Transcript abundances of the prolactin receptor, the leptin receptor and their major suppressor in the sheep mammary gland during pregnancy and lactation

This study aimed to expand the knowledge of the interactions between prolactin (PRL) and leptin in the ovine mammary gland during pregnancy and lactation; we examined the mRNA expression of prolactin receptor (PRLR), the long form of the leptin receptor (LRb) and suppressor of cytokine signaling (SOCS)-3 in mammary gland biopsies collected on days 60, 90 and 120 of pregnancy and on days 30, 60 and 90 of lactation (n = 6 for each time point), along with the plasma PRL and leptin concentrations. The PRL concentrations were stable throughout pregnancy and increased during lactation. The plasma leptin concentrations were comparable among nonpregnant, early-pregnant, late-pregnant and lactating ewes, but this metric peaked during mid-pregnancy. Expression of PRLR and SOCS-3 in the mammary gland fluctuated during the transition from pregnancy to lactation, and differences in LRb expression occurred during the late stages of lactation. The LRb transcript abundance was approximately 31 times higher in ewes on day 60 of lactation than in early-lactating ewes. Expression of SOCS-3 mRNA in biopsies gradually decreased over the course of pregnancy and reached a minimum value during late pregnancy. After lambing, the transcript level of SOCS-3 increased and peaked on day 60 of lactation. During pregnancy, the plasma PRL concentration positively correlated with the abundances of PRLR (r = 0.971, P < 0.01) and SOCS-3 (r = 0.818, P < 0.05). Positive correlations were also observed between the transcript abundances of SOCS-3 and LRb (r = 0.854, P < 0.05). The variations observed in the plasma PRL and leptin concentrations and the changes in expression of key leptin and PRL signal transduction pathway components, such as PRLR, LRb and SOCS-3, indicate that the efficacies of both hormone actions are modulated in a multilevel manner throughout pregnancy and lactation. These interactions may regulate the ability of the mammary gland to respond to current energy requirements and challenges, thus affecting milk yield and lactation duration.

Effect of Temperature on Reproductive Hormones and Egg Quality in the Native Thai Chicken

Environmental influence on the avian reproductive system is well recognised. This study investigates the effects of ambient temperature on egg quality in the native Thai Chicken (Gallus domesticus). Effects on prolactin (PRL) and ovarian steroids in chickens housed under different temperatures were also elucidated. Sixty female chickens were divided into four groups. Groups 1, 2, and 3 were reared under controlled temperatures of 35±2 °C, 31±2 °C, and 27±2 °C, respectively. Group 4 was reared under an uncontrolled natural temperature (approximately 27 °C). Blood samples were collected from each chicken once a week for 11 weeks, and plasma PRL, oestradiol (E), progesterone (P), and testosterone (T) levels were determined utilising enzyme-linked immunosorbent assays. The results revealed that E levels were significantly higher in chickens reared under low ambient temperature (27 °C) when compared with those exposed to 31 °C and 35 °C. No significant differences in PRL, P, and T levels were observed. Egg quality was affected by high ambient temperature. Eggshell thickness of chickens housed at 35 °C was thinner than those of other groups. These results indicate that changes in ambient temperature affect circulating levels of E but not PRL, P, and T. Thermally-stressed environments with high temperatures therefore impact egg quality in the native Thai chicken by reducing eggshell thickness.

Evidence for contrasting roles for prolactin in eusocial naked mole-rats, Heterocephalus glaber and Damaraland mole-rats, Fukomys damarensis

