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At least 91 records · Page 5Linked to original sources
PubMed1986

Multiple forms of pituitary prolactin, a glycosylated form of porcine prolactin with enhanced biological activity.

Three forms of prolactin differing in molecular weight (Mr 23,000, 25,000 and 50,000, respectively) and electrophoretic mobility have been isolated and purified from fresh-frozen porcine pituitary glands. The prolactin form with Mr 25,000 is identified as a glycoprotein having an affinity to concanavalin A. The carbohydrate unit containing GlcNAc3, GalNAc1, Man3, Fuc 0.5, Gal 0.4 is linked to asparagine at the 31 position. The amino acid composition and partial primary structure of the glycosylated prolactin are identical to those of the major prolactin form (Mr 23,000). Based on isoelectric focusing and nondenaturing disc-electrophoresis, the glycosylated prolactin appears more acidic than the major form. The glycosylated form of the hormone has 140% of the activity of the non-glycosylated prolactin when measured by the pigeon crop sac assay. The new form accounts for 30-40% of the total monomeric prolactin in the porcine pituitary. The yield was 200 mg purified glycosylated prolactin from 1000 g pituitary gland. The third form of hormone (Mr 50,000) was shown to be a disulphide linked prolactin dimer.

Amino Acid Sequence↗
PubMed1988

Positive relationship between the nocturnal concentrations of melatonin and prolactin, and a stimulation of prolactin after melatonin administration in young men.

The relationship between the concentrations of melatonin and prolactin over the 24-h cycle has been investigated in a group of young men at three times in the year. Melatonin and prolactin showed a significant positive correlation (P less than 0.001) for all times during the 24-h period but with a greater contribution from concentrations during the nocturnal period, when both hormones were elevated. The positive correlation for nocturnal concentrations was evident in February and March (P less than 0.01) but was of greatest significance in June (P less than 0.001). In blood samples taken at 15-min intervals during the morning (0800-1200) and evening (2000-2400), melatonin and prolactin concentrations were not significantly correlated. Melatonin concentrations increased before prolactin during the evening and decreased before prolactin in the morning. Oral administration of 6 mg melatonin significantly stimulated prolactin release above concentrations measured after placebo administration, in both the morning (P less than 0.05) and evening (P less than 0.01) time periods; the prolactin response being greater in the evening. These results provide evidence for melatonin controlling the nocturnal increase of prolactin via its ability to stimulate prolactin release.

Administration, Oral↗
PubMed1992

Effect of the GABAA agonist muscimol on prolactin secretion from human prolactin-secreting adenomas and GH3 rat pituitary tumour cells.

The effect of muscimol, a specific potent GABAA receptor agonist, on prolactin release from human prolactin-secreting tissue was investigated using a perifusion system. Perifusion studies on normal rat anterior pituitary tissue, which has identical GABA receptors to those found in normal human pituitary glands, show that muscimol has a specific biphasic effect on prolactin release. This is characterized by an initial transient stimulation (222.3 +/- 21.6% of basal) lasting for 5-10 min followed by a more prolonged inhibitory phase (63.9 +/- 3.1% inhibition of basal). Five human prolactin-secreting adenomas were studied, and in none of the tumours could a biphasic response be demonstrated. One of the prolactin-secreting adenomas had a blunted inhibitory response, but the other 4 showed no inhibitory effect of muscimol on prolactin release. Muscimol had no significant effect on basal or thyrotropin-releasing-hormone (TRH)-stimulated prolactin secretion from GH3 rat pituitary tumour cells. These studies suggest that the GABAergic effect on prolactin secretion is absent or altered in both rat and human prolactin-secreting tumour cells.

Adult↗
PubMed1976

Cyclic activity of the pituitary prolactin cells and plasma prolactin levels in the oestrous cycle of the ewe.

