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PubMed1995

Regulated secretion of prolactin by the mouse insulinoma cell line beta TC-3.

Our aim is to use cultured cells capable of regulated protein secretion for the production of recombinant proteins that require particular types of post-translational modifications. Here we have generated a stable transfected beta TC-3 cell line, beta TC-IPR9, that secretes high levels of recombinant prolactin. Transfected cells synthesize both the 27 kDa glycosylated and a 23 kDa nonglycosylated prolactin; the 23 kDa nonglycosylated species was secreted preferentially when cells were placed in secretion medium containing isobutylmethylxanthine (IBMX) and high concentrations of glucose, K+, and Ca2+. When the cells were cultured in medium containing low concentrations of glucose, K+, and Ca2+, most of the prolactin and insulin were not secreted; much of the prolactin was proteolytically converted to a 16 kDa form. Within the first 30 minutes after transferring the cells to medium containing secretagogues there was a 20-fold increase in the rate of secretion of prolactin; all of the 16 kDa species was secreted. The recombinant cells could be cycled several times between medium in which prolactin was biosynthesized and medium in which it was secreted. Preferential secretion of proteolytically processed prolactin in a medium without contaminating proteins offers an example of the advantage of this technology for production of other recombinant proteins.

1-Methyl-3-isobutylxanthine↗
PubMed2005

Nalmefene induced elevation in serum prolactin in normal human volunteers: partial kappa opioid agonist activity?

In humans, mu- and kappa-opioid receptor agonists lower tuberoinfundibular dopamine, which tonically inhibits prolactin release. Serum prolactin is, therefore, a useful biomarker for tuberoinfundibular dopamine. The current study evaluated the unexpected finding that the relative mu- and kappa-opioid receptor selective antagonist nalmefene increases serum prolactin, indicating possible kappa-opioid receptor agonist activity. In all, 33 healthy human volunteers (14 female) with no history of psychiatric or substance use disorders received placebo, nalmefene 3 mg, and nalmefene 10 mg in a double-blind manner. Drugs were administered between 0900 and 1000 on separate days via 2-min intravenous infusion. Serial blood specimens were analyzed for serum levels of prolactin. Additional in vitro studies of nalmefene binding to cloned human kappa-opioid receptors transfected into Chinese hamster ovary cells were performed. Compared to placebo, both doses of nalmefene caused significant elevations in serum prolactin (p<0.002 for nalmefene 3 mg and p<0.0005 for nalmefene 10 mg). There was no difference in prolactin response between the 3 and 10 mg doses. Binding assays confirmed nalmefene's affinity at kappa-opioid receptors and antagonism of mu-opioid receptors. [(35)S]GTPgammaS binding studies demonstrated that nalmefene is a full antagonist at mu-opioid receptors and has partial agonist properties at kappa-opioid receptors. Elevations in serum prolactin following nalmefene are consistent with this partial agonist effect at kappa-opioid receptors. As kappa-opioid receptor activation can lower dopamine in brain regions important to the persistence of alcohol and cocaine dependence, the partial kappa agonist effect of nalmefene may enhance its therapeutic efficacy in selected addictive diseases.

Adolescent↗
PubMed2006

Loss of mammary epithelial prolactin receptor delays tumor formation by reducing cell proliferation in low-grade preinvasive lesions.

