Circulating Concentrations Of Prolactin Research Articles

Effects of endophyte-infected tall fescue on performance of genotyped pregnant beef cows supplemented with rumen-protected niacin

A total of 28 Angus × Simmental pregnant dams (11 cows and 17 heifers) were selected based on genetic resistance to fescue toxicosis based on a commercial genetic test (T-snip™, Ag. Botanica, Columbia, MO). Subsequently, dams were divided based on genetic resistance to fescue toxicosis and randomly assigned to dietary treatments: 1) Susceptible Control (SC; n = 7); 2) Susceptible Niacin (SN; n = 7); 3) Tolerant Control (TC; n = 7); and 4) Tolerant Niacin (TN; n = 7). All animals received 1.16 kg of endophyte-infected (E+) tall fescue seeds for a period of 30 days. Ergovaline concentration in fescue seeds was ∼5,000 ppb on a DM basis. Dams in SN and TN groups received 6 g/hd/day as-fed of top-dressed rumen-protected niacin, following manufacturer's maximum dose recommendation. Dams in the TN group experienced an accelerated reduction in BW as compared to the rest of the treatments. However, TN offspring did not show BW differences at birth or weaning as compared to those born to dams in other treatments. Milk production was estimated by the weigh-suckle-weigh method, and no difference was observed among treatments. All dams had a reduction in circulating prolactin concentration, indicating that all animals were experiencing fescue toxicosis. In addition, blood metabolites that indicate liver health status were markedly decreased at the end of the study. Overall, these results suggest that dams receiving E+ tall fescue seeds were effectively exposed to fescue toxicosis symptoms. Nevertheless, neither rumen-protected niacin supplementation nor genetic test for resistance to fescue toxicosis could be used as an efficient mechanism of dampening these symptoms.

Effects of feeding level, milking frequency, and single injection of cabergoline on blood metabolites, hormones, and minerals around dry-off in dairy cows

This study aimed to investigate the effect of the different dry-off strategies based on reducing feeding level (normal vs. reduced energy density), reducing milking frequency (twice vs. once daily), and administration of a dopamine agonist after last milking (i.e. saline vs. cabergoline injection) on blood metabolites, hormones, and minerals around dry-off. In this experiment, 119 Holstein dairy cows were used in a 2 × 2 × 2 factorial arrangement. In the last week before dry-off, cows were allocated to 1 of the 4 possible dry-off strategies based on feeding level and milking frequency. Within 3 h after last milking, cows were injected with either saline or a D2 dopamine agonist (cabergoline; Velactis, Ceva Santé Animale, Libourne, France; labeled for use only with abrupt dry-off, e.g., no preceding reduction in feeding level or milking frequency before last milking). After dry-off, all cows were fed the same dry cow diet and data collection continued for a week. Blood samples were collected from the coccygeal vein on d -9, -6, -5, -2, 1, 2, 5, and 7 relative to dry-off. Additionally, blood was sampled at 0, 3, and 6 h relative to injection of either cabergoline or saline, equivalent to d 0.125, 0.250, and 0.375 relative to last milking (dry-off). The reduced feeding level before dry-off caused reduced glucose and insulin concentrations as well as increased free fatty acid concentrations, particularly when reduced feeding level was combined with milking the cows 2× daily. The intramuscular injection of cabergoline caused the expected reduction in circulating prolactin concentrations. In addition, dopamine-agonist cabergoline induced an atypical simultaneous pattern of plasma metabolites (i.e., increased glucose and free fatty acid concentrations), hormones (i.e., reduced insulin and increased cortisol concentrations), and minerals (i.e., reduced calcium concentration), indicating that normal metabolic and mineral homeostatic regulations were hindered after the injection of ergot alkaloid cabergoline. In conclusion, reducing milking frequency seems the best management strategy to reduce milk production at dry-off among those tested in this study.

Hyperprolactinemia in a male pituitary androgen receptor knockout mouse is associated with female-like lactotroph development.

