Production of both prolactin and growth hormone by clonal strains of rat pituitary tumor cells. Differential effects of hydrocortisone and tissue extracts

Transcription of sequences upstream of the rat prolactin gene suggests the existence of a second promoter

The transcription of the rat prolactin gene domain has been examined using a modified Southern blot procedure. Cloned genomic DNAs were resolved by electrophoresis in agarose, transferred to nitrocellulose, and probed with radiolabeled RNA that had been synthesized in vitro by nuclei isolated from pituitary tumor cells. Data presented in this paper illustrate that single copy genomic sequences located within 7.3 kb upstream of exon 1 are transcribed. Single copy or low copy number DNA sequences that reside greater than 7.3 kb upstream of exon 1, or downstream of exon 5 were not transcribed at detectable levels. These data suggest that a second promoter may exist upstream of the rat prolactin gene and that this second promoter may be active in pituitary cells.

Thyroid hormone dependent pituitary tumor cell growth in serum-free chemically defined culture. A new regulatory role for apotransferrin

Thyroid hormone dependent GH1 rat pituitary tumor cell growth in serum-free chemically defined medium required a serum-derived mediator (i.e., thyromedin) which was identified as transferrin [Sirbasku, D.A., Stewart, B.H., Pakala, R., Eby, J.E., Sato, H., & Roscoe, J.M. (1990) Biochemistry 30, 295-304]. The transferrin isolated was consistent with the equine R or D variants and was biologically active only as apotransferrin (apoTf). To determine if other variants of horse transferrin also were thyromedins, a purification was developed which yielded seven separate forms. Initially, only four of these had activity when assayed in standard "iron salts containing" medium (ED50 values of 290-1160 nM). To further assess activity, the iron contents of all seven were altered either by saturation with ferric ammonium citrate or by citrate/acid depletion of the metal ion. Thereafter, potencies were compared in "iron salts containing" and "iron salts reduced" media. All seven variants proved to be active as apoTf. Bioassays in which apoTf was maximized showed ED50 values of 2.1-3.8 nM. Conversely, assays in which thyromedins were converted to Tf.2Fe showed no activity. Previously, the only known physiological function of apoTf was that of a carrier/detoxifier of iron; this study indicates a new role in hormone-dependent pituitary cell growth.

Thyroid hormone regulation of rat pituitary tumor cell growth: a new role for apotransferrin as an autocrine thyromedin

In the 40 years of transferrin research, no previous role for apotransferrin has been recognized other than to serve as a plasma carrier for dietary and storage iron. Our studies have revealed a new 'autocrine' growth role for this molecule as well as a possible new cell-cell bridge/CAM function. Certainly, these observations have opened many new areas of investigation both with regard to thyroid hormone action and the function of apotransferrin. In addition, there is now accessible the broader question of tissues other than pituitary which might utilize apotransferrin to regulate responsiveness to thyroid hormones.

Cortisol rapidly reduces prolactin release and cAMP and 45Ca2+ accumulation in the cichlid fish pituitary in vitro

During in vitro incubation, prolactin release is inhibited in a dose-related manner by cortisol. This action is mimicked by the synthetic glucocorticoid agonist dexamethasone but not by other steroids tested. Perifusion studies indicate that the inhibition of [3H]prolactin release by cortisol occurs within 20 min. Cortisol (50 nM) also inhibits cAMP accumulation and reduces 45Ca2+ accumulation in the tilapia rostral pars distalis within 15 min. Cortisol's action on prolactin release is blocked in the presence of either the Ca2+ ionophore A23187 or a combination of dibutyryl cAMP and 3-isobutyl-1-methylxanthine, which increase intracellular Ca2+ and cAMP, respectively. Taken together, these findings suggest that cortisol may play a physiologically relevant role in the rapid modulation of prolactin secretion in vivo. Our studies also suggest that the inhibition of prolactin release by cortisol is a specific glucocorticoid action that may be mediated, in part, through cortisol's ability to inhibit intracellular cAMP and Ca2+ metabolism.

Prolactin-deficient GH3B3 cells are defective in the utilization of the endogenous prolactin promoter yet are fully competent to initiate transcription from a transfected prolactin promoter

Transcription of the prolactin (PRL) gene has been analyzed in wild-type D6, PRL-deficient B3, and revertant r16 GH3 cells. Levels of processed nuclear transcripts from the PRL gene were substantially reduced in the deficient line compared to wild-type cells and returned to greater than wild-type levels in the revertant line. Rare PRL transcripts in the deficient line contained the same 5' end found on transcripts in wild-type and revertant cells as judged by primer extension and S1 nuclease protection assays, implying that the cells are deficient in utilization of the normal wild-type promoter. Deficient cells also contained wild-type levels of the PRL- and growth hormone-specific transcription factor pit-1/GHF-1, and no difference was found in the ability of extracts from wild-type and deficient cells to retard various restriction fragments from both the proximal and the distal PRL promoter regions. The deficient and wild-type cells were equally competent in initiating transcription from a transfected rat PRL promoter containing both the distal and proximal promoter elements. These observations imply that PRL-deficient cells are not defective in a trans-activating factor functioning on these PRL promoter fragments (trans model). Rather, inefficient use of the PRL promoter in the variant cells may reflect an increased methylation state of the PRL gene itself (cis model).

