Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “PROLACTIN”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 649 records · Page 36Linked to original sources
PubMed2006

Prostate response to prolactin in sexually active male rats.

BACKGROUND: The prostate is a key gland in the sexual physiology of male mammals. Its sensitivity to steroid hormones is widely known, but its response to prolactin is still poorly known. Previous studies have shown a correlation between sexual behaviour, prolactin release and prostate physiology. Thus, here we used the sexual behaviour of male rats as a model for studying this correlation. Hence, we developed experimental paradigms to determine the influence of prolactin on sexual behaviour and prostate organization of male rats. METHODS: In addition to sexual behaviour recordings, we developed the ELISA procedure to quantify the serum level of prolactin, and the hematoxilin-eosin technique for analysis of the histological organization of the prostate. Also, different experimental manipulations were carried out; they included pituitary grafts, and haloperidol and ovine prolactin treatments. Data were analyzed with a One way ANOVA followed by post hoc Dunnet test if required. RESULTS: Data showed that male prolactin has a basal level with two peaks at the light-dark-light transitions. Consecutive ejaculations increased serum prolactin after the first ejaculation, which reached the highest level after the second, and started to decrease after the third ejaculation. These normal levels of prolactin did not induce any change at the prostate tissue. However, treatments for constant elevations of serum prolactin decreased sexual potency and increased the weight of the gland, the alveoli area and the epithelial cell height. Treatments for transient elevation of serum prolactin did not affect the sexual behaviour of males, but triggered these significant effects mainly at the ventral prostate. CONCLUSION: The prostate is a sexual gland that responds to prolactin. Mating-induced prolactin release is required during sexual encounters to activate the epithelial cells in the gland. Here we saw a precise mechanism controlling the release of prolactin during ejaculations that avoid the detrimental effects produced by constant levels. However, we showed that minor elevations of prolactin which do not affect the sexual behaviour of males, produced significant changes at the prostate epithelium that could account for triggering the development of hyperplasia or cancer. Thus, it is suggested that minute elevations of serum prolactin in healthy subjects are at the etiology of prostate abnormal growth.

Animals↗
PubMed2006

Matrix metalloproteases from chondrocytes generate an antiangiogenic 16 kDa prolactin.

The 16 kDa N-terminal fragment of prolactin (16K-prolactin) is a potent antiangiogenic factor. Here, we demonstrate that matrix metalloproteases (MMPs) produced and secreted by chondrocytes generate biologically functional 16K-prolactin from full-length prolactin. When incubated with human prolactin at neutral pH, chondrocyte extracts and conditioned medium, as well as chondrocytes in culture, cleaved the Ser155-Leu156 peptide bond in prolactin, yielding - upon reduction of intramolecular disulfide bonds - a 16 kDa N-terminal fragment. This 16K-prolactin inhibited basic fibroblast growth factor (FGF)-induced endothelial cell proliferation in vitro. The Ser155-Leu156 site is highly conserved, and both human and rat prolactin were cleaved at this site by chondrocytes from either species. Conversion of prolactin to 16K-prolactin by chondrocyte lysates was completely abolished by the MMP inhibitors EDTA, GM6001 or 1,10-phenanthroline. Purified MMP-1, MMP-2, MMP-3, MMP-8, MMP-9 and MMP-13 cleaved human prolactin at Gln157, one residue downstream from the chondrocyte protease cleavage site, with the following relative potency: MMP-8 > MMP-13 > MMP-3 > MMP-1= MMP-2 > MMP-9. Finally, chondrocytes expressed prolactin mRNA (as revealed by RT-PCR) and they contained and released antiangiogenic N-terminal 16 kDa prolactin (detected by western blot and endothelial cell proliferation). These results suggest that several matrix metalloproteases in cartilage generate antiangiogenic 16K-prolactin from systemically derived or locally produced prolactin.

Amino Acid Sequence↗
PubMed1987

Evidence that exteroceptive stimuli other than suckling have no major effect on plasma prolactin in lactating rats.

