The permanent effect of reproductive events on blood prolactin levels and its relation to breast cancer risk: a population study of postmenopausal women

Dual role of pregnancy in breast cancer risk

Reproductive history is one of the strongest risk factors for breast cancer in women. Pregnancy can promote short-term breast cancer risk, but also reduce a woman's lifetime risk of breast cancer. Changes in hormone levels before and after pregnancy are one of the key factors in breast cancer risk. This article summarizes the changes in hormone levels before and after pregnancy, and the roles of hormones in mammary gland development and breast cancer progression. Other factors, such as changes in breast morphology and mammary gland differentiation, changes in the proportion of mammary stem cells (MaSCs), changes in the immune and inflammatory environment, and changes in lactation before and after pregnancy, also play key roles in the occurrence and development of breast cancer. This review discusses the dual effects and the potential mechanisms of pregnancy on breast cancer risk from the above aspects, which is helpful to understand the complexity of female breast cancer occurrence.

Inclusion of Plasma Prolactin Levels in Current Risk Prediction Models of Premenopausal and Postmenopausal Breast Cancer

Background

Circulating plasma prolactin is associated with breast cancer risk and may improve our ability to identify high-risk women. Mammographic density is a strong risk factor for breast cancer, but the association with prolactin is unclear. We studied the association between breast cancer, established breast cancer risk factors and plasma prolactin, and improvement of risk prediction by adding prolactin.

Methods

We conducted a nested case-control study including 721 breast cancer patients and 1400 age-matched controls. Plasma prolactin levels were assayed using immunoassay and mammographic density measured by STRATUS. Odds ratios (ORs) were calculated by multivariable adjusted logistic regression, and improvement in the area under the curve for the risk of breast cancer by adding prolactin to established risk models. Statistical tests were two-sided.

Results

In multivariable adjusted analyses, prolactin was associated with risk of premenopausal (OR, top vs bottom quintile = 1.9; 1.88 (95% confidence interval [CI] = 1.08 to 3.26) but not with postmenopausal breast cancer. In postmenopausal cases prolactin increased by 10.6% per cBIRADS category (P_trend = .03). In combined analyses of prolactin and mammographic density, ORs for women in the highest vs lowest tertile of both was 3.2 (95% CI = 1.3 to 7.7) for premenopausal women and 2.44 (95% CI = 1.44 to 4.14) for postmenopausal women. Adding prolactin to current risk models improved the area under the curve of the Gail model (+2.4 units, P = .02), Tyrer-Cuzick model (+3.8, P = .02), and the CAD2Y model (+1.7, P = .008) in premenopausal women.

Conclusion

Circulating plasma prolactin and mammographic density appear independently associated with breast cancer risk among premenopausal women, and prolactin may improve risk prediction by current risk models.

Breast cancer risk factors and mammographic density among high-risk women in urban China

Elevated mammographic density (MD) is an established breast cancer risk factor. Studies examining relationships between MD and breast cancer risk factors are limited in China, where established breast cancer risk factors are less prevalent but dense breasts are more prevalent than Western countries. This study included 11,478 women (45-69 years; 36% premenopausal) participating in an ongoing national cancer screening program in 11 urban provinces in China and predicted as having high-risk for breast cancer. Polytomous logistic regression was performed to assess associations between MD and risk factors by comparing each higher Breast Imaging Reporting and Data System (BI-RADS) category (2, 3, or 4) to the lowest category (BI-RADS, 1). We found associations of increasing age, body mass index, weight, postmenopausal status, and parity with lower MD. Higher levels of education, increasing height, and later first birth were associated with higher MD. These associations did not vary by menopausal status. Additionally, the association between longer period of breastfeeding and lower MD was seen among postmenopausal women only (P_interaction = 0.003). Having first-degree relatives with breast cancer diagnosed before 50 years was associated with lower MD only among premenopausal women (P_interaction = 0.061). We found effects of established breast cancer risk factors on MD showed similar directions in Chinese and Western women, supporting the hypothesis that MD represents cumulative exposure to breast cancer risk factors over the life course. Our findings help to understand the biological basis of the association of MD with breast cancer risk and have implications for breast cancer prevention research in China.

Determinants of prolactin in postmenopausal Chinese women in Singapore

PURPOSE

Mechanistic and observational data together support a role for prolactin in breast cancer development. Determinants of prolactin in Asian populations have not been meaningfully explored, despite the lower risk of breast cancer in Asian populations.

METHODS

Determinants of plasma prolactin were evaluated in 442 postmenopausal women enrolled in the Singapore Chinese Health Study, a population-based prospective cohort study. At baseline all cohort members completed an in-person interview that elicited information on diet, menstrual and reproductive history, and lifestyle factors. One year after cohort initiation we began collecting blood samples. Quantified were plasma concentrations of prolactin, estrone, estradiol, testosterone, androstenedione, and sex hormone-binding globulin (SHBG). Analysis of covariance method was used for statistical analyses with age at blood draw, time since last meal, and time at blood draw as covariates.

RESULTS

Mean prolactin levels were 25.1% lower with older age at menarche (p value = 0.001), and 27.6% higher with greater years between menarche and menopause (p value = 0.009). Prolactin levels were also positively associated with increased sleep duration (p value = 0.005). The independent determinants of prolactin were years from menarche to menopause, hours of sleep, and the plasma hormones estrone and SHBG (all p values < 0.01).

CONCLUSION

The role of prolactin in breast cancer development may involve reproductive and lifestyle factors, such as a longer duration of menstrual cycling and sleep patterns.

STAT3 activation is required for the antiapoptotic effects of prolactin in cervical cancer cells

BACKGROUND

Prolactin (PRL) has been implicated in the development of different types of cancer. However, signaling pathways might be activated depending on various forms of prolactin receptor (PRLR). JAK/STAT is an important pathway associated with PRL effects. The activation of JAK/STAT pathway might activate antiapoptotic genes that could importantly lead to progression of tumorigenesis. Recently, we have reported that PRL is associated with cell survival by inhibition of apoptosis and the precise activated signaling pathways for this process are still questioned. The purpose of this study was to evaluate the activation of different signaling pathways in response to PRL as well as to identify the induction of antiapoptotic genes.

METHODS

Cervical cancer cell lines HeLa, SiHa and C-33 A were stimulated with PRL (200 ng/mL) for 30 and 60 min and non stimulated cells were used to measure basal protein expression. Inhibition assays were performed by using Jak2 specific inhibitor AG490, either alone or in combination with PRL for 48 h. Western blot were carried out to evaluate protein induction of the different signaling pathways and antiapoptotic proteins. Significant effects were determined by using ANOVA test.

RESULTS

STAT3 was significantly activated in cervical cancer lines in comparison with non-tumorigenic keratinocytes HaCaT. No significant differences were found when analyzing MAPK and PI3K signaling pathways. An increase of antiapoptotic genes Bcl-xl, Bcl-2, survivin and Mcl-1 was observed after stimulus with PRL; however, after inhibition with AG490, the induction of antiapoptotic genes was decreased.

CONCLUSION

Our data suggests that STAT3 is an important signaling pathway activated by PRL in cervical cancer cells and it modulates the induction of antiapoptotic genes. Blocking STAT3 could represent a possible therapeutic strategy in cervical cancer.

Circulating sex hormones and terminal duct lobular unit involution of the normal breast

BACKGROUND

Terminal duct lobular units (TDLU) are the predominant source of breast cancers. Lesser degrees of age-related TDLU involution have been associated with increased breast cancer risk, but factors that influence involution are largely unknown. We assessed whether circulating hormones, implicated in breast cancer risk, are associated with levels of TDLU involution using data from the Susan G. Komen Tissue Bank (KTB) at the Indiana University Simon Cancer Center (2009-2011).

