Differential prolactin response to oral metoclopramide in nulliparous versus parous women throughout the menstrual cycle

Long-term alterations in neural and endocrine processes induced by motherhood in mammals

This article is part of a Special Issue "Parental Care". The reproductive experience of pregnancy, lactation and motherhood can significantly remodel the female's biological state, affecting endocrine, neuroendocrine, neural, and immunological processes. The brain, pituitary gland, liver, thymus, and mammary tissue are among the structures that are modified by reproductive experience. The present review that focuses on rodent research, but also includes pertinent studies in sheep and other species, identifies specific changes in these processes brought about by the biological states of pregnancy, parturition, and lactation and how the components of reproductive experience contribute to the remodeling of the maternal brain and organ systems. Findings indicate that prior parity alters key circulating hormone levels and neural receptor gene expression. Moreover, reproductive experience results in modifications in neural processes and glial support. The possible role of pregnancy-induced neurogenesis is considered in the context of neuroplasticity and behavior, and the effects of reproductive experience on maternal memory, i.e. the retention of maternal behavior, together with anxiety and learning are presented. Together, these sets of findings support the concept that the neural and biological state of the adult female is significantly and dramatically altered on a long-term basis by the experiences of parity and motherhood. Remodeling of the maternal brain and other biological systems is posited to help facilitate adaptations to environmental/ecological challenges as the female raises young and ages.

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.

Region-, neuron-, and signaling pathway-specific increases in prolactin responsiveness in reproductively experienced female rats

Pregnancy and lactation cause long-lasting enhancements in maternal behavior and other physiological functions, along with increased hypothalamic prolactin receptor expression. To directly test whether reproductive experience increases prolactin responsiveness in the arcuate, paraventricular, and supraoptic nuclei and the medial preoptic area, female rats experienced a full pregnancy and lactation or remained as age-matched virgin controls. At 5 wk after weaning, rats received 2.5, 100, or 4000 ng ovine prolactin or vehicle intracerebroventricularly. The brains underwent immunohistochemistry for the phosphorylated forms of signal transducer and activator of transcription 5 (pSTAT5) or ERK1/2 (pERK1/2). There was a marked increase in pSTAT5 and pERK1/2 in response to prolactin in the regions examined in both virgin and primiparous rats. Primiparous rats exhibited approximately double the number of prolactin-induced pSTAT5-immunoreactive cells as virgins, this effect being most apparent at the higher prolactin doses in the medial preoptic area and paraventricular and supraoptic nuclei and at the lowest prolactin dose in the arcuate nucleus. Dual-label immunohistochemistry showed that arcuate kisspeptin (but not oxytocin or dopamine) neurons displayed increased sensitivity to prolactin in reproductively experienced animals; these neurons may contribute to the reduction in prolactin concentration observed after reproductive experience. There was no effect of reproductive experience on prolactin-induced pERK1/2, indicating a selective effect on the STAT5 pathway. These data show that STAT5 responsiveness to prolactin is enhanced by reproductive experience in multiple hypothalamic regions. The findings may have significant implications for understanding postpartum disorders affecting maternal care and other prolactin-associated pathologies.

Reproductive experience and expression of dopamine D(2) receptor mRNA: a possible mechanism for reduced prolactin secretion in primiparous rats