Cloning and characterization of the carp prolactin gene

A carp genomic DNA clone containing the carp prolactin (Prl) gene was isolated with carp Prl cDNA as a probe. The organization of the carp Prl gene was determined by restriction nuclease mapping and nucleotide sequencing. The Prl gene comprises approx. 2.8 kilobasepairs (kb) of DNA including the 5'-flanking region, five exons, four introns and the 3'-flanking region. Analysis of the 5'-flanking region reveals (1) the sequence TATATAAT at positions -38 to -31 upstream from the cap site which was found to be a guanine residue, and (2) the palindrome, CTCATTGCATATACAAATGAG at positions -79 to -59. The carp Prl gene matches with the reported cDNA except for one difference in coding region and five in the 3'-flanking region, while the encoded amino acid sequences are identical. The arrangement of exons and introns is very similar to that seen in carp GH as well as mammalian Prl, which, however, have much longer introns.

Photodynamic therapy for rat pituitary tumor in vitro and in vivo using pheophorbide-a and white light

This is the first report on the use of photodynamic therapy (PDT) for rat pituitary tumor in vivo. Rat pituitary tumor (GH3) cells were cultured, GH3 tumor was subcutaneously implanted in nude mice, and pheophorbide-a (Ph-a) and white light were prepared. Photocytotoxicity proportional to Ph-a concentration, intensity of irradiation, and incubation time was observed in vitro. Despite the delay in the disappearance of Ph-a from the tumor, Ph-a in the pituitary gland rapidly decreased after intravenous administration in vivo. Through PDT, the tumor grossly disappeared, the plasma levels of rat growth hormone secreted from the tumor also remarkably decreased, and the development of giantism was inhibited. These results indicate that PDT is effective against rat pituitary tumor.

Functional glucocorticoid inducible enhancer activity in the 5'-flanking sequences of the rat growth hormone gene

Glucocorticoid regulation of rat growth hormone (rGH) gene expression has been investigated in a series of gene transfer studies into cells in culture. It has been established that sequences (-12 to -523) immediately flanking the start site for rGH gene transcription behave as a functional glucocorticoid inducible enhancer when associated with a heterologous promoter (RSV), displaying independence of orientation and position in mediating the glucocorticoid effect. The induction of chloramphenicol acetyl transferase (CAT) gene expression in these constructs by dexamethasone was established at the enzyme and mRNA levels and was inhibited in the presence of the antiglucocorticoid, RU 38486. The glucocorticoid inducible enhancer activity was not restricted to pituitary cells. The constructs containing the rGH-5'-flanking sequences, associated with the RSV promoter, also mediated glucocorticoid induction of CAT gene expression when transiently transfected into MH1C1 cells, a hepatoma cell line. The effect was similarly demonstrable on co-transfection of these constructs with a glucocorticoid receptor expression vector into receptor deficient COS cells. Two elements within these rGH sequences (-97 to -111 and -250 to -264) display partial homology with a consensus sequence computed for a group of glucocorticoid regulatory elements. Mutation of both of these elements or of the more proximal element alone (-97/-111) led to a complete loss of ability to mediate glucocorticoid induction of gene expression. However, the rGH sequences still mediated glucocorticoid induction of gene expression when the distal GRE-like element was mutated or deleted. Thus, the proximal rGH GRE-like element is absolutely required to mediate this glucocorticoid inducible enhancer activity.

Identification of a distal regulatory element in the 5' flanking region of the bovine prolactin gene

The 5'-flanking region of the bovine prolactin gene was cloned and sequenced. The expression of chimeric gene constructs containing 5'-flanking DNA fragments from the prolactin gene joined to a reporter gene encoding human growth hormone (hGH) was examined using transiently transfected rat pituitary cells. Prolactin nucleotide sequences located at position -1213 to -925 enhance the basal level of expression of growth hormone by 5-fold and function in a position- and orientation-independent fashion. In addition to increasing the basal level of growth hormone expression, this enhancer element also responds to induction by epidermal growth factor. The nucleotide sequence of the bovine prolactin gene enhancer element is highly similar to an enhancer element located approximately -1.5 kb from the rat prolactin transcription initiation site. Deletion analysis of the enhancer region shows that sequences -1124 to -985 are necessary and sufficient for enhancer activity.

Expression of a cytomegalovirus-human growth hormone-releasing hormone precursor fusion gene in transfected GH3 cells

Pituitary GH3 cells were transfected with a human growth hormone-releasing hormone (hGRH) precursor minigene fused to the promoter region of either a cytomegalic immediate early gene (pCMV) or the mouse metallothionein-1 gene (mMT) to examine the molecular heterogeneity of the translation products. Expression of the hGRH message occurred following transfection of the cells with each fusion gene. Extracts of pCMV-hGRH-transfected GH3 cells as well as the culture medium contained detectable levels of immunoreactive (ir)-hGRH peptides. Analysis of molecular heterogeneity by reverse-phase high performance liquid chromatography and radioimmunoassay indicated that both mature forms of hGRH (hGRH(1-44)-NH2 and hGRH(1-40)-OH) were synthesized in the cells, although hGRH(1-44)-NH2 was the primary form secreted into the medium. A high molecular weight form of ir-hGRH, believed to represent the hGRH precursor (or a partially processed form of the precursor) was detected in cells and, in smaller amounts, in the medium. Several ir-hGRH peptides, presumed cleavage products of the mature forms of hGRH, were also found. The efficiency of processing of the hGRH precursor and metabolism of the mature hormonal forms in transfected cells grown in the presence of four different peptidase inhibitors varied with the inhibitor present. Transfected GH3 cells, therefore, possess all of the necessary enzymes for and are capable of processing the hGRH precursor to mature GRH and provide a model to study hGRH biosynthesis.