METHODS

We evaluated three highly reproducible measures of TDLU involution, using normal breast tissue samples from the KTB (n = 390): TDLU counts, median TDLU span, and median acini counts per TDLU. RRs (for continuous measures), ORs (for categorical measures), 95% confidence intervals (95% CI), and Ptrends were calculated to assess the association between tertiles of estradiol, testosterone, sex hormone-binding globulin (SHBG), progesterone, and prolactin with TDLU measures. All models were stratified by menopausal status and adjusted for confounders.

RESULTS

Among premenopausal women, higher prolactin levels were associated with higher TDLU counts (RRT3vsT1:1.18; 95% CI: 1.07-1.31; Ptrend = 0.0005), but higher progesterone was associated with lower TDLU counts (RRT3vsT1: 0.80; 95% CI: 0.72-0.89; Ptrend < 0.0001). Among postmenopausal women, higher levels of estradiol (RRT3vsT1:1.61; 95% CI: 1.32-1.97; Ptrend < 0.0001) and testosterone (RRT3vsT1: 1.32; 95% CI: 1.09-1.59; Ptrend = 0.0043) were associated with higher TDLU counts.

CONCLUSIONS

These data suggest that select hormones may influence breast cancer risk potentially through delaying TDLU involution.

IMPACT

Increased understanding of the relationship between circulating markers and TDLU involution may offer new insights into breast carcinogenesis. Cancer Epidemiol Biomarkers Prev; 23(12); 2765-73. ©2014 AACR.

Bioactive prolactin levels and risk of breast cancer: a nested case-control study

BACKGROUND

Prolactin is a lactogenic hormone associated with breast cancer risk in prospective studies, which used immunoassays. The immunoassay captures multiple isoforms and may not fully reflect the biologic activity of prolactin relevant to breast carcinogenesis.

METHODS

We considered plasma bioactive prolactin levels measured by the Nb2 lymphoma cell bioassay, which is sensitive to the somatolactogenic activity of prolactin and growth hormone, within a nested case-control study of invasive breast cancer in the Nurses' Health Studies (NHS/NHSII). We also considered associations with breast cancer risk factors.

RESULTS

We had bioassay measures on 1,329 cases and 1,329 controls. Bioassay levels were inversely associated with parity (4+ vs. 0 children = -18%, P = 0.01), body mass index (30+ vs. <22 kg/m(2) = -16%, P < 0.01), and age at menopause (53+ vs. 48 years = -18%, P = 0.03) and positively with family history of breast cancer (yes vs. no = 14%, P < 0.01). The relative risk (RR) comparing the top versus bottom quartile of bioassay levels was 1.19 [95% confidence intervals (CI), 0.94-1.51; Ptrend = 0.18]. The association was suggestively stronger for postmenopausal (RR = 1.36; 95% CI, 0.93-1.98; Ptrend = 0.12) versus premenopausal women (RR = 0.99; 95% CI, 0.71-1.37; Ptrend = 0.71). There was an association for cases diagnosed <4 years after blood draw (RR = 2.66; 95% CI, 1.45-4.89; Ptrend < 0.01), but not for cases diagnosed later. We did not observe differential associations by estrogen receptor status or other tumor characteristics.

CONCLUSIONS

Our results show similar associations for prolactin levels measured by bioassay and by immunoassay with both breast cancer risk factors and risk.

IMPACT

Future work examining risk prediction model of breast cancer can use the immunoassay to accurately characterize risk.

Rotating night shift work, sleep quality, selected lifestyle factors and prolactin concentration in nurses and midwives

The pattern of secretion of many hormones, including prolactin, is dependent on the circadian rhythm. Night shift work involves exposure to artificial light at night and sleep deficiency, which in turn can affect prolactin synthesis. The aim of this study was to evaluate a possible association between night shift work characteristics, sleep quality, lifestyle factors and prolactin concentration, using data from a cross-sectional study of nurses and midwives. A cross-sectional study was conducted among 327 nurses and midwives currently working on rotating night shifts, and 330 nurses and midwives working during the day (aged 40-60 years) (388 premenopausal and 269 postmenopausal). Information about night shift work characteristics, lifestyle, reproductive factors, sleep pattern and other covariates was collected through a face-to-face interview, and from a one-week work and sleep diary completed by the subjects. Weight and height were measured. Prolactin concentration was measured in the morning blood sample using the electrochemiluminesence immunoassay method. Associations were analyzed using linear regression models adjusted for important confounders. Analyses were carried out separately in pre- and postmenopausal women. None of the night shift work or sleep characteristics was significantly associated with prolactin concentration. Prolactin concentration was significantly (p < 0.05) inversely associated with smoking and time of blood sample collection. These results were consistent among both pre- and postmenopausal women. Nulliparity was significantly positively associated with prolactin among premenopausal women, but inversely among postmenopausal. Age was related to prolactin among postmenopausal women only. Our study indicates that rotating night shift work is not associated with prolactin concentration. Smoking, parity, time of blood collection and age among postmenopausal women were significant determinants of prolactin.

Prolactin determinants in healthy women: A large cross-sectional study within the EPIC cohort

BACKGROUND

Experimental and epidemiologic data suggest that higher circulating prolactin is associated with breast cancer risk; however, how various risk factors for breast cancer influence prolactin levels in healthy women is not clear.

METHODS

We analyzed cross-sectional associations between several suggested reproductive and lifestyle risk factors for breast cancer and circulating prolactin among pre- and postmenopausal women, taking into account the use of current postmenopausal hormone therapy, among 2,560 controls from a breast cancer nested case-control study within the EPIC cohort.

RESULTS

Adjusted geometric mean prolactin levels were significantly higher among premenopausal women, and among postmenopausal women using hormone therapy compared with nonusers (8.2, 7.0, and 6.3 ng/mL, respectively; Pcat = <0.0001). Furthermore, prolactin levels were significantly higher among users of combined estrogen-progestin hormone therapy compared with users of estrogen-alone hormone therapy (6.66 vs. 5.90 ng/mL; Pcat = 0.001). Prolactin levels were lower among parous women compared with nulliparous women (8.61 vs. 10.95 ng/mL; Pcat = 0.0002, premenopausal women); the magnitude of this difference depended on the number of full-term pregnancies (22.1% lower, ≥3 vs. 1 pregnancy, Ptrend = 0.01). Results for parity were similar but lower in magnitude among postmenopausal women. Prolactin did not vary by other studied factors, with the exception of lower levels among postmenopausal smokers compared with never smokers.

CONCLUSIONS

Our study shows that current hormone therapy use, especially the use of combined hormone therapy, is associated with higher circulating prolactin levels in postmenopausal women, and confirms prior findings of lower circulating prolactin in parous women.

IMPACT

Our study extends the knowledge linking various breast cancer risk factors with circulating prolactin.

High expression of prolactin receptor is associated with cell survival in cervical cancer cells

BACKGROUND

The altered expression of prolactin (PRL) and its receptor (PRLR) has been implicated in breast and other types of cancer. There are few studies that have focused on the analysis of PRL/PRLR in cervical cancer where the development of neoplastic lesions is influenced by the variation of the hormonal status. The aim of this study was to evaluate the expression of PRL/PRLR and the effect of PRL treatment on cell proliferation and apoptosis in cervical cancer cell lines.

RESULTS

High expression of multiple PRLR forms and PRLvariants of 60-80 kDa were observed in cervical cancer cell lines compared with non-tumorigenic keratinocytes evaluated by Western blot, immunofluorecence and real time PCR. Treatment with PRL (200 ng/ml) increased cell proliferation in HeLa cells determined by the MTT assay at day 3 and after 1 day a protective effect against etoposide induced apoptosis in HeLa, SiHa and C-33A cervical cancer cell lines analyzed by the TUNEL assay.

CONCLUSIONS

Our data suggests that PRL/PRLR signaling could act as an important survival factor for cervical cancer. The use of an effective PRL antagonist may provide a better therapeutic intervention in cervical cancer.

Circulating prolactin levels and risk of epithelial ovarian cancer

PURPOSE

Indirect evidence from experimental and epidemiological studies suggests that prolactin may be involved in ovarian cancer development. However, the relationship between circulating prolactin levels and risk of ovarian cancer is unknown.