Top quartile serum prolactin levels confer a twofold increase in the relative risk of developing breast cancer. Prolactin exerts this effect at an ill defined point in the carcinogenic process, via mechanisms involving direct action via prolactin receptors within mammary epithelium and/or indirect action through regulation of other hormones such as estrogen and progesterone. We have addressed these questions by examining mammary carcinogenesis in transplants of mouse mammary epithelium expressing the SV40T oncogene, with or without the prolactin receptor, using host animals with a normal endocrine system. In prolactin receptor knockout transplants the area of neoplasia was significantly smaller (7 versus 17%; P < 0.001 at 22 weeks and 7 versus 14%; P = 0.009 at 32 weeks). Low-grade neoplastic lesions displayed reduced BrdU incorporation rate (11.3 versus 17% P = 0.003) but no change in apoptosis rate. Tumor latency increased (289 days versus 236 days, P < 0.001). Tumor frequency, growth rate, morphology, cell proliferation and apoptosis were not altered. Thus, prolactin acts directly on the mammary epithelial cells to increase cell proliferation in preinvasive lesions, resulting in more neoplasia and acceleration of the transition to invasive carcinoma. Targeting of mammary prolactin signaling thus provides a strategy to prevent the early progression of neoplasia to invasive carcinoma.

Animals↗
PubMed1978

Inhibition by low concentrations of ouabain of prolactin-induced lactogenesis in rabbit mammary-gland explants.

1. Explants of mammary tissue from pseudopregnant rabbits were cultured at 37 degrees C in air for 24-48h in Medium 199 buffered with 20mm-Hepes [4-(2-hydroxyethyl)-1-piperazine-ethanesulphonic acid]. The medium contained insulin and corticosterone, or insulin, corticosterone and sheep prolactin in the presence or absence of ouabain, an inhibitor of Na(+)/K(+)-dependent adenosine triphosphatase. The responses of explants were assessed histologically, by measuring the tissue concentration of K(+), and by rates of synthesis of RNA, protein and fatty acids. The effect of ouabain on Na(+) and K(+) concentrations in slices of lactating rabbit mammary-gland tissue incubated for 1h at 37 degrees C in Krebs bicarbonate buffer was also studied. 2. Prolactin increased the concentration of K(+) in mammary explants, an effect prevented by ouabain. In slices of lactating tissue, there was a linear relationship between the log dose of ouabain (from 0.1 to 10mum) and increased Na(+) and decreased K(+) concentrations in the tissue. 3. Ouabain at concentrations up to 1mum did not affect the rate of synthesis of RNA, protein or fatty acids by explants cultured with insulin and corticosterone. By contrast, the stimulatory effect of prolactin on protein synthesis was diminished and the induction of medium-chain fatty acid synthesis by prolactin was almost abolished. RNA synthesis was unaffected. Histological examination showed no tissue damage by 1mum-ouabain. 4. Explants cultured in the presence of 2mum-ouabain for 24h retained their ability to respond to prolactin when the ouabain was removed from the culture medium. Between 24 and 48h they showed responses to prolactin of a magnitude similar to those of explants never exposed to ouabain. 5. These results show that a fully functional Na(+)/K(+)-dependent adenosine triphosphatase system is necessary for prolactin to promote secretory activity in rabbit mammary gland.

Animals↗
PubMed1989

Re-examination of the putative roles of insulin and prolactin in the regulation of lipid deposition and lipogenesis in vivo in mammary gland and white and brown adipose tissue of lactating rats and litter-removed rats.

1. The effects of various treatments to alter either plasma prolactin (bromocryptine administration or removal of litter) or the metabolic activity of the mammary gland (unilateral or complete teat sealing) on the disposal of oral [14C]lipid between 14CO2 production and [14C]lipid accumulation in tissues of lactating rats were studied. In addition, the rates of lipogenesis in vivo were measured in mammary gland, brown and white adipose tissue and liver. 2. Bromocryptine administration lowered plasma prolactin, but did not alter [14C]lipid accumulation in mammary gland or in white and brown adipose tissue. 3. In contrast, complete sealing of teats results in no change in plasma prolactin, but a 90% decrease in [14C]lipid accumulation in mammary gland and a 4-fold increase in white and brown adipose tissue. The rate of lipogenesis in mammary gland was decreased by 95%, but there was no change in the rate in white and brown adipose tissue. Unilateral sealing of teats resulted in a decrease in [14C]lipid accumulation in white adipose tissue. 4. Removal of the litter for 24 h (low prolactin) produced a similar pattern to complete teat sealing, except that there was a 6-fold increase in lipogenesis in white adipose tissue. Re-suckling for 5 h increased plasma prolactin, but did not alter the response seen in litter-removed lactating rats. 5. Changes in lipoprotein lipase activity and in plasma insulin paralleled the reciprocal changes in [14C]lipid accumulation in white and brown adipose tissue and in mammary gland. 6. It is concluded that the plasma insulin is more important than prolactin in regulating lipid deposition in adipose tissue during lactation, and that any effects of prolactin must be indirect.

