SciELO - Scientific Electronic Library Online

Home Pagealphabetic serial listing  

Services on Demand




Related links


Revista chilena de anatomía

Print version ISSN 0716-9868

Rev. chil. anat. vol.17 n.2 Temuco 



* José Manoel dos Santos
** Danilo Carreiro de Teves
*** Edmund Chada Baracat
*** José Maria Soares Júnior
** Manuel de Jesus Simões

* Universidade Anhembi-Morumbi, Brasil.
** Departamento de Morfologia - Universidade Federal de São Paulo-Escola Paulista de Medicina, Brasil
*** Departamento de Tocoginecologia, Universidade Federal de São Paulo - Escola Paulista de Medicina

SUMMARY: The aim of this work was to study the modifications that occur in the rat endometrium in persistent estrous induced by continuous light. The behavior of the rat endometrium was also analyzed after administration of estrogens and progestogens isolated or in association under these circumstances.

The results showed that the endometrium stroma of the rats submitted to continuous light presented typical features of the estrous phase, the glandular and surface epithelia presenting stratification zones which were dependent on ovarian hormones because these characteristics disappear after oophorectomy.

The oophorectomy was unable to block the effects induced by the light because after administration of the estrogen the endometrium presented the same features of the animals in persistent estrous. The administration of estrogen and medroxyprogesterone inhibited the stratification indicating that the progesterone modulated the action of the estrogen.

We concluded that the persistent estrous induced by continuous light is dependent upon hormones mainly the estrogens. The progesterone also blocks the inductions provoked by estrogens.

KEY WORDS: 1. Persistent estrous; 2. Endometrium; 3. Continuos light; 4. Metaplasia.


Rodents present short, successive and regular estral cycles during the whole year, whose characteristics include behavioral, hormonal and morphological changes which are noticeable in ovaries, uterus, vagina and mammary glands (GRÖNROOS & KAUPPILA, 1959; CAMANO & GIUFFRIDA, 1970).

However, there are experimental or physiological conditions that modify the cycle and induce a condition of persistent estrous in rats. These conditions are accompanied by morpho-functional changes of the reproductor female tract which result in endometrial changes.

PARDI et al.(1993) and PATRIARCA et al. (1996) studied persistent estrous induced by testosterone propionate in rats and showed that the epithelium of the endometrium is monolayered and cylindrical, with numberless mitotic figures although in some regions the epithelium show stratification without keratinized cells (metaplasia) closed to the opening of the glands or intercalated in the normal epithelium.

SMANIOTTO (1996) also studied the endometrium of persistent estrous rats induced by testosterone propionate, being submitted to oophorectomy and treated with estrogen or corticosteroid (dexametasone). Results show that the oophorectomy does not modify the features of the different cellular types of the endometrium because after estradiol injections the cells behaved with the same endometrial pattern observed in persistent estrous rats. The presence of epithelial germination and stratification of the surface and glandular epithelia in persistent estrous rats would be dependent on the high levels of circulatory steroid hormones, specially estrogen.

The aim of this work is to observe the morphological behavior of the endometrium of persistent estrous rats induced by continuous light.


We utilized 38 adult virgin female rats (Rattus norvegicus albinus) in a state of persistent estrous obtained by continuous light (400 Lux) during 100 days (TAKEO et al., 1986). Persistent estrous was confirmed by vaginal smear for two weeks. After this period the animals were randomly divided in four groups: control group (GI - 7 rats) and experimental group (21 rats). The experimental groups were bilateral oophorectomized. After 21 days of the ooforectomy the animals of the experimental group were divided in three subgroups. The GII received only the soy oil (s.c) for five days; GIII received 10 mg/day of b-estradiol-3-benzoate (s.c) for five days and GIV received 10 mg/day of b-estradiol-3-benzoate (s.c) and 2.5 mg/day of acetate de medroxiprogesterona (i.p) for five days consecutives.

After 24 hours of the last hormonal administration, the animals were sacrificed for the removal of the uterine horns, which were sectioned, fixed in Bouin liquid and processed for the inclusion in paraplast. Following, the blocks were cut in microtome type Leica RM 2035, adjusted for 3 mm and the specimens were colored by H.E and observed in light microscopy.


Control group (GI) - Most of the endometrium is lined by a single cylindrical epithelium showing numerous mitotic figures. We often observe well defined areas of nonkeratinized stratified epithelium, at times intercalated in the luminal epithelium and at times in the gland region as well as the gland opening on the luminal surface. Particularly noteworthy is the great concentration of eosinophils in the lamina propria. Some endometrial glands lined with single cylindrical epithelium and noticeable stratified areas are visible (Fig. 1).