METHODS

We conducted a nested case-control study of 230 cases and 432 individually matched controls within three prospective cohorts to evaluate whether pre-diagnostic circulating prolactin is associated with subsequent risk of ovarian cancer. We also assessed whether lifestyle and reproductive factors are associated with circulating prolactin among controls.

RESULTS

Prolactin levels were significantly lower among post- versus pre-menopausal women, parous versus nulliparous women, and past versus never users of oral contraceptives in our cross-sectional analysis of controls. In our nested case-control study, we observed a non-significant positive association between circulating prolactin and ovarian cancer risk (OR(Q4vsQ1) 1.56, 95 % CI 0.94, 2.63, p trend 0.15). Our findings were similar in multivariate-adjusted models and in the subgroup of women who donated blood ≥5 years prior to diagnosis. We observed a significant positive association between prolactin and risk for the subgroup of women with BMI ≥25 kg/m(2) (OR(Q4vsQ1) 3.10, 95 % CI 1.39, 6.90), but not for women with BMI <25 kg/m(2) (OR(Q4vsQ1) 0.81, 95 % CI 0.40, 1.64).

CONCLUSIONS

Our findings suggest that prolactin may be associated with increased risk of ovarian cancer, particularly in overweight/obese women. Factors associated with reduced risk of ovarian cancer, such as parity and use of oral contraceptives, were associated with lower prolactin levels, which suggests that modulation of prolactin may be a mechanism underlying their association with risk.

The effect of advanced maternal age upon human milk fat content

BACKGROUND

Little is known about the effect of maternal age on human milk (HM) composition. This study was designed to study fat content, estimated by creamatocrit (CMT), in HM collected in the first 2 weeks of life in older (≥ 35 years) compared with younger (<35 years) mothers.

STUDY DESIGN AND METHODS

Ninety lactating mothers (48 older, 42 younger) of newborns were recruited within the first 3 days of delivery. CMTs were measured at 72 hours, 7 days, and 14 days after delivery for HM in a capillary tube after centrifugation at 5,366 g for 5 minutes.

RESULTS

The groups did not differ in terms of maternal height and diet, infant birth weight, gestational age (GA), or pregnancy weight gain. They differed significantly in terms of maternal age and parity. Mean colostrum CMT was significantly higher in the group of older mothers. Colostrum CMT correlated positively with maternal age (R(2)=0.11, p=0.006) and inversely with GA (R(2)=0.1, p=0.03) but did not relate with either maternal weight or body mass index. CMT at age 7 days and 2 weeks was not affected by maternal age or GA. In multivariate regression analysis colostrum CMT correlated significantly only with maternal age and GA (R(2)=0.3, p<0.001).

CONCLUSIONS

Colostrum fat content of older mothers is much higher than that of younger mothers and inversely related with GA at delivery. This increase in colostrum fat content obtained from mothers with advanced age may be due to increased fat synthesis and excretion in milk, reduced water content of milk, or a combination of both.

Prolactin in men's health and disease

PURPOSE OF REVIEW

To review physiology of prolactin (PRL), cause and managment of hyperprolactinemia, and discuss evolving diverse roles of PRL in men's health.

RECENT FINDINGS

Hyperprolactinemia can be physiologically found after sexual activities, exercise, lactation, during pregnancy, and after stressful venipuncture. Elevated PRL can be caused by medications use, renal failure, hypothyroidism, and by prolactinoma - PRL secreting tumors. Symptomatic hyperprolactinemia and prolactinomas should be treated to lower PRL levels, decrease tumor size, and restore gonadal function. Three modes of treatment are typically utilized: pharmacological, radiosurgery with gamma radiation, and external beam radiation. Pharmacological treatment of prolactinomas is mainly based on dopamine agonists. The most frequently used dopamine agonists are bromocriptine and cabergoline. Cabergoline becoming the preferred drug in the treatment of prolactinomas because of higher response rate and less side-effects. Bromocriptine has been recently approved to improve glycemic control in diabetes mellitus.

SUMMARY

PRL plays a diverse role in men's reproduction and health. Detecting and treating elevated PRL may not only improve infertility and hypogonadism but also have a positive effect on the metabolic profile of patient and control of glycemic control and metabolic profile - an important advantage considering dramatic and worldwide increase in obesity and diabetes.

Obstetric history and mammographic density: a population-based cross-sectional study in Spain (DDM-Spain)

High mammographic density (MD) is used as a phenotype risk marker for developing breast cancer. During pregnancy and lactation the breast attains full development, with a cellular-proliferation followed by a lobular-differentiation stage. This study investigates the influence of obstetric factors on MD among pre- and post-menopausal women. We enrolled 3,574 women aged 45–68 years who were participating in breast cancer screening programmes in seven screening centers. To measure MD, blind anonymous readings were taken by an experienced radiologist, using craniocaudal mammography and Boyd’s semiquantitative scale. Demographic and reproductive data were directly surveyed by purpose-trained staff at the date of screening. The association between MD and obstetric variables was quantified by ordinal logistic regression, with screening centre introduced as a random effect term. We adjusted for age, number of children and body mass index, and stratified by menopausal status. Parity was inversely associated with density, the probability of having high MD decreased by 16% for each new birth (P value < 0.001). Among parous women, a positive association was detected with duration of lactation [>9 months: odds ratio (OR) = 1.33; 95% confidence interval (CI) = 1.02–1.72] and weight of first child (>3,500 g: OR = 1.32; 95% CI = 1.12–1.54). Age at first birth showed a different effect in pre- and post-menopausal women (P value for interaction = 0.030). No association was found among pre-menopausal women. However, in post-menopausal women the probability of having high MD increased in women who had their first child after the age of 30 (OR = 1.53; 95% CI = 1.17–2.00). A higher risk associated with birth of twins was also mainly observed in post-menopausal women (OR = 2.02; 95% CI = 1.18–3.46). Our study shows a greater prevalence of high MD in mothers of advanced age at first birth, those who had twins, those who have breastfed for longer periods, and mothers whose first child had an elevated birth weight. These results suggest the influence of hormones and growth factors over the proliferative activity of the mammary gland.

Prolactin serum levels and breast cancer: relationships with risk factors and tumour characteristics among pre- and postmenopausal women in a population-based case-control study from Poland

Background:

Previous prospective studies have found an association between prolactin (PRL) levels and increased risk of breast cancer. Using data from a population-based breast cancer case–control study conducted in two cities in Poland (2000–2003), we examined the association of PRL levels with breast cancer risk factors among controls and with tumour characteristics among the cases.

Methods:

We analysed PRL serum levels among 773 controls without breast cancer matched on age and residence to 776 invasive breast cancer cases with available pretreatment serum. Tumours were centrally reviewed and prepared as tissue microarrays for immunohistochemical analysis. Breast cancer risk factors, assessed by interview, were related to serum PRL levels among controls using analysis of variance. Mean serum PRL levels by tumour characteristics are reported. These associations also were evaluated using polytomous logistic regression.

Results:

Prolactin levels were associated with nulliparity in premenopausal (P=0.05) but not in postmenopausal women. Associations in postmenopausal women included an inverse association with increasing body mass index (P=0.0008) and direct association with use of recent/current hormone therapy (P=0.0006). In case-only analyses, higher PRL levels were more strongly associated with lobular compared with ductal carcinoma among postmenopausal women (P=0.02). Levels were not different by tumour size, grade, node involvement or oestrogen receptor, progesterone receptor, or human epidermal growth factor receptor 2 status.

Conclusions:

Our analysis demonstrates that PRL levels are higher among premenopausal nulliparous as compared with parous women. Among postmenopausal women, levels were higher among hormone users and lower among obese women. These results may have value in understanding the mechanisms underlying several breast cancer risk factor associations.