Reproductive experience (i.e. pregnancy and lactation) leads to reduced levels of circulating prolactin in both women and rats. Stimulation of prolactin secretion by dopamine antagonists is also blunted following reproductive experience in both species. Whereas a parity-induced reduction in haloperidol-stimulated prolactin secretion is evident in ovariectomised rats, it is unknown whether a similar attenuation of prolactin secretion is present in reproductively experienced, cycling pro-oestrous rats. The present study examined this possibility. Moreover, to determine possible mechanisms involved in parity-mediated changes in prolactin secretion, both dopamine utilisation within the arcuate nucleus/median eminence and expression of dopamine D(2) receptor mRNA (short and long forms) in the anterior pituitary were measured across the afternoon of pro-oestrous in reproductively experience and inexperienced females. Prolactin secretion was lower on the afternoon of pro-oestrous in primiparous females compared to age-matched, nulliparous controls. In addition, haloperidol-stimulated prolactin secretion was reduced in ovariectomised, reproductively experienced females. Although no differences in dopamine utilisation were observed as a function of reproductive experience, parity did affect the expression of both forms of D(2) receptor mRNA in the anterior pituitary. Compared with nulliparous controls, primiparous females had increased D(2 long) mRNA expression at 12.00 h on pro-oestrous as well as increased D(2 short) mRNA expression at 14.00 h. Because the ratio of D(2 long)/D(2 short) can significantly effect lactotroph proliferation and prolactin secretion, a shift in relative expression of the two D(2) receptor isoforms within the anterior pituitary of parous females may help account for the reduction in prolactin secretion that occurs following reproductive experience.

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.

Reproductive experience increases prolactin responsiveness in the medial preoptic area and arcuate nucleus of female rats

The experience of pregnancy plus lactation produces long-term enhancements in maternal behavior as well as reduced secretion of prolactin, a key hormone for the initial establishment of maternal care. Given that prolactin acts centrally to induce maternal care as well as regulate its own secretion, we tested whether prolactin receptors in brain regions known to regulate behavioral and neuroendocrine processes were up-regulated and more responsive to prolactin in reproductively experienced females. Diestrous primiparous (8 wk after weaning) and age-matched virgin rats were treated with 250 microg ovine prolactin sc or vehicle and the brains collected 2 h later for measurement of mRNA for genes involved in prolactin signaling. Reproductively experienced rats had lower serum prolactin concentrations, compared with virgin rats, suggesting enhanced prolactin feedback on the arcuate neurons regulating prolactin secretion. In the medial preoptic area and arcuate nucleus (regions involved in regulating maternal behavior and prolactin secretion, respectively), the level of long-form prolactin receptor mRNA was higher in primiparous rats, and prolactin treatment induced a further increase in receptor expression in these animals. In the same regions, suppressors of cytokine signaling-1 and -3 mRNA levels were also markedly increased after prolactin treatment in reproductively experienced but not virgin rats. These results support the idea that reproductive experience increases central prolactin responsiveness. The induction of prolactin receptors and enhanced prolactin responsiveness as a result of pregnancy and lactation may help account for the retention of maternal behavior and shifts in prolactin secretion in reproductively experienced females.

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.

Altered Functional Status of the Hypothalamic Dopaminergic Tone in Patients with Chronic Graft-versus-Host Disease after Allogeneic Hematopoietic Stem Cell Transplantation: A Pilot Study

We compared the functional status of the hypothalamic dopaminergic tone in patients given an allogeneic hematopoietic stem cell transplantation (allo-HSCT) with chronic graft-versus-host disease (GVHD) with that observed in patients with allo-HSCT without chronic GVHD and in healthy controls. The effect of acute dopaminergic blockade with intravenous metoclopramide on serum prolactin (PRL) concentrations was evaluated. Twenty volunteers, 20 to 52 years of age, seronegative for both hepatitis C virus and the human immunodeficiency virus, were studied: (1) 10 clinically healthy men (group 1), and (2) 9 patients with leukemia, and 1 patient with refractory aplastic anemia who underwent allo-HSCT, 5 of whom (3 men and 2 women) developed chronic GVHD (group 2), and 5 (3 men and 2 women) who did not develop chronic GVHD (group 3). Serum PRL concentrations were measured both fasting and after intravenous administration of metoclopramide (10-mg bolus). The area under the PRL curve was calculated. Patients in group 2 were older than those in groups 1 and 3 (P<.018), but their body mass index was similar. Fasting serum PRL concentrations were similar among the 3 groups; however, group 2 had higher PRL concentrations throughout the test (P<.001) and a greater area under the PRL curve than groups 1 and 3 (P<.001), without differences between the last 2 groups. The differences remained significant after adjustment for age (P<.01). Our results in a small group of patients with chronic GVHD after allo-HSCT suggest the existence of an increased functional level of their hypothalamic dopamine tone, which would favor a tendency toward a diminished endogenous production, release of pituitary PRL, or both. This could represent an adaptive mechanism aiming to maintain circulating PRL concentrations within a physiological range.