Circulating prolactin concentration in rodents and humans is sexually dimorphic. Oestrogens are a well-characterised stimulator of prolactin release. Circulating prolactin fluctuates throughout the menstrual/oestrous cycle of females in response to oestrogen levels, but remains continually low in males. We have previously identified androgens as an inhibitor of prolactin release through characterisation of males of a mouse line with a conditional pituitary androgen receptor knockout (PARKO) which have an increase in circulating prolactin, but unchanged lactotroph number. In the present study, we aimed to specify the cell type that androgens act on to repress prolactin release. PARKO, lactotroph-specific, Pit1lineage-specific and neural-specific conditional androgen receptor knockout male mice were investigated using prolactin ELISA, pituitary electron microscopy, immunohistochemistry and qRT-PCR. Lactotroph-specific, Pit1lineage-specific and neural-specific conditional AR knockouts did not duplicate the high circulating prolactin seen in the PARKO line. Using electron microscopy to examine ultrastructure, we showed that pituitary androgen receptor knockout male mice develop lactotrophs that resemble those seen in female mice. Castrated PARKO males have significantly reduced circulating prolactin compared to intact males. When expression of selected oestrogen-regulated anterior pituitary genes was examined, there were no differences in expression level between controls and knockouts. The cell type that androgens act on to repress prolactin release is not the lactotroph, cells in the Pit1-lineage, or the dopaminergic neurons in the hypothalamus. PARKO males develop a female-specific lactotroph ultrastructure that this is likely to contribute to the increase in circulating prolactin. Castrated PARKO males have significantly reduced circulating prolactin compared to intact males, which suggests that removal of both circulating oestrogens and androgens reduces the stimulation of pituitary prolactin release. Further investigation is needed into prolactin regulation by changes in androgen-oestrogen balance, which is involved sexual dimorphism of development and diseases including hyperprolactinemia.

Metoclopramide induces preparturient, low-level hyperprolactinemia to increase milk production in primiparous sows

Inadequate milk production by sows often limits the growth of piglets. A successful lactation requires prolactin (PRL)-induced differentiation of the alveolar epithelium within the mammary glands of sows between days 90–110 of gestation. We hypothesized that induction of late gestational hyperprolactinemia in primiparous sows by oral administration of the dopamine antagonist metoclopramide (MET) would enhance mammary epithelial differentiation, milk yield, and piglet growth rate and that these effects would carry over into a subsequent lactation. Twenty-six gilts were assigned to receive either MET (n = 13, 0.8 mg/kg) or vehicle (CON, n = 13) twice daily from days 90–110 of gestation. The same sows were followed into their second lactation without additional treatment. On day 90 of gestation, circulating PRL concentrations peaked 45 min after feeding MET (P < 0.001) and then returned to baseline 3 h later. This response occurred daily out to day 104 of gestation (P < 0.05). Compared with CON, MET-treated gilts had enlarged alveoli on gestation day 110 (P < 0.05). Treatment with MET did not affect feed intake, body weight, or body fatness during pregnancy or lactation. Piglets born to MET-treated sows had both increased body weights and average daily gain on lactation days 14 and 21 (P < 0.05). Milk intake by piglets was estimated from deuterium oxide dilution. Although milk intake by piglets nursing MET sows was not statistically different from those nursing CON sows on day 21 of lactation (P = 0.18), there was a greater increase in milk consumption by piglets born to MET-treated sows between days 9 and 21 of lactation than for those in CON litters (P < 0.001). In one group of second parity sows (n = 11) that were treated with MET during their first gestation, milk yield increased by 21% during their second lactation (P < 0.05) in association with a 14% decline in body fatness across lactation compared with a 7% decline in CON sows (P < 0.05). These findings demonstrate that MET-induced hyperprolactinemia in primiparous sows during late pregnancy can increase milk yield and piglet growth rate, setting the stage for further large-scale studies.

Prolactin concentrations predict parental investment and nest survival in a free-living shorebird

The hormonal milieu that exists during reproduction is one of the key factors influencing the trade-off between reproductive investment and self-maintenance. Much previous work in birds has focused on prolactin as a physiological mediator since prolactin is involved in the onset and maintenance of parental care. However, how prolactin relates to reproductive success in terms of altering parental behavior in wild bird populations is not fully understood. Here, we report prolactin concentrations in breeding Kentish plovers (Charadrius alexandrinus), a small shorebird with variable mating systems and parental care, as an ecological model of mating system evolution. Throughout the breeding season, we estimated the circulating prolactin concentrations in male and female plovers during incubation. In addition, we monitored parental behavior and determined the fate of nests. We found that prolactin concentrations decreased during incubation but increased with clutch completion date. In addition, males and females with high prolactin concentrations spent more time on incubation than those with low prolactin concentrations. Importantly, higher prolactin concentrations in either males or females predict higher nest survival. Our results suggest that prolactin is an indicator of parental behavior in a wild shorebird population, although additional studies including experimental manipulation of prolactin concentrations are necessary to verify this relationship.

