometrial changes, polyps, and even malignancy on a firmer foundation. This study is valuable only because it evokes speculation. Obviously, changes observed in so few cases can do little more than demonstrate a trend. Furthermore, no attempt was made to convert fancy into fact through actual clinical testing of our results. Indeed, such an undertaking would be astronomical in scope. At this point in the study of endometrial metabolism, we are content to philosophize on the clinical implications, hoping thereby to stimulate a closer surveillance of these facts by other investigators. This study is only a bare beginning. Its greatest contribution is that it shows that human endometrium is readily obtainable and easily studied. Because of the tremendous import of this tissue in the economy of the female org-anism and because present methods facilitate study of this tissue, it is to be hoped that human endomerium will be exhaustively studied in the near future. In so doing one of the greatest enigmas in medical science may be solved.

Summary 1. Oxygen consumption rises during the late proliferative and late secretory phases. 2. Highest values for aerobic glycolysis occurred during the secretory phase, an effect opposite to that in anaerobic glycolysis. 3. The activities of malic and succinic dehydrogenases, cytochrome oxidase, and adenosine triphosphatase rise during the proliferative phase and attain their maximum activity during the early secretory. 4. Enzymatic activity seems to parallel hormonal activity.

S'l'UERMER AND S'l'EIN

Am. l Ob,t. & Gvuec February, -19;.7

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