Adipose Tissue↗
PubMed2002

Brain structures mediating the suckling stimulus-induced release of prolactin.

Suckling-induced prolactin release is a widely studied neuroendocrine reflex, comprising a neural afferent and a humoral efferent component. The information on the brain structures involved in this reflex is fairly limited. The present studies focused on this question. The following hypothalamic interventions were made in lactating rats and the dams were tested for the suckling-induced prolactin response: (i) unilateral or (ii) bilateral frontal cuts at the level of the anterior and posterior hypothalamus; (iii) administration of 5,7-dihydroxytryptamine or (iv) 6-hydroxydopamine into the hypothalamic paraventricular nucleus (PVN) to destroy serotonergic and catecholaminergic innervation of the cell group, respectively; (v) lesion of the medial subdivision of the PVN; and (vi) horizontal knife cuts below the PVN. Bilateral posterior and bilateral or unilateral anterior frontal cuts caused blockade of the suckling-induced release of prolactin. Likewise, most dams receiving 5,7-dihydroxytryptamine in the PVN did not respond to the suckling stimulus. Immunocytochemistry revealed that, in those rats which did not show a rise in plasma prolactin, there were almost no serotonergic fibres and terminals in the PVN, while in dams which exhibited a response, numerous serotonergic elements were evident. 6-Hydroxydopamine treatment did not cause significant alteration in the prolactin response. Lesion of the medial, largely parvocellular subdivision of the PVN, or horizontal knife cuts below this cell group, blocked the hormone response. The findings demonstrate for the first time that: (i) interruption of the connections between the brain stem and the hypothalamus interferes with the prolactin response to the suckling stimulus; (ii) serotonergic fibres terminating in the hypothalamic PVN are involved in the mediation of the suckling stimulus; and (iii) within the PVN, neurones in the medial, largely parvocellular subdivision of the cell group take part in the transfer of the neural signal, eventually inducing prolactin release.

5,7-Dihydroxytryptamine↗
PubMed2001

Prolactin and lipopolysaccharide treatment increased apoptosis and atresia in rat ovarian follicles.

Follicular atresia is associated with the presence of increased macrophages within the follicle. What is not known is whether, in the adult rat, macrophages are instrumental in inducing apoptosis and/or atresia or whether they are simply secondary to a hormonally mediated event. As prolactin is an immunoreactive hormone and stimulates the expression of monocyte chemoattractant, the present experiments compared the effects of prolactin treatment with that of an immune challenge with lipopolysaccharide (LPS) on the invasion of macrophages into the follicular and luteal compartments of the ovary and the occurrence of apoptosis/atresia in relation to macrophage invasion. Rats were treated for 3 days with either prolactin or LPS and ovaries obtained at pro-oestrus or oestrus. Prolactin and LPS increased the number of atretic vs. healthy follicles (P < 0.008, chi2) in pro-oestrus ovaries and increased the mean number of apoptotic cells and macrophages (P < 0.05 for some groups). Macrophages were typically observed in the thecal layer, apoptotic cells in the granulosa cell layer, although 84% follicles which had macrophages within the granulosa cell layer also contained relatively high numbers of apoptotic nuclei. Prolactin and LPS treatment in vivo reduced the progesterone response to follicle stimulating hormone (FSH) (P < 0.001) in cultures of ovarian dispersates but did not inhibit the response to forskolin. In contrast, prolactin or LPS added in vitro to the cultures inhibited the progesterone response to forskolin. Results show that both prolactin and LPS increase follicular apoptosis and atresia and reduce the progesterone response to FSH.

