Plasma PRL Concentrations Research Articles

Regulation of Prolactin Release at the End Stage of Chicken Embryogenesis.

Difference of onset of increase of PRL content in the anterior pituitary gland and plasma PRL concentration during the late stage of chicken embryogenesis is well known. To investigate the disagreement, changes in PRL content and PRL mRNA levels, and the effects of vasoactive intestinal polypeptides (VIP) on PRL release and PRL mRNA expression were examined using western blot analysis and real-time PCR quantification. Changes in SPRL content were strongly correlated with PRL mRNA levels. The increase in PRL content on day 17 of incubation may be caused by the increase in PRL mRNA levels on day 16 of incubation. Additionally, the effects of VIP on PRL release from the embryonic anterior pituitary gland were not observed until day 18 of embryogenesis. These results suggest that increased levels of PRL mRNA and PRL content in the anterior pituitary gland are closely correlated. However, the increased expression of PRL mRNA observed on day 17 and the initiation of PRL release from the anterior pituitary gland on day 19 were differentially regulated. According to the results of western blot analysis, the proportion of glycosylated PRL (G-PRL) and non-glycosylated PRL (NG-PRL) in the anterior pituitary gland at the end stage of development differed from the proportion of PRL released from the anterior pituitary gland. According to the results of two-dimensional western blot analysis, no isoforms with different isoelectric points were detected in the culture medium on days 19 and 20. These data suggest that the peptide chains of G-PRL and NG-PRL were not modified. In conclusion, the differentiation of PRL-producing cells and the maturation of the hypothalamus and anterior pituitary gland were completed at the end stage of incubation, and that different factors regulated the initiation of PRL mRNA expression before day 18 of incubation.

TSH and PRL, side-effect markers in aripiprazole treatment: adjunctive aripiprazole-induced thyrotropin oversuppression in a young man with schizophrenia

A 26-year-old Japanese man was admitted to our unit with exacerbated paranoid schizophrenia. Prior to his admission, daily administration of olanzapine had been sufficient to maintain a partial remission of...

Seasonal Expression of Prolactin Receptor in the Scented Gland of Male Muskrat (Ondatra zibethicus).

Prolactin (PRL) has numerous actions in mammalian biological systems including mammary development and biological processes. The aim of this study was to investigate the seasonal changes of prolactin receptor (PRLR) expression in the scented gland of muskrat during the breeding and nonbreeding seasons. Histologically, glandular cells, interstitial cells and excretory tubules were identified in the scented glands in both seasons, whereas epithelial cells were sparse in the nonbreeding season. PRLR was observed in glandular cells of scented glands during the breeding and nonbreeding seasons with stronger immunostaining during the breeding season. Consistent with the immunohistochemical results, both the mean of protein and mRNA levels of PRLR were higher in the scented glands of the breeding season, and relatively lower level in the nonbreeding season. In addition, differential seasonal changes were also detected in the expression profile of microRNAs (miRNAs) in the scented gland of muskrat. Besides, plasma PRL concentration was remarkably higher in the breeding season than that in the nonbreeding season. These results suggested that muskrat scented gland was the direct target organ of PRL, and stronger expression of PRLR in scented glands during the breeding season indicated that PRL may directly regulate scented glandular function of the muskrats.

Prolactin acts on the hypothalamic–pituitary axis to modulate follicle-stimulating hormone gene expression in the female brushtail possum ( Trichosurus vulpecula)

Brushtail possums exhibit a distinct preovulatory pattern of prolactin (Prl) secretion suggesting that Prl is involved in normal reproductive function. In some mammals, Prl is essential for corpus luteum (CL) function and/or modulation of steroidal effects on hypothalamic–pituitary activity. The aim of this study was to test the effects of biologically active recombinant possum Prl (recPosPrl) on both pituitary gland and CL function in possums. To confirm biological activity, administration of recPosPrl-N2C1 (10 μg) resulted in an 18-fold stimulation ( P < 0.05) of progesterone (P 4) production by possum granulosa cells in vitro. Based on these findings, minipumps containing either recPosPrl-N2C1 ( n = 10) or saline ( n = 8) were inserted into lactating female possums. The expression levels of pituitary-derived PRL, LHB, FSHB and GNRHR and CL-derived LHR mRNA were quantified. Following a resumption of reproductive activity, no differences in ovulation incidence or plasma Prl concentrations were observed. Plasma Prl levels were less variable ( P < 0.001) in Prl-treated possums, confirming a self-regulatory role for Prl in this species. There was a marked down-regulation ( P < 0.001) of FSHB mRNA at the mid-luteal stage in Prl-treated possums, whereas mean PRL, LHB, GNRHR and LHR mRNA expression levels were not different between experimental groups. Plasma P 4 concentrations were not different ( P = 0.05) in Prl-treated possums, although tended to be higher in the peri-ovulatory and early-luteal phase. We conclude in the brushtail possum that Prl is self-regulated via a short-feedback loop common to all mammals studied and is able to modulate FSHB expression probably at the level of the hypothalamus and/or pituitary gland.