The relative proportions of prolactin cells, somatotrophs and gonadotrophs were determined in the adenohypophyses of 28 Merino ewes on selected days during the oestrous cycle. Plasma prolactin levels were measured in 16 of the animals at 3-hr intervals during the 24 hr before autopsy. From Days 1 to 5 of the cycle (Day 0=day of ovulation), plasma prolactin levels were 20-40 ng/ml and the prolactin cells were filled with granules. Plasma levels increased to 168 ng/ml between Days 6 and 9, and marked degranulation of the prolactin cells occurred. The greatest degranulation was found on Days 16 and 0, and was associated with a prolactin surge to a concentration of 610 ng/ml. The rise in plasma prolactin and intensive degranulation of prolactin cells at the time of ovulation and formation of the CL suggest that prolactin is important at this stage of the oestrous cycle.

Animals↗
PubMed1976

Effect of prolactin and growth hormone on prolactin and LH receptors in the dwarf mouse.

Dwarf mice (DW/J;dw/dw) which exhibit a deficiency of prolactin and GH secretion were treated for 8 days with ovine prolactin and/or human GH (10 or 20 mug/day) and the effect on hepatic and testicular prolactin receptors was investigated. In both sexes there was a significant increase in body weight after all hormone treatments, but an increment in testicular weight was observed only after prolactin administration. Prolactin treatment increased the specific binding % of prolactin in liver membranes in females but not males, and in testicular homogenates (together with an increase in LH receptors). The results suggest that lack of prolactin but not of GH retards sexual development in these mice. Treatment with prolactin partly counteracts this deficiency, and the effect may be mediated by the induction of hepatic and testicular prolactin and LH receptors.

Animals↗
PubMed1988

Effect of serotonin antagonists on prolactin and progesterone secretion in rats: evidence that the stimulatory and inhibitory actions of serotonin on prolactin release may be mediated through different receptors.

The serotoninergic regulation of prolactin release was studied in female rats in different reproductive states using ketanserin, a specific S2 receptor blocker, ICS 205-930 ((3 alpha-tropanyl)1H-indol-3-carboxylic acid ester), a specific S3 receptor blocker and p-chlorophenylalanine (pCPA), a serotonin synthesis inhibitor. Administration of ketanserin to pro-oestrous rats inhibited the afternoon prolactin surge; this inhibition was prevented by progesterone. On day 3 of pregnancy, pCPA or ketanserin blocked the afternoon prolactin surge, and administration of oestrogen (on day 2) and progesterone (on day 3) in combination, but not alone, prevented this effect. On day 9 of pregnancy, treatment with oestrogen (on day 8) and progesterone (on day 9) induced an afternoon surge of prolactin which was prevented by administration of ketanserin or pCPA. On days 9 and 16, pCPA induced a slight increase in serum prolactin in rats not treated with steroids, but ketanserin had no effect. On day 13, ketanserin and pCPA had no effect on serum prolactin levels, but after increasing serotoninergic transmission by injecting fluoxetine and 5-hydroxytryptophan, serum prolactin levels were decreased. On day 19, ketanserin produced a transient increase in the serum concentration of prolactin, probably produced by the marked decrease in the serum concentration of progesterone induced by the S2 receptor blocker. Administration of ICS 205-930 to pro-oestrous rats or rats on day 19 of pregnancy had no effect on serum concentrations of prolactin and progesterone.(ABSTRACT TRUNCATED AT 250 WORDS)

5-Hydroxytryptophan↗
PubMed1986

Effect of acrylonitrile on the rat pituitary: enlargement of Golgi region in prolactin cells, crinophagy in prolactin cells and growth hormone cells.

Since it has been shown that acrylonitrile prevents the appearance of spontaneous pituitary adenomas, we have investigated its effect in acute experiments on rat pituitaries by histology, immunocytochemistry, electron microscopy and morphometry; in addition, serum prolactin and growth hormone levels were measured by radioimmunoassay. Electron microscopy of prolactin cells revealed hypertrophy of the Golgi region without significant change in volume densities and diameters of forming and storage granules. In the 24 h group, crinophagy was observed in prolactin cells and growth hormone cells. Corticotrophs, thyrotrophs and gonadotrophs were unaltered. Dilation, congestion and rupture of capillaries, as well as pericapillary and intercellular oedema were evident in the 24 h group. One hour after intravenous acrylonitrile injection, serum prolactin levels were within the normal range, whereas at 24 h, hyperprolactinemia was noted. Serum growth hormone concentrations were unchanged. It can be concluded that acrylonitrile has a complex effect on prolactin cells. Hypertrophy of Golgi complex and hyperprolactinemia may reflect increased prolactin synthesis and release. Since volume densities and diameters of secretory granules in prolactin cells remained unchanged, it appears that newly synthesized prolactin was preferentially released and not the prolactin stored in secretory granules. Crinophagy may be the morphological manifestation of a discrepancy between hormone synthesis and release suggesting increased degradation of unused hormone by lysosomes.