Animals↗
PubMed2003

Changes in agouti-related peptide during the ring dove breeding cycle in relation to prolactin and parental hyperphagia.

Ring doves (Streptopelia risoria) exhibit marked increases in food consumption and decreases in body weight when they are provisioning their young. This study examined changes in hypothalamic immunostaining for agouti-related peptide (AGRP), an endogenous melanocortin receptor antagonist and appetite stimulant, during the ring dove breeding cycle. Because prolactin is orexigenic in doves, and is elevated in blood at the onset of parental hyperphagia, we also explored the possibility that prolactin-induced hyperphagia is associated with AGRP changes. The numbers of AGRP-immunoreactive (ir) cells within the tuberal hypothalamus were maximal during the prelaying period of the breeding cycle but decreased dramatically during early incubation. AGRP-ir cell numbers began to increase again during late incubation and reached a peak during the early and late posthatching stages. Because posthatching elevations in AGRP-ir were temporally associated with marked elevations in parental food intake, and because AGRP is orexigenic in doves, these findings suggest that increased AGRP activity in the dove tuberal hypothalamus may contribute to parental hyperphagia. Rising prolactin secretion during late incubation and early posthatching may initiate this increase in AGRP-ir, since intracerebroventricular administration of prolactin significantly elevated food intake and AGRP-ir cell numbers in the tuberal hypothalamus of nonbreeding doves. Prolactin-induced elevations in AGRP-ir cell numbers persisted when the confounding effects of weight gain that accompany prolactin-induced hyperphagia in nonbreeding doves were eliminated by a food restriction procedure, thereby suggesting that prolactin can directly influence AGRP activity under neutral energy state conditions.

Agouti-Related Protein↗
PubMedDate not supplied

Relationship between serum prolactin levels and histology of benign and malignant breast lesions: a detailed study of 153 consecutive cases.

This study was aimed at investigating the relationship between serum prolactin levels and the morphology of operable female breast lesions. One hundred fifty-three consecutive patients with operable benign and malignant breast lesions in whom preoperative serum prolactin levels had been determined were stratified into five groups according to their serum prolactin levels. The histologic findings in these groups were analyzed and compared. Most patients (93%) had serum prolactin levels within the normal limits. Of the 54 patients with benign lesions, only 4(7%) had slightly elevated serum prolactin levels. Two of these patients had fibroadenomas, one had a phyllodes tumor and one had fibrocystic change. Of the 99 patients with carcinoma, 7 (7%) had hyperprolactinemia. Five of the seven tumors were invasive and two were in situ. All seven tumors were of low or intermediate grade of malignancy. The two cases with the highest prolactin levels (3057 and 1822 mU/L) were both intermediate-grade ductal carcinoma in situ (DCIS). It is concluded that the great majority of patients presenting with operable breast lesions have normal serum prolactin levels, and that elevated levels, when present, occur with equal frequency in patients with benign and malignant breast lesions. Hyperprolactinemic patients presenting with carcinoma in this study, none of whom had a history of recent pregnancy or lactation, tended to have histologically low- or intermediate-grade tumors, but this needs to be confirmed by investigating more cases.

Biomarkers, Tumor↗
PubMed1982

Effects of insulin, cortisol and prolactin on lipid, protein and casein syntheses in goat mammary tissue in organ culture.

The actions of insulin, prolactin and cortisol on protein, lipid and casein syntheses were examined in goat mammary explants in culture. The synthesis of the three products was stimulated by insulin and prolactin associated or not with cortisol. Casein synthesis was stimulated only when prolactin was present in the culture medium. Prolactin alone was able to significantly support the induction of casein synthesis. After preculture in the presence of insulin alone, the tissue lost part of its capacity to respond to the prolactin stimulus but, when precultured in the presence of insulin + cortisol, it retained its total sensitivity. These data suggest that insulin, prolactin and cortisol are involved in the maintenance of goat mammary tissue in culture but that prolactin essentially stimulates milk synthesis.

