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PubMed1991

A comparison of plasma prolactin levels in young female Long-Evans and Holtzman rats as measured by Nb2 lymphoma bioassay and radioimmunoassay.

This study was conducted to determine the plasma levels of prolactin in prepubertal and young, postpubertal, proestrus rats of mammary tumor-susceptible (Sprague-Dawley) and tumor-resistant (Long-Evans) strains using a sensitive bioassay-Nb2 lymphoma cell replication. Prepubertal Long-Evans rats had significantly higher levels of prolactin than did Holtzman Sprague-Dawley rats of the same age. Likewise, Long-Evans rats secreted significantly more prolactin into the blood on the afternoon and evening of proestrus than did Holtzman rats. Finally, ovariectomized Long-Evans rats released more prolactin into the blood at 1 day, but not at 8 or 15 days, of treatment with diethylstilbestrol. Prolactin levels determined by conventional radioimmunoassay and by bioassay were similar except on the afternoon of proestrus, when, in both strains of rats, the bioassay to radioimmunoassay ratio increased significantly above 1.0 during the late evening. In addition, the ratio was significantly less than 1.0 in the early and late afternoon in the Holtzman rats, but not Long-Evans rats. These data indicate that a strain of rats that is resistant to experimentally induced mammary cancer has higher prolactin levels in the blood than does a strain that is susceptible to mammary cancer at a time when mammary gland growth is rapid. Furthermore, there are times during the proestrus prolactin surge when the bioassay yielded higher and lower values of prolactin than radioimmunoassay of the same samples, suggesting functional heterogeneity of prolactin that may impact on mammary gland or other target tissue function.

Animals↗
PubMed1996

Effects of luteinizing hormone-releasing hormone on pulsatile prolactin secretion in adult hyperprolactinemic female rats.

Regulation of prolactin secretion involves complex interactions of multiple inhibitory and stimulatory factors. Among them, luteinizing hormone-releasing hormone (LHRH) has been shown, when analyzed in single samples, to exert both stimulatory and inhibitory influences on prolactin secretion. In the present study, we have further examined the effects of LHRH on prolactin secretion by studying the pulsatile pattern of the hormone after the administration of the neuropeptide. For this purpose, adult sham-operated and pituitary-grafted female rats, exhibiting diestrus smears were bled for 3 hr during the morning (1030 to 1330 hr). Two pulses of LHRH (10 ng/kg body wt) were administered 60 and 120 min after starting the bleeding period. Pituitary grafting increased the mean serum prolactin levels, absolute amplitude of the hormone peaks, and its mean half-life, compared with control animals. In sham-operated rats, LHRH administration diminished mean serum prolactin levels, the absolute pulse amplitude and frequency of prolactin peaks. In pituitary-grafted animals, LHRH administration only decreased the pulse frequency of prolactin peaks. These data suggest that LHRH significantly suppressed pulsatile prolactin secretion, and that this effect was blunted by exposure to previously elevated circulating prolactin levels.

Animals↗
PubMed1996

Possible interactions of cyclosporine and hyperprolactinemia modulating the episodic secretion of prolactin.

The interrelationship between the effects of prolactin and cyclosporine (CsA) appears to be very complex and until now poorly understood. The aim of the present work was to analyze whether chronic treatment with CsA could modify the episodic secretion of prolactin in male rats and whether the presence of an ectopic pituitary could counteract the effects of the drug on the pulsatile secretion pattern of this hormone. At 30 days of age, male rats were implanted with one anterior pituitary under the kidney capsule or where sham-operated. Both pituitary-grafted and sham-operated rats were injected sc for 30 days with the vehicle or CsA (5 mg/kg/day), beginning on the day of surgery. Pituitary grafting and/or CsA administration changed the pulsatile secretion pattern of prolactin. In pituitary-grafted male rats, mean serum prolactin levels, absolute pulse amplitude, and half-life of the hormone increased, while the pulse frequency decreased, compared with the values found in sham-operated rats. CsA administration to sham-operated rats increased the relative amplitude of prolactin peaks and diminished the half-life of the hormone, compared with rats of the same group treated with vehicle. However, CsA treatment in pituitary grafted rats led to lower mean serum prolactin levels and absolute amplitude, while the frequency, duration, and relative amplitude of prolactin pulses were not modified. Plasma prolactin levels did not change in control animals, whereas a reduction in circulating values of the hormone was found in pituitary grafted animals. These data suggest that CsA modifies the pulsatile secretory pattern of prolactin in pituitary-grafted male rats. The different effects observed in the control and pituitary-grafted animals might be due to a direct effect of the drug on the ectopic lactotrophs that are submitted to local regulatory influences different from those of the in situ pituitary which are submitted to the regulatory influence of the hypothalamus.