Breastfeeding and prolactin levels in lactating women with a family history of alcoholism

OBJECTIVE

Many motivated new mothers fail to reach public health goals for breastfeeding, highlighting the need to identify risk factors. Because having a family history of alcoholism is associated with blunted prolactin responses to an alcohol challenge in nonlactating individuals, this study aimed to identify associations in family history of alcoholism, prolactin, and breastfeeding behaviors in lactating women.

METHODS

This was a 2-day experimental study that used within-subject alcohol or control beverage consumption and between-subject family history of alcoholism factors. The participants were non-alcohol-dependent lactating women; 7 were family history-positive (FHP) for alcohol dependence, and 21 were family history-negative (FHN). Consumption of 0.4 g/kg alcohol or nonalcoholic beverage occurred in separate randomized sessions, followed by use of a breast pump. Basal and suckling-induced prolactin, blood alcohol concentrations, milk yield, self-reported drug effects, neophobia, and breastfeeding patterning were measured.

RESULTS

Although no group differences in alcohol pharmacokinetics were detected, FHP women exhibited blunted prolactin to breast stimulation after drinking the control and alcohol beverage and felt more of the stimulant-like effects of alcohol than did FHN women. FHP women reported more frequent daily breastfeeding than did FHN women.

CONCLUSIONS

This is the first evidence that family history of alcoholism is associated with a blunted magnitude, rapidity, and duration of the prolactin response to breast stimulation and an alcohol challenge in lactating women. More frequent breastfeeding by FHP women suggests behavioral compensation for perceived and/or actual poor lactation. Alcohol did not enhance lactational performance, further disputing the lore that alcohol is a galactagogue.

Energy balance, early life body size, and plasma prolactin levels in postmenopausal women

OBJECTIVE

We examined the relationships of prolactin with birth weight; childhood, adolescent and adult body size measures; adult physical activity and inactivity; and alcohol consumption among 1,423 postmenopausal women from the Nurses' Health Study.

METHODS

Information on exposures was collected on biennial questionnaires beginning in 1976. Blood was collected from 32,826 participants in 1990; prolactin was measured in a subset of women who were controls for a nested breast cancer case-control study. Generalized linear models were adjusted for assay batch, medication use at blood draw, and other potential predictors of prolactin.

RESULTS

No associations were observed for adult factors (p-trend >or= 0.17), body mass index at age 18, birth weight, or height (p-trend >or= 0.27). There was an inverse association between body size at ages 5 (p-trend = 0.03) and 10 (p-trend = 0.05) and prolactin, with levels 9% lower among women with the heaviest versus leanest average childhood body size. This association was more pronounced among women with a birth weight <7 pounds (p-trend = 0.004; p-interaction between birth weight and childhood body size = 0.01).

CONCLUSIONS

Our results suggest that few adult lifestyle risk factors are associated with prolactin levels in postmenopausal women; however, childhood body size may be a predictor of levels later in life.

Prolactin and breast cancer etiology: an epidemiologic perspective

A number of epidemiologic studies of prolactin and breast cancer etiology have recently become available. Retrospective case-control studies have suggested a modest positive or null relationship between circulating prolactin concentrations and risk of breast cancer. However these studies are limited by small sample sizes and the collection of blood after case diagnosis. Several large prospective studies, in which blood was collected prior to diagnosis, have observed modest positive associations between prolactin and risk. In a pooled analysis of approximately 80% of the world's prospective data, the relative risk (RR) comparing women in the top vs bottom quartile of prolactin levels was 1.3 (95% confidence interval (CI): 1.1, 1.6, p-trend = 0.002). The results were similar for premenopausal and postmenopausal women. Most notably, high prolactin levels were associated with a 60% increased risk of estrogen receptor (ER) positive tumors, but not with ER negative tumors. Limited genetic data suggest a role of polymorphisms in the prolactin and prolactin receptor genes in risk of breast cancer. Studies of survival have suggested that high pretreatment prolactin levels were associated with treatment failure, earlier recurrence, and worse overall survival. Parity and certain medications are the only confirmed factors associated with prolactin levels in women. Overall, epidemiologic data suggest that prolactin is involved in breast cancer etiology. Further research to better elucidate these associations and their underlying mechanisms is warranted.

Prolactin does not cause breast cancer and may prevent it or be therapeutic in some conditions

The polypeptide hormone prolactin (PRL), ubiquitous and multifunctional in vertebrates, always interested biologists, was of restricted concern to clinicians and researched little compared to insulin and growth hormone. PRL in lactation initially aroused relatively little interest, but it rose when with ovarian steroids and chemical carcinogens, it was implicated in rodent mammary carcinoma. It declined when PRL suppression did not counter breast cancer. Meanwhile, long-known, estrogen-related cancers in the ovary and breast did not deter wide estrogen use for contraception and supplementation despite risk, and estrogen blockers and inhibitors have improved treatment and are on trial for prophylaxis, despite serious short and long term side-effects. Despite the great differences between steroid and polypeptide, research on PRL and breast cancer mirroring that on estrogens is now growing. This is mainly negative, much due to recent prospective research reporting minor rises in plasma levels as a basis, together with some recent laboratory research, for a hypothesis that PRL induces post-menopausal breast cancer. That view contradicts a reproductive biology that evolved to benefit women and offspring. Elevated PRL in pregnancy and probably that in lactation, reduce risk. Many exogenous chemical and physical PRL-stimulants also do not increase risk. It has not been shown that PRL increases risk of breast cancer and some older and recent cell and tissue data suggest it may be the key, two-sided, in human breast tissue homeostasis. Excessive disturbance of this is unlikely to originate in PRL itself. The natural biology of PRL, the reproductive woman's hormone par excellence, and research in various fields, suggest a positive potential in the PRL family for direct prevention and treatment of breast cancer, possibly greater than that in the estrogens. It is time to debate and research this.

Effects of parity on pregnancy hormonal profiles across ethnic groups with a diverse incidence of breast cancer

Epidemiologic evidence suggests that a full-term pregnancy may affect maternal risk of breast cancer later in life. The objective of this cross-sectional study was to compare circulating levels of maternal hormones affecting breast differentiation (human chorionic gonadotropin and prolactin) and proliferation [alpha-fetoprotein, insulin-like growth factor I (IGF-I), and estradiol] between women at a low to moderate risk (Asians and Hispanics), as compared with women at a high risk for breast cancer (Caucasians and African-Americans). Between May 2002 and December 2004, a total of 586 pregnant women were approached during a routine prenatal visit. Among them, 450 women (206 Caucasian, 126 Asian, 88 Hispanic, and 30 African-American) met the inclusion criteria and signed the informed consent. Only singleton pregnancies were considered. Blood samples were drawn during the second trimester of pregnancy. Laboratory analyses were done using the IMMULITE 2000 immunoassay system. Gestational age standardized mean levels of estradiol, IGF-I, and prolactin were significantly higher in Hispanic women compared with Caucasian women. Mean concentration of IGF-I was significantly higher in African-American women compared with Caucasian and Asian women. No significant differences in pregnancy hormone levels were observed between Caucasian and Asian (predominantly second-generation Chinese) women in this study. Irrespective of ethnicity, women who had their first pregnancy had substantially higher mean levels of alpha-fetoprotein, human chorionic gonadotropin, estradiol, and prolactin compared with women who previously had at least one full-term pregnancy. These data suggest that circulating pregnancy hormone levels may explain some of the ethnic differences in breast cancer risk.