159 Relationships among circulating prolactin concentrations, hair coat score, and weights of grazing cows

Abstract Prolactin (PRL) is a pleiotropic protein hormone synthesized and released from the anterior pituitary. Concentrations of PRL can serve as a biomarker of cattle exposure to ergot alkaloids. Our objective was to determine relationships among prolactin concentrations, hair coat score, and body weights of non-lactating crossbred beef cows (n = 71). Cows were weighed, hair coat scored (1 = 100% shed, and 5 = 0% shed), and blood samples collected in May, June, and July. Cows were grazing mixed grass pastures that included native endophyte-infected tall fescue. Serum PRL concentrations were determined by validated RIA. Based on May samples, cows were categorized as high (n = 11; 159 ± 29 ng/mL PRL), medium (n = 48; 51 ± 4 ng/mL PRL), or low (n = 12; 21 ± 4 ng/ mL PRL). Data were analyzed with Pearson correlations, and repeated measures ANOVA with month and prolactin category (PRLCAT) as main effects. Concentrations of PRL were correlated (r &amp;gt; 0.53; P &amp;lt; 0.0001) over the three months, and May PRL concentrations were correlated (r &amp;gt; 0.29; P &amp;lt; 0.02) with cow body weights in May, June, and July. Cows in the low PRLCAT had lower (P &amp;lt; 0.01) concentrations of PRL in all three months. Hair coat score decreased (P &amp;lt; 0.0001) each month (4.3, 2.7, and 1.3; respectively, May, June, July), and was higher (P &amp;lt; 0.05) for cows with low PRLCAT (3.3 vs. 2.7 and 2.4 for low, medium, and high, respectively). Cow body weight increased (P &amp;lt; 0.0001) from May to July. Cows in the low PRLCAT had lower (P &amp;lt; 0.05) body weights than medium and high PRLCAT cows (484 vs. 555, and 575 kg; respectively). Concentrations of PRL in May could be useful in identifying cattle with slick hair coats and heavier body weights.

Decreased beta-cell function in breastfeeding obese and non-obese women: A prospective observational study

Obesity is associated with lower breastfeeding rates. The underlying pathophysiological mechanisms are not well-understood, but there is increasing evidence on an association between parameters of maternal glucose metabolism and prolactin concentrations. In this cross-sectional observational study we investigate the relationship between breastfeeding, maternal obesity, and maternal glucose metabolism postpartum with beta cell function as a primary outcome measure. We investigated 106 women (44% obese) prospectively recruited during the pregnancy, who underwent a 75g - 2h oral glucose tolerance test (OGTT) between the 3rd and 5th months postpartum. At this time point, we tested the relationship between breastfeeding status, maternal prolactin concentrations, maternal obesity, and fasting and dynamic indices of glucose metabolism using multivariate logistic regression in a post hoc analysis of prospective observational data. During the study visit at a mean of 122 (SE 9.3) days after delivery, 47% of obese women and 68%of non-obese women were breastfeeding (p<0.05). Lactation and higher prolactin concentrations were associated with lower prepregnancy weight and lower postpartum insulin concentrations. Prehepatic beta-cell function was decreased in both obese (mean (SD); 0.16 (0.04) vs. 0.19 (0.05), p<0.05) and non-obese (0.12 (0.05) vs. 0.16 (0.06), p<0.01), lactating women. Obese lactating women have significantly lower first (1135.1 (306.7) pmol/L vs. 1517.3 (475.8) pmol/L, p<0.01) and second phase insulin secretion (mean (SD), 300.2 (70.7) pmol/L vs. 393.1 (115.5) pmol/L, p<0.01) as shown by Stumvoll indices when comparing to obese non-lactating women. Prehepatic beta-cell function and Stumvoll 1st phase insulin secretion index, but not BMI, were independently and negatively associated with breastfeeding and circulating prolactin concentrations. Beta-cell function during lactation relates to breastfeeding and circulating prolactin concentrations independently of obesity. The well-known positive effects of lactation on maternal and offspring outcomes might reflect a causative relationship of higher breastfeeding rates in metabolically healthier women.

Circulating prolactin concentrations and risk of type 2 diabetes in US women.