Animals↗
PubMed2004

Mechanism of prostaglandin (PG)E2-induced prolactin expression in human T cells: cooperation of two PGE2 receptor subtypes, E-prostanoid (EP) 3 and EP4, via calcium- and cyclic adenosine 5'-monophosphate-mediated signaling pathways.

We previously reported that prolactin gene expression in the T-leukemic cell line Jurkat is stimulated by PGE(2) and that cAMP acts synergistically with Ca(2+) or protein kinase C on the activation of the upstream prolactin promoter. Using the transcription inhibitor actinomycin D, we now show that PGE(2)-induced prolactin expression requires de novo prolactin mRNA synthesis and that PGE(2) does not influence prolactin mRNA stability. Furthermore, PGE(2)-induced prolactin expression was inhibited by protein kinase inhibitor fragment 14-22 and BAPTA-AM, which respectively, inhibit protein kinase A- and Ca(2+)-mediated signaling cascades. Using specific PGE(2) receptor agonists and antagonists, we show that PGE(2) induces prolactin expression through engagement of E-prostanoid (EP) 3 and EP4 receptors. We also found that PGE(2) induces an increase in intracellular cAMP concentration as well as intracellular calcium concentration via EP4 and EP3 receptors, respectively. In transient transfections, 3000 bp flanking the leukocyte prolactin promoter conferred a weak induction of the luciferase reporter gene by PGE(2) and cAMP, whereas cAMP in synergy with ionomycin strongly activated the promoter. Mutation of a C/EBP responsive element at -214 partially abolished the response of the leukocyte prolactin promoter to PGE(2), cAMP, and ionomycin plus cAMP.

Adjuvants, Immunologic↗
PubMed2001

Risperidone added to clozapine: impact on serum prolactin levels.

BACKGROUND: Several years ago, we reported that the addition of risperidone to clozapine improved response in some patients with schizophrenia. Risperidone, in general, is well tolerated when administered as monotherapy, but has been linked to a persistent elevation of serum prolactin and associated symptoms. The goal of this study was to determine whether the addition of risperidone to clozapine results in an elevation of serum prolactin levels in patients with chronic schizophrenia or schizoaffective disorder. METHOD: Twenty patients on clozapine-risperidone combination therapy were matched for age and gender with 20 patients treated with clozapine monotherapy. Demographic information was gathered along with clozapine and risperidone dose and the length of time on risperidone. Serum prolactin levels were measured from a single blood sample. RESULTS: The 2 groups did not differ in age, race, gender, diagnosis, age at clozapine initiation, age at onset, Abnormal Involuntary Movement Scale scores, or clozapine dose. The mean +/- SD serum prolactin level was 8.42+/-4.17 ng/mL for clozapine monotherapy patients and 35.76+/-17.43 ng/mL for combination therapy patients. The 2 medication categories showed a significant difference in log prolactin values (t = -7.97, df = 38, p < or = .0001). Sixteen combination therapy patients (80%) exhibited elevated prolactin levels (range for entire group, 9.7-69.8 ng/mL) while only 2 clozapine monotherapy patients (10%) exhibited prolactin elevation levels (range for entire group, 2.4-20.2 ng/mL; df = 1, p < .0001). CONCLUSION: The combination of risperidone and clozapine appears to result in a moderate elevation of serum prolactin levels. Additionally, controlled prospective studies are needed to clarify the risks of long-term elevations of serum prolactin level.