Effect of extracellular matrix on prolactin secretion and mRNA accumulation in GH3 cells

The matrix upon which cells grow affects their morphology, growth rate, response to external stimuli, and protein synthesis. GH3 cells, a well-characterized rat pituitary tumor cell line, synthesize and secrete growth hormone and prolactin (Prl). These cells are rounded, attach loosely, and form clumps when plated on plastic. GH3 cells plated on an extracellular matrix (ECM) from bovine corneal endothelial cells become flattened and strongly adherent to the culture dish, and have an initial increased rate of proliferation. Cells cultured on plastic have a 48-hr lag period before the start of cell division; this can be shortened by increasing the concentration of serum in the medium. Since GH3 cells store little Prl, hormone release is a good index of Prl synthesis. Prl secretion from cells cultured on extracellular matrix is twice as great as from cells cultured on plastic. The increase in Prl secretion from cells grown on extracellular matrix paralleled by a concomitant increase in the accumulation of prolactin mRNA. Cells cultured on plastic secrete more Prl in response to TRH stimulation than do cells cultured on ECM. Cells grown on either surface were unresponsive to dopamine. Thus, culturing cells on ECM may change their morphology and affect the synthesis and regulation of specific cellular proteins and their mRNAs.

Increase in T-type calcium current in atrial myocytes from adult rats with growth hormone-secreting tumors

Growth hormone (GH) has pronounced effects on protein synthesis and cell growth in cardiac muscle from adult animals, although the mechanism of its action is not understood. Because Ca2+ has been implicated as a regulator of mitogenic processes in a number of tissues, we investigated whether GH affects the transmembrane movement of Ca2+ through voltage-activated channels of cardiac myocytes. Atrial and ventricular myocytes were isolated from adult rats with GH-secreting tumors and studied electrophysiologically by using patch-clamp techniques. Tumor-bearing rats re-enter an active growth phase and double their body weight over age-matched controls 8 weeks after introduction of the tumor. Atrial myocytes from tumor-bearing animals showed a 3-fold increase in the density of T-type Ca2+ current compared with cells from control animals, although the voltage dependency of activation and inactivation of T-type current was not altered. The increase in T-current density of atrial myocytes preceded by at least a week any measurable change in heart weight, body weight, or myocyte size. L-type Ca2+ currents in atrial and ventricular cells were not affected. The results suggest that a tumor-derived growth factor, most likely GH, can cause a specific enhancement of T-type Ca2+ current in atrial myocytes.

Gonadotropes in a novel rat pituitary tumor cell line, RC-4B/C. Establishment and partial characterization of the cell line

An epithelial cell line (RC-4B/C) was established from a pituitary adenoma obtained from a 3-yr-old (ACI/fMai X F344/fMai)F1 male rat. Before Year 5 in vitro, RC-4B/C cells could not be viably recovered from cryogenic storage. Recovery of viable cells from cryogenic storage in Year 5 was associated with a more transformed phenotype, including the appearance of endogenous C-type rat retroviral particles. The ultrastructural appearance of the cells was similar to that of differentiated anterior pituitary cells; the cultured cells contained numerous, electron dense, secretory granules, Golgi complexes, and extended arrays of rough endoplasmic reticulum. Immunocytochemical study showed that all cell types present in the rat anterior pituitary gland were present in the cell line. The percentage of luteinizing hormone beta (LH beta) cells in the cell line was higher (19.9%) and that of growth hormone cells was lower (12.2%) than in normal male rat pituitary, whereas the cell line contained a comparable percentage of follicle stimulating hormone beta (FSH beta), prolactin (PRL), ACTH, and thyrotropin beta cells. Radioimmunoassay data demonstrated the PRL content of the cells was comparable to that of normal male rat pituitary gland, whereas the content of LH and FSH was 70- and 800-fold lower, respectively. Assay of specific receptor sites for gonadotropin releasing hormone (GnRH) using Scatchard plots of the data established the RC-4B/C cells contained GnRH receptor sites of the same affinity as in the pituitary gland, but of twofold lower capacity. These data suggest the RC-4B/C cell line warrants further study as a model for the induction and maintenance of the gonadotropic function of the pituitary gland.

Medium flow rate modulates autocrine-paracrine feedback of GH and PRL release by perifused GH3 cells

We previously documented both the spontaneous acceleration of growth hormone (GH) and prolactin (PRL) production by GH3 cells during perifusion and the suppression of their production during plate culture. We here present the role played by medium flow itself in this differential behavior. Increasing rates of perifusion flow (pump rates of 1 to 5 ml/h, equivalent to chamber flow rates of 0.19 to 1.3 microliters.min-1.mm-2 of cross-sectional area) were associated with enhanced GH and PRL secretion. Flow rate-dependent basal hormone secretion rates were established quickly and were stable for the first 10 to 14 h of perifusion. The previously documented independent, spontaneous, and continuously accelerating production of both hormones that followed during the subsequent 40 (PRL) to 60 (GH) h of perifusion was also shown to be flow-rate related. Any time the rate of medium flow was changed within an experiment, the rate of hormone secretion was modulated. However, that modulation did not interrupt ongoing flow-associated acceleration of hormone production once the latter had begun. In addition, GH3 cell product(s) from one cell column reversibly inhibited secretion from cells in a downstream column. The inhibition did not occur when cells in the downstream column had been exposed to trypsin. Other work had suggested that neither GH, PRL, insulinlike growth factor-I, leucine, nor nutrient exhaustion were responsible for the effect. These data are consistent with autocrine-paracrine feedback regulation of GH3 cells by a secretory product(s). Feedback would thus provide a mechanism to effect flow-rate-dependent modulation of GH and PRL release, and to explain accelerating hormone production during perifusion.