Etiological diagnosis of hyperprolactinemia

There are numerous etiologies of hyperprolactinemia, a common reason for consultation. Diagnostic measures must be capable of identifying the tumors, the most frequent of which are prolactin adenomas. Hypothalamic–pituitary MRI is the reference morphological examination. In clinical practice, it is usually performed very early, following the discovery of increased plasma concentrations of PRL. This approach is warranted for marked increase in PRL in the absence of drugs with hyperprolactinemic effects (> 10 × upper limit of normal) since a diagnosis of PRL adenoma is extremely likely under such circumstances. When hyperprolactinemia is moderate, which is the most common finding in practice, all etiologies are possible in theory and it is important to follow a rational diagnostic plan (history-taking to identify use of any drugs with hyperprolactinemic effects paying attention to renal and hepatic history, investigation for endocrine diseases occasionally associated with hyperprolactinemia such as hypothyroidism or polycystic ovary syndrome (PCOS), confirmation of hyperprolactinemia by a second assay when the initial level is less than five times the upper normal limit, pregnancy testing for women of childbearing age) in order to rule out all non-tumoral causes of hyperprolactinemia before proceeding with imaging. Absence of any consequences of hyperprolactinemia on gonadic function or the existence of a concomitant disease that could account for the clinical signs, demonstration of wide variations in PRL from one assay to another in a single patient could prompt screening for macroprolactinemia before MRI is ordered. Macroprolactinoma could also occur in the case of normal or doubtful MRI or discrepancy in response to medical or surgical treatment. T1- and T2-weighted coronal sections (with or without T1 after gadolinium injection) are generally sufficient for diagnosis of microprolactinoma. Dynamic tests may be useful if MRI is normal or unclear. Gadolinium injection with sagittal and axial sections is essential for examination of large lesions. In this case, when the increase of PRL is moderate (< 150 mg/ml), a non-lactotropic lesion may be suspected without misdiagnosing a hook effect. Careful analysis of the images allows differentiation between tumoral lesions and pituitary hyperplasia.

Diagnostic étiologique d'une hyperprolactinémie

There are numerous etiologies of hyperprolactinemia, a common reason for consultation. Diagnostic measures must be capable of identifying the tumors, the most frequent of which are prolactin adenomas. Hypothalamic-pituitary MRI is the reference morphological examination. In clinical practice, it is usually performed very early, following the discovery of increased plasma concentrations of PRL. This approach is warranted for marked increase in PRL in the absence of drugs with hyperprolactinemic effects (> 10 x upper limit of normal) since a diagnosis of PRL adenoma is extremely likely under such circumstances. When hyperprolactinemia is moderate, which is the most common finding in practice, all etiologies are possible in theory and it is important to follow a rational diagnostic plan (history-taking to identify use of any drugs with hyperprolactinemic effects paying attention to renal and hepatic history, investigation for endocrine diseases occasionally associated with hyperprolactinemia such as hypothyroidism or polycystic ovary syndrome (PCOS), confirmation of hyperprolactinemia by a second assay when the initial level is less than 5 times the upper normal limit, pregnancy testing for women of childbearing age) in order to rule out all non-tumoral causes of hyperprolactinemia before proceeding with imaging. Absence of any consequences of hyperprolactinemia on gonadic function or the existence of a concomitant disease that could account for the clinical signs, demonstration of wide variations in PRL from one assay to another in a single patient could prompt screening for macroprolactinemia before MRI is ordered. Macroprolactinoma could also occur in the case of normal or doubtful MRI or discrepancy in response to medical or surgical treatment. T1- and T2-weighted coronal sections (with or without T1 after gadolinium injection) are generally sufficient for diagnosis of microprolactinoma. Dynamic tests may be useful if MRI is normal or unclear. Gadolinium injection with sagittal and axial sections is essential for examination of large lesions. In this case, when the increase of PRL is moderate (< 150 mg/ml), a non-lactotropic lesion may be suspected without misdiagnosing a hook effect. Careful analysis of the images allows differentiation between tumoral lesions and pituitary hyperplasia.