Adult↗
PubMed2000

[Plasma prolactin concentration and the effect of metergoline in pseudopregnant Afghan hounds].

The effects of metergoline, a 5-hydroxytryptamine (serotinin) antagonist, on the plasma concentrations of prolactin in overtly pseudopregnant Afghan hounds and on the clinical symptoms of overt pseudopregnancy were studied. Plasma concentrations of prolactin and progesterone were determined in six Afghan hounds with signs of overt pseudopregnancy for 2-3 weeks and in three Afghan hounds that were not pseudopregnant at the time of blood sampling. In the overtly pseudopregnant bitches the plasma concentrations of prolactin before treatment (35.5 +/- 8.5 micrograms l-1) were significantly higher than the plasma concentrations of prolactin of the three bitches that were not pseudopregnant (6.3 +/- 0.5 micrograms l-1); the latter values were similar to those of non-psueodopregnant beagle bitches during the total luteal phase. The six pseudopregnant Afghan hounds were treated for 10 days with the antiserotoninergic drug metergoline. At 2 h after the onset of treatment with metergoline, the mean plasma concentration of prolactin had decreased to 10.8 +/- 2.9 micrograms l-1. The plasma concentrations of prolactin continued to decline to 5.4 +/- 1.0 micrograms l-1 at 4 h and to 1.0 +/- 0.1 microgram l-1 during treatment days 3-10. Signs of pseudopregnancy, such as swelling of the mammary glands and digging, decreased during the treatment period. The treatment was associated with mild behavioural side effects such as whimpering and aggressiveness. These side effects are probably not related to suppression of prolactin but are due to a direct effect on serotoninergic pathways in the brain. It is concluded that high plasma concentrations of prolactin are associated with the development and maintenance of pseudopregnancy. The serotonin antagonist metergoline strongly suppresses plasma concentration of prolactine in pseudopregnant dogs and decreases the clinical signs of pseudopregnancy.

Animals↗
PubMed1976

Effect of apomorphine plus 5-hydroxytryptophan on plasma prolactin levels in male rats.

The relative potency of dopaminergic inhibition and serotonergic stimulation of prolactin secretion in male rats was compared. 5-Hydroxytryptophan (5-HTP), 100 mg/kg, i.p., the precursor of serotonin, produced a 6-11 fold increase in plasma prolactin. Apomorphine, a dopamine agonist, at doses of 1-10 mg/kg, i.p., had no significant effect on plasma prolactin. However, when apomorphine was given with or before 5-HTP, it nearly completely blocked the increase in prolactin produced by 5-htp. these results indicate that inhibition of prolactin secretion by dopaminergic stimulation can overcome the prolactin releasing effect of serotonin. The results are consistent with the hypothesis that prolactin secretion is ordinarily under a weak serotonergic stimulation and a profound dopaminergic inhibition. It is also possible that apomorphine affects plasma prolactin levels by increasing prolactin clearance.

5-Hydroxytryptophan↗
PubMed2001

Study of acute pharmacologic effects of prolactin on calcium and water transport in the rat colon by an in vivo perfusion technique.