Prolactin, a multifunctional hormone, is involved in regulating insulin sensitivity and glucose homeostasis in experimental studies. However, whether circulating concentrations of prolactin are associated with risk of type 2 diabetes remains uncertain. We analysed the prospective relationship between circulating prolactin concentrations and type 2 diabetes risk in the Nurses' Health Study (NHS) and NHSII with up to 22years of follow-up. Total plasma prolactin was measured using immunoassay in 8615 women free of type 2 diabetes and cardiovascular disease at baseline blood collection (NHS 1989-1990; NHSII 1996-1999) and a subset of 998 NHS women providing a second blood sample during 2000-2002. Baseline bioactive prolactin was measured in a subset of 2478 women using the Nb2 bioassay. HRs were estimated using Cox regression. A total of 699 incident type 2 diabetes cases were documented during 156,140 person-years of follow-up. Total plasma prolactin levels were inversely associated with type 2 diabetes risk; the multivariable HR comparing the highest with the lowest quartile was 0.73 (95% CI 0.55, 0.95; ptrend = 0.02). The associations were similar by menopausal status and other risk factors (pinteraction > 0.70). Additional adjustment for sex and growth hormones, adiponectin, and inflammatory and insulin markers did not significantly alter the results. The association of plasma bioactive prolactin with type 2 diabetes risk was non-significantly stronger than that of total prolactin (HR comparing extreme quartiles, 0.53 vs 0.81 among the subset of 2478 women, pdifference = 0.11). The inverse association of total prolactin with type 2 diabetes was significant during the first 9years after blood draw but waned linearly with time, whereas for bioactive prolactin, the inverse relationship persisted for a longer follow-up time after blood draw. A normally high circulating total prolactin concentration was associated with a lower type 2 diabetes risk within 9-10years of follow-up since blood draw in US women. Our findings are consistent with experimental evidence, suggesting that among healthy women, prolactin within the biologically normal range may play a protective role in the pathogenesis of type 2 diabetes.

The subfornical organ: A novel site for prolactin action.

Prolactin (PRL) is a peptide hormone that performs over 300 biological functions, including those that require binding to prolactin receptor (PRL-R) in neurones within the central nervous system (CNS). To enter the CNS, circulating PRL must overcome the blood-brain barrier. Accordingly, areas of the brain that do not possess a blood-brain barrier, such as the subfornical organ (SFO), are optimally positioned to interact with systemic PRL. The SFO has been classically implicated in energy and fluid homeostasis but has the potential to influence oestrous cyclicity and gonadotrophin release, which are also functions of PRL. We aimed to confirm and characterise the expression of PRL-R in the SFO, as well as identify the effects of PRL application on membrane excitability of dissociated SFO neurones. Using a quantitative real-time polymerase chain reaction, we found that PRL-R mRNA in the SFO of male and female Sprague Dawley rats did not significantly differ between juvenile and sexually mature rats (P=.34), male and female rats (P=.97) or across the oestrous cycle (P=.54). Patch-clamp recordings were obtained in juvenile male rats to further investigate the actions of PRL at the SFO. Dissociated SFO neurones perfused with 1μmolL-1 PRL resulted in 2 responsive subpopulations of neurones; 40% depolarised (n=15/43, 11.3±1.7 mV) and 14% hyperpolarised (n=6/43, -6.7±1.4 mV) to PRL application. Within the range of 10pmolL-1 to 1μmolL-1 , the concentrations of PRL were not significantly different in either the magnitude (P=.53) or proportion (P=.19) of response. Furthermore, PRL application significantly reduced the transient K+ current in 67% of SFO neurones in voltage-clamp configuration (n=6/9, P=.02). The stability in response to PRL and expression of PRL-R in the SFO suggests that PRL function is conserved across physiological states and circulating PRL concentrations, prompting further investigations aiming to clarify the nature of PRL function in the SFO.

Using domperidone to induce and sustain hyperprolactinemia in late-pregnant gilts