Elevated prolactin (PRL) has been associated with the expression of social and cooperative behaviours in a number of vertebrate species, as well as suppression of reproduction. As social mole-rats exhibit both of these traits, PRL is a prime candidate in mediating their social phenotype. While naked and Damaraland mole-rats (NMRs and DMRs) have evolved eusociality independently within their family, both species exhibit an extreme skew in lifetime reproductive success, with breeding restricted to a single female and one or two males. Non-breeding NMRs of both sexes are physiologically inhibited from reproducing, while in DMRs only the non-breeding females are physiologically suppressed. Newly emerging work has implicated the dopamine system and PRL as a component in socially induced reproductive suppression and eusociality in NMR, but the DMR remains unstudied in this context. To investigate evolutionary convergence in the role of PRL in shaping African mole-rat eusociality, we determined plasma PRL concentrations in breeders and non-breeders of both sexes, comparing DMRs with NMRs. Among samples from non-breeding NMRs 80% had detectable plasma PRL concentrations. As a benchmark, these often (37%) exceeding those considered clinically hyperprolactinaemic (25 ng ml −1 ) in humans: mean ± s.e.m.: 34.81 ± 5.87 ngml −1 ; range 0.00–330.30 ng ml −1 . Conversely, 85% of non-breeding DMR samples had undetectable values and none had concentrations above 25 ng ml −1 : 0.71 ± 0.38 ng ml −1 ; 0.00–23.87 ngml −1 . Breeders in both species had the expected variance in plasma PRL concentrations as part of normal reproductive function, with lactating queens having significantly higher values. These results suggest that while elevated PRL in non-breeders is implicated in NMR eusociality, this may not be the case in DMRs, and suggests a lack of evolutionary convergence in the proximate control of the social phenotype in these mole-rats.

MicroRNA-9 regulates fetal alcohol-induced changes in D2 receptor to promote prolactin production

Fetal alcohol exposure (FAE) is known to increase prolactin (PRL) secretion from the pituitary lactotropes. In this study, we determined whether microRNAs (miRs) are involved in FAE-induced alteration in PRL release. We employed a rat animal model of FAE involving feeding pregnant Fisher 344 rats with a liquid diet containing 6.7% alcohol between gestational days 7–21 (AF). Both cyclic and estradiol-implanted FAE females showed increased levels of plasma PRL and pituitary Prl mRNA but reduced levels of pituitary dopamine D2 receptor (D2r) and its short spliced form (D2s). FAE increased the expression levels of miR-9 and miR-326 and did not produce any significant changes in miR-153 or miR-200a levels in the pituitary. Effects of FAE on miR-9 and miR-326 were associated with reduced levels of D2r and D2s, increased levels of Prl in the pituitary, and in plasma. These effects of FAE on D2r, D2s and Prl were enhanced following estradiol treatment. In PRL-producing MMQ cells, ethanol increased miR-9 but not miR-326, reduced levels of D2r and D2s and increased levels of Prl. Treatment of MMQ cells with an anti-miR-9 oligo reduced ethanol effects on miR-9, D2r, D2s and Prl. miR-9 mimic oligos reduced the luciferase activity of reporter vector containing D2r 3′UTR, but failed to reduce the mutant luciferase activity. These data suggest that FAE programs the pituitary to produce increased amounts of miR-9 expression that represses the D2r gene and its spliced variant D2s by targeting its 3′UTR leading to an increase in PRL production and secretion.

Effect of milking behavior on circulatory hormones and milk production in lactating Murrah buffaloes

The effect of milking temperament on plasma hormones, metabolites, milk yield and composition in lactating Murrah buffaloes was studied. Animals were selected from the institute herd and grouped as docile and nervous buffaloes, based on temperament score before and during milking. Blood sampling times were; before milking (-20 min.), after concentrate intake, after teat massage, during milking and 20 min. post- milking. Plasma prolactin (PRL), growth hormone (GH) and cortisol (CORT) concentrations were measured by enzyme-immunoassay procedures. Milk yields of individual buffaloes were recorded and milk composition (fat, protein, lactose, SNF, SCC) determined. Milk yield was significantly lower (P<0.05) in nervous buffaloes in comparison to docile buffaloes. Mean fat, protein, lactose and SNF varied non-significantly between the groups. Milk SCC and plasma NEFA concentration was more (P<0.05) in nervous buffaloes than in docile buffaloes. Milking temperament significantly influenced plasma PRL (P<0.01) and CORT release (P<0.05) but GH was unaffected. Concentrate feeding prior to milking induced release of plasma PRL and CORT without affecting GH and oxytocin levels. Teat stimulus further enhanced release of PRL, oxytocin and CORT hormone in both the groups. Plasma PRL, cortisol, oxytocin and GH varied significantly (P<0.01) before, during and after milking (P<0.01). Basal PRL, GH and CORT were attained 20 minutes after the completion of milking in both the groups. The results show that the behavior of buffaloes at milking influenced release of galactopoietic hormones (PRL, CORT, GH and oxytocin), milk yield and SCC, while milk fat, protein, lactose and SNF remain unaffected.