We investigated the acute effect of intraperitoneally administered prolactin on calcium and water transport in colon of sexually mature female Wistar rats using an in vivo perfusion technique. Test solution containing (in mM) NaCl, 100; KCl, 4.7; MgSO4, 1.2; CaCl2, 20; D-glucose, 11; sodium ferrocyanide (Na4Fe(CN)6), an index of net water transport, 20; and 0.7 (microCi 45CaCl2 (1 Ci = 37 GBq) was perfused througth the 8-cm colonic loop for 60 min at perfusion rates of 0.5 or 1.0 mL x min(-1). Calcium and water transport was also studied under a no flow condition to stimulate the condition often found in the colon by in vivo ligated colonic loop for 30 min. Control results showed no correlation between calcium transport and water flux. Flow of luminal solution at 0.5 and 1.0 mL x min(-1) was found to reverse net calcium absorption from 0.04+/-0.01 nmol x g(-1) dry weight x h(-1) to net calcium secretion of 0.04+/-0.04 and 0.9+/-0.02 nmol x g(-1) dry weight x h(-1), respectively. Neither 0.4, 0.6, nor 1.0 mg x kg(-1) prolactin had any effect on calcium fluxes in the colon. On the other hand, at a perfusion rate of 1 mL x min(-1), 0.4 mg x kg(-1) prolactin significantly decreased net water absorption from 3.86+/-0.90 to 0.88+/-0.64 mL x g(-1) dry weight x h(-1) (P < 0.001), and the higher doses of 0.6 and 1.0 mg x kg(-1) prolactin reversed net water absorption to net water secretion of 2.20+/-0.63 and 2.33+/-0.89 mL x g(-1) dry weight x h(-1), respectively (P < 0.001). The stimulatory effect of prolactin on water transport was completely abolished by reducing the perfusion rate from 1.0 mL x min(-1) to zero. The stimulatory effect of prolactin on water secretion at perfusion rate of 1.0 mL x min(-1) was also abolished when luminal [Na+] was reduced from 180 to 80 mM. We concluded that, unlike in the small intestine, calcium fluxes in the colon are not related to water transport and did not respond at all to prolactin. Water transport, on the other hand, was reversed from net absorption to secretion by prolactin. We propose that this prolactin-induced water secretion is probably mediated by recycling of luminal sodium in the vicinity of tight junctions.

Animals↗
PubMed1976

Cell-free synthesis of a prolactin precursor directed by mRNA from cultured rat pituitary cells.

Polyadenylate-rich mRNA extracted from an established line of functional rat pituitary tumor cells (GH3) which respond to the addition of thyrotropin-releasing factor with the synthesis and secretion of prolactin directed cell-free synthesis using a cell-free protein-synthesizing system derived from wheat embryos. The products of translation, when analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and fluorography, did not include any protein co-migrating with rat prolactin. One prominent protein synthesized was precipitated using anti-prolactin antiserum. This protein was larger than the prolactin standard with an apparent molecular weight of 28,000 +/- 2,000. Addition of a GH3 cell extract to the translation system resulted in the appearance of a protein which co-migrated with rat prolactin and was immunoprecipitated with anti-rat prolactin antiserum. Addition of thyrotropin-releasing factor to spinner cultures of GH3 cells for 48 to 72 hours increased de novo prolactin biosynthesis. Levels of mRNA coding for prolactin determined by translation of total mRNA and quantitation of preprolactin synthesized were stimulated 3- to 6-fold relative to the levels in control cultures, suggesting that regulation of prolactin synthesis was accomplished, at least in part, at a transcriptional level.

Cell Line↗
PubMed1991

An immunocytochemical study of effects of light deprivation on prolactin cells in the adenohypophysis of the golden hamster.

Population ratio and morphology of prolactin cells were studied by employing immunohistochemical methods in the adenohypophysis of normal and experimental golden hamsters of both sexes at 16 weeks of age. Prolactin cells occupied 29% of the total adenohypophyseal cells in the intact males exposed to 14/10 h light/dark schedule. After stimulation of the pineal activity by binding or exposure of males to continuous darkness for eight weeks, prolactin cells became atrophic and were reduced in population to 17% and 13%, respectively. Pinealectomy prevented to some extent the effects of the above treatments; thus, prolactin cells constituted 27% in the pinealectomized and blinded hamsters, and 19% in the pinealectomized and darkness-treated group; and their morphology was comparable with that of the intact controls. Prolactin cells in the normal females were apparently larger in size and more numerous as compared with those of the normal males, comprising 47% of cell population in the anterior pituitary. In response to light deprivation, prolactin cells were atrophic with a diminished cytoplasm and decreased in cell number as reflected in the population ratio of 27% in the blinded and 21% in the darkness-treated groups. In pinealectomized females combined with binding or darkness-treatment, prolactin cells contained an abundance of secretory granules in the cytoplasm and maintained the population ratio comparable to that in the intact females. The present study revealed that light deprivation exerts an inhibitory effect on the secretory activity of prolactin cells and also causes hypoplasia of prolactin cells in the hamster adenohypophysis, the effects being mediated by the pineal gland.