Prolactin controls mammary development as well as the lactogenic and galactopoietic processes in sows and increasing prolactin during gestation can augment milk yield. The dopamine receptor antagonist domperidone can increase circulating prolactin concentrations in pigs, but the ideal dose to achieve sustained hyperprolactinemia remains unknown. An experiment was performed to develop a protocol for using domperidone in studies of rapid and sustained hyperprolactinemia in late-pregnant gilts. On day 90 of gestation, gilts were divided into 4 groups: (1) intramuscular (IM) injections of canola oil (3 mL, controls [CTL], n = 9), (2) IM injections with 0.1 mg/kg BW of domperidone (low [LO], n = 8), (3) IM injections with 0.5 mg/kg BW of domperidone (medium [ME], n = 11), and (4) IM injections with 1.0 mg/kg BW of domperidone (high [HI], n = 11). Injections were given daily at 8:05 from days 90 to 109 of gestation. Treated gilts also received domperidone per os (0.5 mg/kg BW) at 8:00 and 20:00 on days 89, 90, and 91 of gestation. Three jugular blood samples were collected from all gilts at 6-h intervals on days 89, 90, and 91 of gestation, then twice daily on days 92, 93, and 94. Thereafter, samples were obtained at 8:00 every other day until day 114 of gestation. Blood was sampled serially from 9 CTL and 11 HI gilts on days 89 and 94 of gestation. On day 89 of gestation, prolactin concentrations for LO, ME, and HI gilts increased within 6 h of domperidone per os (P < 0.001). From days 89 until 93 of gestation, the area under the curve (AUC) for LO, ME, and HI gilts was greater than that for CTL gilts (P < 0.001), whereas from days 89 until 114, ME and HI gilts had greater AUC than CTL and LO gilts (P < 0.05). Results demonstrate that the combination of per os treatment with IM injections of 0.5 mg/kg of domperidone in an oil emulsion leads to the rapid and sustained release of prolactin over 24 d in late-pregnant gilts. Higher doses of domperidone failed to further increase circulating prolactin levels. These findings provide a useful strategy to induce sustained hyperprolactinemia in late-pregnant gilts.

Abstract MP54: Circulating Prolactin Concentrations and Risk of Type 2 Diabetes in US Women

Background: Prolactin, a multifunctional hormone, is involved in regulating insulin sensitivity and glucose homeostasis in experimental and cross-sectional human studies. However, whether circulating levels of prolactin are associated with risk of type 2 diabetes (T2D) remains unclear. Methods: We analyzed the prospective relationship between circulating prolactin levels and T2D risk in in the Nurses’ Health Study (NHS) and Nurses’ Health Study II (NHSII) with up to 22 years of follow-up. Total plasma prolactin was measured using immunoassay in 8,637 women free of T2D and cardiovascular disease at baseline blood collection (NHSI: 1989-1990; NHSII: 1996-1999) and a subset of 1,017 NHS women who provided a second blood sample in 2000-2002. In addition, baseline bioactive prolactin levels were measured in a subset of 2,658 women using the Nb2 lymphoma cell bioassay. We calculated hazard ratios (HRs) using Cox regressions. Results: A total of 701 incident T2D cases were documented during 159,517 person-years of follow-up. Circulating prolactin levels were inversely associated with T2D risk; the multivariable HR comparing the highest with the lowest quartile of prolactin levels was 0.71 (95% confidence interval, 0.54-0.93; P trend =0.02). The associations were similar by menopausal status and risk factors ( P &gt;0.70 for interaction). Additional adjustment for sex hormones, growth factors, adipokine, and inflammatory markers did not alter the results. The association of bioactive prolactin with T2D risk was suggestively stronger than that of total prolactin (comparable HR=0.56 vs. 0.82 among the 2,658 women). The inverse association of total plasma prolactin with incident T2D waned linearly with time, with a significant association observed during the first 9 years after blood draw. Conclusion: High circulating prolactin level was independently associated with lower risk of T2D in women. Our findings are consistent with experimental evidence, supporting a possible protective role for prolactin in the pathogenesis of T2D.

Restraint stress increases prolactin-mediated phosphorylation of signal transducer and activator of transcription 5 in the hypothalamus and adrenal cortex in the male mouse.

Prolactin is a pleiotropic peptide hormone produced by the lactotrophs in the anterior pituitary. Its rate of secretion is primarily regulated by a negative-feedback mechanism where prolactin stimulates the activity of the tuberoinfundibular dopaminergic (TIDA) neurones, increasing their release of dopamine, which accesses the pituitary via the median eminence to suppress further prolactin secretion. In addition to its well established role in lactation, circulating prolactin is secreted in response to stress, although the mechanism by which this is achieved or its cellular targets remains unknown. In the present study, we show that 15minutes of restraint stress causes an approximately seven-fold increase in circulating prolactin concentration in male mice. Monitoring prolactin receptor activation, using immunohistochemistry to determine the level and distribution of tyrosine phosphorylated signal transducer and activator of transcription 5 (pSTAT5), we show that this stress-induced increase in prolactin interacts with both central and peripheral targets. Restraint stress for 15minutes significantly increased pSTAT5 staining in the arcuate nucleus, median eminence and the zona fasciculata of the adrenal cortex. In each case, this response was prevented by pretreating the animals with bromocriptine to block prolactin secretion from the pituitary. Interestingly, in contrast to many cells in the arcuate nucleus, stress reduced pSTAT5 staining of the TIDA neurones (identified by dual-labelling for tyrosine hydroxylase). This suggests that there is reduced prolactin signalling in these cells and thus potentially a decline in their inhibitory influence on prolactin secretion. These results provide evidence that prolactin secreted in response to acute stress is sufficient to activate prolactin receptors in selected target tissues known to be involved in the physiological adaptation to stress.