The ability of exteroceptive stimuli from pups to increase plasma prolactin in lactating dams was investigated. Prolactin profiles were measured during 30 min of suckling followed by complete or partial separation from pups. Prolactin profiles were also measured subsequent to complete or partial isolation from pups in dams which had been with pups permanently before the experiment. In addition, plasma prolactin was measured in dams which after a night of isolation were partially united with pups. Finally, the effect of ether stress on prolactin profiles after interruption of suckling by pups was determined. Vigorous suckling after a period of isolation induced a sharp increase of plasma prolactin. Subsequent to pup removal, either partial or complete, prolactin profiles showed a widespread variation. Also dams which before experimentation were kept permanently with pups, showed a great variation in prolactin profiles subsequent to either complete or partial separation from pups. Plasma prolactin either decreased rapidly or gradually. In several dams a rapid or a gradual decline of plasma prolactin was interrupted by one or more episodes of prolactin release. Partial reunion with pups after a night of isolation, either in mid-lactation or in late lactation, did not induce a rise of plasma prolactin. It is concluded that exteroceptive stimuli from pups are not effective as prolactin releasing signal. Because ether stress did not induce a steep rise of plasma prolactin, we conclude that the episodic rises of plasma prolactin in dams, subsequent to partial or complete removal of pups, are due to spontaneous activity of the hypothalamo-pituitary system.

Animals↗
PubMed1992

Effect of somatostatin on prolactin in rainbow trout (Oncorhynchus mykiss) pituitary cells in primary culture.

To study the control of prolactin secretion in fish, an in-vitro technique using a monolayer cell culture system of rainbow trout pituitary glands was developed. Such secretion was characterized by measurement of both prolactin release and prolactin mRNA content using a trout prolactin cDNA as a probe. This cell culture technique, already used to study the regulation of gonadotrophin secretion in rainbow trout, was further validated by measuring total DNA and protein content. Both parameters appeared to be stable after 2 days of culture. Studying the effect of somatostatin (SRIF) on prolactin cells indicated that a maximal inhibitory effect (62%) was observed after 24 h of treatment. Significant inhibition of prolactin release was obtained for SRIF doses ranging from 50 nM to 1 microM. However, in the same experiment, SRIF was much more potent as an inhibitor of growth hormone release. Short-term (< 12 h) incubation with SRIF did not induce a significant change in prolactin release, whereas growth hormone release was reduced at as early as 1 h after SRIF exposure. SRIF did not have a significant effect on total prolactin content or prolactin mRNA levels, suggesting the absence of an effect on prolactin synthesis. No increase in the magnitude of the inhibitory effect of SRIF was observed when using pituitary cells from immature, mature male or mature female trout. When comparing effects on primary cultures containing cells from the whole pituitary with a prolactin cell-enriched population, SRIF appeared to have the same inhibitory effect on prolactin release, supporting a direct action of SRIF on prolactin cells. These results provide further support for SRIF being a prolactin-inhibiting factor in rainbow trout and acting as a modulator of a dominant stimulatory control of prolactin release.

Actins↗
PubMed1980

Differential sensitivity of prolactin release to dopamine and thyrotrophin-releasing hormone in intact and pituitary stalk-sectioned rhesus monkeys.