Acrylonitrile↗
PubMed1997

Dietary fat and protein intake differ in modulation of prostate tumor growth, prolactin secretion and metabolism, and prostate gland prolactin binding capacity in rats.

The combined effects of dietary fat and protein concentration on prostate tumor growth and endocrine homeostasis were evaluated in male rats. A 2 x 2 factorial experiment examined the effects of protein (5 and 20% of energy as casein) and fat (10 and 40% of energy as corn oil) on the growth of the Dunning R3327-H transplantable prostate adenocarcinoma in Copenhagen x Fisher F1 rats. Rats fed protein-restricted diets for 20 wk exhibited lower energy intakes, final body weights and tumor growth rates. Weanling male Sprague-Dawley rats fed protein-restricted diets for 4 wk had serum concentrations of prolactin, growth hormone and testosterone which were 68, 17 and 85% of controls, respectively. After 16 wk of feeding, there were no effects of dietary protein on serum hormone concentrations despite reduced energy intake and body weight. The metabolic clearance rate of serum prolactin was lower in rats fed the low protein diets for 4 or 16 wk; however, no differences were noted when adjusted for body weight. In vivo studies employing intravenously injected 125I-labeled prolactin revealed slight alterations in the metabolism of circulating prolactin monomer or binding to serum proteins in protein-restricted rats. The maximal binding capacity of prolactin receptors on the prostate membrane fraction was 42% lower in rats fed diets restricted in protein despite normal serum hormone concentrations at 16 wk. Dietary fat had no effect on tumor growth or prolactin homeostasis although a slightly greater serum testosterone was noted in rats fed high fat diets. In contrast, restriction of dietary protein caused significant changes in energy intake, serum hormone concentrations, prolactin metabolism, prostatic prolactin binding capacity and prostate tumor growth rates. These studies support the hypothesis that dietary protein and energy intake, particularly during periods of rapid growth and development, may alter prostate biology and modulate the risk of future prostate cancer progression.

Adenocarcinoma↗
PubMed2004

Stress- as well as suckling-induced prolactin release is blocked by a structural analogue of the putative hypophysiotrophic prolactin-releasing factor, salsolinol.

Prolactin is secreted from the anterior lobe of the pituitary gland in response both to suckling and to stress. We recently observed that 1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline (salsolinol), produced in the neurointermediate lobe of the pituitary gland, as well as in the medial basal hypothalamus, can selectively release prolactin from the anterior pituitary. Therefore, it has been proposed that salsolinol is a putative endogenous prolactin-releasing factor (PRF). Here, we report that one structural analogue of salsolinol, 1-methyl-3,4-dihydroisoquinoline (1MeDIQ), can block salsolinol-induced release of prolactin, but does not affect prolactin release in response to thyrotropin releasing hormone (TRH), alpha-methyl-p-tyrosine (alpha MpT) (an inhibitor of tyrosine hydroxylase), domperidone (a D(2) dopamine receptor antagonist), or 5-hydroxytryptophan (5-HTP), a precursor of serotonin). 1MeDIQ profoundly inhibited suckling-, immobilization-, as well as formalin-stress induced prolactin release without any influence on corticosterone secretion. The 1MeDIQ-induced reduction in prolactin response to immobilization stress was dose-dependent. These results suggest that salsolinol can play a pivotal role in the regulation of prolactin release induced by either physiological (suckling) or environmental (stress) stimuli.

Adaptation, Physiological↗
PubMed1997

Prolactin receptor subtypes: a possible mode of tissue specific regulation of prolactin function.