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.

Reproductive experience influences grooming behavior during pregnancy in rats

The pregnancy-induced increase in self-licking observed in rats is important for mammary gland development and lactation. Reproductive experience has epidemiologial implications such as a decrease in the incidence of mammary gland cancer in women and it also influences various behavioral, neurochemical and endocrine parameters. The aim of the present study was to investigate the influence of reproductive experience on grooming behavior patterns during pregnancy in rats. Self-grooming behavior was measured in age-matched virgin, primi- and multigravid (days 7, 8, 9, 19, and 20 of pregnancy) rats. General grooming (head, forelimbs and shoulders) was not significantly different among virgin, primi- and multigravid rats during pregnancy. Confirming previous work, pregnant rats spent significantly more time in specific grooming (mammary glands, nipple lines, genital and pelvic regions) than did virgin animals. In addition, self- licking of mammary glands was significantly increased in multi- as compared to primigravid rats on days 8, 9, 19 and 20 of pregnancy. The increase in mammary gland grooming observed in multigravid rats appears to be a consequence of previous reproductive experience. These data show that reproductive experience modulates mammary gland grooming during pregnancy, possibly contributing to successful reproduction.

Increased hypothalamic dopaminergic tone only in early parous women with either malignant or benign breast tumors

OBJECTIVE

To investigate whether the serum prolactin (PRL) response to a dopamine antagonist was different in nonobese, euthyroid women with malignant or benign breast tumors in comparison with healthy women, considering their age at first full-term pregnancy or their nulliparity.

METHODS

Serum PRL concentrations before and 60, 90, and 120 minutes after oral administration of metoclopramide (10 mg) were studied in 122 nonobese, nonsmoking, euthyroid women: 28 who had invasive breast cancer, stage I or II (group 1), 34 who had benign breast disease (group 2), and 60 who were clinically healthy (group 3). These three main groups were subdivided into early and late parous women (< or = 25 and >25 years, respectively) and nulliparous women, and the menopausal status was also considered.

RESULTS

Early parous women with invasive breast cancer (both premenopausal and postmenopausal) and early parous premenopausal women with benign breast disease had significantly higher serum PRL concentrations in response to administration of metoclopramide (P<0.05) and a greater area under the PRL curve (P<0.05) than those observed in early parous healthy women. No other significant differences in the serum PRL response were noted between or within groups.

CONCLUSION

The results of this study suggest the existence of an increased hypothalamic dopaminergic tone in early parous women but not in late parous or nulliparous women with malignant or benign breast tumors in comparison with similar healthy women. This finding may represent an adaptive protective mechanism attempting to prevent persistently increased serum PRL concentrations, a factor that could adversely affect the clinical evolution of the disease.

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.

Increased sensitivity of dopamine systems following reproductive experience in rats

Several studies have suggested that alterations in forebrain dopamine activity during the postpartum period may result in the onset of postpartum psychosis in women [J. Psychosom. Obstet. Gynecol. 19 (1998) 104; Prog. Neuro-Psychopharmacol. Biol. Psychiatry 17 (1993) 571; J. Clin. Psychiatry 51 (1990) 365.]. The present study investigated whether increased dopamine activity in these forebrain regions is a normal consequence of reproductive experience in rodents. Both intact and ovariectomized parous and nulliparous females were tested for their responses to the dopamine agonist apomorphine using two behavioral measures, prepulse inhibition (PPI) and oral stereotypy. In addition, dopamine and DOPAC levels were measured in tissue from the striatum and nucleus accumbens together with circulating plasma prolactin levels. The results of the behavioral studies demonstrate an increased response to apomorphine in parous females. Parous subjects also had increased levels of dopamine and DOPAC in striatal tissue and lower levels of circulating prolactin. Ovariectomy in nulliparous females resulted in a potentiated response to apomorphine with regard to the disruption of PPI, as well as a significant decrease in the plasma prolactin levels, as compared with intact nulliparous females. These data suggest that increased dopamine activity in forebrain regions occurs as a consequence of parity, which persists for a minimum of several weeks postpartum. These findings support the hypothesis that increased dopamine sensitivity in forebrain dopamine regions may be one potential mechanism underlying the development of postpartum psychosis in women.