The effects of dopamine and thyrotrophin-releasing hormone (TRH) on prolactin release was studied in 14 intact and six pituitary stalk-sectioned (SS) female rhesus monkeys (Macaca mulatta). Baseline prolactin values were ninefold higher in SS animals (149+/-16 ng/ml) than in intact animals (16+/-1 ng/ml). Prolactin release after intravenous administration of TRH in doses of 0, 125, 250, 500 and 1000 ng revealed that SS monkeys were more sensitive to the prolactin-releasing activity of this tripeptide than were intact animals. A significant (P less than 0.05) increment in serum prolactin was observed in SS animals after injection of 125 ng TRH whereas 250 ng was required to raise prolactin levels in the circulation of intact animals significantly (P less than 0.05). Furthermore, at each comparable dose level of TRH, the increment in serum prolactin was distinctly greater in SS animals than in intact monkeys. Infusion of dopamine at the rate of 10 microgram/kg body weight per min significantly (P less than 0.05) lowered prolactin levels within 60 min in intact animals and no further decline was observed with 20 or 40 microgram dopamine. Serum prolactin concentrations were not affected by saline infusion or by 5 microgram dopamine. Infusion of dopamine at the rate of 10 microgram/kg body wt per min also resulted in significant (P less than 0.01) suppression of serum prolactin in SS animals. This prolactin decrease was apparent within 40 min. Prolactin release after 500 ng TRH was less in these dopamine-treated SS monkeys than after an infusion of saline. Higher doses of dopamine (20 and 40 microgram) did not cause a further decrease in basal serum prolactin concentrations, but these two dopamine treatments blocked the increase in prolactin elicited by 500 ng TRH. The results suggest that the removal of hypothalamic influence, possibly related to the effects of dopamine, renders the pituitary gland more sensitive to the prolactin-releasing action of TRH.

Animals↗
PubMed1980

Demonstration of prolactin-releasing activity in the pigeon.

The capacity of the pigeon pituitary gland to release prolactin was investigated in vivo, to evaluate its hypothalamic regulation and to establish the dominant hypothalamic factor for prolactin secretion. After 3 days of systemic administration of some physiological and pharmacological agents, followed by 2 consecutive days of local intradermal injections of prolactin into their crop sacs, the crop mucosa was scraped, dried and weighed. The substances tested were: oestradiol and tamoxifen (antioestrogen), thyrotophin-releasing hormone (TRH) and anti-TRH serum, perphenazine (releases prolactin in mammals) and bromocriptine (suppresses prolactin in mammals). Prolactin and anti-prolactin serum were tested as controls. While prolactin markedly proliferated and anti-prolactin serum significantly inhibited the mucosal weight, oestradiol, TRH and perphenazine dramatically depressed proliferation of the mucosa, suggesting that prolactin secretion was inhibited. Tamoxifen, anti-TRH serum and bromocriptine significantly increased the proliferation of the crop mucosa, indicating an increase in the endogenous release of prolactin. Since the effect of these substances on prolactin release in the pigeon is the opposite from their well-established effects in mammals, these results suggest, in a specific and homologous model, that the dominating regulator for prolactin in the pigeon is contrary to that in the mammal, namely prolactin-releasing factor, and that TRH may play a significant role in the physiological regulation of prolactin secretion.

Animals↗
PubMed1987

The occurrence of pituitary prolactin depletion-transformation in lactating rats: dependence on strain of rats, homogenization conditions and method of assay.

The objectives of this study were to determine whether pre-release transformation (depletion) of pituitary prolactin occurs as the result of suckling to the same extent in several strains of lactating rats, the molecular nature of the transformed hormone, whether the quantity of transformed (depleted) prolactin recovered is dependent upon the type of homogenization buffer used and whether the method of assay influences the extent to which transformed prolactin is detected. During the course of these experiments other factors such as the methods of handling and storing pituitaries and homogenates were also found to influence the amount of prolactin recovered. The results indicated that transformation of prolactin is a very labile event which is affected by many factors. Strain and supplier of rats was critical to the observation of suckling-induced depletion of prolactin, with Spartan- and Holtzman-derived Sprague-Dawley strains exhibiting the most consistent responses. When transformation was observed, it mattered little which buffer was used for homogenization; however, alkaline or acidic buffers extracted more prolactin than did neutral buffers. Triton X-100 also significantly enhanced the efficiency of extraction by neutral buffers. Maintaining pituitaries on dry ice immediately upon removal from the animal increased the amount of prolactin recovered, as did freezing the homogenate for 1-5 weeks before assay. The addition of the protease inhibitor, benzamidine hydrochloride, did not affect the pituitary content of prolactin. Assay of prolactin by polyacrylamide electrophoresis and densitometry yielded more prolactin than either radioimmunoassay or the Nb2 lymphoma bioassay. The molecular nature of pituitary prolactin, extracted at neutral pH, as judged by gel filtration was altered slightly but consistently by suckling, such that large molecular forms increased at the expense of the smallest molecular form. We conclude from these studies that great care must be exercised when attempting to characterize dynamic changes in pituitary prolactin content in lactating rats. Strain and supplier of rats, methods of handling and storing pituitaries, types of buffers used for homogenization and methods of assay all influence the amount of prolactin recovered and can influence the extent to which rapid changes in pituitary prolactin are detected.