Adipose Tissue↗
PubMed1984

The effect of prolactin on estradiol-17 beta and testosterone plus 5 alpha-dihydrotestosterone secretion by porcine luteal cells in vitro.

Prolactin (1, 5, 10 micrograms/ml) inhibited 5 alpha-dihydrotestosterone (DHT), testosterone (T) and estradiol-17 beta (E2) secretion by luteal cells isolated from porcine corpus luteum on the 13th day of the estrous cycle. The effect of prolactin upon luteal cells on the 5th and 17th day of the cycle was different. Inhibition of DHT, T and E2 secretion in luteal cells on the 5th day of the cycle occurred only after 6 hours of incubation, at prolactin doses of 5 and 10 micrograms/ml of the medium. Luteal cells obtained from corpora lutea with considerable physiological luteolysis (17th day of the cycle) did not react to the presence of prolactin in the incubation medium. The results showed that the effect of prolactin upon luteal cells depended on the intensity of steroidogenesis. Luteal cells on the 5th day of the estrous cycle produced progesterone in the amounts 34 +/- 9.1 ng/ml, on the 13th day: 62 +/- 11.5, and on the 17th day: 7.9 +/- 1.9. The effect of prolactin was most pronounced in case of cells on the 13th day of the cycle. These cells were characterized by the highest production of progesterone. The in vitro observations suggest the role of prolactin in inhibiting synthesis or release of DHT, T and E2 from luteal cells.

Animals↗
PubMed1985

Interrelationship between prolactin and progesterone in normal mammary gland growth in SHN virgin mice.

In order to clarify the interrelationship between prolactin and progesterone on normal mammary gland growth, SHN strain of virgin mice were given the pituitary grafting under the kidney capsule, the subcutaneous implantation of progesterone pellet or the bilateral ovariectomy singly or in combination at 40 days of age. All mice were killed 60 days after treatments and mammary end-bud formation, mammary DNA content and plasma prolactin level were examined. The single pituitary grafting elevated plasma prolactin levels in both the intact and the ovariectomized animals, however, mammary gland growth was enhanced only in the former. Progesterone pellet implantation also stimulated mammary gland growth in the intact mice, while prolactin changed little. Progesterone effect was nullified by ovariectomy associated with the decline in plasma prolactin level. The simultaneous single pituitary grafting and progesterone pellet implantation in combination or the grafting with three pituitaries restored mammary gland regression by ovariectomy. All findings have demonstrated that the manifestation of progesterone effect on mammary glands is dependent upon prolactin and that the role of prolactin is both direct on the glands and indirect through its luteotropic effect - through its stimulation of ovarian progesterone secretion.

Animals↗
PubMed2002

Atrial natriuretic hormone, vessel dilator, long acting natriuretic hormone, and kaliuretic hormone decrease circulating prolactin concentrations.

The present investigation was designed to test whether four cardiac hormones--long acting natriuretic hormone, vessel dilator, kaliuretic hormone and atrial natriuretic hormone--decrease the circulating concentration of prolactin in humans (n = 30). Vessel dilator, kaliuretic hormone, long acting natriuretic hormone and atrial natriuretic hormone decreased the circulating concentration of prolactin to 3 %, 31 %, 27 %, and 23 % of control values, respectively, at the end of their infusions when infused at concentrations of 100 ng/kg body weight per minute for 60 minutes (p < 0.001 for each). Vessel dilator, kaliuretic hormone, long acting natriuretic hormone and atrial natriuretic hormone had sustained effects on modulating prolactin's concentrations, with circulating concentrations of 1 %, 64 %, 28 %, and 2 % of control values (p < 0.001) 3 hours after stopping their respective infusions. These results suggest that there are four circulating prolactin-inhibitory hormones in addition to the hypothalamic mediators, dopamine and corticotropin-releasing hormone, which modulate prolactin release. These peptide hormones' ability to decrease circulating prolactin concentrations may be mediated in part by dopamine and in part by their demonstrated ability to decrease corticotropin-releasing hormone concentrations, which stimulate prolactin release.