Prolactin mediates its effect on target cells through an interaction with membrane-anchored receptors. In the last decade, several subtypes of the receptor have been isolated from different species. This has generated a great deal of interest in the roles of the receptor subtypes and the possible divergent signalling pathways in mediating the pleiotropic effects of prolactin on target tissues. Our current knowledge of the signalling pathway of prolactin is derived mainly from the interaction of the hormone with one of its receptor subtypes (the long form) isolated from rats. In vitro expression studies have led to the identification of the regions within the long form prolactin receptor that are essential for the association of the tyrosine kinase Jak-2, and the phosphorylation events leading to activation of the prolactin responsive beta-casein promoter. To date, a specific target gene that may be activated after interaction of prolactin with the short form of the receptor has not been identified. However, the different receptor subtypes are present in the same cell type in vivo and their expression is hormone regulated, possibly through multiple promoters that control transcription of the prolactin receptor gene. Comparative studies suggest that the signalling pathways and the relevance of different receptor subtypes on prolactin function may vary between species.

Animals↗
PubMed1986

Ontogeny of prolactin receptors in rat decidual tissue: binding by a locally produced prolactin-like hormone.

The objectives of this investigation were to determine whether decidual tissue possesses specific binding sites for prolactin, and to examine whether the locally produced prolactin-like hormone binds to these receptors. Characterization of the binding of prolactin to decidual tissue from rats at day 9 of pseudopregnancy revealed specific, high-affinity sites. Binding approached saturation with increasing concentrations of either the ligand or the protein. Cytosolic extracts of day-9 decidual tissue, containing various amounts of decidual luteotrophin which possesses several of the physiological and biochemical characteristics of prolactin, displaced the binding of 125I-labelled prolactin to decidual membranes in a linear fashion. Prolactin-binding sites were detectable 72 h after induction of decidualization and 48 h after the appearance of decidual luteotrophin in the decidua. Prolactin receptor concentrations increased significantly between days 8 and 9, reached a plateau between days 9 and 12 and declined abruptly on days 14 and 15, accompanied by a similar decline in decidual luteotrophin concentration in the tissue. Thus rat decidual tissue possesses specific receptors for prolactin to which decidual luteotrophin locally produced can bind, thereby suggesting an auto/paracrine role for this substance.

Animals↗
PubMed1994

Prolactin-induced proliferation of Nb2 cells involves tyrosine phosphorylation of the prolactin receptor and its associated tyrosine kinase JAK2.

The interaction of prolactin with its receptor in the Nb2 cell line has been shown to induce the phosphorylation of cell-associated proteins and mitogenesis. It has been reported previously that one of these proteins, phosphorylated upon prolactin stimulation, was a tyrosine kinase. We have identified this kinase as JAK2, and demonstrate its association with the prolactin receptor. In addition, we show that the prolactin receptor itself becomes tyrosine phosphorylated upon ligand stimulation in Nb2 cells. These actions are time-dependent and occur rapidly after prolactin stimulation, with first the kinase being activated within 5 min and then the receptor being phosphorylated maximally at 20 min. Moreover, phosphorylation of both JAK2 and the receptor as well as Nb2 cell proliferation are dependent on the concentration of lactogenic hormone, resulting in a bell-shaped response curve similar to that observed in the two site model of hGH action. This indicates that early events in signal transduction as well as later events like mitogenesis and proliferation involve prolactin receptor dimerization. Together these data indicate that the prolactin receptor in Nb2 cells is associated to JAK2 and that upon ligand stimulation, and receptor dimerization, the kinase and the receptor are tyrosine-phosphorylated, which represents the first event in the process of prolactin receptor signal transduction in Nb2 cells.

Blotting, Western↗
PubMed1993

Expression of the extracellular domain of the rat liver prolactin receptor and its interaction with ovine prolactin.

A clone of the extracellular domain of the rat liver prolactin receptor was generated by the RNA-based polymerase chain reaction, and the NH2-terminal 210 amino acids were expressed in HeLa cells using a vaccinia virus/T7 hybrid expression system. The protein was isolated from serum-free culture medium directly by chromatography on an ovine prolactin affinity column and yielded approximately 1.5 mg of protein/liter of suspension culture. The extracellular domain of the rat prolactin receptor inhibited the ovine prolactin-dependent mitogenesis of rat lymphoma Nb2 cells with an IC50 of 7.1 pM and bound 125I-labeled ovine prolactin with a Kd of 1.21 +/- 0.19 nM. In contrast, the binding of the 125I-labeled extracellular domain to ovine prolactin exhibited positive cooperativity with a Hill coefficient of 1.73. High pressure gel filtration chromatography was used to demonstrate the formation of a complex consisting of one molecule of ovine prolactin and two molecules of the extracellular domain of the rat prolactin receptor. Complex formation occurred with human growth hormone, but not with ovine growth hormone, a non-lactogen.