Endocrine and ovarian response after a 2-day controlled suckling and eCG treatment in lactating rabbit does

Synchronization methods are used to obtain higher fertility when artificial insemination (AI) is applied to lactating rabbit does. The most common methods are eCG administration or temporary doe–litter separation. Nevertheless, drawbacks have been reported, such as negative side effects of hormonal treatment in the doe and low litter growth due to absence of suckling, respectively. Recently, improved reproductive performance (without visible consequences on young rabbit growth), has been obtained by applying a 2-day controlled nursing method before AI, by allowing for a 10 min nursing of the litter 24 h of separation. The present study was undertaken to examine the pituitary (PRL, LH, FSH) and the ovarian response (follicle size and number) to those methods. A total of 442 lactating does inseminated on day 11 post-partum were distributed in three experimental groups: 2CN (closing of nest box on day 9, controlled nursing on days 10 and 11), eCG (20 IU administered on day 9 post-partum) and CONTROL (untreated). Blood samples were obtained from 10 does per group at 48, 24 and 0 h before AI, and 1 h after AI. Both 2CN and eCG treatments similarly improved sexual receptivity (76.3, 77.5 and 58.2%, respectively; P < 0.001) and fertility (63.1, 64.1 and 48.4%, respectively; P < 0.05) in lactating does, compared to the CONTROL group. Similar plasma FSH levels in all groups of does and sampling times were observed. Due to the absence of suckling, plasma concentration of PRL on day 10 post-partum in the 2CN group was lower than in the CONTROL group ( P < 0.05); this endocrine change in PRL levels could explain the better reproductive performances obtained with 2CN treatment. At 1 h after exogenous administration of GnRH (at the moment of AI) a high LH response was observed in all groups ( P < 0.001). Ovaries from 20 rabbits treated in the same way but uninseminated (2CN, n = 10; eCG, n = 5; CONTROL, n = 5 does) were obtained on day 11 post-partum in order to check the morphometric status (weight, width and height) and to make histological and immunohistochemical studies to detect growth hormone receptor (GH-R). As a result, synchronization methods did not show any significant difference in relation to the CONTROL group. However, a small increase in the number of primary follicles was evidenced in the 2CN group with respect to the eCG group, similarly to the CONTROL group (23.0 ± 3.7, 9.4 ± 4.9 and 14.8 ± 4.92 primary follicles, respectively; P = 0.1). GH-R immunostaining-presence was more evident in the 2CN and the eCG groups, including primordial follicles and oocytes themselves. Thus, there could have been some direct effects of GH on follicular development, as described in other species. Some ovarian parameters described open new ways to study intra-ovarian mechanism of follicular development in the post-partum period of rabbit does.

Endocrine regulations of reproductive seasonality, follicular development and incubation in Magang geese

This study investigated the regulatory mechanisms of seasonal breeding, developments of ovarian follicles and incubation in Magang geese, a short day breeding bird. Throughout the year, plasma PRL concentrations increased in non-breeding season in spring and summer (from April to early August), and remained low in the rest of the year, while LH concentrations peaked in August and September and remained low in non-breeding season (March to June). Lengthening photoperiod increased PRL and decreased LH secretions, which inhibited follicular development, terminated lay and induced moulting, while shortening photoperiod decreased PRL and increased LH secretion and reinitiated lay. Long photoperiod stimulated PRL secretion occurred with increased gene expressions of PRL in the pituitary gland and VIP in the hypothalamus, but inhibition of LH secretion was without decreases in gene expressions of LH β subunit and GnRH. Under breeding conditions, terminating incubation decreased PRL but increased LH concentrations and resumed lay in 24 days following recruitment of about 10 large white follicles into hierarchical development. Plasma concentrations of progesterone and inhibin peaked at peak lay, whereas LH concentrations exhibited a bi-phasic pattern with troughs at peak lay and incubation when PRL concentrations were high. Ninety percent geese exhibited incubation behaviour after laying one clutch of approximately eight eggs in approximately 30 days. In conclusion the seasonal reproductive activities in Magang geese is directly inhibited by long photoperiod and directly stimulated by short photoperiod via PRL and LH secretions, whose interplays also cause occurrences of four to five lay and incubation cycles in the breeding season.

Influences of sex and saline intake on diurnal changes in plasma melatonin and osmoregulatory hormones of Pekin ducks ( Anas platyrhynchos)