Rats in persistent estrous after bilateral oophorectomy (GII) - The surface uterine lining is made up of cubic cells with spherical nucleus and single cubic epithelium. Some neutrophils are seen between epithelial cells. The few endometrial glands are also lined by a single cubic epithelium (Fig. 2).

Rats in persistent estrous after bilateral oophorectomy and treated with estradiol benzoate (GIII) - The endometrial epithelium is single and cylindric showing some regions of stratified and keratinized epithelium (Fig. 3). The cells of the single cylindric epithelium are high with elongated nucleus in the basal position of the cell. The stratified portion presents eight to ten lines of cells - the cells of the basal region are cubic, becoming more and more plane the more distant they are from the basal cells, some of them showing keratinization. Leukocytes are often observed between epithelial cells. The numerous endometrial glands are made up of a single cubic epithelium, which presents some regions of stratification with five to six lines of cells.

Rats in persistent estrous after bilateral oophorectomy and treated with estradiol benzoate and medroxyprogesterone acetate (GIV) - The endometrial lining is of the single cubic type. The numerous endometrial glands are also lined by cubic cells. The stroma is rich in cells (Fig. 4).

Fig. 1. Photomicrograph showing an aspect of the rat endometrium in persistent estrous (G-I). Observe stratification in the glandular epithelium (SE). H.E. 280 X.

Fig. 2. Photomicrograph showing the rat endometrium submitted to bilateral oophorectomy (G-II). Observe the single cubic epithelium and two different regions in the lamina propria: one rich in cells (C) and the other rich in collagen fibers (CF). 140 X.

Fig. 3. Photomicrograph showing an aspect of the rat endometrium submitted to bilateral oophorectomy and treated with estradiol benzoate (G-III). Observe the stratification of the superficial epithelium and numerous eosinophils in the lamina propria (arrows). 140 X.

Fig. 4. Photomicrograph showing the rat endometrium submitted to bilateral oophorectomy and treated with medroxiprogesterone acetate (G-IV). Observe the single cubic epithelium (arrow) and lamina propria rich in cells and glands (head arrow). 140 X.


Many authors showed that the exposition of rats to continuous light interrupts the estral cycle inducing the state of persistent estrous (BROWMAN, 1937; FISKE, 1941; EVERETT, 1961; TAKEO et al., 1975, 1986; TAKEO, 1984). These phenomena are supposed to be related to the pineal gland because when rodents are exposed to the continuous light stimulus they develop the persistent estrous, the situation that can be abolished by injections of bovine pineal extracts (BROWMAN, 1937; WURTMAN, AXELROD & CHU, 1963; WURTMAN, AXELROD & PHILIPS, 1963).

It should be emphasized that the authors that studied the persistent estrous induced by continuos light observed the behavior of vaginal smears and the rat ovaries but not the endometrium. In consequence we decided to study the morphological aspects of the endometrium submitted to continuos light.

The rat epithelium of the endometrium in persistent estrous induced by continuos light was well developed, cylindrical single, with areas of stratification in its superficial and glandular aspects similar to persistent estrous induced by testosterone propionate. These modifications would be influenced by the testosterone propionate depending on the high levels of circulating estrogens (PARDI et al., 1993; PATRIARCA et al., 1996; SMANIOTTO, 1996). It should be mentioned, however, that VRONTAKIS et al. (1993) reported that the most significant estrogenic action on the estrous is the stimulation of DNA synthesis and the cell proliferation.

In ooforectomized animals the endometrium is less developed without any area of stratification. However the endometrium of those animals in persistent estrous after bilateral ooforectomy and treated with estradiol benzoate, presents again the same features of those found in control animals indicating that the estradiol would be the responsible for this action. The administration of estradiol in animals with regular estral cycles stimulates the hypertrophy of the stroma and epithelium but not endometrial metaplasia (SIMÕES, 1984).

It's not known with precision the level of circulating estrogens in persistent estrous rats, induced by androgens. It's only known that the ovaries "in vitro", under theses circumstances, showed increasing production of androgens and estrogens, being the estrous in consequence under continuous influence of these hormones (RODRIGUES DE LIMA, 1966 and CHIÓRBOLI, 1970).

We believe that the same phenomena happens to rats exposed to continuous light, in respect to the circulating levels of estradiol. The ovaries of the rats submitted to continuous light present big ovarian cysts and numerous interstitial cells which are related to the production of these hormones. Perhaps the continuous influence of steroid hormones induces an abnormal proliferation of the endometrial epithelium related to the keratinization. Even after ooforectomy this effect is supposed to be linked to the genome of epithelial cells, because the replacement of estradiol in these animals produces a new keratinization in this epithelium, a fact that does not happen in rats with normal estral cycles (SIMÕES et al., 1984).