Animals↗
PubMed1992

Concanavalin-A-bound and -unbound prolactin in normal and hyperprolactinaemic rats.

Concanavalin-A (Con-A)-bound and -unbound forms of prolactin were studied in female Wistar-Furth rats, both normal and with hyperprolactinaemia induced by treatment with oestrogen or a prolactinoma graft. In normal rats, Con-A-bound prolactin was the major circulating form (more than 50%) and a minor pituitary component (less than 10%), essentially as 25 kDa prolactin. In oestrogen-treated rats, plasma prolactin levels were 100-fold higher and pituitary weight was fivefold higher than in the controls, but total pituitary prolactin content was unmodified. Under oestrogen, Con-A-bound prolactin represented about one-third of the total hormone levels in the plasma and less than 10% in the pituitary. In the pituitary, bound prolactin was found essentially as 25 kDa and unbound prolactin as 22, 30 and 40-45 kDa. A similar increase in plasma prolactin levels was induced 6 months after the graft of a prolactinoma. Pituitary weights and total pituitary prolactin contents were slightly decreased. Plasma and pituitary Con-A-bound prolactin levels were similar to those observed in oestrogen-treated rats. On the other hand, unbound prolactin was only present as a 22 kDa monomer. In the tumour, Con-A-bound prolactin (essentially as 25 kDa prolactin) represented one-third of the total hormone level and unbound prolactin was composed of the 22 and 45 kDa forms, this latter form being partially transformed into 22 kDa by heating.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1997

Opioidergic regulation of prolactin secretion during pregnancy: role of ovarian hormones.

We have recently demonstrated the existence of a neuromodulatory regulation of prolactin secretion by the opioid system showing a paradoxical opioid-induced prolactin suppression at the end of pregnancy. The aim of this study was to determine a possible interaction between the opioid system and ovarian hormones on the release of prolactin during pregnancy. Serum prolactin levels measured at 1800 h were significantly higher on days 3 and 6 of pregnancy when compared with the other days of gestation. These increases in serum prolactin were reduced significantly by naloxone (2 mg/kg) administered at 1730 h and by RU-486 (10 mg/kg) administered at 0800 h. The response induced by RU-486 was potentiated by naloxone only on day 3. On days 7, 13 and 16, prolactin secretion was not modified by RU-486 and/or naloxone treatment. In RU-486 pretreated rats, naloxone administration increased serum prolactin levels only on day 16 of pregnancy. Interestingly, progesterone treatment (0.5 mg/rat) on days 13, 14 and 15 of pregnancy prevented the high increase in serum prolactin induced by RU-486 and naloxone on day 16 of pregnancy. The progressive increase and decrease of serum progesterone concentration during pregnancy was not modified by naloxone treatment. The participation of oestrogen in the regulation of prolactin secretion by the opioid system on days 3, 16 and 19 was examined by treating these groups of rats with oestradiol benzoate or tamoxifen citrate. Oestradiol (2 micrograms/rat) significantly increased serum prolactin levels on day 3 and naloxone administration did not modify this increase. No effect was observed after oestradiol (5 micrograms/rat) and naloxone treatment on days 16 and 19 of pregnancy. Oral administration of tamoxifen (500 micrograms/kg) the previous day did not modify the serum prolactin concentration measured at 1800 h in oil-treated rats on days 3, 16 and 19 of pregnancy. The antioestrogen completely abolished the naloxone-induced prolactin secretion on day 16 in rats pretreated with RU-486 but no effect was observed on day 19. When tamoxifen was administered on days 14 and 15 of pregnancy, the high serum prolactin levels on day 19 induced by treatment with RU-486 and naloxone were significantly reduced. In conclusion, these results provide an important new insight into the existence of a dual neuromodulatory regulation of prolactin secretion by the opioid system during pregnancy. After a stimulatory action during the first days, there is a change to an inhibitory control at the end of pregnancy, starting around day 16. Moreover, the activation of the inhibitory modulation of the opioid system on prolactin secretion on days 16 and 19 of pregnancy seems to be mediated by changes in the oestrogen and progesterone action.