Somatomammotrophic cells in GH-secreting and PRL-secreting human pituitary adenomas

A morphological study has been carried out on 20 GH-secreting adenomas removed from acromegalic normoprolactinemic patients, on 29 PRL-secreting adenomas removed from hyperprolactinemic patients without signs of acromegaly and on one normal human anterior pituitary gland collected at autopsy. The protein A-gold immunoelectron microscopic technique has been utilized in order to verify the presence of mixed cells producing both GH and PRL (somatomammotrophs) in these pituitary tissues. In the normal pituitary a considerable number of somatomammotrophs (15-20%) was found, thus supporting the idea that these cells are normal components of the human anterior pituitary gland. In 10 GH-secreting adenomas and in 10 PRL-secreting adenomas somatomammotrophs were present in a variable number (from 4 to 20% of the whole cell population in GH adenomas and from 1 to 47% in PRL tumors). It can be concluded therefore that these cells, largely present in all GH/PRL-secreting adenomas, can also be found in GH-secreting and PRL-secreting tumors without clinical evidence of a mixed secretion. Adenomatous somatomammotrophs displayed ultrastructural features of adenomatous somatotrophs and mammotrophs (prominent Golgi complexes, abundant rough endoplasmic reticulum, irregular nuclei). The size and the number of granules were variable. In some cells GH and PRL were stored in distinct secretory granules, in others in mixed granules or both in mixed and distinct granules, thus suggesting that in adenomatous somatomammotrophs the efficiency of the mechanisms of sorting of the two hormones varies from one cell to another.(ABSTRACT TRUNCATED AT 250 WORDS)

The tilapia prolactin cell: A model for stimulus-secretion coupling

The tilapia prolactin (PRL) cell responds rapidly (10-20 min) to small physiological changes in medium osmotic pressure (OP), releasing increasing quantities of hormone as medium OP is reduced. This release is rapidly (≤ 10 min) inhibited by somatostatin (SRIF). There is now extensive evidence that tilapia PRL cell function is regulated through the second messengers Ca(++) and cAMP. Our studies have shown that PRL release is augmented by treatments that lead to increased levels of intracellular Ca(++) or cAMP. On the other hand, PRL release is blocked when tissues are incubated in Ca(++)-depleted medium or upon the addition of Co(++), an inhibitor of Ca(++)-mediated processes. The use of(45)Ca(++) to characterize the movement of Ca(++) into PRL cells has provided evidence that an increase in the influx of extracellular Ca(++) may participate in PRL release upon exposure to hyposmotic medium. Our studies have also shown that SRIF suppresses the increase in(45)Ca(++) accumulation that is brought about when OP is reduced. We have also examined the effects of OP and SRIF on cAMP levels. The reduction of medium OP did not alter cAMP metabolism during 20 min of incubation. By contrast, cAMP accumulation in the presence of IBMX was enhanced at 1 hr of incubation in reduced OP. Thus, an increase in cAMP turnover may play a role in maintaining PRL release under sustained stimulation. SRIF reduced the accumulation of cAMP during 10 min of incubation with IBMX and also reduced the forskolin-stimulated increase in cAMP. Thus, SRIF may suppress adenylate cyclase activity. Finally, our studies have revealed that the forskolin-stimulated increase in cAMP levels is not dependent upon medium Ca(++). The presence of Ca(++) in the medium is required, however, for PRL release even when the cAMP messenger system has been activated. Moreover, cAMP accumulation was augmented when intracellular Ca(++) was increased. This raises the possibility that reduced OP may stimulate an increase in cAMP turnover indirectly through its action(s) on cytosolic Ca(++).

Autocrine-paracrine inhibition of growth hormone and prolactin production by GH3 cell-conditioned medium

In previous work we have shown that perifused GH3 cells exhibit spontaneously accelerating growth hormone (GH) and prolactin (PRL) secretory rates. This behavior contrasts with GH and PRL secretion rates that are decreasing or stable over the same 3-d period in static cell culture. We now report that GH3 cells maintained in serum-supplemented medium produce an autocrine-paracrine factor(s) which inhibits GH secretion in plate culture; PRL release is frequently reduced as well. The inhibitory effect of conditioned medium on GH secretion was concentration dependent, whereas PRL release was stimulated at low and inhibited at high concentrations over the same range. Extensive dialysis of conditioned medium using membranes with a molecular weight cut-off of 12,000-14,000 did not remove GH inhibition but produced a retentate that stimulated PRL secretion. Heat-inactivation of conditioned medium did not abolish inhibition of GH release but did remove the PRL-stimulatory effect. IGF-I added to fresh culture medium did not reproduce the GH-inhibitory effects of conditioned medium. We conclude that GH3 cell secretory behavior in perifusion and plate culture systems may be partially explained by the production of an autocrine-paracrine factor: its accumulation in plate culture inhibits GH and PRL secretion whereas its removal, by perifusing medium, allows GH and PRL secretion to accelerate.

Double-labeling immunogold electron-microscopic study of hormonal colocalization in nontumorous and adenomatous rat pituitaries

According to the one cell, one hormone theory, the pituitary gland is composed of 5 cell types which secrete 6 hormones. Recent investigations indicate that this theory must be modified, as there are some bihormonal cells containing 2 hormones, i.e., mammosomatotrophs prolactin-growth hormone (PRL-GH). This study was undertaken in order to elucidate whether other adenohypophysial cells are capable of producing 2 hormones and to demonstrate the presence of cells coexpressing PRL-GH, PRL-thyrotropin (TSH), or TSH-GH. Sixteen nontumorous and 16 adenomatous male and female Sprague-Dawley and Long Evans rat pituitaries were removed immediately after the animals were killed and processed for transmission electron microscopy and the immunogold double-labeling technique. Coexpression of PRL-GH, PRL-TSH, and TSH-GH was found in both nontumorous and adenomatous pituitaries. Double labeling was present not only in the same cell cytoplasm but also in the same secretory granules. The question of whether these double-labeled cells represent different cell populations, transitional cell types, or precursor cells requires further investigation.