Actions of angiotensin II and dopamine in the medial preoptic area on prolactin secretion

Dopamine (DA) is known as a primary regulator of prolactin secretion (PRL) and angiotensin II (Ang II) has been recognized as one brain inhibitory factor of this secretion. In this work, estrogen-primed or unprimed ovariectomized rats were submitted to the microinjection of saline or Ang II after previous microinjection of saline or of DA antagonist (haloperidol, sulpiride or SCH) both in the medial preoptic area (MPOA). Our study of these interactions has shown that 1) estrogen-induced PRL secretion is mediated by Ang II and DA actions in the MPOA, i.e. very high plasma PRL would be prevented by inhibitory action of Ang II, while very low levels would be prevented in part by stimulatory action of DA through D(2) receptors, 2) the inhibitory action of Ang II depends on estrogen and is mediated in part by inhibitory action of DA through D(1) receptors and in other part by inhibition of stimulatory action of DA through D(2) receptors.

Age-Related Alterations in Pituitary and Testicular Functions in Long-Lived Growth Hormone Receptor Gene-Disrupted Mice

The somatotropic axis, GH, and IGF-I interact with the hypothalamic-pituitary-gonadal axis in health and disease. GH-resistant GH receptor-disrupted knockout (GHRKO) male mice are fertile but exhibit delayed puberty and decreases in plasma FSH levels, testicular content of LH, and prolactin (PRL) receptors, whereas PRL levels are elevated. Because the lifespan of GHRKO mice is much greater than the lifespan of their normal siblings, it was of interest to compare age-related changes in the hypothalamic-pituitary-gonadal axis in GHRKO and normal animals. Plasma IGF-I, insulin, PRL, LH, FSH, androstenedione and testosterone levels, and acute responses to GnRH and LH were measured in young (2–4 and 5–6 months of age) and old (18–19 and 23–26 months of age) male GHRKO mice and their normal siblings. Plasma IGF-I was not detectable in GHRKO mice. Plasma PRL levels increased with age in normal mice but declined in GHRKO males, and did not differ in old GHRKO and normal animals. Plasma LH responses to acute GnRH stimulation were attenuated in GHRKO mice but increased with age only in normal mice. Plasma FSH levels were decreased in GHRKO mice regardless of age. Plasma testosterone responses to LH stimulation were attenuated in old mice regardless of genotype, whereas plasma androstenedione responses were reduced with age only in GHRKO mice. Testicular IGF-I mRNA levels were normal in young and increased in old GHRKO mice, whereas testicular concentrations and total IGF-I levels were decreased in these animals. These findings indicate that GH resistance due to targeted disruption of the GH receptor gene in mice leads to suppression of testicular IGF-I levels, and modifies the effects of aging on plasma PRL levels and responses of the pituitary and testes to GnRH and LH stimulation. Plasma testosterone levels declined during aging in normal but not in GHRKO mice, and the age-related increase in the LH responses to exogenous GnRH was absent in GHRKO mice, perhaps reflecting a delay of aging in these remarkably long-lived animals.

Regulation of gene expression in human mammary epithelium: effect of breast pumping