Reproductive experience modifies dopaminergic function, serum levels of prolactin, and macrophage activity in female rats

Reproductive experience (RE), i.e. pregnancy and lactation, induces physiological changes in mammals. Recent data show that neuroimmune interactions are modulated by a diversity of events involving neurotransmitters and neuropeptides. These molecules, particularly dopamine (DA), were reported to mediate the relevant cross talk between immune and neuroendocrine systems. Moreover, DA-mediated regulation of leukocyte function is a reasonable approach to investigate the DA-operated regulatory switch for immune-competent cells, such as macrophages. Therefore, the goals of the present study were to determine the effects of RE on: (1) dopaminergic function through hypothalamic levels of DA, dihydroxyphenylacetic acid (DOPAC), homovanilic acid (HVA), serotonin (5-HT), and 5-hydroxyindole acetic acid (5-HIAA); (2) basal levels of circulating prolactin (PRL); and (3) activity of peritoneal macrophage (phagocytosis and oxidative burst). A total of 16 adult (200-250 g) female Wistar rats were used, divided in two groups: nulliparous and primiparous. Approximately 2-3 weeks after weaning pups from the primiparous group, both groups of rats were tested. The findings indicate that: (1) DOPAC concentrations, DOPAC/DA and HVA+DOPAC/DA ratios decreased in primiparous rats as compared to virgin rats, (2) primiparous rats showed significantly lower serum PRL levels, and (3) phorbol miristate acetate (PMA)-induced oxidative burst was decreased in peritoneal macrophage from primiparous rats as compared to virgin rats. To test the possible positive correlation between serum levels of PRL and the intensity of oxidative burst by peritoneal macrophage, an extra experiment was done with adult virgin female rats treated with domperidone, an antagonist of DA receptors. Domperidone-treated animals showed increased serum levels of PRL and simultaneous increase in peritoneal macrophage oxidative burst. Thus, suggesting an indirect participation of hyperprolactinemia, induced by this treatment in peritoneal macrophage activity of female rats. These results suggest that a previous RE can modulate the activity of dopaminergic hypothalamic systems, while decreasing PRL serum levels and the oxidative burst of peritoneal macrophage. The neurochemical and hormonal RE-induced changes correlate with the immune alterations.

Reproductive factors and family history of breast cancer in relation to plasma prolactin levels in premenopausal and postmenopausal women

Many reproductive factors are associated with breast cancer risk, potentially through a hormonal pathway. The peptide hormone prolactin is essential in mammary development and lactation and may be a link between risk factors and breast cancer. While higher prolactin levels are associated with increased breast cancer risk, few determinants of prolactin levels are known. We conducted a cross-sectional analysis among 1,089 premenopausal and 1,311 postmenopausal women within the Nurses' Health Study (NHS) and the NHS II to examine the associations of reproductive factors, benign breast disease and family history of breast cancer with plasma prolactin levels. Parous women had significantly lower prolactin levels than nulliparous women (parous vs. nulliparous multivariate-adjusted geometric means = 14.1 ng/mL vs. 16.6 ng/mL, p<0.001 for premenopausal and 9.1 vs. 10.1, p=0.04 for postmenopausal women), although levels did not decrease with increasing number of children for either premenopausal (p-trend = 0.23) or postmenopausal (p-trend = 0.07) parous women. Age at first birth was not associated with prolactin levels. The reduction in prolactin levels among parous premenopausal women appeared to attenuate with increasing time since first birth, but the trend was not statistically significant (p-trend = 0.12). Age at menarche, duration of lactation and benign breast disease were not associated with prolactin levels. Family history of breast cancer was associated with significantly higher prolactin levels when compared with no family history among premenopausal (15.9 ng/mL vs. 14.3 ng/mL, p=0.04) but not postmenopausal (p=0.73) women. In conclusion, the associations of parity and family history with breast cancer risk may be mediated, at least in part, by prolactin levels.

Serum prolactin levels are positively associated with mammographic density in postmenopausal women

BACKGROUND

Prolactin is a polypeptide hormone that promotes normal breast proliferation and differentiation, but it is also implicated in the development and growth of mammary tumors. Mammographic density is a strong, independent predictor of breast cancer and, therefore, a potential surrogate indicator of breast cancer risk.

METHODS

To test the hypothesis that serum prolactin is positively related to mammographic density, we conducted a cross-sectional analysis of baseline data from the Postmenopausal Estrogen/Progestin Interventions (PEPI) Mammographic Density Study. Based on prior work, we further hypothesized that this association would be apparent only in women who had not recently used postmenopausal hormone therapy (HT).

RESULTS

In linear regression models adjusted for age, body mass index, race, smoking, alcohol use, parity and physical activity, among the 400 women who were not recent users of HT, prolactin was positively and statistically significantly associated with mammographic density (Beta log base 2 prolactin 0.0369 [95% CI: 0.0094-0.0645]. Thus, for each doubling of serum prolactin, there was an absolute increase in mammographic density of 3.69%. Additional adjustment for serum levels of estradiol, progesterone, sex hormone binding globulin and age at first pregnancy did not affect this result. There was no association between prolactin and mammographic density among the 169 participants who had recently used HT.

CONCLUSION

The correspondence between higher prolactin and higher mammographic density is consistent with prolactin's mitogenic properties and the associations between prolactin and breast tumor promotion. These results support the thesis that prolactin deserves investigation as a target for breast cancer risk reduction.

Effects of Raloxifene on Circulating Prolactin and Estradiol Levels in Premenopausal Women at High Risk for Developing Breast Cancer

BACKGROUND

Prolactin is a peptide hormone necessary for normal breast development that may contribute to breast tumorigenesis. Estrogen is a significant positive regulator of prolactin synthesis; therefore, raloxifene, a selective estrogen receptor modulator under study as a breast cancer prevention agent, may modulate both estradiol and prolactin levels by inhibiting estradiol from binding to its receptor.

METHODS

Premenopausal women at increased risk for invasive breast cancer participated in a pilot chemoprevention trial and were given 60 mg raloxifene daily for 24 months. Fasting serum samples collected at baseline and after 12 months on drug were used to measure circulating prolactin, estradiol, and sex hormone binding globulin (SHBG) levels.

RESULTS

Of the 27 subjects who completed 12 months of raloxifene, 23 had paired prolactin samples, and 20 had paired estradiol and SHBG samples. Prolactin levels did not significantly change with raloxifene treatment, but SHBG levels increased (mean change = 7.3 nmol/L; P = 0.0001; 95% confidence interval, 3.9-10.7). Estradiol (mean change = 42 pg/mL; P = 0.048; 95% confidence interval, 1-84 pg/mL) levels were elevated when comparing 15 of the 20 women with paired estradiol measurements who also had both of these samples taken during the early follicular phase of the menstrual cycle.

CONCLUSIONS

This report is the first to examine the long-term effects of raloxifene on prolactin, estradiol, and SHBG levels in premenopausal women who are also at increased risk for developing invasive breast cancer. Raloxifene had no significant effect on prolactin levels but did increase estradiol and SHBG measurements.

Reproductive experience reduces circulating 17beta-estradiol and prolactin levels during proestrus and alters estrogen sensitivity in female rats

The reproductive experiences of pregnancy, parturition, and lactation affect a range of neural and endocrine processes after the end of lactation. In women, previous parity results in reduced circulating prolactin (PRL) and androgen levels years after giving birth. Reductions in PRL secretion also occur in reproductively experienced, female rats. In the present study we examined the status and regulation of estradiol (E(2)) and PRL during the reproductive cycle after reproductive experience. These hormones regulate one another and have been implicated in a number of disease and aging processes. Using a rat model, the patterns of E(2) and PRL secretion, pituitary PRL content, and estrogen receptor alpha expression were characterized from 1200-1800 h on proestrus in age-matched, primiparous and nulliparous animals. The possible effect of parity on estrogen sensitivity was then examined by challenging nonlactating, ovariectomized, age-matched, multiparous and nulliparous rats with estradiol benzoate (EB; 0, 1, 5, 25, and 125 microg/kg) and measuring PRL responses 24 and 48 h later. Previous parity resulted in modest, yet significant, reductions in E(2) and PRL levels on proestrus, a limited increase in pituitary estrogen receptor alpha expression, and a significant shift in estrogen sensitivity, as measured by EB-induced PRL secretion. Nulliparous animals were more sensitive than multiparous rats to the two lower doses of EB, whereas multiparous animals were more responsive to the highest EB dose. These unique parity-induced alterations in the female's endocrine state that persist beyond lactation may impact a multitude of estrogen-mediated processes over the female's adult life span.