Animals↗
PubMed1992

An immunoradiometric assay for squirrel monkey prolactin.

Determination of immunoreactive prolactin in squirrel monkeys has been hampered by the lack of specific antibodies. We investigated the adaptability of a commercially available immunoradiometric assay for human prolactin, which employs two separate monoclonal antibodies (MAb I and II) to human prolactin, to determine the presence of squirrel monkey prolactin. We found that immunoreactivity curves for prolactin in squirrel monkey pituitary homogenates and serum were parallel to human prolactin standards, suggesting that the epitopes recognized by these antibodies were common to both human and squirrel monkey prolactin. Both nonglycosylated (23 kD) and glycosylated (26 kD) forms of squirrel monkey prolactin were detected in squirrel monkey pituitary homogenates by Western blot analysis using [125I]-MAb II. Neither sheep nor rat prolactin was recognized by Western blot analysis, indicating that the assay may be specific for primate prolactins. We examined the effect of ketamine HCl, an anesthetic that has been shown to elevate serum prolactin levels in other primates, on prolactin secretion in squirrel monkeys. Serum prolactin levels increased greater than fourfold after the administration of ketamine HCl (30 mg/kg b.w., i.m.) compared with control levels. Serum prolactin levels were unaffected by anesthesia with pentobarbital sodium (15 mg/kg b.w., i.v.). This assay provides a reliable and sensitive method for determining immunoreactive squirrel monkey prolactin.

Animals↗
PubMed1993

Characterization of a monoclonal antibody against human prolactin receptors.

Tamoxifen is the first line of therapy for most human breast cancers. It not only works through the estrogen receptor but also can directly affect the binding of prolactin to its receptor. To define this latter mechanism, the nature of the prolactin receptor needs to be clearly defined. Monoclonal antibody (MAb) B6.2, and IgG1 raised against a membrane-enriched fraction from metastatic human breast cancer cells, was as effective as polyclonal anti-prolactin receptor antibody in inhibiting the binding of prolactin to membranes from human tissue and to T47D human breast cancer cells. Control MAbs, MOPC-2I and the anti-NCA B1.1 MAb, had no effect on binding. Epidermal growth-factor receptors on these same cells were unaffected by B6.2. Prolactin-induced growth of the T47D cells was blocked by addition of B6.2 to the media while the control antibodies were without effect. Specific binding of B6.2 to the cells was completely inhibited by prolactin. Binding of both prolactin and B6.2 was inhibited by growing the T47D cells in the presence of tunicamycin A1 under conditions where protein synthesis was not affected but glycosylation of proteins was. An affinity column of B6.2 was used to purify its antigen from T47D cells. The primary purification product, a M(r) 90,000 protein, specifically bound the lactogenic hormones human prolactin, human growth hormone and ovine prolactin but not the somatogenic hormone, bovine growth hormone and was precipitated by the polyclonal anti-prolactin receptor antibody but not by control MAbs. When tryptic and V8 digests of the B6.2 antigen and purified prolactin receptors were compared, identical electrophoretic profiles were obtained. Mouse 3T3 cells, when stably transfected with the gene for the long form of the human prolactin receptor, reacted with B6.2 and polyclonal anti-prolactin receptor antibody. Parental 3T3 cells, devoid of prolactin receptors, were negative for all antibodies tested. Thus, MAb B6.2 provides a useful tool for further studies on purification and characterization of these receptors from human tissues and may provide new insights into treatment for breast cancer.

3T3 Cells↗
PubMed1992

Prolactin localization, binding, and effects on peroxidase release in rat exorbital lacrimal gland.