Animals↗
PubMed1990

[Inhibitory effect of arachidonic acid on the synthesis of prolactin in human decidual tissues].

Much evidence indicates that human tissues produce prolactin. However, little is known as to which agents regulate its production in decidual tissues. Therefore, it is of interest to examine the effect of arachidonic acid on the production of prolactin, since it is present in considerably large amounts in decidual tissues. The addition of arachidonic acid to culture media resulted in a significant reduction in the amount of prolactin secreted from incubated decidual tissues in a dose-related fashion. Other poly-unsaturated fatty acids, i.e. linoleic and gamma-linolenic acid also inhibited its secretion, whereas saturated fatty acid and mono-unsaturated fatty acids, such as oleic acid, were without effect. The addition of phospholipase A2 and phospholipase C, enzymes to liberate arachidonic acid from phospholipids, also suppressed the secretion of prolactin. Indomethacin and BW-755C, inhibitors of cyclooxygenase and lipoxygenase, respectively, had essentially no effect on the secretion of prolactin. Translatable mRNA for prolactin was detected in decidual tissues. Arachidonic did not alter either the amount of mRNA in prolactin of the amount of its mRNA as a percentage of total mRNA. Thus, it appears that arachidonic acid possibly plays a role as a physiological regulator of prolactin secretion in human decidual tissues. The action of arachidonic acid is not mediated by cyclooxygenase or lipoxygenase products, suggesting that arachidonic acid itself, or its metabolites other than prostaglandin and leukotriene, may be involved in the regulation of prolactin secretion.

Arachidonic Acid↗
PubMed1988

Possible mechanisms of action of ethanol-induced release of prolactin from rat anterior pituitary.

We have demonstrated previously that ethanol increases the in vitro synthesis and release of prolactin by the anterior pituitary gland. In the present study we have examined the possible role of calcium and calmodulin in the ethanol-stimulation of in vitro prolactin release from hemipituitary glands. We also investigated the effect of inhibitors of arachidonic acid metabolism on the release of prolactin induced by ethanol. In addition we studied the effect of ethanol on the release of prostaglandins and the conversion of arachidonic acid to hydroperoxides. Basal and ethanol-stimulated prolactin release was almost blocked completely by omitting calcium from the incubation medium. In vitro addition of calmodulin-blocking agents such as pimozide and trifluoperazine reduced basal and ethanol-induced prolactin release. Acetylsalicylic acid, an inhibitor of the cycloxygenase pathway, had no effect on prolactin release. Nordihydroguaiaretic acid, an inhibitor of the lipoxygenase pathway, blocked completely the release of prolactin induced by ethanol. Ethanol (5 and 10 mM) significantly increased the release of prostaglandin E2 and prostaglandin F2 alpha and the conversion of [14C]arachidonic acid to 5-hydroxyeicosatetraenoic acid. The results of this study show that ethanol increases prolactin release by a calcium-dependent mechanism. Besides, our data suggest that arachidonic acid metabolism is involved in ethanol-stimulated prolactin secretion and that lipoxygenase pathway metabolites are at least partially responsible for this effect.

Animals↗
PubMed1988

Immunohistochemical identification of prolactin-producing cells in pituitary isografts in CBA mice.