In animals treated simultaneously with estradiol and medroxyprogesterone no stratification was observed in the endometrium. This finding is also supported by MARKAVERICH et al. (1981), BIGSBY & CUNHA (1988) and HOWE et al. (1990), which stated that the progestagens would inhibit the rat uterine growth induced by estrogens because they would antagonize the synthesis of the estrogen receptor in the endometrial epithelium. BIGBY & CUNHA (1988) reported that progesterone would block the mitotic activity in the uterine epithelium.

The different researchers that studies the rat endometrium in persistent estrous induced by testosterone propionate reported the presence of stratification and keratinization of endometrial epithelia (metaplasia).

In this work it was also found this phenomenon (metaplasia) in rats submitted to continuous light and in consequence, in a state of persistent estrous.

RESUMEN: Los principales objetivos de este trabajo son analizar las modificaciones que ocurren en el endométrio de ratas en estro persistente inducida por luz contínua y observar la respuesta endometrial a administración de estrógenos y/o progestágenos sobre el endometrio, en esas condiciones experimentales.

Los resultados mostraron que el estroma endometrial de ratas sometidas a luz continua presentaba características típicas de la fase de estro, siendo que los epitelios superficial y glandular presentaban áreas de estratificación, dependientes de las hormonas ováricas y que tales características desaparecen después de la ooforectomía.

La ooforectomía no bloquea el efecto inducido por la luz, ya que después de la administración del estrógeno, el endometrio presentaba las mismas características de los animales en estro persistente. Cuando se administró el acetato de medroxiprogesterona juntamente con el estrógeno, hubo un bloqueo de las áreas de estratificación, indicando que la progesterona es moduladora del estrógeno.

En este trabajo concluimos que el estro persistente inducido por la luz continua, depende de las hormonas ováricas y que la principal hormona es estrógeno. También se observó que la progesterona bloquea las inducciones provocadas por el estrógeno.

PALABRAS CLAVE: 1. Estro persistente; 2. Endometrio; 3. Luz continua; 4. Metaplasia.


BARRACLOUGH, C. A. Production of anovulatory, sterile rats by single injection of testosterone propionate. Endocrinology, 68:62-7, 1961.

BARRACLOUGH, C. A. & GORSKI, R. A. Evidence that the hypothalamus in responsible for androgen-induced sterility in the female rat. Endocrinology, 68:68-79, 1961.

BIGSBY, R. M. & CUNHA, G. R. Progesterone and dexamethasone inhibition of uterine epithelial proliferation in two models of estrogen-independent growth. Am. J. Obstet. Gynec., 158:646-50, 1988.

BRANHAN, W.S.; ZEHER, D.R. & SHEEHAN, D.M. Differential sensitivity of rat uterine growth and epithelium hypertrophy to estrogens and antiestrogens. Proc. Soc. Exp. Biol. Med., 203: 297 - 303, 1993.

BROWMAN, L.G. Light in its relation to activity and estrous rhythms in the albino rat. J. Exp. Zool., 75:375-88, 1937.

BURCH, G.E. & PHILLIP, J. H. Neurohumoral functions of the hypothalamus. J. Med. Sci., 248:79 - 101, 1964.

CAMANO, L. & GIUFFRIDA, R. Modificações citológicas e histológicas do epitélio vaginal de ratas. Mater. Inf. (São Paulo), 29:213-54, 1970.

CHIÓRBOLI, E. Contribuição ao estudo in vitro de hormônios esteróides, pelo ovário das ratas normais e precocemente tratadas com testosterona. (Tese de Doutorado. Escola Paulista de Medicina). São Paulo, 1970.

CHU, E.W.; WURTMAN R. J. & AXELROD, J. An inhibitory effect of melatonin on the estrus cycle of the rodent. Endocrinology, 75:238-42, 1964.

EVERETT, J.W. Spontaneous persistent estrus in a strain of albino rats. Endocrinology, 25:123, 1939.

EVERETT, J. W. The mammalian female reproductive cycle and its controlling mechanisms. In:Young, Sex and Internal Secretion. Baltimore, Willians & Wilkins, 1961. pp 497-555.

FISKE, V. W. Effect of light on sexual maturation, estrous cycles and anterior pituitary of the rat. Endocrinology, 29:183-96, 1941.

GORSKI, R.A. & WAGNER, J.W. Gonadal activity and sexual differentiation of the hypothalamus. Endocrinology, 76: 226-39, 1965.

GRÖNROOS, M. & KAUPPILA, O. Hormonal cycle changes in rats under normal condition and under stress as revealed by vaginal smears after Shorr staining. Act Endocr. (Kbh), 32: 261-71; 1959.