Prolactin immunoreactivity has been detected in human tears and in lacrimal glands, and it has been suggested that this hormone might be a modulator of lacrimal secretion as well as a component of lacrimal gland fluid. The present study was designed to confirm the immunocytochemical localization of prolactin in the rat lacrimal gland, to determine the source of the prolactin, and to evaluate the acute effects of prolactin on lacrimal secretory function. We have confirmed that prolactin-like immunoreactivity is present in secretory vesicles of acinar cells of male and female Sprague-Dawley rats. Prolactin message was present at detectable levels in RNA extracts of lacrimal glands from males, indicating that at least a component of the prolactin-like immunoreactivity was the product of synthesis within the lacrimal glands. Crude membrane fractions from acini isolated from males bound 43.1 +/- 3.2 femtomoles prolactin/mg protein (mean +/- standard error of the mean; n = 6), which was significantly (P less than 0.01) more than comparable fractions from females (15.4 +/- 2.4 fmoles/mg protein, n = 6). Preincubating membranes at 65 degrees for 20 min to release endogenous ligands increased prolactin binding to 84.8 +/- 20.8 fmoles/mg protein for males and 63.8 +/- 17.4 fmoles/mg protein for females (P greater than 0.1), suggesting that, on average, similar numbers of receptors are expressed in acinar cells of male and female rats but a larger fraction of the receptors is occupied by endogenous prolactin-like peptides in females. Because prolactin binding triggers prolactin receptor internalization in various cell types, we propose that the prolactin-like immunoreactivity in lacrimal acinar cells of females has been accumulated from the circulation, while the immunoreactivity seen in males results, at least in part, from de novo synthesis. Ovine prolactin at concentrations of 10-20 ng/ml inhibited carbachol-induced peroxidase release by 19.6% +/- 6.9% (n = 8, P less than 0.02) but failed to alter peroxidase release in the absence of carbachol. These observations suggest that prolactin might function as an endocrine, paracrine, or autocrine modulator in the lacrimal gland.

Animals↗
PubMed1977

Prolactin binding to R3230AC mammary carcinoma and liver in hormone-treated and diabetic rats.

Specific 125I-labeled prolactin binding was measured in membrane particles prepared from R3230AC mammary carcinoma and liver of tumor-bearing Fischer rats after either prolactin, estrogen, or lergotrile mesylate treatment, or after the induction of diabetes by streptozotocin. Hormone binding to tumors was decreased by treatment with prolactin (0.5 or 1 mg/day) or estradiol valerate (7.5 mg/kg/week). In contrast, prolactin treatment did not affect prolactin binding to liver membrane particles, but estradiol valerate treatment resulted in a four-fold increase in prolactin binding to this tissue. Lergotrile mesylate, which lowers plasma prolactin levels, did not affect tumor growth or prolactin binding to either tumor or liver. Prolactin binding to both tumor and liver was significantly reduced in diabetic rats, suggesting that insulin may play an important role in controlling tissue sensitivity to prolactin. Specific binding of 125I-labeled prolactin to enzymatically dissociated cells from R3230AC tumors was demonstrated in vitro. The binding capacity of the cells was found to be of the same order of magnitude as the binding capacity in membrane preparations when appropriate corrections were applied for yields of cells and membranes. R3230AC tumor, which is responsive to prolactin appears therefore to be a useful model system for further study aimed at elucidation of growth and metabolic response to the hormone prolactin in breast cancer.

Acetonitriles↗
PubMed1980

Immunocytochemical analysis of prolactin production by monolayer cultures of GH3 rat anterior pituitary tumor cells: I. Long-term effects of stimulation with thyrotropin-releasing hormone (TRH).