Adult↗
PubMed2006

Increased prolactin in acute coronary syndromes as putative Co-activator of ADP-stimulated P-selectin expression.

Prolactin and leptin are newly recognized platelet co-stimulators due to enhancement of ADP-induced platelet aggregation. The aim of our study was to assess whether both hormones prolactin and leptin play a role as co-activators of platelet activation in patients with acute coronary syndromes. Twenty-one patients with acute coronary syndromes, 10 with stable angina pectoris and 10 controls were studied. Patients with acute coronary syndromes showed significantly higher prolactin and leptin values and a significant increased P-selectin expression on platelets compared to patients with stable angina pectoris or controls. However, patients with acute myocardial infarction as a subgroup of acute coronary syndromes showed the highest prolactin levels as well as ADP stimulated P-selectin expression. In the myocardial infarction subgroup prolactin values showed a significant correlation to ADP stimulated P-selectin expression on platelets (r (2)=0.41; p=0.025), whereas leptin was not correlated. Our data indicate an association between increased prolactin values and enhanced P-selectin expression on platelets in patients with acute coronary syndromes. Therefore, the stress hormone prolactin could be a co-stimulator of platelet activation in these patients. In contrast, the putative platelet activator leptin does not seem to play a major role in acute coronary syndromes.

Adenosine Diphosphate↗
PubMed1991

Polyamine influences on the prolactin stimulation of phosphoprotein synthesis in hydroxyurea synchronized MCF-7 human mammary epithelial cells.

The actions of prolactin on the rate of synthesis of an isoelectrically precipitable (pH 4.6) phosphoprotein fraction of the MCF-7 human mammary epithelial cell line were determined in cells synchronized at the G1:S interphase of the cell cycle employing hydroxyurea in a serum-free defined medium. Cells not allowed to enter the S-phase of DNA replication, by maintaining hydroxyurea in the incubation medium, exhibited an increased rate of [3H] leucine incorporation into the isoelectrically precipitable phosphoprotein fraction when exposed to prolactin and 1-5 mM spermidine. Cells released from the hydroxyurea induced synchrony exhibited an increased rate of [3H] leucine incorporation in response to prolactin when ornithine, putrescine, or spermidine were present. The polyamine spermine was ineffective in allowing prolactin's action on phosphoprotein synthesis. In synchronized cells released from the hydroxyurea block, prolactin was shown to effect an increased rate of phosphoprotein synthesis at the posttranscriptional G1 stage of the cell cycle. All prolactin responses were attained with physiological concentrations of the hormone. During and subsequent to the synchrony period with hydroxyurea, the presence or absence of insulin was found to be useful for the "staging" of the cell cycle to maintain cell synchrony and obtain prolactin effects on phosphoprotein synthesis.

Cell Cycle↗
PubMed1985

[Is amniotic fluid prolactin an osmoregulatory hormone of clinical importance?].

The present paper reports on the amniotic fluid prolactin concentrations in 61 pregnancies with undisturbed amniotic fluid volume from the 17th to the 41st week of pregnancy. The amniotic fluid prolactin concentrations reach a peak in the 19th week of pregnancy with a slight decrease to the 21st week. After a plateau from the 23rd to the 31st week of pregnancy, prolactin concentrations decrease to very low levels in late gestation. In pregnancies with disturbed amniotic fluid volume the prolactin concentrations are pathologically changed in comparison with "normal" pregnancies. The authors conclude that the amniotic fluid prolactin concentrations have a characteristic profile depending on the stage of pregnancy. From the pathologic prolactin concentrations in patients with hydramnios and otherwise pathologic pregnancies it may be concluded that prolactin is a clinically relevant osmoregulatory hormone for humans too.