Laminin induces formation of neurite-like processes and potentiates prolactin secretion by GH3 rat pituitary cells

Tumor-derived GH3 rat pituitary cell lines are widely utilized to study mechanisms of prolactin secretion and responsiveness to secretagogues. These cells served here as a model with which to study relationships between shape and function. When GH3 cells were routinely grown in serum-supplemented medium, they exhibited the polygonal phenotype of epithelial cells, with scarce secretory granules. In contrast, when seeded in a serum-free medium, they attached loosely and contained more secretory granules. In both cases, they released prolactin in a nonpolarized manner. We show in the present work that laminin extracted from Englebreth-Holm-Swarm (EHS) tumors was a potent attachment and spreading factor for GH3/B6 cells seeded in serum-free medium. Moreover, it induced the formation of neurite-like processes, which were increased in number and length by chronic treatment with a specific secretagogue, thyroliberin (TRH). These changes in cell shape were correlated with a potentiation of prolactin secretion, both basal and TRH-stimulated. Furthermore, using immunocytochemistry and electron microscopy, we revealed--at the dilated tip of processes--an accumulation not only of prolactin, but also of synaptophysin, a vesicle membrane marker, and of several organelles, such as secretory granules, smooth vesicles, dense bodies and mitochondria. The cytoplasmic processes contained long parallel bundles of microtubules and showed a strong immunoreactivity for beta 2-tubulin. In addition, we found immunocyto-chemical evidence for the presence of 200-k Da neurofilament protein in GH3/B6 cell processes as well as in neurites of cultured hypothalamic neurons. We conclude that, in GH3/B6 cells, laminin induced the differentiation of neurite-like processes, which were the site of polarized organelle transport and exhibited some neuronal markers.

Co-localization pattern of growth hormone (GH) and prolactin (PRL) within the anterior pituitary cells in the female rat and female musk shrew

By a double immunocytochemical labeling procedure, using the protein A-gold method combined with electron microscopy, the co-localization pattern of growth hormone (GH) and prolactin (PRL) was detected in the anterior pituitary cells of female rats and female musk shrews. Two types of co-localization of GH and PRL were demonstrated. First, GH- and PRL-containing secretory granules were intermixed within closely aggregated and interdigitated cell clusters that were composed of GH and PRL cells. This phenomenon was characteristically seen in pregnant rats and pregnant musk shrews. Therefore, the occurrence of an intermixture of GH and PRL granules might be related to an enhanced cellular function for PRL synthesis. In another pattern of co-localization of GH and PRL, both hormones were co-packaged in the same secretory granules within a single cell. Such cells were scarce, small, irregularly shaped, and observed only in pregnant rats. These mixed GH-PRL cells contained not only mixed GH-PRL granules but also granules containing only GH or PRL. This suggests that these bihormonal cells are able to synthesize, synchronously or asynchronously, GH and PRL. Furthermore, granule extrusion from the mixed cells was clearly shown in this study. It seems likely that the mixed GH-PRL cells reveal active cellular function in the pituitary gland of the pregnant rat.

Rat pituitary tumor cells in serum-free culture. II. Serum factor and thyroid hormone requirements for estrogen-responsive growth

The effect of 17 beta-estradiol (E2) on growth of GH4C1 rat pituitary tumor cells was investigated under serum-free conditions and with medium containing charcoal-extracted serum. Serum-free TRM-1 medium was a 1:1 (vol/vol) mixture of F12-DME supplemented with 50 micrograms/ml gentamicin, 15 mM 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid, 10 micrograms/ml insulin, 10 micrograms/ml transferrin, 10 ng/ml selenous acid, 10 nM 3,5,3'-triiodothyronine (T3), 50 microM ethanolamine, and 500 micrograms/ml bovine serum albumin. The cells grew continuously in TRM-1 but were E2 responsive only when growth was retarded by reducing the T3 concentration to 10 pM (TRM-MOD). Addition of 1 to 10 nM E2 to TRM-MOD increased growth by 0.3 to 0.9 cell population doublings over controls in 9 d. By using medium supplemented with charcoal-extracted sera, basal growth became 1 to 1.5 cell population doublings in 9 d. Addition of 0.1 pM E2 to medium containing charcoal-extracted serum caused a significant increase in cell number whereas pM-nM concentrations stimulated 200 to 570% increases over controls. The effect of steroid hormone was the same in phenol-red-containing and indicator-free medium. The data presented confirm that the major requirements for demonstration of estrogenic effects in culture were optimum concentrations of thyroid hormones and the presence of yet-to-be-characterized serum factors.

