Alterations in progesterone receptors in the rat uterus bearing an intra-uterine device during the oestrous cycle and early pregnancy

Neoplasia with use of intrauterine devices

BACKGROUND

One of the mechanisms by which intrauterine devices (IUDs) prevent pregnancy is the creation of a sterile inflammatory response in the endometrium. Additionally, hormone-releasing IUDs or intrauterine systems (IUSs) release progestins or progesterone into the uterus. Both of these mechanisms may affect users' risk for neoplasia.

STUDY DESIGN

We searched the PubMed database for studies on IUD use and risk for neoplasia conducted between 1960 and September 2006 and published in all languages. We excluded case reports and case series. For the association between ever using an IUD and risk for endometrial cancer, we conducted a meta-analysis using a Bayesian random-effects model to account for between-study heterogeneity.

RESULTS

We found no evidence of increased risk for neoplasia with IUD use. Nine case-control studies and one cohort study found reduced risks for endometrial cancer with having ever used an IUD (pooled adjusted odds ratio=0.6, 95% confidence interval=0.4-0.7). No trend in associations was observed with characteristics of IUD use, type of IUD and histologic type of cancer. Four case-control studies found no association between IUD use and risk for cervical cancer. One study found no increased incidence of breast cancer among levonorgestrel-releasing IUS users as compared with the general population in Finland. Finally, three studies found no association between IUD use and occurrence of hydatidiform moles or malignant sequelae.

CONCLUSIONS

Use of an IUD does not appear to increase the risk for neoplasia. While nearly all studies found that IUD use was associated with a decreased risk for endometrial cancer, it remains unclear whether this association is causal.

Progesterone receptor mRNA levels during pregnancy, labor, lactation and the estrous cycle in rat uterus

Progesterone plays important roles in the regulation of female reproduction. In this study, progesterone receptor (PR) mRNA levels in rat uterus during pregnancy, labor, lactation and the estrous cycle were examined by competitive RT-PCR. During pregnancy and lactation, PR mRNA levels had decreased on day 20 of pregnancy (P20) and P21 compared with P15 but increased during labor. After a decline on day 1 of lactation (L1), PR mRNA levels had increased again on L3 and L14 compared with P15, P18, P20, P21 and P21pm (at 2200-2300 h on P21). There was no significant change in the PR mRNA level during the estrous cycle. The PR mRNA level did not change during 1 week of progesterone treatment or afterwards. Injection of 17beta-estradiol did not affect PR mRNA levels in rats treated with progesterone or those without any injections. In rats on P18, 17beta-estradiol injection did not change PR mRNA levels after sham-operation but induced an increase in PR mRNA levels of rats ovariectomized 6 h before the treatment. These results suggest that uterine PR mRNA levels are differently regulated during late pregnancy, labor and lactation, and during labor estrogen is one of the essential factors for the increase in PR mRNA levels.

Endometrial cancer in relation to intra-uterine device use

Data from a population-based case-control study were used to evaluate the risk of endometrial cancer among women who have used an intra-uterine device (IUD). Incident cases were identified between 1985 and 1991 among women aged 45-74 years who were residents of one of 3 counties in Washington State. Controls were selected by random digit dialing, and both groups of subjects received an in-person detailed interview. In this study population, women who had ever used an IUD were estimated to have a risk of endometrial cancer that was 0.61 times that of other women (95% CI 0.41-0.89). The reduction in cancer risk was not found to be dependent on duration of IUD use. There was a suggestion that women who had used intra-uterine contraception relatively late in reproductive life experienced a greater reduction in risk than those whose use was more distant or at a younger age. The relative risk among the small number of women who were currently using an IUD was 0.49 (95% CI 0.12-2.80). These results apply to the use of inert and copper IUDs as there was no use of progestin-releasing IUDs among women in the study population. The data from this and several other studies of the question support the hypothesis that use of an IUD has a favorable effect on the subsequent risk of endometrial cancer. The reason(s) for such a reduced risk is unclear.

Intrauterine devices and endometrial cancer. The WHO Collaborative Study of Neoplasia and Steroid Contraceptives

The relationship between intrauterine device (IUD) use and the development of endometrial cancer was assessed in data from seven countries that were collected between 1979 and 1988 for a multinational hospital-based case-control study. Two hundred twenty-six cases of endometrial cancer were compared with 1,529 controls matched for age, hospital, and year of interview. No significant association between use of an IUD and risk of endometrial cancer was observed (OR = 0.74, 95% CI = 0.4-1.33). There were no trends in risk with respect to duration of use, time since first use, or ages at first or last use. No cases had used a copper IUD (OR = 0, 95% CI = 0-1.71). Although women over age 55 who had used an IUD were at significantly increased risk, this unexpected finding is based on small numbers of users and requires independent confirmation. These results, along with those from other studies, provide reassurance that risk of endometrial cancer is unlikely to be increased by use of an IUD.