Prolactin producing cells were investigated in pituitary isografts placed from female donor to female host CBA mice and also in the in situ pituitary gland of the graft-bearing host mice. Prolactin-producing cells were identified immunohistochemically using anti-mouse prolactin serum. Light microscopically, the cells with immunoreactive prolactin granules are present throughout the entire area of pituitary isografts, but less frequently in the in situ pituitary gland of the host mice. Electron microscopically, prolactin-producing cells may be classified into 3 types mainly based upon immunoreactive prolactin granules. Prolactin-producing cells in the pituitary grafts are classified as modified type III cells containing numerous immunoreactive prolactin granules resembling those found in the type III cells well-developed endoplasmic reticulum and enlarged Golgi apparatus. In contrast, following 5 d of the treatment with 2-bromo-alpha-ergocriptine, both type III and modified type III cells were decreased in number and type II cells were increased, and the cytoplasmic organella in these prolactin-producing cells appeared to be poorly developed.

Animals↗
PubMedDate not supplied

Prolactin as a marker of rejection in human heart transplantation.

Prolactin has been shown to play a role in the modulation of the immune system. In addition, recent laboratory evidence suggests that circulating prolactin might fluctuate as a function of immunologic events. To evaluate the role of prolactin as a predictor of rejection, 22 heart and heart-lung transplant patients were studied from July 1985 to May 1986. Daily plasma prolactin levels were measured by radioimmunoassay. Endomyocardial biopsy and histologic evaluation of the allografts were used to define rejection episodes. Thirteen of 14 documented rejection episodes were preceded by a specific elevation of circulating prolactin. A significant elevation of prolactin occurred 6 and 8 days before 14 rejection episodes that were diagnosed by biopsy but not before 109 biopsies were taken that had negative results. The normal values for circulating prolactin are defined by a preoperative mean in a range of 0 to 15 ng/ml (95% confidence limit). The sensitivity of prolactin to predict rejection is 79%, the specificity is 92%, and the positive predictive value is 61%. A large data variability gives a low accuracy to the test as a predictor of allograft rejection. To be useful clinically, the accuracy needs to be improved through a better understanding of prolactin physiology and its relation to the immune system.

Adult↗
PubMed1987

Plasma prolactin concentrations in non-pregnant mares at different times of the year and in relation to events in the cycle.

Plasma prolactin concentrations were measured in mares using an homologous radioimmunoassay. An annual rhythm in plasma prolactin was found, with concentrations higher during the summer than during the winter. In addition to this seasonal pattern, occasional high concentrations of prolactin were seen when concentrations were otherwise basal. Blood samples taken from mares during an oestrous cycle in October-November showed that prolactin values were basal for most of the cycle, with a marked rise in prolactin shortly before the onset of oestrus. This prolactin peak was associated with an increase in the size of the largest follicle, and with a peak of PGFM in some mares, but did not appear to be related to the LH surge. In oestrous cycles in March and May-June, there was a wide variation in the baseline of prolactin secretion, in accordance with the seasonal pattern already mentioned. However, the peak of prolactin seen around oestrus in October-November was less obvious in March and May-June. Post-partum mares showed a high but irregular profile of prolactin concentrations with no clear-cut pattern in relation to the oestrous cycle.

Animals↗
PubMed1986

Detection of prolactin messenger RNA in rat anterior pituitary by in situ hybridization.

The effects of chronic diethylstilbestrol treatment on rat prolactin mRNA was analyzed by in situ hybridization histochemistry. Forty-day-old female rats were treated with 10 mg diethylstilbestrol in Silastic tubes for 3, 6, and 9 weeks. Estrogen treatment for 9 weeks increased pituitary wet weight (51.6 +/- 2.4 versus 7.9 +/- 0.31 mg for controls), serum prolactin (4155 +/- 571 versus 47.1 +/- 8.9 ng/ml for controls), and the percentage of immunoreactive prolactin cells (69% +/- 3% versus 34% +/- 2% for controls). In situ hybridization studies showed an increase in rat prolactin mRNA with increasing duration of estrogen treatment. After 9 weeks of estrogen treatment, there was a 2.3-fold increase in rat prolactin mRNA. 3H-cDNA was distributed diffusely throughout the anterior pituitary in both normal and hyperplastic pituitaries. There were no separate foci of adenomatous pituitary with increased labeling or with increased immunoreactive PRL cells. Although transplantable pituitary MtT/W15 tumors secreted very large amounts of PRL, compared with pituitaries from DES-treated rats, rat prolactin mRNA as evaluated by mean grain counts was considerably less in the MtT/W15 tumor than in DES-treated pituitary cells. These results show that in situ hybridization histochemistry can be used to detect changes in rat prolactin mRNA in tissue sections from the anterior pituitary with chronic estrogen treatment and that these pituitaries show a diffuse increase in immunoreactive prolactin cells and cellular prolactin mRNA, rather than distinct adenomatous areas within the glands.