Amniotic Fluid↗
PubMed2000

The effects of L-arginine on the release of prolactin from decidual explants in vitro.

OBJECTIVE: Our aim was to elucidate a role for the L -arginine-nitric oxide-cyclic guanosine monophosphate pathway in the control of decidual prolactin release in vitro. STUDY DESIGN: In decidua obtained from normal vaginal deliveries, we examined the effects of L -arginine; a stable analog of cyclic guanosine monophosphate, 8-bromo-cyclic guanosine monophosphate; and two nitric oxide synthase inhibitors, L -nitro arginine methyl ester (L -NAME) and L -nitro monomethyl arginine (L -NMMA) on the release of prolactin from decidual tissue in vitro. RESULTS: L -arginine, at 100 micromol/L, produced an increase in medium prolactin concentration after a 2-hour exposure; however, its inactive isomer, D -arginine, at the same concentration, did not. The increase in prolactin release initiated by L -arginine was sustained after a 24-hour incubation. In addition, 8-bromo-cyclic guanosine monophosphate (10 micromol/L) stimulated prolactin release. At 2 hours, the effects of L -arginine were reversed by L -NAME (100 micromol/L), which by itself was without effect. Incubation of tissue with L -NAME for 24 hours inhibited prolactin secretion (24 hours; P <.05, vs control); however, L -NMMA was without effect. CONCLUSIONS: These results suggest that the L -arginine-nitric oxide-cyclic guanosine monophosphate pathway is involved in the regulation of prolactin secretion by decidual tissue.

Arginine↗
PubMed1981

Prolactin induces release of a factor from membranes capable of stimulating beta-casein gene transcription in isolated mammary cell nuclei.

Crude microsomes from lactating rabbit mammary gland were incubated with prolactin. The incubation mixture was centrifuged and the supernatant was incubated with isolated mammary cell nuclei from lactating rabbits treated for 4 days by bromocryptin to antagonize prolactin and to deinduce casein gene transcription. Nuclei were incubated with HgCTP, and the newly synthesized mercurated RNA was isolated on SH-Sepharose columns. The content of beta-casein mRNA sequences in the fraction eluted with 2-mercaptoethanol was estimated with a [(3)H]cDNA probe obtained from partially purified beta-casein mRNA. The supernatant markedly stimulated beta-casein gene transcription but not 28S rRNA transcription. The same effect was obtained with other lactogenic hormones such as human growth hormone and ovine placental lactogen but was not observed with bovine growth hormone, insulin, parathyroid hormone, luteotropic hormone, or epidermal growth factor. Prolactin and human growth hormone were totally inactive when added directly to nuclei. The factor stimulating beta-casein gene transcription was also generated by membranes containing prolactin receptors such as those from liver, ovary, adrenals, and brain but not by membranes from heart, lung, and muscle, which do not bind prolactin. The factor stimulated beta-casein transcription when added to mammary nuclei from pseudopregnant or bromocryptin-treated lactating rabbits, in which the transcription rate is submaximal, but was ineffective on mammary nuclei prepared from untreated fully lactating rabbits. The factor was unable to induce beta-casein gene transcription in nuclei isolated from rabbit liver and reticulocytes. The factor did not stimulate the transcription of globin genes in nuclei isolated from reticulocytes or the transcription of mammary "housekeeping" genes evaluated by a cDNA probe prepared from total mRNA isolated from an unstimulated mammary gland. The transcription of beta-casein genes was abolished by adding alpha-amanitin to the medium in the presence or in the absence of the factor, indicating that the generation of mercurated beta-casein mRNA sequences depended upon the transcriptional activity of RNA polymerase II. The addition of the factor to the incubation mixture did not enhance total and alpha-amanitin-sensitive RNA synthesis. These data suggest that the binding of prolactin to its receptor in vitro induces the formation of a second messager, which specifically stimulates the transcription of prolactin-sensitive genes.

Animals↗