Melatonin (MT) inhibits salt gland secretion of Pekin ducks [Ching, A.C.T., Hughes, M.R., Poon, A.M.S., Pang, S.F., 1999. Melatonin receptors and melatonin inhibition of duck salt gland secretion. Gen. Comp. Endocrinol. 116, 229–240]. The present study examined simultaneous diurnal changes in plasma concentrations of MT and four osmoregulatory hormones of Pekin ducks to assess the possible interactions among these hormones that might contribute to inhibition of extrarenal salt secretion. The study compared diurnal changes in freshwater (FW) and saline-acclimated (SA) male and female ducks. We hypothesized plasma concentrations of osmoregulatory hormones: (1) differ between sexes (partially accepted); (2) vary diurnally (accepted, influenced by sex and treatment); (3) are correlated with MT (partially accepted); and their diurnal variation is affected by (4) sex (partially accepted); and (5) saline acclimation (partially accepted). We compared body mass, plasma osmolality (Osm pl), plasma volume, concentrations of plasma ions, and arginine vasotocin (AVT), angiotensin II (AII), prolactin, (PRL), and aldosterone (ALDO), in relation to plasma melatonin (MT). At night body mass increased in FW ducks and decreased in SA ducks. This likely reflects the higher plasma PRL concentration of female ducks and its middark increase only in SA ducks. Plasma volume increased at night in all but FW males. Plasma sodium and osmolality were higher in SA ducks and did not vary diurnally in either FW or SA ducks. Midday MT did not differ between males and females or between FW and SA ducks; at middark, all ducks, except FW females, increased MT. Midday AVT was higher in SA ducks. Only FW ducks increased AVT at middark. Changes in AVT and MT were positively correlated in males and negatively correlated in females. Males had higher AII and, at night, AII increased in SA ducks and decreased in FW ducks. AVT and AII were negatively correlated. ALDO was highly correlated with AII and unaffected by sex, saline, or time. At night, only AVT was elevated in FW ducks, while MT, AII, and PRL were elevated in SA ducks. FW and SA ducks appear to follow different, but equally effective, hormonal strategies to maintain osmotic homeostasis at night. We conclude that the effect of MT on salt gland secretion is probably a direct effect. These may be influenced by gender.

Prolactin in the brushtail possum ( Trichosurus vulpecula): Development of homologous radioimmunoassay using recombinant possum prolactin

We report the production of recombinant possum prolactin (posPrl), and its use in the development and validation of a highly specific homologous radioimmunoassay for the measurement of prolactin (Prl) in brushtail possums. This enabled the subsequent investigation of some basic mechanisms involved in the regulation of Prl secretion in this species. Recombinant posPrl spanning the entire coding region was expressed in Escherichia coli, resulting in a 199 amino acid protein with a molecular weight ∼23 kDa. The potency of posPrl was 45.3 ± 4.8% that of ovine Prl in a radioreceptor assay using possum mammary gland receptors and induced a 3.4 ± 0.8-fold increase in progesterone secretion in primary possum granulosa cells. Antiserum (G27) was raised against recombinant posPrl and was highly specific for possum Prl (∼30% binding at 1:60,000 final dilution), and exhibited negligible cross-reactivity (<0.0001%) with possum growth hormone. Serial dilutions of pituitary gland extracts, and plasma samples from male and female possums gave parallel inhibition curves to recombinant posPrl standards in the assay. Biological validation of the RIA included treating possums with drugs known to alter Prl secretion in other mammals. In seasonally anoestrous female possums, administration of 20 μg thyrotropin-releasing hormone (TRH) resulted in a 15-fold increase ( P < 0.01) in plasma Prl concentrations. In mid-late lactating female possums, a bolus of cabergoline (dopamine agonist; 75 μg) reduced ( P < 0.05) plasma Prl levels to baseline for 24 h, while repeated administration (6 × 75 μg at 12 h intervals) suppressed ( P < 0.01) plasma Prl concentrations until 24 h after the last injection. Prolonged inhibition of Prl levels subsequently caused marked ( P < 0.01) attenuation in rate of bodyweight increase of pouch young. The amplitude of the Prl surge in response to a bolus of TRH (15 μg) was 5-fold lower in cabergoline-treated, compared to control mid-late lactating possums. In conclusion, we report the development and validation of a robust and sensitive RIA for measuring Prl concentrations in the plasma of brushtail possums.

Macroprolactinaemia associated with prolactin adenoma.

Macroprolactinaemia, defined as hyperprolactinaemia with a predominance of, or only, the big big prolactin (bbPRL) isoform, is considered idiopathic and poorly symptomatic. Since its association with a PRL adenoma is poorly documented, we examined a series of 13 patients with tumoral hyperprolactinaemia for the presence of macroprolactinaemia. From a series of 36 patients with hyperprolactinaemia studied for PRL isoforms, we selected 13 with hyperprolactinaemia and a prolactinoma, and divided them into two groups on the basis of the predominant PRL isoform, the large PRL group (five patients), with a predominance of the big big PRL isoform, and the monomeric PRL (mPRL) group (eight patients), with a predominance of the mPRL isoform. Plasma PRL concentrations were measured by radioimmunoassay, while plasma PRL heterogeneity was studied by gel filtration chromatography. The plasma autoantibody-bound PRL and the histology of the tumours were also studied. Macroprolactinaemia was seen in five out of the 13 patients with a PRL adenoma. The clinical and biological characteristics of the groups with and without macroprolactinaemia were similar. In the large PRL group, no evidence for anti-PRL autoantibodies was found and the prolactinomas were either typical or exhibited unusual aggregates of immunoreactive PRL deposits, the latter suggesting the tumoral origin of these large forms. Our results suggest that PRL adenoma may be associated with macroprolactinaemia.