Reproductive experience reduces striatal dopaminergic responses in freely moving female rats

Reproductive experience influences basal and pregnancy profiles of circulating prolactin levels in women and female rats, respectively. Endocrine responses to dopaminergic antagonists are modified by reproductive experience as well. Striatal extracellular dopamine metabolites were measured in vivo by HPLC-ED in perfusates obtained by microdialysis in non-anaesthetized, freely moving, intact and ovariectomized, nulliparous and primiparous rats. Data were collected for at least 7 h. This period always included the light-dark shift at 18:00 h. In a second experiment, microdialysis was performed in ovariectomized nulliparous and primiparous rats treated with haloperidol (1.0 mg/kg s.c.). During the 1 h before and after the onset of the light-dark shift, HVA concentrations in the perfusates increased in nulliparous compared with primiparous rats. The haloperidol-induced increase in DOPAC and HVA was less intense in primiparous rats than that in nulliparous ovariectomized rats. These data revealed a different pattern of striatal dopaminergic anticipation and response to the shift in the light-dark cycle in nulliparous as compared with primiparous intact females. In addition, a distinct striatal dopaminergic response to haloperidol was observed in primiparous as compared to nulliparous ovariectomized rats. The results suggest that reproductive experience can modulate the activity of dopaminergic terminals in the striatum.

Prolactin response to metoclopramide and thyrotropin-releasing hormone in normoprolactinemic and hyperprolactinemic women: a comparison of diagnostic validity

The objective was to define the diagnostic validity of prolactin response tests by comparing the stimulating effect of thyrotropin-releasing hormone (TRH) and metoclopramide on prolactin secretion in patients with and without functional hyperprolactinemia. Prolactin response studies were performed in 18 patients with functional hyperprolactinemia (defined as prolactin serum levels > or = 16 and < 50 ng/ml during the follicular phase without evidence of prolactinoma) and 18 controls with similar age who had normal serum prolactin levels. Tests were done on the 7th, 8th or 9th day of the follicular phase under standardized conditions (at 08.00-09.00, after a 1-h rest and overnight fasting) with 200 micrograms TRH or 10 mg metoclopramide i.v. After metoclopramide, higher maximal prolactin levels were observed in the study group as well as in the control group than after TRH (metoclopramide mean: 243 +/- 62 ng/ml vs. 181 +/- 100 ng/ml, U-test: p = 0.0019; TRH mean: 101 +/- 23 ng/ml vs. 41 +/- 20 ng/ml, U-test: p = 0.0001). There was no significant difference in the relative increment of prolactin serum levels between both groups, neither after metoclopramide nor after TRH (after metoclopramide, mean: 13.5 +/- 5.8 vs. 17.2 +/- 9.2, U-test: p = 0.137; after TRH, mean 3.6 +/- 1.1 vs. 3.8 +/- 1.9, U-test: p = 0.899). No correlation between prolactin basal and peak levels, either after TRH or after metoclopramide, could be found, neither in the study (metoclopramide test: p = 0.738; TRH test: p = 0.076) nor in the control group (metoclopramide test: p = 0.331; TRH test: p = 0.360). While significantly higher prolactin peaks were recorded after metoclopramide than after TRH in both groups, no difference in the response to TRH and metoclopramide, regarding absolute and relative increment, could be found.