Rat pituitary tumor cells in serum-free culture. I. Selection of thyroid hormone-responsive and autonomous cells

The growth of GH4C1, GH3, GH1, and GH3C15 rat pituitary tumor cell lines was studied in a serum-free medium (designated TRM-1) formulated with 1:1 (vol/vol) mixture of Ham's F12 nutrient mixture and Dulbecco's modified Eagle's medium (F12-DME) containing 15 mM 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES), 50 micrograms/ml gentamicin supplemented with 10 micrograms/ml bovine insulin, 10 micrograms/ml human transferrin (Tf), 10 ng/ml selenous acid, 10 nM 3,5,3'-triiodothyronine (T3), 50 microM ethanolamine (Etn), and 500 micrograms/ml bovine serum albumin. Of the lines evaluated, only the GH1 failed to grow in TRM-1. Passage of the GH4C1 and GH3 lines from serum-containing medium into TRM-1 caused an initial selection resulting in cells that grew progressively at higher rates and finally were maintained indefinitely in TRM-1. These populations showed a requirement for supraphysiologic concentrations of T3 (1.0 to 10 nM). After adaptation of the GH4C1 line in TRM-1 for greater than or equal to 20 generations, removal of components gave a less complex mixture containing 15 mM HEPES, 50 micrograms/ml gentamicin, 10 micrograms/ml Tf, 10 nM T3, and 50 microM Etn (designated TRM-2) that supported serial passage of the cells. Under these conditions, thyroid hormone dependence was lost progressively. When T3 was removed from TRM-2 adapted cells, a third population was selected that no longer required thyroid hormones and was only slightly stimulated by T3. These studies demonstrated that the combination of serum-containing and serum-free conditions can be used to select pituitary cell populations that a) required both serum-factor(s) and T3 for optimum growth, b) required supraphysiologic concentrations of T3 without serum proteins other than Tf and albumin, and c) were completely autonomous in that they proliferated in medium supplemented only with Tf and nutrients without necessity of other serum factor(s) or T3.

TRH and BAY K 8644 synergistically stimulate prolactin release but not 45Ca2+ uptake

Thyrotropin-releasing hormone (TRH) (1 microM) and the Ca2+-channel agonist BAY K 8644 (1 microM) each induced transient increases in prolactin secretion from primary cultures of rat anterior pituitary cells in perifusion. When BAY K 8644 was added after a TRH-induced secretory peak, the additional effect of BAY K 8644 on prolactin release was approximately twofold greater over a 30-min period than the effect of BAY K 8644 on previously untreated cells. TRH and BAY K 8644 were also synergistic when added in the opposite order or simultaneously. Substitution of other agents for BAY K 8644 revealed that only high K+ (40 mM) was at least additive with TRH in stimulating prolactin secretion; treatment with TRH inhibited, rather than facilitated, subsequent stimulation of prolactin secretion by angiotensin II (100 nM) or the ionophore A23187 (20 microM). The cooperative effect was not specific for TRH because BAY K 8644 also acted synergistically with angiotensin II or 40 mM K+. In GH4C1 cells, in which TRH and BAY K 8644 were also synergistic in releasing prolactin, measurements with the fluorescent indicator indo-1 showed that TRH and BAY K 8644 could each elevate cytosolic Ca2+ above the level stimulated by the other. Unexpectedly, TRH was found to inhibit BAY K 8644-stimulated 45Ca2+ uptake in both GH4C1 and primary cultured cells. These results indicate that BAY K 8644 and TRH synergistically stimulate prolactin secretion by a mechanism other than a cooperative effect on the activity of dihydropyridine-sensitive Ca2+ channels.

The effects of estrogens on tumor growth and on prolactin and growth hormone mRNA expression in rat pituitary tissues

Estrogens inhibit tumor growth and modify PRL and GH expression in the MtT/W15 transplantable rat pituitary tumor. The effects of estradiol (E2) and diethylstilbestrol (DES) on PRL and GH mRNA levels were investigated. Estrogens increased GH mRNA levels and decreased PRL mRNA levels as detected by in situ hybridization and Northern blot hybridization with oligonucleotide probes, while inhibiting tumor growth. Similar changes in immunoreactive GH and PRL were seen in the tumor cells. The pituitary glands of tumor-bearing rats treated with estrogen for 3 weeks were increased in weight with a concurrent increase in pituitary PRL mRNA when analyzed by dot blot hybridization. These results indicate that estrogens have an inhibitory effect on the growth of the MtT/W15 tumor and increase GH protein and mRNA levels, while causing PRL protein and mRNA levels to decrease. The pituitaries of tumor-bearing rats concomitantly undergo PRL cell hyperplasia with an increase in PRL mRNA. These results also demonstrate a paradoxical effect of estrogens on different pituitary tissues.

Mixed growth hormone and prolactin-secreting human pituitary adenomas: a pathologic, immunocytochemical, ultrastructural, and immunoelectron microscopic study

A study of 30 adenomas from patients with signs of growth hormone (GH) and prolactin (PRL) hypersecretion revealed the presence of mammosomatotroph cells (MSC) containing both hormones in all cases. Although the number of immunostained cells varied from case to case, in 14 of 25 tumors, all stained cells were MSC. Nine tumors had the ultrastructural appearance of densely granulated growth hormone adenomas, while 11 cases resembled sparsely granulated growth hormone adenomas with frequent fibrous bodies. Exocytosis was present in six of these 11 cases, a feature unusual for pure growth hormone adenomas. Nine tumors consisted of a mixture of cells with the morphology of GH and PRL cells. In the four cases examined, immunoelectron microscopy using double immunolabeling with protein A-gold particles revealed the presence of secretory granules containing both hormones in some tumor cells recognized as mammosomatotroph cells.