Dissociation of prolactin secretion from tuberoinfundibular dopamine activity in late pregnant rats.

This study investigated whether the PRL surge that precedes parturition is accompanied by a decrease in activity of hypothalamic tuberoinfundibular dopamine (TIDA) neurons, as occurs during the PRL surges of early pregnancy. Serial blood samples were collected at regular intervals during early and late pregnancy via chronic indwelling jugular cannulae, and concentrations of plasma PRL were determined by RIA. In addition, pregnant rats were killed at either 1200 and 0300 h on different days throughout pregnancy. Levels of TIDA neuronal activity were estimated using concentrations of 3,4-dihydroxyphenylacetic acid (DOPAC) in the median eminence as an index of dopamine metabolism. During early pregnancy, plasma PRL concentrations showed characteristic diurnal and nocturnal surges peaking at 1700 and 0300 h, respectively, whereas during late pregnancy, there was a broad nocturnal surge throughout the night preceding parturition. During early pregnancy, DOPAC was elevated at 1200 h, associated with suppressed plasma PRL, whereas at 0300 h, during the nocturnal PRL surge, DOPAC was significantly reduced (P < 0.05). On the last day of pregnancy DOPAC levels were significantly reduced at both 1200 and 0300 h compared with those at 1200 h in early pregnancy regardless of the PRL concentration. This experiment was repeated with additional groups to further characterize the timing of the fall in TIDA activity during late pregnancy. DOPAC concentrations were elevated throughout the second half of pregnancy, then fell significantly between 0300-1200 h on day 21, approximately 36 h before parturition. As in the previous experiment, the timing of changes in DOPAC concentrations in the median eminence was dissociated from the antepartum PRL surge. These data indicate that the regulation of PRL secretion during late pregnancy is different from that of early pregnancy. Despite the prolonged reduction in activity of TIDA neurons during late pregnancy, PRL secretion still occurs as a nocturnal surge, suggesting that dopamine is not the only regulator of PRL secretion at this time.

Nocturnal variation of prolactin secretion in the Mouflon ( Ovis gmelini musimon) and domestic sheep ( Ovis aries): seasonal changes

Seasonal changes in nocturnal prolactin secretion and their relationship with melatonin secretion were monitored in wild (Mouflon, Ovis gmelini musimon) and domesticated sheep (breed Manchega, Ovis aries). Two groups of eleven adult females each, were maintained outdoors under natural photoperiod. Plasma concentrations of prolactin and melatonin were determined during the summer and winter solstices and the autumn and spring equinoxes. Blood samples were collected every 3 h during the night hours, and 1 h before and after the onset of darkness and sunrise. Maximum mean plasma concentrations of prolactin during the dark-phase in Mouflons were observed in the summer solstice, ( P<0.001) and in the summer solstice and spring equinox in Manchega ewes ( P<0.001). Mean plasma concentrations of prolactin were higher in the wild species ( P<0.001) during the summer solstice. In contrast, during the spring equinox, mean levels of prolactin were higher in Manchega ewes than in Mouflons ( P<0.05). Plasma prolactin concentrations showed a nocturnal rhythm in both breeds, with seasonal variations ( P<0.001). The increase in plasma melatonin levels during the first hour after sunset was accompanied to increasing concentrations of PRL 1 h after the onset of darkness, only in the autumn and spring equinox for the Mouflon, and in the summer solstice and spring equinox for the Manchega ewes. In Mouflons, the fall of plasma PRL concentrations about the middle dark-phase in all the periods studied, coincided with high levels of melatonin. A similar relation was observed in Manchega ewes only in the winter solstice and spring equinox. The current study shows that the nocturnal rhythm of prolactin secretion exhibits seasonal variation; differences in the patterns of prolactin secretion between Mouflon and Manchega sheep are taken to represent the effects of genotype.

The Regulation of Prolactin Receptor Messenger Ribonucleic Acid Levels in the Sheep Liver before Birth: Relative Roles of the Fetal Hypothalamus, Cortisol, and the External Photoperiod

