Cytoplasmic estrogen receptor concentrations in the endometrium of Finnish and Japanese women

Europ. J. Ohstet. Gynec. reprod. Biol., 17 (19X4) 321-325

321

Elsevier

EJO 00083

Cytoplasmic estrogen receptor concentrations in the endometrium of Finnish and Japanese women R. Punnonen,

A. Lukola and R. Kudo

Depurtment of Obstetrics and Gvnecologv, Biochemistr): und Phormucy, kbo Akudemi.

Universi{v Cetztrui Hospital of Tunzpere, Depurtmetlt of

Turku, Finlmd, and Depurtment

of Obstetrics md Gvnecolog~~,

Sapporo Medicul College, Supporo, Jupm

Accepted

for publication

14 February

1984

PUNNONEN, R.. LUKOLA, A. and KUDO, R. (1984): Cytoplasmic estrogen receptor concentrations in the endometrium of Finnish and Japanese women. Europ. J. Ohstet. Gvnec. Reprod. Biol., 17/5, 321-325. Cytoplasmic estrogen receptor concentrations in the endometrium were determined in 13 Finnish and 20 Japanese women. All the women were premenopausal and aged between 40 and 50. The concentration of estrogen receptors in the proliferative endometrium for Finnish women was 246.9i46.2 fmol/mg protein (mean k S.E.M.) and that for Japanese women 45.7? 17.1 fmol/mg protein. The difference is significant (P < 0.01). In the secretory endometrium the corresponding figures were 97.8 k 33.7 fmol/mg protein for Finnish and 20.0*6.4 fmol/mg protein for Japanese women (P < 0.05). During the proliferative phase the serum estrone concentration was significantly higher in Finnish than in Japanese women (P < 0.05). cytoplasmic

estrogen

receptor;

endometrium;

Finnish

and Japanese

women

Introduction The sensitivity estradiol receptors signifies tion

refractoriness

(Clark

of the endometrium

development 1976;

of the target tissue to estrogens is related (ER) in the target cells. Lack of cytoplasmic

of endometrial

Kistner,

et al., 1978;

McGuire

by endogenous hyperplasia

et al., 1975).

or exogenous

to the content of estrogen receptors Prolonged

estrogens

and even carcinoma

(Andrews,

results

stimulain the

1961; Hertz,

1976).

Since endometrial carcinoma is much more common in Finland than in Japan (Waterhouse et al., 1976), we studied the concentrations of total cytoplasmic ER in the endometrium of Finnish and Japanese women.

Address for correspondence:

Central

Hospital

0028-2243/84/$03.00

Reijo Punnonen, M.D., Department of Tampere, SF-33520 Tampere 52, Finland. Q 1984 Elsevier Science Publishers

B.V.