Effects of pulmonary exposure to chemically-distinct welding fumes on neuroendocrine markers of toxicity

ABSTRACTExposure to welding fumes may result in disorders of the pulmonary, cardiovascular, and reproductive systems. Welders are also at a greater risk of developing symptoms similar to those seen in individuals with idiopathic Parkinson’s disease. In welders, there are studies that suggest that alterations in circulating prolactin concentrations may be indicative of injury to the dopamine (DA) neurons in the substantia nigra. The goal of these studies was to use an established model of welding particulate exposure to mimic the effects of welding fume inhalation on reproductive functions. Since previous investigators suggested that changes in circulating prolactin may be an early marker of DA neuron injury, movement disorders, and reproductive dysfunction, prolactin, hypothalamic tyrosine hydroxylase (TH) levels (a marker of DA synthesis), and other measures of hypothalamic-pituitary-gonadal (HPG) function were measured after repetitive instillation of welding fume particulates generated by flux core arc-hard surfacing (FCA-HS), manual metal arc-hard surfacing (MMA-HS) or gas metal arc-mild steel (GMA-MS) welding, or manganese chloride (MnCl2). Exposure to welding fume particulate resulted in the accumulation of various metals in the pituitary and testes of rats, along with changes in hypothalamic TH and serum prolactin levels. Exposure to particulates with high concentrations of soluble manganese (Mn) appeared to exert the greatest influence on TH activity levels and serum prolactin concentrations. Thus, circulating prolactin levels may serve as a biomarker for welding fume/Mn-induced neurotoxicity. Other reproductive measures were collected, and these data were consistent with epidemiological findings that prolactin and testosterone may serve as biomarkers of welding particulate induced DA neuron and reproductive dysfunction.

Providing the plant extract silymarin to lactating sows: effects on litter performance and oxidative stress in sows

Silymarin is an extract from the plant milk thistle that was shown to have antioxidant and hyperprolactinemic properties. Taking into account the essential role of prolactin for lactating sows and the systemic oxidative stress occurring during lactation, it is of interest to investigate the potential beneficial effects of silymarin on lactating sows. A study was therefore carried out to determine the effects of providing either 1 or 8 g/day of the plant extract silymarin to lactating sows. Sows in first, second or third parity were fed conventional diets during gestation and, at farrowing, were assigned as controls (CTL, n=33), or were fed 1 g/day (SYL1, n=33) or 8 g/day (SYL8, n=33) of silymarin. The silymarin was provided in two equal amounts per day, and was fed throughout a 20-day lactation. The performance of sows and their litters was assessed and circulating concentrations of prolactin (days 7 and 18), urea (days 7 and 18) and oxidative status, via protein carbonyls and superoxide dismutase activity (day 18), were measured in sows. Milk samples were obtained on day 18 to measure standard composition. There was no effect of silymarin (P>0.10) on circulating prolactin or urea, or on oxidative damage to proteins or antioxidant potential in sows. Lactation feed intake, backfat and BW of sows were unaffected by treatment (P>0.10) as was the case for milk composition and piglet growth (P>0.10). Results demonstrate that providing up to 8 g/day of the plant extract silymarin to lactating sows had no beneficial effects in terms of circulating prolactin concentrations or oxidative status of sows, or in terms of performances of sows and their litters.

Hyperprolactinemia in end-stage renal disease and effects of frequent hemodialysis.

End-stage renal disease is associated with elevations in circulating prolactin concentrations, but the association of prolactin concentrations with intermediate health outcomes and the effects of hemodialysis frequency on changes in serum prolactin have not been examined. The FHN Daily and Nocturnal Dialysis Trials compared the effects of conventional thrice weekly hemodialysis with in-center daily hemodialysis (6 days/week) and nocturnal home hemodialysis (6 nights/week) over 12 months and obtained measures of health-related quality of life, self-reported physical function, mental health and cognition. Serum prolactin concentrations were measured at baseline and 12-month follow-up in 70% of the FHN Trial cohort to examine the associations among serum prolactin concentrations and physical, mental and cognitive function and the effects of hemodialysis frequency on serum prolactin. Among 177 Daily Trial and 60 Nocturnal Trial participants with baseline serum prolactin measurements, the median serum prolactin concentration was 65 ng/mL (25th-75th percentile 48-195 ng/mL) and 81% had serum prolactin concentrations >30 ng/mL. While serum prolactin was associated with sex (higher in women), we observed no association between baseline serum prolactin and age, dialysis vintage, and baseline measures of physical, mental and cognitive function. Furthermore, there was no significant effect of hemodialysis frequency on serum prolactin in either of the two trials. Serum prolactin concentrations were elevated in the large majority of patients with ESRD, but were not associated with several measures of health status. Circulating prolactin levels also do not appear to decrease in response to more frequent hemodialysis over a one-year period.