We have investigated the separate actions of hypothalamo-pituitary disconnection (HPD), with or without cortisol administration, and changes in the external photoperiod on the regulation of the levels of messenger RNA (mRNA) encoding long (PRLR1) and short (PRLR2) forms of PRL receptor in the liver of the fetal lamb. In pregnant Merino ewes (n = 20), the hypothalamus and pituitary were surgically disconnected in 13 fetuses (HPD group), and fetal vascular catheters were implanted in the HPD group and in an additional 7 fetuses (intact+ saline group) between 104–120 days gestation (d). Fetal sheep in the HPD group were infused with either cortisol (3.5 mg/4.8 ml saline/24 h; HPD + F; n = 5) or saline for 5 days between 134–141 d, and saline was also infused in the intact group within the same gestational age range. A second group of pregnant ewes (n = 12) was kept in a 12-h light, 12-h dark cycle from 70 d until implantation of fetal vascular catheters between 106–120 d, after which ewes were allocated to either a long photoperiod (16 h of light, 8 h of darkness; LL group; n = 6) or a short photoperiod (8 h of light, 16 h of darkness; SL group; n = 6) regimen. Circulating cortisol concentrations were higher (P < 0.05) in the intact fetal sheep (18.7 ± 3.8 nmol/liter) than in the HPD + saline group (1.5 ± 0.6 nmol/liter), and were further increased (P < 0.05) in the HPD + cortisol group (97.4± 23.7 nmol/liter). Fetal PRL concentrations were lower (P < 0.05) in the HPD + saline (10.6 ± 4.3 ng/ml) and HPD ± cortisol (5.6 ± 2 ng/ml) groups compared with those in the intact group (38.9 ± 6.8 ng/ml). The levels of hepatic PRLR mRNA were higher (P < 0.05) in the intact (PRLR1, 27.4 ± 6.1; PRLR2, 17.7 ± 2.5) and HPD + cortisol (PRLR1, 23.4 ± 0.4; PRLR2, 15.3 ± 3.0) groups than in the HPD + saline group (PRLR1, 10.6 ± 1.8; PRLR2, 8.9 ± 1.8) at 140/141 d. The mean plasma PRL concentration in the LL group (70 ± 9 ng/ml) was higher (P < 0.05) than that in the SL group (34 ± 15 ng/ml), whereas the levels of hepatic PRLR1 mRNA (LL group, 4.6 ± 0.9; SL group, 4.3 ± 0.8) and PRLR2 mRNA (LL group, 3.4 ± 0.4; SL group, 3.0 ± 0.5) at 140–141 d were not different. These data indicate that cortisol acts directly or indirectly to maintain hepatic PRLR mRNA levels in the sheep fetus during late pregnancy. In contrast, changes in the external photoperiod and circulating PRL concentrations in the sheep fetus do not directly alter PRLR expression in the fetal liver. These studies provide further insight into the role that the PRL axis may play in the transduction of signals about the external environment to the fetus as it prepares for the transition to extrauterine life.

Terminal follicular growth, ovulation rate and hormonal secretion after melatonin pretreatment prior to FGA-PMSG synchronisation in Suffolk ewes at the onset of the breeding season

The first experiment was performed in order to determine the effect of exogenous melatonin followed by a fluorogestone acetate (FGA) and pregnant mare's serum gonadotrophin (PMSG) treatment on terminal follicular dynamics, ovulation rate and luteinizing hormone (LH) pulsatility in Suffolk ewes at the beginning of the breeding season. Therefore, 10 ewes (MEL/FGA/PMSG) were injected melatonin 22 days before receiving sponges containing 40 mg of FGA for 14 days and 800 IU of PMSG at the removal of pessaries. Ten other ewes (FGA/PMSG) were synchronised with the same FGA/PMSG treatment without melatonin. The second experiment was undertaken to determine the effects of exogenous melatonin followed by a FGA-PMSG synchronisation on the plasma FSH, E 2 and P 4 concentrations. The investigations on terminal follicular growth and LH pulsatility were repeated. Six ewes were submitted to a MEL/FGA/PMSG treatment and six other to a FGA/PMSG control following the same design as in the first experiment. Melatonin treatment was effective in increasing ( p < 0.05) the circulating melatonin during a period of more than 14 days but was ineffective in lowering plasma PRL concentrations. LH pulsatility during and after the hormonal treatment and the concentrations of plasma FSH and P 4 were comparable among MEL/FGA/PMSG and FGA/PMSG groups. Concentrations of plasma E 2 during the luteal phase but not during the follicular phase of the synchronised estrous cycle were lower ( p < 0.05) in ewes treated with melatonin when compared to controls. The two groups differed only at the time of selection : the percentage of medium follicles undergoing atresia was lower ( p < 0.05) in the MEL/FGA/PMSG than in the FGA/PMSG (38% and 35.5% versus 65% and 61.5%); this resulted in a increased ( p < 0.05) mean number of large follicles (4.7 ± 0.5 versus 3.2 ± 0.5) and ovulation rate (2.6 ± 0.4 versus 1.45 ± 0.35).

The regulation of prolactin receptor messenger ribonucleic acid levels in the sheep liver before birth: relative roles of the fetal hypothalamus, cortisol, and the external photoperiod.