Little is known of the molecular regulation of human milk production because of limitations in obtaining mammary tissue from lactating women. Our objectives were to evaluate whether RNA isolated from breast milk fat globules (MFGs) could be an alternative to mammary biopsies and to determine whether intense breast pumping, which increases prolactin (PRL) secretion, will upregulate α-lactalbumin (α-LA, a major determinant of lactose synthesis) transcription. RNA was isolated from MFG and transcripts of interest were identified and quantitated by real-time RT-PCR using an external standard for normalization. In addition, we performed microarray studies to determine MFG RNA gene expression profile. Ten lactating women were studied using two protocols: protocol A with intense pumping from 0800 to 0814 h followed by short pumping and protocol B with intense pumping from 1200 to 1214 h preceded by short pumping. Plasma PRL and MFG α-LA mRNA expression were measured. During protocol A, plasma PRL (61±7–248±43 μg/l by 14 min) and α-LA (3.5±0.9 fold by 6 h; P<0.03) increased. During protocol B, PRL gradually increased over 4 h from 69±14 to 205±28 μg/l, and further to 329±23 μg/l by 12 min of intense pumping; α-LA mRNA expression did not increase significantly. We conclude that MFGs provide a unique source to study the in vivo regulation of gene expression in mammary epithelial cells. α-LA mRNA is abundant in the MFG and its expression may be regulated by hormonal and temporal factors.

Intracerebroventricular administration of the prolactin (PRL) receptor antagonist, S179D PRL, disrupts parturition in rats

The prolactin (PRL) receptor antagonist S179D PRL delays the onset of maternal behavior in steroid-primed nulliparous female rats. The present study investigated the role of the neural PRL system in the process of parturition. A preliminary study indicated that S179D PRL treatments administered by ALZET minipump to the lateral ventricle severely disrupted parturition. To examine the likely causes of this disruption, a group of timed-pregnant catheterized rats was continuously infused with S-179D PRL (0.001 and 0.1 ng/h) or vehicle control to the lateral ventricles for 3 days (gestation days 21–23), and serial blood samples were taken throughout this period. Effects of the treatments on parturition were recorded, and blood samples were assayed for PRL, progesterone, and oxytocin. Significantly fewer S179D PRL-treated rats successfully delivered by 1500 h on day 23 of gestation when compared with controls. The higher dose of S179D PRL also significantly suppressed the prepartum rise in PRL throughout the prepartum period, while the lower dose only affected plasma PRL during the first 24 h of treatment. No significant effects of the antagonist on plasma progesterone or oxytocin were detected. We conclude that disruption of parturition by S179D PRL is not caused by significant alterations in the plasma concentrations of progesterone or oxytocin. S179D PRL may indirectly act on parturition through the modulation of prepartum PRL. These findings suggest a previously unrecognized role for PRL in the regulation of parturition.

Differential regulation of suppressor of cytokine signaling-3 in the liver and adipose tissue of the sheep fetus in late gestation

It is unknown whether the JAK/STAT/suppressor of cytokine signaling-3 (SOCS-3) intracellular signaling pathway plays a role in tissue growth and metabolism during fetal life. We investigated whether there is a differential profile of SOCS-3 expression in the liver and perirenal adipose tissue during the period of increased fetal growth in late gestation and the impact of fetal growth restriction on SOCS-3 expression in the fetal liver. We also determined whether basal SOCS-3 expression in the fetal liver and perirenal adipose tissue is regulated by endogenous fetal prolactin (PRL). SOCS-3 mRNA abundance was higher in the liver than in the pancreas, spleen, and kidney of the sheep fetus during late gestation. In the liver, SOCS-3 mRNA expression was increased ( P < 0.05) between 125 ( n = 4) and 145 days ( n = 7) gestation and lower ( P < 0.05) in growth-restricted compared with normally grown fetal sheep in late gestation. The relative expression of SOCS-3 mRNA in the fetal liver was directly related to the mean plasma PRL concentrations during a 48-h infusion of either a dopaminergic agonist, bromocriptine ( n = 7), or saline ( n = 5), such that SOCS-3 mRNA expression was lower when plasma PRL concentrations decreased below ∼20 ng/ml [ y = 0.99 − (2.47/ x) + (4.96/ x2); r2 = 0.91, P < 0.0001, n = 12]. No relationship was shown between the abundance of phospho-STAT5 in the fetal liver and circulating PRL. SOCS-3 expression in perirenal adipose tissue decreased ( P < 0001) between 90–91 ( n = 6) and 140–145 days ( n = 9) gestation and was not related to endogenous PRL concentrations. Thus SOCS-3 is differentially expressed and regulated in key fetal tissues and may play an important and tissue-specific role in the regulation of cellular proliferation and differentiation before birth.