Two elements of the rat prolactin 5' flanking region are required for its regulation by estrogen and glucocorticoids

The 5'-flanking region of the rat prolactin gene contains two DNase I-hypersensitive (HS) sites. We used gene transfer experiments to determine the nucleotide (nt) sequences within and around these two HS sites that may contain the information necessary for regulation of prolactin gene expression by estrogens and glucocorticoids. A chimeric gene construct (pPRL.CAT) was prepared by covalently linking the sequence of the rat prolactin gene to the bacterial chloramphenicol acetyltransferase-coding gene, cat. Rat GH3 cells were transfected with pPRL.CAT and six mutants that possess deletions within and around the two HS sites. Incubation of such transfectants with estrogen or dexamethasone indicated the existence of two functionally important elements within the 5'-flanking region of the rat prolactin gene. The element required for estrogen up-regulation of the prolactin gene is located between nt residues -1530 through -1950. The glucocorticoid down-regulatory element is located between nt -200 and +75.

Distribution of growth hormone and prolactin in secretory granules of the normal and neoplastic human adenohypophysis

Growth hormone [GH] and prolactin [PRL] can be demonstrated simultaneously in electron micrographs by means of the double immunocytochemical labeling technique using colloidal gold particles of two different sizes. This method was used to study biopsy specimens obtained from 15 patients suffering from acromegaly, 11 patients suffering from prolactinomas, and eight biopsy specimens obtained during adenomectomy from the normal, paraadenomatous pituitary tissue. Four granule populations with different immunoreactions were found: (1) granules containing GH only, (2) granules containing PRL only, (3) mixed granules containing GH and PRL, and (4) granules displaying no immunoreactivity. The existence of mixed granules indicated that the two hormones are synthesized by the same cell and in communicating compartments of the cells; i.e., the rough-surfaced endoplasmic reticulum. The number of GH-containing granules (pure GH granules and mixed GH-PRL granules) was greater than that of PRL-containing granules (pure PRL granules and mixed PRL-GH granules) in adenomas causing acromegaly and in the normal pituitary tissue, whereas the opposite was true for prolactinomas. The number of PRL-containing granules was larger in biopsy specimens from patients who had acromegaly and hyperprolactinemia than in patients with acromegaly and normal serum PRL levels.

The mechanism of [3H]dexamethasone uptake into prolactin producing rat pituitary cells (GH3 cells) in culture

Glucocorticosteroids stimulate growth hormone (GH) synthesis and inhibit prolactin (PRL) synthesis and cell growth in cultured GH3 cells, a clonal cell strain derived from a rat pituitary tumour. This model system was used to study the mechanism by which glucocorticosteroids enter target cells. The cellular uptake of [3H]dexamethasone was temperature dependent and was further inhibited by addition of an excess amount of cold dexamethasone. Half maximal uptake was obtained after about 5 min at 37 degrees C. The initial rates of [3H]dexamethasone uptake were a linear function of the extracellular hormone concentration. The uptake of [3H]dexamethasone in intact cells studied at different temperatures resulted in linear Arrhenius plots, with a calculated energy of activation of 91.0 kJ x mole-1 x degree-1. Scatchard analysis of specifically cell bound [3H]dexamethasone at equilibrium (0 degrees C) showed a straight line with a calculated dissociation constant (Kd) of 1.6 x 10(-9) M and a maximal uptake of 180 x 10(-15) mole/mg cell protein. Specific binding of [3H]dexamethasone to cytosol proteins could only be demonstrated at 0 degrees C. These results indicate that [3H]dexamethasone diffuses passively into the cell, and binds to specific receptors in an energy dependent way.

A permissive role for extracellular Ca2+ in regulation of prolactin production by 1,25-dihydroxyvitamin D3 in GH3 pituitary cells

A clonal strain of rat pituitary tumor cells (GH3) that spontaneously synthesizes and secretes prolactin (PRL) and growth hormone (GH) was used as model system to study the mechanism of action of 1,25-(OH)2D3. We have previously demonstrated that these cells possess specific cytosol binding proteins for 1,25-(OH)2D3 (Haug and Gautvik, 1985). When the GH3 cells were incubated in a serum-free, chemically defined medium of low extracellular Ca2+ concentration, 1,25-(OH)2D3 stimulated PRL production in a dose-dependent manner. The stimulation was detectable at 10(-11) M, and the maximum effect (2-fold increase) was observed at 10(-9) M (ED50 = 2 x 10(-11) M). The dose-response curve was bell-shaped, and at 10(-6) M 1,25-(OH)2D3 even suppressed PRL production to about 75% of controls. The stimulatory effect was first seen after 2 days and was maximal after 4 days. On a molar basis 25-OHD3 and 1-OHD3 were at least 100 times less potent than 1,25-(OH)2D3, while 24,25-(OH)2D3 had no effect on PRL production. At an extracellular concentration of Ca2+ as low as 4 x 10(-5) M the stimulatory effect of 1,25-(OH)2D3 was small (1.3-fold). Increasing extracellular Ca2+ to 1.5 x 10(-4) M increased the 1,25-(OH)2D3-induced PRL response to 2.1-fold. In contrast to the biphasic effect of 1,25-(OH)2D3 on PRL production, GH production was decreased to about 60% of controls at 10(-8) M and above. These findings indicate that in serum-free medium the stimulatory effect of 1,25-(OH)2D3 on PRL production is critically dependent on the concentration of extracellular Ca2+.

GH3 cell secretion of growth hormone and prolactin increases spontaneously during perifusion

GH3 cell secretory activity was studied in long-term perifusion to define previously reported spontaneous increases in growth hormone (GH) and prolactin production (PRL). Mechanically harvested cells (1 X 10(7)/column) were perifused at 4 ml/h for 72 h. A basal period of variable duration (8 to 12 h), during which hormone secretion was stable, was followed by steadily increasing secretion rates. Changes in cell number were not sufficient to account for increased hormone secretion rates: a) there was no significant change in cell count after 72 h (0.97 +/- 0.03 X 10(7); n = 18); b) mean cell column DNA content increased 25.5% above the base value, whereas GH secretion rose 385% and PRL rose 178% (n = 5). Observed differences in the duration of the basal secretion period, the basal secretory rate, and the magnitude of secretory rate increase were associated with several variables: a) variability within a subline was a function of passage number: GH secretion decreased and PRL secretion increased with subculture number; b) cells with identical lot and freeze numbers, but received at different times, behaved differently; c) the presence of an antifungal agent (nystatin) altered hormone secretion reproducibly.