Ergovaline, an endophytic alkaloid. 2. Intake and impact on animal production, with reference to New Zealand

On the basis of published reports, the daily intake of the alkaloid ergovaline from the consumption of endophyte-containing ryegrass in New Zealand ranges from 0.008 to 0.287 mg ergovaline/kg LW0.75.day. Most of the reports are based on the use of standard endophyte-containing ryegrass and, thus, it is difficult to disassociate the impact of ergovaline consumption from that of lolitrem B. However, physiological effects of ergovaline consumption, such as reduced circulating prolactin concentration, vasoconstriction and elevated core temperature, have been detected at fairly low ergovaline intake, whereas decreased feed intake, liveweight gain and milk production have not generally been observed in animals at an intake below 0.07 mg ergovaline/kg LW0.75.day. Intakes above this value represent only 17% of published values. There are insufficient data to suggest a threshold ergovaline intake associated with heat stress with animal-welfare implications. The relationship between published ergovaline intake and the corresponding ergovaline concentration in pasture is poor (R2 = 0.48), but on average an intake of 0.07 ergovaline/kg LW0.75.day is associated with an ergovaline concentration in ryegrass of 0.70 mg/kg DM. About 16–18% of published ergovaline concentrations in ryegrass pasture exceed this value. The ergovaline concentration in ryegrass is greater in the basal parts of the plant than in the leaf and during the late summer–autumn than in spring. Animals grazing in the lower sward horizons (horizontal grazing plane) are more at risk of high ergovaline intake, although the reduction in grazing intake induced by grazing at low pasture height aids in limiting ergovaline intake. As pasture growth rates decline in late summer, supplementary feed may be used to maintain stocking rate and, if such feeds have zero ergovaline concentration, they serve to dilute the mean dietary ergovaline intake. Ergovaline-containing ryegrass pastures are widely used in New Zealand. It appears that farmers consider the risks of depressed animal production on these pastures to be less than the benefits ergovaline bestows through its deterrent effect of specific insect attack and thus greater survival and pasture persistence.

Macroprolactinaemia in a 33-year old premenopausal Nigerian woman: A case report

Background: Macroprolactin is a 150-170kDa heteropolymeric complex of monomeric prolactin and immunoglobulin G (IgG) that contributes less than 1% of circulating prolactin concentration in plasma. It exerts little or no biological action in vivo. Its elevated plasma concentration (macroprolactinaemia) is a notable cause of frequent misdiagnosis, unnecessary investigation, and inappropriate treatment in patients with biochemical hyperprolactinaemia.Objective: To highlight the need for macroprolactin screening in premenopausal women with biochemical hyperprolactinaemia.Method: We report an investigated case of macroprolactinaemia in a 33-year old premenopausal nulliparons woman with sustained hyperprolactinaemia, normoovulatory and regular menstrual cycles, and no radiological evidence of pituitary tumour (prolactinoma).Result: The patient had persistent hyperprolactinaemia even after treatment with bromocriptine for 1 month. The menstrual cycle remained regular with clinical and biochemical presumptive evidence of ovulation.Conclusion: Macroprolactinaemia is a potential cause of (pseudo) hyperprolactinaemia in women of childbearing age. Its occurrence should be suspected and investigated especially in patients with hyperprolactinaemia and regular normoovulatory cycles. The polyethyleneglycol (PEG) precipitation test is a simple and cost-effective screening test for macroprolactinaemia.Keywords: Prolactin, hyperprolactinaemia, macroprolactin, macroprolactinaemia

The effect of milking reinitiation following extended nonmilking periods on lactation in primiparous dairy cows