Animals↗
PubMed1994

A radioimmunoassay for recombinant-derived chicken prolactin suitable for the measurement of prolactin in other avian species.

A homologous radioimmunoassay for chicken prolactin is described. The assay is based on recombinant-derived chicken prolactin that has been used to raise an antibody and produce 125I-labeled tracer and assay standards. The radioimmunoassay measures a minimum of 0.03 +/- 0.01 ng of the recombinant prolactin with 50% displacement of binding by 0.6 +/- 0.1 ng. Chicken plasma and pituitary immunoreactivity dilute in parallel with the standard curve. The mean (+/- SE) concentrations of plasma prolactin were 12.1 +/- 1.5, 433.2 +/- 5.5, and 1609.8 +/- 18.5 ng/ml in out-of-lay, laying, and incubating bantam hens, respectively. The binding of recombinant prolactin was not displaced by extracts of neural lobe or plasma from a hypophysectomized hen. Plasma prolactin concentrations were increased after intravenous administration of chicken vasoactive intestinal polypeptide or quipazine, a 5-HT agonist. The assay measures immunoreactive prolactin in other birds. Plasma from quail, turkey, great tit, and wryneck displaced the 125I-labeled prolactin tracer parallel to the standard curve. Starling, ring dove, and penguin plasma displaced the binding in a nonparallel manner.

Animals↗
PubMedDate not supplied

Prolactin secreting adenoma in man and the role of prolactin in spermatogenesis.

The case of a 23-year-old man with a pituitary prolactin secreting adenoma is described. With the exception of prolactin all endocrinological parameters were normal. This finding provided an ideal opportunity to assess the role of prolactin on spermatogenesis. Sperm analysis and light microscopy examination of testicular biopsy showed normal spermatogenesis. Electron microscopic studies of the testicular specimen revealed the presence of undivided spermatids, containing two or more nuclei, partially embedded in a developing common acrosome. Morphological studies demonstrated a constant "paired" situation. In most instances two sperms were contained in a single membrane; no single sperm was detected. Following treatment with 5 mg/day bromocriptine prolactin levels decreased and this peculiar abnormality disappeared. In fact, after 2 months of treatment the sperm abnormalities were markedly reduced, whereas no change was found after a period of 120 days. Since this was the only alteration found in the patient with high prolactin levels, a correlation was sought between prolactin levels and cell division. Considering the similarities between prolactin and growth hormone, it might be possible to attribute to prolactin a growth hormone role in the germinal epithelium. This action could be either direct or indirect via an intermediate growth factor.

Adenoma↗
PubMed1980

Decidual production of prolactin in late gestation: further evidence for a decidual source of amniotic fluid prolactin.

The capacity of human decidual tissue to synthesize prolactin de novo throughout late gestation was investigated and correlated with the levels of prolactin (PRL) in amniotic fluid. Maximal concentrations of PRL in both amniotic fluid and samples of decidua were found prior to the thirtieth week of gestation and declined simultaneously until term. A high correlation (r = 0.90, p < 0.00005) was found when the levels of PRL in amniotic fluid and the initial (preincubation) content of PRL in decidua from the same patient were compared. A very high correlation (r = 0.96, p < 0.00005) was seen between the ability of the decidua to produce prolactin in vitro and the corresponding levels of prolactin in amniotic fluid. No significant difference in any parameter tested was noted with respect to either the sex of the fetus or the mode of delivery (p > 0.05). These data are interpreted as indicating (1) that decidual tissue varies throughout late gestation, in both its initial content of prolactin and its ability to synthesize prolactin de novo, in a manner which correlates to a high degree with variations in amniotic fluid prolactin levels and (2) that the decidual tissue is the major source of amniotic fluid prolactin.

Amniotic Fluid↗