The basal and TRH stimulated levels of prolactin in low risk climacteric patients with increased breast density: A matched pair case control trial

OBJECTIVE

To detect any significant alteration of basal and TRH stimulated circulating prolactin levels in those with an extremely dense breast composition as compared to ones with a fatty pattern in mammography in climacteric patients with a low risk probability for developing invasive breast cancer within five years according to a validated risk model.

MATERIALS AND METHOD

In this matched pairs case-control trial a total of 67 climacteric patients with an extremely dense breast composition were compared to a control group of 71 climacteric patients with an almost entirely fat pattern composition in terms of basal and TRH stimulated circulating prolactin levels. All participants in the study had an estimated 5 years breast cancer risk less than 1.67% according to the validated model of Gail. Subgroup analysis was done according to menopausal status (premenopausal versus postmenopausal) and according to the hormone replacement therapy (HRT) in postmenopausal patients (current users of HRT versus never used HRT).

RESULTS

We did not detect any statistically relevant differences between groups or subgroups in terms of basal, stimulated and Delta levels (stimulated-basal) of prolactin (ng/ml). The differences between groups of extremely dense composition versus almost fatty pattern in terms of DeltaPRL (ng/ml) (+/-S.D.) were not statistically significant (68.1+/-34.5 versus 69.1+/-43.0; unpaired t test, Welch corrected p=0.88, 95% CI -12.1 to 14.0).

CONCLUSION

Our results do not suggest a contribution of circulating prolactin to increased mammographic density in climacteric patients with low risk probability to develop breast cancer. A study of similar kind is warranted in high risk patients.

Hormonal aspects in the causation of human breast cancer: epidemiological hypotheses reviewed, with special reference to nutritional status and first pregnancy

Epidemiology of breast cancer has identified early age at menarche, late first pregnancy, low parity and late menopause as risk factors, but in addition genetic factors, height, weight and living in western countries play a significant role. The international variation in incidence is almost exclusively due to non-genetic factors. Hypotheses in prevention-oriented research are reviewed: 1. obesity-related oestrogen production as a stimulus of the tumour in postmenopausal women; 2. nutritional status and energy expenditure during puberty and adolescence, developed for fertility and fecundity and extended later to breast cancer; 3. reproductive life during early adulthood, age at first pregnancy and its specific effects on breast tissues. The message of preventability of breast cancer is that mammary epithelial differentiation should come early. Our insight concerning events in puberty and early adulthood can be consolidated in one concept on the risk of extended proliferation of breast epithelium during early adulthood in the absence of full differentiation induced by pregnancy. The combined effects of Western-type nutrition, lack of exercise and Western-type women's emancipation sets the stage for breast cancer already at a young age. Since it is unlikely that emancipated women in affluent societies will return to the original life-style of getting pregnant as soon as it is biologically possible, a novel daring way of protection has to be considered. Could a "Breast Differentiation Pill" be developed to offer protection?

Lactation reduces prolactin levels in reproductively experienced female rats

Long-term alterations in prolactin (PRL) secretion following reproductive experience have been demonstrated in both women and female rats. In the rat, these changes include decreased PRL secretion in response to a dopamine antagonist challenge following ovariectomy, decreased post-coital diurnal and nocturnal prolactin surges in multigravid versus primigravid females, as well as decreased suckling-induced prolactin release in multiparous versus primiparous females. To date, there have been no studies examining PRL secretion following reproductive experience in cycling female rats. Studies in women, however, have demonstrated a reduction in basal PRL secretion during the menstrual cycle. The purpose of the present work was to determine whether similar changes occur in the rat during the estrous cycle and to what extent lactation is involved in these effects. In addition to examining PRL, potential parity-induced changes in estradiol secretion were also studied. The findings revealed a significant decrease in PRL levels during the afternoon of proestrus, which was only observed in primiparous females that had lactated. Significant differences in estradiol secretion were not detected following reproductive experience. Thus, a reduction in the PRL surge on the afternoon of proestrus is a consequence of reproductive experience that requires both pregnancy and lactation.

Prolactin acts as a potent survival factor for human breast cancer cell lines

Human breast cancer is the leading cause of cancer death in women from Western societies, and a large study of the epidemiology demonstrated strong associations between human prolactin and risk of breast cancer. Using established models of apoptosis of human breast cancer cell lines, we assessed the role of prolactin in breast cancer cell growth and survival. We showed that prolactin had no effect on the metabolic activity or total cell number of any cell lines. We confirmed endogenous prolactin production by these cells and that the levels varied. In the presence of a prolactin-neutralising antibody, each of the cell lines responded with the induction of apoptosis as opposed to growth inhibition. The sensitivity of the cell lines to the physiological inducer of apoptosis, C2-ceramide, appeared relative to the levels of endogenous prolactin that they contained. We then showed that exogenously added prolactin acted as a potent survival factor against apoptosis in all the cell lines examined. In addition, we demonstrated that a prolactin-neutralising antibody in combination with C2-ceramide caused an anticipated, additive increase in cell death. This study demonstrated that prolactin protects human breast cancer cell lines against apoptosis and this may have important implications for cancer treatment.

Prolactin and the prolactin receptor: new targets of an old hormone

Prolactin (PRL) is one of a family of related hormones including growth hormone (GH) and placental lactogen (PL) that are hypothesized to have arisen from a common ancestral gene about 500 million years ago. Over 300 different functions of PRL have been reported, highlighting the importance of this pituitary hormone. PRL is also synthesized by a number of extra-pituitary tissues including the mammary gland and the uterus. Most of PRL's actions are mediated by the unmodified 23 kDa peptide, however, PRL may be modified post-translation, thereby altering its biological effects. PRL exerts these effects by binding to its receptor, a member of the class I cytokine receptor super-family. This activates a number of signaling pathways resulting in the transcription of genes necessary for the tissue specific changes induced by PRL. Mouse knockout models of the major forms of the PRL receptor have confirmed the importance of PRLs role in reproduction. Further knockout models have provided insight into the importance of PRL signaling intermediates and the advent of transcript profiling has allowed the elucidation of a number of PRL target genes.

The role of prolactin in mammary carcinoma

The contribution of prolactin (PRL) to the pathogenesis and progression of human breast cancer at the cellular, transgenic, and epidemiological levels is increasingly appreciated. Acting at the endocrine and autocrine/paracrine levels, PRL functions to stimulate the growth and motility of human breast cancer cells. The actions of this ligand are mediated by at least six recognized PRL receptor isoforms found on, or secreted by, human breast epithelium. The PRL/PRL receptor complex associates with and activates several signaling networks that are shared with other members of the cytokine receptor superfamily. Coupled with the recently identified intranuclear function of PRL, these networks are integrated into the in vitro and in vivo actions induced by ligand. These findings indicate that antagonists of PRL/PRL receptor interaction or PRL receptor-associated signal transduction may be of considerable utility in the treatment of human breast cancer.

The association of breast mitogens with mammographic densities

Radiologically dense breast tissue (mammographic density) is strongly associated with risk of breast cancer, but the biological basis for this association is unknown. In this study we have examined the association of circulating levels of hormones and growth factors with mammographic density. A total of 382 subjects, 193 premenopausal and 189 postmenopausal, without previous breast cancer or current hormone use, were selected in each of five categories of breast density from mammography units. Risk factor information, anthropometric measures, and blood samples were obtained, and oestradiol, progesterone, sex hormone binding globulin, growth hormone, insulin-like growth factor-I and its principal binding protein, and prolactin measured. Mammograms were digitised and measured using a computer-assisted method. After adjustment for other risk factors, we found in premenopausal women that serum insulin-like growth factor-I levels, and in postmenopausal women, serum levels of prolactin, were both significantly and positively associated with per cent density. Total oestradiol and progesterone levels were unrelated to per cent density in both groups. In postmenopausal women, free oestradiol (negatively), and sex hormone binding globulin (positively), were significantly related to per cent density. These data show an association between blood levels of breast mitogens and mammographic density, and suggest a biological basis for the associated risk of breast cancer.