Thyrotropin-releasing hormone (TRH) stimulates prolactin production in cultured GH3 rat anterior pituitary tumor cells. For correlation of cell-by-cell prolactin distribution and intracellular hormone concentration, GH3 cells were grown to plateau-phase density on glass coverslips in plastic dishes. Acetone-fixed, cell-bearing coverslips were stained for prolactin by an immunoglobulin-peroxidase bridge technique (Mason et al., '69); cells on the plastic dishes were assayed for prolactin (microcomplement fixation immunoassay, Tashjian, '73) and protein content. Intracellular prolactin, unaffected quantitatively by acetone fixation and choice of substratum, was localized immunocytochemically by a granular brown precipitate, abolished if anti-prolactin serum was preabsorbed with rat prolactin or omitted from the protocol. Intracellular prolactin was maximized with colchicine (5.0 X 10(-6) M; final 3 hr of incubation) in control and TRH-treated (10 ng/ml; 48 hr) GH3 cell cultures. A total of 8,500 cells were classified by light microscopy as unstained, heavily (H) or moderately (M) stained for prolactin. In controls, 35% of cells were prolactin-positive: 5% H and 29% M. After TRH, 45% were positive: 7% H and 38% M. Although prolactin-positive cells were unevenly distributed, comprising 25% to 46% of cells in individual microscopic fields in controls, TRH increased the proportion of M cells in all areas. TRH treatment raised prolactin levels to 450% of control, but mathematical analysis attributed less than 30% of the increase to new prolactin-positive cells. We conclude that TRH acts on GH3 cultures principally by raising the mean hormone content of individual positive cells rather than by increasing the proportion of cells committed to prolactin production.

Animals↗
PubMed1985

Stimulus requirements for prolactin and LH secretion in incubating ring doves.

To study the regulation of prolactin secretion and incubation behavior during breeding, stimuli available during the prehatching period were manipulated, and plasma prolactin and LH and pituitary prolactin concentrations were assayed. Four groups were compared: (a) nest and eggs removed (b) eggs replaced with infertile eggs, (c) eggs replaced with infertile eggs and partners separated, and (d) unmanipulated controls. The increase in prolactin secretion that normally occurs at the end of incubation was reversed when the nest and eggs were removed but was unaffected by the absence of the mate. Prolactin secretion was not maintained in males sitting beyond the normal incubation period (on infertile eggs), while it was maintained in females but only in the presence of the mate. In the control birds, the increase in plasma prolactin was accompanied by an increase in pituitary content; while in the manipulated groups, an inhibition of prolactin secretion was associated with a transient increase in pituitary content. Plasma LH levels were low in control birds during the time of high prolactin secretion, and in all groups where the disruption of normal breeding stimuli caused an early fall in prolactin, there was a concomitant increase in LH secretion. In animals which had been separated from their mates and provided with a nest bowl and eggs, continuous observations of incubation behavior were made and plasma was sampled every third day. Parallel changes in prolactin and sitting behavior occurred in some of the animals, while others continued to incubate after prolactin had declined. In no instance did an animal which maintained high prolactin show a decline in incubation. This suggests that prolactin can serve to maintain incubation, while incubation does not necessarily stimulate prolactin secretion at this phase of the breeding cycle.

Animals↗
PubMed1981

Newly synthesized prolactin is preferentially secreted by the adenohypophysis in a primary cell culture system.

A relationship between prolactinin synthesis and release was studied using a dispersed adenohypophysial cell primary-culture system. Newly synthesized prolactin was identified by the amount of prolactin-associated tritium activity. No new prolactin was synthesized during a 1-h incubation with 3H-Leu. After 4 h a significant amount of newly synthesized prolact was released into the medium but no labelled prolactin was detected in the cells. Radioimmunoassayable prolactin, however, was equally divided between the cells and the medium indicating that the newly synthesized prolactin was preferentially secreted. In contrast, approx. 2 times more newly labelled GH was found in the cell extract than in the medium while by GH-radioimmunoassay, the cells contained twice as much GH as the medium in the control group. During the 1-h incubation, estradiol (1.0 ng/ml) increased prolactin content in the medium, although no newly synthesized prolactin appeared in the medium or the cells. During the 4-h incubation period significantly more labelled prolactin was released into the medium in the presence of estradiol (1.0 ng/ml) than in the control. These results indicate that (1) estradiol has a stimulatory effect on prolactin secretion, (2) estradiol activates a prolactin-synthesis mechanism, (3) newly synthesized prolactin is preferentially released, and (4) the rate of release of newly synthesized prolactin and GH having different mechanisms of hypothalamic control, an inhibiting factor for the prolactin and a releasing factor for GH.