HOLINKA, C. F.; BRESSLER, R. S.; ZEHR, D.R. & GURPIDE, E. Comparation of effects on estetrol and tamoxifen with those of estriol and estradiol on the immature rat uterus. Biol. Reprod., 22: 913-26, 1980.

HOWE, R. S.; LEE, Y. H.; FRISCHIKOFF, S. A.; TEUSCHER, C. & LYTTLE, C. R. - Glicocorticoid and progestin regulation of eosinophil chemotatictil factor and complement C3 in the estrogen - treated rat uterus. Endocrinology, 126:3193-9, 1990.

LAWTON, I.E. & SCHWARTZ, N. B. Pituitary - ovarian in rats exposed to constant light: a chronological study. Endocrinology, 81:497-508, 1967.

MARKAVERICH, B. M.; UPCHURCH, S. & CLARK, J. H. Progesterone and dexamethasone antagonism of uterine growth: a role for second nuclear binding site for estradiol in estrogen action. J. Steroid. Biochem., 14:125, 1981.

PARDI, P. C.; SIMÕES, M. J. & BINVIGNAT, O. Ultraestructural study of the remodeling of the endometrial stroma of persistent-estrous rats. Rev. Chil. Ciên. Méd. Biol., 3:2-4, 1993.

PATRIARCA, M.T.; TEVES, D.C.; SMANIOTTO, S.; EVÊNCIO NETO, J.; SIMÕES, M. J. & RODRIGUES DE LIMA, G. Morfological action of tamoxifen in the endometrium of persistente estrous rats. Acta Obstet. Gynecol. Scand., 75:1996 (en prensa).

RODRIGUES DE LIMA, G. Contribuição para o estudo da fisiopatologia de ratas em estro permanente - Sensibilidade uterina à ocitocina. São Paulo, 1966. [Tese de Doutoramento - Escola Paulista de Medicina].

SIMÕES, M. J. Aspectos morfológicos e morfométricos do endométrio de ratas albinas nas subfases inicial, intermediária e final do proestro e metaestro. (Tese de Doutorado. Univ. de São Paulo). São Paulo, 1984.

SINGH, K. B. Persistent estrous: An experimental model of the policystic ovaries. Obstet. Ginec. Survey., 104: 1008-11, 1969.

SMANIOTTO, S. Aspectos morfológicos do endométrio de ratas em estro permanente ou ooforectomizadas, tratadas com estrogênio e ou dexametasona. São Paulo, 1996. [Tese de Mestrado - Universidade Federal de São Paulo - Escola Paulista de Medicina].

TAGUCHI, O. & NISHIZUKA, Y. Reproductive tract abnormalities in female mice treated neonatally with tamoxifen. Am. J. Obstet. Gynecol., 151:675-8, 1985.

TAKEO, Y. Influence of continuous illumination on estrus cycle of rats: time course changes in levels of gonadotropins and ovarian steroids until occurrence of persistent estrus. Neuroendocrinology, 39:97-104, 1984.

TAKEO, Y.; KOHNO, J. & HOKANO, M. Ultrastructural evidence for estradiol synthesis in the ovary of persistent-estrus rats exposed to continuous illumination. Acta Anat. (Basel), 127:161-70, 1986.

TAKEO, Y.; SHIRAMA, K.; SHIMIZU, K. & MAEKAWA, K. Correlation between sexual maturation and induction of persistent estrus by continuous illumination. Endocr. Jap., 22:453-6, 1975.

TAKEWAKI, K. Some aspects of hormonal mechanism involved in persistent estrus in the rat. Experimentia, 18:1-6, 1962.

VRONTAKIS, M.; SCHROEDTER, I.; LEITE, V. & FRIESEN, H. G. - Estrogen regulation and localization of galanine gene expression in the rat uterus. Biol. Reprod., 49:415-20, 1969.

WURTMAN, R. J.; AXELROD, J. & CHU, E. W. Melatonin, a pineal substance; effect on the rat ovary. Science, 141:277-8, 1963.

WURTMAN, R. J.; AXELROD, J. & PHILIPS, L.S. Melatonin synthesis in the gland pineal: control by light. Science, 142:1071-3, 1963.

YING, S.Y. & GREEP, R. D. Inhibition of ovulation by melatonin in the cyclic rat. Endocrinology, 92:333, 1973.

Dirección para correspondencia:
Prof. Dr. Manoel de Jesus Simões
Disciplina de Histologia e Biologia Estrutural
Departamento de Morfologia
Universidade Federal de São Paulo - Escola Paulista de Medicina
Rua Botucatu 740
CEP 04023-900
São Paulo -SP

Recibido : 26-03-1999
Aceptado: 18-07-1999

Creative Commons License All the contents of this journal, except where otherwise noted, is licensed under a Creative Commons Attribution License