In dairy cows, extended periods of nonmilking results in reduced milk secretion, modifications in milk composition, and eventually involution of the mammary glands. The aim of this study was to determine the effect of extended nonmilking periods on the recovery of milk yield and composition, and levels of prolactin and insulin-like growth factor-I in pasture-fed cows after resuming milking. Pasture-fed, primiparous, nonpregnant, Friesian dairy cows at mid lactation (mean ± standard deviation, 97±2d in milk, 14.0±2.5 L/d) were divided into 3 groups (n=6 per group). The cows were subjected to nonmilking periods of 7, 14, or 28d. Twice-daily milking was resumed for 7d following the nonmilking periods. Milk yield recoveries at the end of the 7-d remilking period were 91, 51, and 29% for the 7, 14, and 28-d nonmilked groups, respectively. The somatic cell count declined to less than 400,000 cells/mL by d 3 and 6 of remilking for the 7- and 14-d-nonmilked groups, respectively, but remained greater than 800,000 cells/mL in the 28-d-nonmilked group through the 7-d remilking period. By d 7 of remilking, the somatic cell count for the 7-d-nonmilked group was not different from pretrial values. Upon remilking, the milk fat content returned to pretrial values for the 7- and 14-d-nonmilked groups, although it remained lower than pretrial for the 28-d-nonmilked group. All 3 nonmilked groups had a higher milk protein content following 7d of remilking, compared with pretrial values. The lactose content returned to pretrial values for the 7-d-nonmilked group but remained lower for the 14- and 28-d-nonmilked groups. Circulating prolactin concentrations increased once remilking was resumed, compared with the pretrial and nonmilking periods. Prolactin concentrations did not majorly differ between the groups, with the levels upon 7d of remilking remaining higher than the pretrial concentrations and the nonmilked periods. Plasma concentrations of insulin-like growth factor-I increased during the nonmilking period and were greater in all 3 nonmilked groups on d 1 of remilking than pretrial values and returned to pretrial concentrations following remilking for the 7-d-nonmilked group, whereas the 14- and 28-d-nonmilked groups remained higher than the pretrial values. These data indicate that the process of involution is fully reversed after remilking following 7d of milk stasis but more extended periods of nonmilking prevent the complete recovery of lactation. However, even after 28d of milk stasis, the milk synthesis capacity of the mammary gland could still be partially recovered.

A polymorphism in XKR4 is significantly associated with serum prolactin concentrations in beef cows grazing tall fescue

Fescue toxicosis is a common syndrome of poor growth and reproductive performance of beef cattle grazing endophyte-infected tall fescue infected with Lolium arundinaceum Schreb. Together with decreased feed intake, decreased growth rates and tissue necrosis due to vasoconstriction, depressed circulating serum prolactin concentrations are typically observed in cattle afflicted with fescue toxicosis. Polymorphisms within the XK, Kell blood group complex subunit-related family, member 4 (XKR4) gene located on BTA14 have been previously reported to be associated with rump fat thickness, residual feed intake, average daily feed intake and average daily gain in cattle. Associations also have been reported between XKR4 genotype and effectiveness of the dopamine antagonist iloperidone as a treatment of schizophrenia in humans. Domperidone, a related dopamine antagonist, mediates effects of fescue toxicosis on livestock, including restoring depressed concentrations of prolactin. A mixed-breed population of 592 beef cattle grazing endophyte-infected tall fescue was used to examine the association between XKR4 genotype and circulating prolactin concentrations. The SNP rs42646708 was significantly (P = 0.0002) associated with serum prolactin concentrations and explained 2.45% of the phenotypic variation. Effect of genotype at the SNP was tested across five breeds, with significant associations within both Angus (P = 0.0275) and Simmental (P = 0.0224) breeds. These results suggest XKR4 may play a role in mediating the negative effects of fescue toxicosis, and polymorphisms within this gene may be useful markers for selection for genetic resistance to the debilitating effects of endophyte-infected tall fescue.

TIDAL WAVES: Network mechanisms in the neuroendocrine control of prolactin release

Neuroendocrine tuberoinfundibular dopamine (TIDA) neurons tonically inhibit pituitary release of the hormone, prolactin. Through the powerful actions of prolactin in promoting lactation and maternal behaviour while suppressing sexual drive and fertility, TIDA neurons play a key role in reproduction. We summarize insights from recent in vitro studies into the membrane properties and network behaviour of TIDA neurons including the observations that TIDA neurons exhibit a robust oscillation that is synchronized between cells and depends on intact gap junction communication. Comparisons are made with phasic firing patterns in other neuronal populations. Modulators involved in the control of lactation - including serotonin, thyrotropin-releasing hormone and prolactin itself - have been shown to change the electrical behaviour of TIDA cells. We propose that TIDA discharge mode may play a central role in tuning the amount of dopamine delivered to the pituitary and hence circulating prolactin concentrations in different reproductive states and pathological conditions.