Epidemiology of endocrine-related risk factors for breast cancer

Ovarian and other hormones are major determinants of breast cancer risk. Particularly important is the accumulative exposure of the breast to circulating levels of the ovarian hormones estradiol and progesterone. A number of breast cancer risk factors can be understood in light of how they affect women's hormone profiles. Age is a marker for the onset and cessation of ovarian activity. Racial differences in hormone profiles correlate with breast cancer incidence patterns. Age at menarche not only serves as the chronological indicator of the onset of ovarian activity, but as a predictor of ovulatory frequency during adolescence and hormone levels in young adults, and has a long-lasting influence on risk. Age at menopause, another established breast cancer risk factor, marks the cessation of ovarian activity. Pregnancy history and lactation experience also are hormonal markers of breast cancer risk. Postmenopausal obesity, which is associated with higher levels of estrogen following cessation of ovarian activity, increases breast cancer risk, whereas physical activity, which can limit menstrual function, reduces risk. A relatively recent area of investigation is prenatal exposures like preeclampsia and low birth weight; both may be associated with lower in utero exposure to estrogen and also may predict lower breast cancer risk as an adult. Improved understanding of these exposures and their potential interactions with breast cancer susceptibility genes may, in the future, improve our prospects for breast cancer prevention.

Mammographic densities as a marker of human breast cancer risk and their use in chemoprevention

Differences in the parenchymal pattern of the breast on mammography reflect differences in the amounts of stromal, epithelial, and fat tissue present in the breast. Stroma and epithelium are radiologically dense, whereas fat is lucent. Extensive areas of mammographically dense breast tissue are strongly associated with an increased risk of breast cancer. A variety of interventions, including gonadotropin-releasing hormone inhibitor, tamoxifen, stopping hormone replacement therapy (HRT), and adopting a low-fat, high-carbohydrate diet, all influence the tissue composition of the breast and reduce mammographic densities. Of the interventions examined to date, only tamoxifen has been shown to reduce the incidence of breast cancer, at least in the short term. Conversely, HRT, which increases density, also increases risk of breast cancer. These results suggest that mammographic density may be a short-term marker of the effect on the breast of potential preventive interventions for breast cancer.

Reproductive experience modulates dopamine-related behavioral responses

Reproductive experience (RE), i.e., mating, pregnancy, parturition and lactation, has long-term physiological effects. It reduces the basal levels of circulating prolactin in parous women, decreases the intensity of nocturnal and diurnal prolactin surges in multigravid rats during early pregnancy, as well as the hormonal and neurochemical responses to the dopamine receptor antagonists metoclopramide and haloperidol. In the present study, we evaluated the possible influences of RE on some dopaminergic-related behaviors: (1) acute responses to a new environment represented by an open-field arena plus injection stress; (2) modulation of behavior after a short-term withdrawal subsequent to 7 days amphetamine (AMPH) pretreatment; (3) stereotypy elicited by AMPH and apomorphine (APO); and (4) APO-induced hypothermia. In the 3-min open-field test, there was a decrease in locomotor activity as a function of RE. Behavioral depression was mild and AMPH pretreatment revealed RE alterations. APO-induced stereotyped behavior was slightly more intense in primiparous animals, although no significant differences were found in AMPH-induced stereotyped behavior. No differences were observed between intact and ovariectomized primiparous and nulliparous animals in APO-induced hypothermia. Our data suggest that RE modifies some DA-related behavioral responses. The physiological relevance of the phenomenon is discussed.

Reproductive history in relation to plasma hormone levels in healthy post-menopausal women

OBJECTIVES

We sought to examine the relationship between reproductive history and measures of selected gonadotrophins and steroid hormones among post-menopausal women. Previous studies have suggested that there is a negative correlation between parity and post-menopausal serum estrogens, which may be a mechanism by which pregnancies protect women from the development of breast cancer.

METHODS

We analyzed women who experienced a natural menopause within the Healthy Women Study cohort both 1 and 8 years after menopause. Lifetime reproductive history was obtained and blood was assayed for estrone, estradiol, androstenedione, testosterone, follicle stimulating hormone (FSH), and luteinizing hormone (LH) at 1 year post-menopause and for many of these steroid hormones at 8 years post-menopause. Also at 8 years post-menopause, a hip bone mineral density measure was obtained.

RESULTS

Age at menopause related to a modest increase in estrone at 1 year but a decrease in estrone and estradiol at eight years. Adjustment for body mass index (BMI), oral contraceptive use, alcohol use, cigarette smoking, and education had little impact on these findings. There were no other internally consistent relationships between reproductive variables and steroid hormones or hip-bone mineral density.

CONCLUSIONS

These observations do not support the hypothesis that parity acts to diminish endogenous levels of post-menopausal estrogens.

The short-term and long-term effect of a pregnancy on breast cancer risk: a prospective study of 802,457 parous Norwegian women

Time-related effects of a pregnancy on breast cancer risk were examined in a population-based prospective study of 802,457 parous Norwegian women aged 20-56 years. The mean follow-up time was 16.4 years. A total of 4787 women were diagnosed with breast cancer. We observed a short-term increase in risk of breast cancer after a full-term pregnancy, with a maximum 3-4 years after delivery, followed by a long-lasting decrease in risk. The maximum risk was about twice the risk for women whose last delivery was 20 or more years previously (incidence rate ratio = 1.99, 95% confidence interval = 1.70-2.33). Compared with nulliparous women, those with one or two children were at higher risk in the first decade after the last pregnancy, whereas those with three or more children were at lower risk in most categories of time since the last birth. The positive association between breast cancer risk and age at last birth was markedly reduced after adjustment for time since last birth. We conclude that there is a non-linear relationship between breast cancer incidence and time since last birth. Part of the relation with age at last birth may be attributed to the association with time since last birth.

Serum prolactin levels and their relationship to survival in women with operable breast cancer

The prognostic value of serum prolactin levels was assessed in a sequential series of 739 patients who were initially treated at Guy's Hospital, London, between 1975 and 1980. Prolactin was measured in 472 patients 1 day before (Hpr1) and in 457 patients 10 days after (Hpr2) mastectomy. Follow-up of the patients was up to August 1992 giving 6139 women-years with a median follow-up time of 11.5 years (13.7 for patients still living and 5.1 for those dead). The association between the three prolactin variables and reproductive and clinical factors was examined before assessing the prognostic value of prolactin levels in terms of overall, disease-specific and disease-free survival. Multivariate survival models were used in order to adjust for the effect of other prognostic variables. These were found to be: tumour size, degree of nodal involvement, tumour grade and age at diagnosis. The results showed that high Hpr2 or high postoperative increase in prolactin (i.e. Hpr2-Hpr1) were significantly related to shorter disease-specific survival (p = 0.04 and 0.01, respectively) in postmenopausal women. In addition there was some indication, which did not attain formal significance, for this association to occur for disease-free survival. Thus the rise in blood prolactin levels after surgery may be a weak indicator of poor prognosis of breast cancer in postmenopausal women.

Reproductive factors and family history of breast cancer in relation to plasma estrogen and prolactin levels in postmenopausal women in the Nurses' Health Study (United States)

Parity, age at first birth, age at menarche, and a family history of breast cancer have each been associated consistently with breast cancer risk. Whether this increase in risk is mediated, at least in part, through changes in endogenous hormone levels is unclear. We conducted a cross-sectional study of the relationships between these factors and plasma hormone levels in 216 healthy postmenopausal women in the Nurses' Health Study (United States). The hormones evaluated were estradiol, percent and total free estradiol, percent and total bioavailable estradiol, estrone, estrone sulfate, and prolactin. After controlling for age, body mass index (weight/height2), and alcohol use, we observed inverse associations between estrone sulfate and parity (r = -0.15, P = 0.03) and between percent bioavailable estradiol and age at first birth (r = -0.17, P = 0.02). Although women with a family history of breast cancer tended to have higher estrogen levels compared with women without such history, the differences were not statistically significant. Age at menarche was not related significantly to any of the hormones. These data provide some additional evidence that the inverse relationship observed between parity and breast cancer risk may be mediated, at least in part, through decreased estrogen levels. Our data do not support a substantial influence of either family history of breast cancer or age at menarche on postmenopausal estrogen or prolactin levels.