Animals↗
PubMed1979

Reaction of the histidines of prolactin with ethoxyformic anhydride. A binding site modification.

The seven histidines of bovine prolactin were modified with ethoxyformic anhydride and two classes of reactivity were apparent: 5 histidines were in the more reactive class (k = 0.097 min-1) and 2 histidines were less reactive (k = 0.011 min-1). The activity of the modified prolactins was determined by measuring their ability to bind to prolactin receptors from rabbit mammary glands. This assay showed that prolactin was fully active when 0 to 5 histidines were modified. If all 7 residues were modified, the hormone was unable to bind to its receptor. Circular dichroism studies indicated no significant differences in conformation for prolactins which had 2 to 7 histidines modified. Modification of human growth hormone and human placental lactogen with ethoxyformic anhydride resulted in a loss of the ability of these lactogenic hormones to bind to the prolactin receptor. For all three hormones, essentially full activity was recovered when the modifying group was removed by treatment with hydroxylamine. Sequence comparisons indicate that only 2 of the 3 growth hormone histidines and 2 of 7 placental lactogen histidines were homologous with histidines in bovine prolactin and that, in each case, they correspond to His-27 and His-30 in bovine prolactin. It is postulated that these residues serve to identify a portion of the binding domain of bovine prolactin.

Amino Acid Sequence↗
PubMed1984

n-Butyrate effects thyroid hormone stimulation of prolactin production and mRNA levels in GH1 cells.

Using cultured GH1 cells, a growth hormone and prolactin-producing rat pituitary cell line, we have shown that n-butyrate and other short chain carboxylic acids stimulate histone acetylation and elicit a reduction of thyroid hormone nuclear receptor which is inversely related to the extent of acetylation (Samuels, H. H., Stanley, F., Casanova, J., and Shao, T. C. (1980) J. Biol. Chem. 255, 2499-2508). In this study, we compared the n-butyrate and propionate modulation of receptor levels to regulation of the growth hormone and prolactin response by 3,5,3'-triiodo-L-thyronine (L-T3). n-Butyrate (0.1-10 mM) did not stimulate growth hormone production. L-T3 stimulated the growth hormone response 4- to 5-fold and n-butyrate (0.5-1 mM) increased L-T3 stimulation of growth hormone production 1.5- to 2-fold compared to L-T3 alone. L-T3 stimulation of growth hormone production at higher n-butyrate concentrations decreased in parallel with the n-butyrate-mediated reduction of receptor levels. In contrast with the growth hormone response, n-butyrate (0.5 mM) increased basal prolactin production about 5-fold. Prolactin production, which is inhibited 25 to 50% by L-T3, was stimulated between 20- and 70-fold by L-T3 + n-butyrate (0.5-1 mM) and this decreased at higher n-butyrate levels. Prolactin mRNA and growth hormone mRNA levels paralleled the changes in prolactin and growth hormone production rates. These effects of L-T3, n-butyrate, or L-T3 + n-butyrate appeared unrelated to changes in cAMP levels or global changes in DNA methylation of the growth hormone or prolactin genes. Propionate elicited the same effects as n-butyrate but at a 5- to 10-fold higher concentration consistent with their relative effect on stimulating acetylation of chromatin proteins. These results suggest that prolactin gene expression is under partial regulatory repression which is reversed by a carboxylic acid-mediated postsynthetic modification event which allows for stimulation of the prolactin gene by thyroid hormone.

Animals↗