of Obstetrics

and Gynecology,

University

322

Material and methods Patients and tissue samples The endometrium specimens for ER studies were taken in connection with hysterectomies from 13 Finnish and 20 Japanese women. All the patients were premenopausal and they were between 40 and 50 years of age. The indication for hysterectomy was generally one of uterine myomas. Immediately after the hysterectomy endometrium was separated by curettage. One half of the endometrium was taken for routine histopathologic examination. The other half was placed in liquid nitrogen immediately after the hysterectomy and stored until the ER determinations, which were all performed in the same laboratory. Simultaneously with the removal of the uterus, blood specimens were taken from the antecubital vein for estrogen and progesterone determinations. ER assay The frozen tissue samples were cut into small pieces, which were thawed and washed several times with cold physiological saline. Homogenization was performed in 4 volumes (v/w) 40 mM Tris-HCl/l mM dithiothreitol buffer, pH 7.4, with an Ultraturrax homogenizzer. The homogenate was centrifuged for 1 h at 100 000 x g at 2°C and the resulting supernatant fluid was used for assay of cytoplasmic ER. Aliquots of the cytosol (0.1 ml) were incubated with various concentrations (0.08-5.0 nM) of [3H]estradiol (spec. act. 110 Ci/mmol; New England Nuclear) for 16 h at 0-4’C. Nonspecific binding was determined by parallel incubation with [3H]estradiol plus a lOO-fold excess of unlabelled ligand. In order to measure the total cytoplasmic ER content (occupied + unoccupied), the 16 h incubation at 4OC was followed by 1 h incubation at 3O’C. The unbound ligand was removed by a dextran/charcoal suspension. The protein concentration in the cytosols was determined by the method of Lowry et al. (1951). The radioactivity in the samples was monitored in a liquid scintillation counter (LKB, Wallac 8100). The binding results were calculated by the method of Scatchard (1949). Serum estrone (E,), estradiol (E2) and progesterone concentrations were determined by radioimmunoassay. The statistical analysis was performed with Student’s two-tailed test. Results Table I shows the endometrial cytosol ER concentrations and the serum estrone, estradiol and progesterone concentrations in Finnish women. The corresponding figures, except for serum estradiol, are presented for Japanese women in Table II. In Finnish women the concentration of ER in the proliferative endometrium (246.9 + 46.2 fmol/mg protein; mean f SE.) was significantly higher (P -c 0.05) than in the secretory endometrium (97.8 + 33.7 fmol/mg protein). In Japanese women too the ER content seemed to be higher in the proliferative (45.7 k 17.1 fmol/mg protein) than in the secretory endometrium (20.0 k 6.4 fmol/mg protein). The difference, however, was not statistically significant. Comparison of the binding data between the Japanese and the Finnish group shows that both in the proliferative and the secretory endometrium the ER content is significantly higher in Finnish women

323

TABLE

I

The endometrial cytosol estrogen and progresterone concentrations

Proliferative endometrium

Secretory endometrium

TABLE

receptor (ER) concentrations in finnish women

Day of the cycle

ER (fmol/mg

10 10 13 11 11 12

24 22 17 20 23 22 16

and the serum estrone (E,), estradiol

:mol/l)

(nmol/l)

Progesterone (nmol/l)

320.0 360.5 238.8 318.7 57.1 180.0

0.39 0.62 0.49 0.50 0.58 0.35

0.65 1.25 1.03 1.79 0.95 0.37

(5 <5 (5 <5 <5 <7

246.9 k46.2

0.43 f 0.04

75.4 56.5 12.5 16.0 174.1 91.6 258.3 97.8 f 33.7

0.28 0.59 0.43 0.37 0.30 0.32 0.28 0.42 + 0.07

0.65 0.90 0.89 0.10 0.15 1.58 0.74

32 19 30 39 15 11 19

E2

protein)

(E,)

II

The endometrial cytosol estrogen receptor (ER) concentrations gesterone concentrations in Japanese women Day of the cycle Proliferative endometrium

Secretory endometrium

23 28 23 10 17 24 8 27 8 9 27 20 6

25 22 23 23 14 25 19

ER (fmol/mg

protein)

21.8 19.2 88.4 2.2 6.5 8.1 15.0 10.9 88.0 8.6 50.9 2.6 195.7

and

the serum

estrone

(E,)

E, (nmol/l)

Progesterone (nmol/l)