Multiple births, sex of children and subsequent breast-cancer risk for the mothers: a prospective study in Norway

Endocrinological changes occurring during pregnancy may influence the subsequent cancer risk of the mother. Further, the endocrinological milieu may differ according to different birth characteristics. In the present study possible relations between multiple births, sex of children and breast-cancer risk were examined in a population-based, prospective study of 802,269 parous Norwegian women aged 20-56 years. A total of 4,782 women were diagnosed with breast cancer during follow-up. Of these, 97 had ever experienced a multiple birth. We found a slightly lower risk of breast cancer among women ever having had a multiple birth than among women with singletons only (IRR = 0.89, 95% CI = 0.73-1.09). The reduction in risk was mainly observed among women with a multiple last birth. Further, the reduction in risk seemed to diminish with increasing parity, and among women with 4 or more full-term pregnancies, ever having had a multiple birth was associated with an elevated risk (IRR = 1.48, 95% CI = 0.97-2.25). The sex of the first or last child did not affect the subsequent breast-cancer risk. Further, we found no associations with the sex distribution among all children or in multiple births, despite a tendency toward a reduced risk among women with several daughters only.

The association of height, weight, menstrual and reproductive events with breast cancer: results from two prospective studies on the island of Guernsey (United Kingdom)

The association with breast cancer of menstrual and reproductive events, family history of breast cancer, and body size have been studied on two cohorts of 6,706 volunteers on the island of Guernsey (United Kingdom), 168 of whom had breast cancer detected during follow-up. The median follow-up time of the non-cases was 21 years in the first study and 10 years in the second. A time-dependent Cox regression model was fitted to the data with age as the time-dependent variable in order to represent the effect of changing menopausal status. Other variables examined in the model were age at menarche, parity, age at first birth, family history of breast cancer, height, weight (both directly measured), relative weight (weight [kg]/height[m]), and Quetelet's body mass index (weight[kg]/height[m]2). Interactions between age and all other covariates also were examined. Family history was found to be the most important risk factor for women aged less than 51 years (relative risk [RR] = 3.5, 95 percent confidence interval [CI] = 2.0-6.0), and intervals between menarche and first birth longer than 14 years were found to increase significantly the risk of breast cancer in women older than 61 years (RR = 2.4, CI = 1.3-4.4). Height was the only indicator of body size which was associated significantly with risk of breast cancer, the estimated regression coefficient indicating an increase in risk of about 70 percent for women on the 90th centile of height relative to those on the 10th centile. A survey of the literature showed that the association between risk of breast cancer and height was found in those studies which used direct measurements of height but not in others which used self-reported values.

A molecular variant of angiotensinogen associated with preeclampsia

Pregnancy-induced hypertension (PIH) is a heterogeneous disorder which complicates 5-7% of all pregnancies and remains a leading cause of maternal, fetal and neonatal morbidity and mortality. Severe preeclampsia is the most distinctive and life-threatening form; a multi-system disorder more common in first pregnancies, it is characterized by high blood pressure and proteinuria. In a series of Caucasian women with pregnancy-induced hypertension, we have observed a significant association of preeclampsia with a molecular variant of angiotensinogen, T235, found previously to be associated with essential hypertension. This finding is corroborated in a sample ascertained in Japan. Together, these observations support a new pathophysiological interpretation of preeclampsia and of its relation to some forms of essential hypertension.

Prior parity reduces post-coital diurnal and nocturnal prolactin surges in rats

Mating stimuli received by female rats activate a neuroendocrine mnemonic system which produces daily diurnal and nocturnal prolactin (PRL) surges for the first half of gestation, surges which help maintain corpora lutea function and a viable pregnancy. Since these PRL surges may be regulated in part by endogenous opioids and opioid sensitivity declines as a function of multiple births, we decided to investigate the possibility that prior parity might affect the post-coital diurnal and nocturnal PRL surges, reducing their magnitude and/or occurrence. Age-matched, nulliparous and primiparous rats were mated to males from our colony. On days 5 or 10 of pregnancy females received jugular catheters. Blood samples were collected at regular intervals from 1000 h on day 7 to 1000 h on day 8, and from 1000 h on day 12 to 1000 h on day 13 of gestation in separate sets of multigravid and primigravid rats. Measurement of plasma PRL by radioimmunoassay revealed that prior reproductive experience altered the patterns and levels of plasma PRL. Plasma PRL levels were significantly reduced during both the diurnal and nocturnal surges on days 7-8 in multigravid rats when compared with levels in primigravid rats. No differences in PRL levels were found between primigravid and multigravid groups on days 12 to 13 of gestation. The changes in diurnal and nocturnal PRL surges during early pregnancy indicate that prior parity reduces the subsequent secretion of PRL, possibly by altering the neuroendocrine regulation of this hormone.

Neural and endocrine sensitivities to opioids decline as a function of multiparity in the rat

Hormonal changes during pregnancy regulate the onset of maternal behavior at parturition. In addition, the concentrations of beta-endorphin and mu opioid receptors are higher during pregnancy and lower during lactation. Previous studies have shown that sensitivity of female rats to the disruptive behavioral effects of morphine changes as a function of the number of pregnancies and/or lactations the females undergo. The objectives of the present study were to determine whether central infusions of the endogenous opioid, beta-endorphin, would disrupt maternal behavior. Next, we investigated the possibility that the neural sensitivity to beta-endorphin changes with repeated pregnancies. And finally, we examined whether opioid-mediated endocrine responses also change as a function of multiparity. In the first study, bilateral infusions of low doses (0.06-0.72 nmol) of beta-endorphin into the medial preoptic area (MPOA) of lactating, primiparous rats disrupted maternal behavior. When comparable doses of beta-endorphin were infused into the MPOA of age-matched, multiparous rats, the behavioral effects of beta-endorphin were significantly attenuated. In response to suckling stimulation, an opioid-mediated endocrine response, primiparous mothers secreted more prolactin than did multiparous rats. Moreover, multiparous, but not primiparous, mothers were insensitive to the ability of naloxone, an opiate antagonist, to block suckling-induced increases in prolactin. These findings indicate that reductions in neural sensitivity to opioids develop as females undergo repeated pregnancies and lactations, changes which affect both behavioral and endocrine functions.

Influence of cigarette smoking on pituitary and sex hormone balance in healthy premenopausal women

Plasma gonadotropin FSH and LH, PRL, sex steroids (17-beta E2, E1, and P), SBP binding capacity, and urine estrogens (E1, E2, and E3) were measured in 485 premenopausal healthy women, subdivided according to smoking habits. The aim of the study was to verify if cigarette smoking influences sex hormone balance. Baseline PRL levels were significantly lower (P less than 0.002) in smoker (n = 174) than in nonsmoker (n = 311) women. No difference was found in the other parameters of the two groups, particularly in plasma and urine estrogenic pattern. Our data suggest that smoking directly affects PRL levels by involving the hypothalamic mechanism that regulates PRL secretion.

Serum hormone levels in British and rural Chinese females

The comparison of blood levels of oestradiol, testosterone, prolactin, and sex-hormone binding globulin (SHBG) was made of 3250 rural Chinese and 300 British women, aged 35 to 64. To reduce the number of assays performed the blood samples were combined so as to form 390 and 30 pools, respectively. The Chinese had significantly less oestradiol and testosterone. Prolactin levels were similar in both races. SHBG was significantly lower in postmenopausal British women. In the Chinese women, testosterone was positively and prolactin negatively correlated with breast cancer mortality.