We have investigated the separate actions of hypothalamo-pituitary disconnection (HPD), with or without cortisol administration, and changes in the external photoperiod on the regulation of the levels of messenger RNA (mRNA) encoding long (PRLR1) and short (PRLR2) forms of PRL receptor in the liver of the fetal lamb. In pregnant Merino ewes (n = 20), the hypothalamus and pituitary were surgically disconnected in 13 fetuses (HPD group), and fetal vascular catheters were implanted in the HPD group and in an additional 7 fetuses (intact + saline group) between 104-120 days gestation (d). Fetal sheep in the HPD group were infused with either cortisol (3.5 mg/4.8 ml saline/24 h; HPD + F; n = 5) or saline for 5 days between 134-141 d, and saline was also infused in the intact group within the same gestational age range. A second group of pregnant ewes (n = 12) was kept in a 12-h light, 12-h dark cycle from 70 d until implantation of fetal vascular catheters between 106-120 d, after which ewes were allocated to either a long photoperiod (16 h of light, 8 h of darkness; LL group; n = 6) or a short photoperiod (8 h of light, 16 h of darkness; SL group; n = 6) regimen. Circulating cortisol concentrations were higher (P < 0.05) in the intact fetal sheep (18.7 +/- 3.8 nmol/liter) than in the HPD + saline group (1.5 +/- 0.6 nmol/liter), and were further increased (P < 0.05) in the HPD + cortisol group (97.4 +/- 23.7 nmol/liter). Fetal PRL concentrations were lower (P < 0.05) in the HPD + saline (10.6 +/- 4.3 ng/ml) and HPD + cortisol (5.6 +/- 2 ng/ml) groups compared with those in the intact group (38.9 +/- 6.8 ng/ml). The levels of hepatic PRLR mRNA were higher (P < 0.05) in the intact (PRLR1, 27.4 +/- 6.1; PRLR2, 17.7 +/- 2.5) and HPD + cortisol (PRLR1, 23.4 +/- 0.4; PRLR2, 15.3 +/- 3.0) groups than in the HPD + saline group (PRLR1, 10.6 +/- 1.8; PRLR2, 8.9 +/- 1.8) at 140/141 d. The mean plasma PRL concentration in the LL group (70 +/- 9 ng/ml) was higher (P < 0.05) than that in the SL group (34 +/- 15 ng/ml), whereas the levels of hepatic PRLR1 mRNA (LL group, 4.6 +/- 0.9; SL group, 4.3 +/- 0.8) and PRLR2 mRNA (LL group, 3.4 +/- 0.4; SL group, 3.0 +/- 0.5) at 140-141 d were not different. These data indicate that cortisol acts directly or indirectly to maintain hepatic PRLR mRNA levels in the sheep fetus during late pregnancy. In contrast, changes in the external photoperiod and circulating PRL concentrations in the sheep fetus do not directly alter PRLR expression in the fetal liver. These studies provide further insight into the role that the PRL axis may play in the transduction of signals about the external environment to the fetus as it prepares for the transition to extrauterine life.

Pituitary and Testicular Function in Growth Hormone Receptor Gene Knockout Mice *

The role of GH in the control of pituitary and testicular function is poorly understood. GH receptor gene knockout (GHR-KO) mice were recently produced. As these mice are good experimental animals to assess the influence of the effects of GH and insulin-like growth factor-I (IGF-I), the present studies were undertaken. Young adult male GHR-KO mice and their normal siblings were tested for fertility and subsequently injected (i.p.) with saline or GnRH (1 ng/g BW) in saline. Fifteen minutes later, blood was obtained via heart puncture. Plasma IGF-I, PRL, LH, and testosterone concentrations were measured by RIAs. In addition, the testicular testosterone response to LH treatment was evaluated in vitro. The results indicate that the absence of GH receptors (GHRs) was associated with an increase (P < 0.005) in plasma PRL levels, and circulating IGF-I was not detectable. Although the basal plasma LH levels were similar in GHR-KO mice relative to those in their normal siblings, the circulating LH response to GnRH treatment was significantly (P < 0.001) attenuated. Plasma testosterone levels were unaffected by disruption of the GHR gene. However, basal (P < 0.01) and LH-stimulated (P < 0.001) testosterone release from the isolated testes of GHR-KO mice were decreased. The rate of fertility in GHR-KO male mice was also reduced. These results indicate that the lack of GHRs (with GH resistance and lack of IGF-I secretion) induces hyperprolactinemia and alters the effect of GnRH on LH secretion as well as testicular function. Thus, GH and IGF-I influence pituitary and gonadal functions in male mice.

Differential actions of the dopamine agonist bromocriptine on growth of SMtTW tumors exhibiting a prolactin and/or a somatotroph cell phenotype: relation to dopamine D2 receptor expression.