0.25 0.24

15 <5 <5 C5 <5 <5 15 <5 <5 <5 <5 is 15

0.15 0.35 0.36 0.36 0.26 0.36 0.28 0.23 0.27 0.28

45.7 _c 17.1

0.28 f 0.02

10.9 50.0 5.3 10.9 55.0 22.8 10.4 20.0 _+6.4

0.45 0.34 0.34 0.35 0.27 0.31 0.38 0.35 f 0.02

18 38 17 23 14 12 13

and pro-

324

(proliferative: P < 0.01;secretory: P < 0.05). The serum estrone concentration is also higher in Finnish women, but reaches statistical significance (P < 0.05) only during the proliferative phase of the menstrual cycle. In Finnish women no difference in the E, concentration between the two phases was observed, whereas in Japanese women the E, concentration was significantly (P -c0.05) higher in the secretory phase of the menstrual cycle. Discussion The endometrial cytoplasmic estrogen receptor content is known to be highest in the early proliferative phase, decreasing toward the late proliferative phase (Bayard et al., 1978). We too found a higher ER content in the proliferative endometrium than in the secretory endometrium, although the difference was statistically significant only for Finnish women. The lower ER content in the secretory endometrium is thought to be related to depression of the ER level by progesterone (Hsue et al., 1976). The depressive effect of progesterone on the estrogen receptor system is also thought to be related to increased 17fi-estradiol dehydrogenase activity (Pollow et al., 1975). This enzyme, which is induced by progestins, converts estradiol to estrone, which is a less active estrogenic compound. During the secretory phase significantly more of the endometrial estrogen is found as estrone than during the proliferative phase (Tseng and Gurpide, 1974). In our study serum estrone concentrations were of the same order of magnitude during both phases in Finnish women, whereas in Japanese women the estrone level was significantly higher in the secretory phase. In Finnish women the serum estrone concentrations during the proliferative phase were significantly higher than in the corresponding phase of Japanese women. In menstruating women estrone has little clinical significance. The finding may, however, reflect the greater estrogenicity of the Finnish women. A finding of interest was that the concentrations of estrogen receptors in both proliferative and secretory endometrium were significantly higher in Finnish than in Japanese women. The clinical significance of this finding is difficult to evaluate. A higher estrogen receptor content, however, would mean a higher response magnitude of target cells to estrogens. The incidence of endometrial cancer in Japan is considerably lower than in western countries. For example, the average annual incidence of endometrial cancer per 100000 females in Miyagi Prefecture, Japan, during 1968-1971 was 1.3 and in Osaka Prefecture during 1970-1971 0.8. In Finland the corresponding incidence during 1966-1970 was 12.5 (Waterhouse et al., 1976). Whether the lower incidence of endometrial cancer in Japanese women is correlated with the lower receptor content found in the present investigation, or is due to ethnic differences or to undefined environmental factors, remains to be established. The data presented, however, indicate that further studies in this area are warranted. Acknowledgement This study was supported

by a grant from the Pauio Foundation.

325

References Andrews, W.C. (1961): Estrogens and endometrial carcinoma. Obstet. Gynec. Surv., 16, 747-767. Bayard, F., Damilano S., Robe], P. and Baulieu, E.E. (1978): Cytoplasmic and nuclear estradiol and progesterone receptor in human endometrium. J. Clin. Endocr. Metab., 46, 635-648. Clark, J.H., Peck, E.J., Hardin, J.W. and Eriksson, H. (1978): In: Receptors and Hormone Action II, pp. l-29. Editors: B.W. O’Malley and L. Birnbaumer. Academic Press., New York. Hertz, R. (1976): The estrogen cancer hypothesis. Cancer, 38, 534-540. Hsue, A.J.W., Peck, E.J. and Clark, J.G. (1976): Control of uterine estrogen receptor levels by progesterone. Endocrinology, 98, 438. Kistner, R.W. (1976): Estrogen and endometrial cancer. Obstet. and gynec., 48, 479-482. Lowry, O.H., Rosebrough, N.J., Farr, A.L. and Randall, R.J. (1951): Protein measurement with the folin phenol reagent. J. Biol. Chem., 193, 265-275. McGuire, W.L., Carsone, P.P., Sears, M.E. and Escher, G.C. (1975): In: Estrogen receptor in Human Breast Cancer, pp. 1-7. Editors: W.L. McGuire, P.P. Carsone and E.P. Vollmer. Raven Press, New York. Pollow, K., Lubbert, H., Boquoi, E., Krentzer, G., Jeske, R. and Pollow, B. (1975): Studies on 17p-hydroxysteroid dehydrogenase in human endometrium and endometrial carcinoma. I. Subcellular distribution and variations of specific enzyme activity. Acta endocr. (Kbh.) 79, 134-145. Scatchard, G. (1949); The attraction of proteins for small molecules and ions. Ann. N. Y. Acad. Sci., 51,660-672. Tseng, L. and Gurpide, E. (1974): estradiol and 20a-dihydro-progesterone dehydrogenase activities in human endometrium during the menstrual cycle. Endocrinology, 94, 419-423. Waterhouse, J., Muir, C., Correa. P. and Powell, J. (1976): In: cancer Incidence in Five Continents, Vol. III. Editors: J. Waterhouse, C. Muir, P. Correa and J. Powell. JARC Scientific Publications No. 15, Lyon.