Animals↗
PubMed1984

Prolactin production from proliferative phase leiomyoma.

In vivo and in vitro endometrial stromal synthesis of prolactin occurs after progesterone-induced decidualization. Synthesis of prolactin by myometrium in vitro suggests that cells whose embryologic origin is the loose mesenchyme surrounding the paramesonephric ducts may retain the capacity to synthesize prolactin. Since physiologic myometrial synthesis of prolactin has not been demonstrated in vivo, prolactin genome expression in pathologic conditions was considered. Follicular phase leiomyomas were diced to 8 mm3 and cultured in Dulbecco's modified Eagle's medium (DMEM) with either no hormones, estradiol 200 pg/ml, progesterone 20 ng/ml, or estradiol and progesterone. Media were sampled and changed every other day for 8 days, followed by culture in tritium-labeled leucine DMEM for 2 days. Portions of leiomyomas were homogenized for initial prolactin content, and all samples were assayed for prolactin by radioimmunoassay. Follicular phase leiomyomas contained prolactin (47 +/- 15 ng/gm) in excess of normal serum values. Synthesis was demonstrated during all time periods from leiomyomas not exposed to progesterone. Progesterone variably suppressed the synthesis of prolactin until after 144 hours of culture. Determination of molecular weight on a 60 by 1.5 cm Sephadex G-100 column revealed identical estimates for pituitary, decidual, and leiomyoma prolactin. Tritium-labeled leucine incorporation into prolactin was confirmed by immunoprecipitation of Sephadex G-100 column fractions. Similar antigenicity was confirmed by parallel dilution curves for pituitary, decidual, and leiomyoma prolactin. Preliminary bioactivity in lymphoma proliferation assays confirmed prolactin activity. The conclusion reached was that proliferative phase leiomyomas contained elevated prolactin presumably secondary to in vivo synthesis. This synthesis was confirmed in vitro.

Culture Techniques↗
PubMed2003

The tertiary structure and backbone dynamics of human prolactin.

Human prolactin is a 199-residue (23 kDa) protein closely related to growth hormone and placental lactogen with properties and functions resembling both a hormone and a cytokine. As a traditional hormone, prolactin is produced by lactotrophic cells in the pituitary and secreted into the bloodstream where it acts distally to regulate reproduction and promote lactation. Pituitary cells store prolactin in secretory granules organized around large prolactin aggregates, which are produced within the trans layer of the Golgi complex. Extrapituitary prolactin is synthesized by a wide variety of cells but is not stored in secretory granules. Extrapituitary prolactin displays immunomodulatory activities and acts as a growth factor for cancers of the breast, prostate and tissues of the female reproductive system. We have determined the tertiary structure of human prolactin using three-dimensional (3D) and four-dimensional (4D) heteronuclear NMR spectroscopy. As expected, prolactin adopts an "up-up-down-down" four-helical bundle topology and resembles other members of the family of hematopoietic cytokines. Prolactin displays three discrete structural differences from growth hormone: (1) a structured N-terminal loop in contact with the first helix, (2) a missing mini-helix in the loop between the first and second helices, and (3) a shorter loop between the second and third helices lacking the perpendicular mini-helix observed in growth hormone. Residues necessary for functional binding to the prolactin receptor are clustered on the prolactin surface in a position similar to growth hormone. The backbone dynamics of prolactin were investigated by analysis of 15N NMR relaxation phenomena and demonstrated a rigid four-helical bundle with relatively mobile interconnecting loops. Comparison of global macromolecular tumbling at 0.1mM and 1.0mM prolactin revealed reversible oligomerization, which was correlated to dynamic light scattering experiments. The existence of a reversible oligomerization reaction in solution provides insight into previous results describing the in vitro and in vivo aggregation properties of human prolactin.

Amino Acid Sequence↗