Dopamine (Da) and Da agonists are known to inhibit secretion and proliferation of normal and tumoral PRL cells, through receptors of D2 subtype. Because of the lack of an experimental model, the relationship between bromocriptine (BR) sensitivity and D2 receptor expression is poorly documented. Such a relationship was analyzed using five lineages of spontaneous transplantable rat pituitary tumors (SMtTW) exhibiting different PRL/GH phenotypes. From plasma PRL and GH concentrations of rats bearing the tumors and tumor messenger RNA contents, tumors were classified as PRL (SMtTW2), somatotroph (SMtTW10), or somatomammotroph (SMtTW5) tumors. Two lineages (SMtTW3 and SMtTW4) represented variants producing PRL and GH but with a high predominance of PRL. With the exception of SMtTW4 tumors, which were malignant, all the tumors were benign and differed in their growth rate. Hormone production and growth of tumors with a PRL or a somatomammotroph phenotype were reduced by about 90% under BR treatment, whereas somatotroph tumors and the PRL malignant tumors were totally insensitive to BR. D2 receptor messenger RNA was present in all BR-sensitive tumors and was not detected in BR-resistant tumors. In conclusion, using five lineages of SMtTW tumors that are representative of the most frequent tumors encountered in human pituitary pathology, we found a full concordance between tumor responses to BR and the expression of D2 receptor by the tumors. The identification of a tumor lineage with a malignant phenotype, secreting high amounts of PRL and presenting a resistance to BR, supports the idea that Da-resistant prolactinomas are aggressive tumors.

Identification of Mammosomatotrophs in the Turkey Hen Pituitary: Increased Abundance during Hyperprolactinemia*

We have previously reported that the hyperprolactinemia in incubating turkey hens is associated with recruitment of lactotrophs in the pituitary gland. In this study we have used double immunofluorescence and in situ hybridization histochemistry to 1) identify mammosomatotrophs in the anterior pituitary gland of egg-laying turkey hens and incubating hens, and 2) verify PRL gene expression within mammosomatotrophs by colocalizing PRL messenger RNA in GH-immunoreactive (ir) cells. The pituitaries of laying and incubating turkey hens were collected, and the midsagittal sections were dual labeled for either PRL and GH or PRL messenger RNA and GH. The plasma PRL concentrations were higher in incubating hens (231 +/- 10.6 ng/ml) than in laying hens (43 +/- 7.4 ng/ml; P < 0.01). In the midsagittal pituitary sections, mammosomatotrophs were predominantly found scattered in the caudal lobe of the anterior pituitary gland, in the ventral half of the cephalic lobe, and at the junction of cephalic and caudal lobes. In incubating hens, the proportion of mammosomatotrophs was 7.4 +/- 1.52% (mean +/- SEM) of the total number of GH-ir and/or PRL-ir cells counted, which was significantly higher (P < 0.05) than that found in laying hens (0.6 +/- 0.23%). Furthermore, PRL gene expression was observed in many GH-ir cells in the incubating hen pituitary gland. These data suggest that 1) mammosomatotrophs are present in the turkey pituitary gland, and 2) there is an increased abundance of mammosomatotrophs in the incubating turkey hen that may contribute to hyperprolactinemia.

Alterations in anterior pituitary function of dogs with pituitary-dependent hyperadrenocorticism.

For the purpose of obtaining an integral picture of anterior pituitary function in canine pituitary-dependent hyperadrenocorticism (PDH), 47 dogs with PDH and eight control dogs received combined administration of four hypophysiotropic hormones (CRH, GHRH, GnRH and TRH) and measurements were made of ACTH, cortisol, GH, LH, PRL and TSH. Basal plasma levels in 47 dogs with PDH were higher for ACTH, cortisol and PRL, lower for GH, and not different for LH (n = 25 noncastrated dogs) and TSH compared with controls (n = 8). In dogs with PDH the responses to combined hypophysiotropic stimulation, measured as increment and area under the curve (AUC), were not different for ACTH, lower for GH and TSH (increments and AUC) and higher for cortisol (increments), LH (AUC, n = 25 noncastrated dogs) and PRL (increments and AUC) than in controls. We conclude that pituitary function is altered in several respects in dogs with PDH. 1) In spite of persisting hypercortisolemia and the neoplastic transformation of the corticotropic cells, these cells usually remain responsive to combined hypophysiotropic stimulation. 2) Basal plasma GH concentrations and GH responsiveness in the combined stimulation test are decreased, probably as a result of the glucocorticoid-induced increase in somatostatin tone. 3) Plasma PRL concentrations and the PRL response to stimulation are increased, probably as a result of cosecretion with ACTH by the transformed corticotropic cells. 4) Despite the well known effect of glucocorticoids of decreasing circulating concentrations of gonadal steroids and thyroxine, the basal plasma concentrations of LH and TSH remain unchanged and there is a tendency to hyperresponsiveness to stimulation for LH and hyporesponsiveness for TSH. The most likely explanation for these changes is a dual effect of glucocorticoids: a direct effect on the gonads and thyroids and/or the transport and metabolism of their secretory products, and an influence on the sensitivity of the feedback control at the hypothalamic-pituitary level.