Age-related changes in the metoclopramide-induced prolactin release in nulliparous women

OBJECTIVE

To assess the metoclopramide-stimulated PRL response in nulliparous women as a function of chronological age (CA).

DESIGN

Open and prospective study.

SETTING

Outpatient endocrine clinic of a third level medical institution.

PATIENTS

Fifty-one clinically healthy volunteer nulliparous women 15.8 to 48.2 years of age, with regular menses at least 1 year before the study (except 3 postmenopausal women) and no regular drug ingestion during the last 6 months, studied on days 18 to 22 of their menstrual cycle.

INTERVENTIONS

After a 30-minute rest, three basal blood samples were obtained; oral metoclopramide (10 mg) was administered followed by subsequent blood samples at 60, 90, and 120 minutes.

MAIN OUTCOME MEASURES

Duplicate serum PRL determinations were performed by RIA in all samples with P and E2 only in the pool of the basal samples. Hypothesis was formulated before data collection.

RESULTS

All menstruating women had serum P levels > or = 4.0 ng/mL (> or = 12.72 nmol/L). A linear correlation was observed between CA and the serum PRL response, and also between CA and serum E2. Multiple regression analysis showed that CA and body mass index had the most marked effect on PRL response. Women < or = 25.0 years old had a serum PRL response and mean basal serum E2 levels lower than women > 25.1 years old.

CONCLUSIONS

The metoclopramide-induced PRL response in nulliparous women augmented linearly as CA increased, suggesting a gradual decrease in the dopaminergic tone in older women, perhaps partially compensated by a high estrogen level to prevent an unrestrained rise in serum PRL levels.

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.

Parity-associated alterations of medial preoptic opiate receptors in female rats

Preoptic area opiate receptor density was measured by quantitative autoradiography using [3H]naloxone in female rats during their first and second pregnancies and lactations and in a separate group of ovariectomized, nulliparous animals. Opiate receptor density in the medial preoptic area (MPOA) was elevated on day 12 of gestation in both primigravid and multigravid rats when compared with ovariectomized subjects. MPOA receptor density was reduced in primiparous mothers on day 5 of lactation relative to pregnancy. In contrast, receptor density in the MPOA did not decline in multiparous (second lactation) rats relative to pregnancy levels. Opiate receptor density was significantly higher on day 5 of lactation in multiparous than in primiparous mothers. No difference in receptor density was detected in the adjacent lateral preoptic area among the treatment groups. An examination of hormone titers revealed that basal prolactin levels were significantly higher in primigravid than multigravid rats, and that during lactation prolactin titers were negatively correlated with MPOA opiate receptor density in the primiparous mothers. The data demonstrate that multiple pregnancies and lactations result in changes of MPOA opiate receptor density and of circulating hormone levels. The findings are discussed in terms of the concurrent changes in neural opiate sensitivity associated with multiparity.

Basal and metoclopramide-stimulated prolactin (PRL) serum levels in users and non-users of a copper intrauterine device (TCu-380 IUD)

The study was undertaken to analyze the basal and metoclopramide-stimulated serum PRL levels in healthy parous women users (group 1, n = 12) and non-users (group 2, n = 12) of a TCu-380 IUD. All women had regular menses and were studied between days 18 to 22 of their cycle; none had lactated nor regularly ingested any type of medication during the last six months. After a 10-12 hour overnight fast, peripheral venous blood samples were obtained through an indwelling catheter at -30, -15 and 0 minutes and at 60, 90 and 120 minutes after oral metoclopramide (10 mg). There were no significant differences in serum PRL between both groups, in basal levels nor throughout the test, whether analyzing the mean values at each sampling time, the sum of PRL levels from 60-120 minutes, or the peak levels. No correlation was observed between PRL levels and any of the clinical or obstetric characteristics of the women in both groups. Serum progesterone was greater than or equal to 4.0 ng/ml in all women. Thus, the use of alpha TCu-380 IUD did not induce any significant changes in basal nor in stimulated serum PRL levels.