Intrauterine device use and risk of endometrial cancer

The relationship between intrauterine device (IUD) use and risk of endometrial cancer has been analysed in a case-control study conducted in Italy between 1983 and 1992, including 453 patients with histologically confirmed endometrial cancer and 1,451 controls admitted for acute, non-gynaecological, non-hormonal, non-neoplastic conditions to the same network of hospitals where cases had been identified. Two (0.4%) cases versus 36 (2.3%) controls reported ever using an IUD. The corresponding multivariate relative risk was 0.4 (95% CI 0.1-1.0). The results of this study and the few published available epidemiological data suggest a protective role of IUD use on endometrial carcinogenesis, but potential selective mechanisms for IUD utilisation (indication bias) should be carefully considered in the interpretation.

Intra-uterine contraception and the risk of endometrial cancer

Despite the increasing world-wide popularity of contraceptive intra-uterine devices (IUDs), their potential long-term effects on the risk of developing endometrial carcinoma have been poorly studied. This paper reports on the relationship between intra-uterine contraception and endometrial cancer by analyzing epidemiological data from a large, multicenter, population-based, case-control study of epithelial endometrial cancer. Cases were 437 women, 20 to 54 years of age, with histologically confirmed epithelial endometrial cancer ascertained through 6 population-based cancer registries in the United States. Controls were 3200 women selected at random from the populations of these areas. The age- and parity-adjusted odds ratio (OR) for the association between ever having used intra-uterine contraception and endometrial cancer was 0.51 (95% confidence interval (CI) 0.3-0.8). Although the protective effect increased with duration of use, a dose-response relationship among users was not statistically demonstrable. The association did not vary significantly with age at first or last IUD use or with time elapsed since first or last IUD use. Years of education significantly modified the effect of intra-uterine contraception. Thus, intra-uterine contraception appeared to be strongly protective for women with at least 13 years of education (OR = 0.29, 95% CI, 0.15-0.6). It is proposed that intra-uterine contraception exerts its protective effect through local structural and biochemical changes in the endometrium that may alter endometrial sensitivity and response to circulating estrogen and progesterone.

Progesterone therapy results in partial reversibility of uterine abnormalities of the adult anovulatory rat

The effects of progesterone therapy (5 mg, administered subcutaneously daily for 6 days) on the abnormal uterus of adult anovulatory Wistar rats have been studied. These rats, rendered anovulatory by neonatal treatment with testosterone propionate or clomiphene citrate, displayed severe hyperplasia and metaplasia of the uterine luminal epithelium and a disproportionately high content of nuclear oestrogen receptor, as a result of constant oestrogen stimulation unrelieved by progesterone [White, Moore, Elder & Lim (1981) Biochem. J. 196, 557-565]. Progesterone therapy resulted in the virtual elimination of the hyperplasia and metaplasia and a corresponding decrease in the content of nuclear oestrogen receptor with the proportion of the unoccupied nuclear receptor being increased to values exhibited by normal cyclic females. There was also a decrease in the content of progestin receptors, a putative index of oestrogenic stimulation. Further, in the testosterone-treated group, progesterone therapy resulted in the restoration of oestrogen receptor translocational responses to oestradiol stimulation. Progesterone treatment of these anovulatory rats thus provides a model system for investigating the biochemical mechanisms underlying progestin antagonism and regulation of oestrogen-stimulated cell proliferation.

The relationship of the oestrogen and progestin receptors in the abnormal uterus of the adult anovulatory rat. Effects of neonatal treatment with testosterone propionate or clomiphene citrate

The neonatal administration of testosterone propionate to Wistar rats resulted in anovulatory adults in persistent vaginal oestrus. Clomiphene citrate had a similar effect. In both groups of adults, hyperplasia of the uterine epithelium and occasional metaplasia was observed. The uterine nuclear and cytosol oestrogen and progestin receptors of these anovulatory rats were found to have affinities for their respective ligands similar to those of normal females. The nuclear oestrogen receptor comprised occupied and unoccupied components, as in normal females. The content of the nuclear oestrogen receptor was comparable with that of females in the late dioestrous or pro-oestrous phase. This content was higher in the clomiphene-treated group. Despite the relatively high nuclear oestrogen receptor content the content of progestin receptors, a putative index of the oestrogenic response, was lower in the treated rats than in normal adult females throughout the cycle. Administration of oestradiol to both treatment groups resulted in depletion of cytosol oestrogen receptor content 1 h later, which, however, was not reflected by an increase in the content of nuclear oestrogen receptors. There was no measurable increase in progesterone receptor content in treated rats after daily administration of oestrogen (5 microgram/rat) for 3 days. These changes in sex-hormone-receptor interactions involving an impairment of the normal oestrogenic response may be associated with the abnormal differentiation of the uterus in these sterile, anovulatory animals.