CONCLUSIONS

a) rates of GH and PRL secretion rise spontaneously in perifusion without a proportional increase in GH3 cell number; b) fluctuations in the rate of GH3 cell secretion of GH and PRL are not entirely random but are determined by several definable variables.

Melatonin reduces the production and secretion of prolactin and growth hormone from rat pituitary cells in culture

A culture of clonal tumour cells from rat pituitary gland that secrete both prolactin and growth hormone were used to investigate whether the pineal hormone melatonin can act directly on the pituitary gland to control prolactin production. Melatonin inhibition of prolactin and growth hormone production was significant but mild. Concentrations of between 10(-8) M and 10(-6) M reduced both prolactin and growth hormone production and prolactin secretion by 10-50%. 17 beta-oestradiol (OE) and thyrotrophin-releasing hormone (TRH) stimulated prolactin production but had no significant effect on growth hormone production. Melatonin reduced the effects of both of these compounds. Both TRH and vasoactive intestinal peptide (VIP) stimulated secretion of prolactin, and TRH also of growth hormone. Melatonin reduced these effects significantly. TRH and VIP increased cAMP production two- and 12-fold, respectively. Melatonin had no effect on basal or stimulated cAMP production. The melatonin-induced changes in prolactin and growth hormone production and secretion seen here do not approach the magnitude of the fluctuations seen in plasma in vivo. It is concluded that while melatonin does have a direct effect on the lactotroph in the regulation of prolactin production, its main physiological target must be elsewhere.

Thymosin fraction 5 stimulates the release of prolactin from cultured GH3 cells

Thymosin fraction 5, a bovine thymus preparation, has recently been implicated in the regulation of neuroendocrine function. The purpose of the present study was to investigate the effects of thymosin fraction 5 treatment upon the GH3 rat pituitary cell line. Thymosin fraction 5 stimulated prolactin (PRL) release from these cells in a dose and time dependent manner. These results suggest that a product of the endocrine thymus may regulate the release of PRL.

Steroid inhibition of calcitriol-induced prolactin production in GH4C1 cells. Specificity and sensitivity

The induction of prolactin (PRL)-gene expression by calcitriol (1,25-dihydroxyvitamin D3, 1,25-dihydroxycholecalciferol) in clonal rat pituitary tumour (GH4C1) cells was selectively inhibited by cortisol [IC50 (concentration causing 50% inhibition) = 3.2-4.1 nM]. The steroid specificity of this effect was investigated and various steroids were found to inhibit calcitriol-stimulated PRL production with the following relative potencies: cortisol, 1; dexamethasone, 8; 11-deoxycortisol, 0.5; corticosterone, 0.4; aldosterone, 0.07; testosterone and oestradiol, less than 0.003. The steroid antagonist RU 38486 did not affect basal or calcitriol-stimulated PRL production, but antagonized the effect of 10 nM-cortisol in a concentration-dependent manner. Neither progesterone nor 11-deoxycortisol antagonized the effect of 10 nM-cortisol. Calcitriol-induced PRL production was 14 times more sensitive to dexamethasone inhibition than was non-stimulated PRL production. Growth-hormone production was stimulated by dexamethasone, in the presence or absence of calcitriol, with a concentration-dependence similar to that of dexamethasone inhibition of basal PRL production. These data indicate that steroid inhibition of calcitriol-stimulated PRL production is a specific glucocorticoid effect. The sensitivity of calcitriol-stimulated PRL production to dexamethasone was 14-26-fold greater than that of other measured responses in the same cells. Two of the possible explanations for this selectively increased sensitivity to glucocorticoids are: amplification of the glucocorticoid effect via an induced mediator; and the presence of very-high-affinity glucocorticoid-receptor-binding sites on DNA.

Antiestrogens are partial estrogen agonists for prolactin production in primary pituitary cultures

The antiestrogens Ly-117018 and tamoxifen increased prolactin production about 2-fold in primary cultures of male rat anterior pituitary cells. The dose-response relationship was biphasic; 10(-10) M Ly-117018 and 10(-7) M tamoxifen caused maximal stimulation, but higher concentrations caused no stimulation and completely antagonized the 5-fold stimulation caused by estrogen. The calmodulin antagonists, trifluoperazine, pimozide and W7 also prevented estrogen induction of prolactin production. Increasing concentrations of estradiol reversed inhibition by tamoxifen but not by pimozide. These results indicate that, in normal pituitary cells, estrogen antagonists may behave as partial agonists at low concentrations and as full antagonists at higher concentrations (tamoxifen, prolactin, calmodulin, 17 beta-estradiol).

Characterization of antiestrogen stimulation of cell number and prolactin production

The antiestrogens LY117018 and tamoxifen increased prolactin production about 4-fold and cell number about 2.5-fold in the pituitary tumor cell line, GH4C1; these increases were 30-40% of the maximal effects of estradiol. The antiestrogens competed with binding of [3H]estradiol, and LY117018 was more active than tamoxifen in biological activities and binding activity. The antiestrogens inhibited stimulation caused by 10(-10) M estradiol; the inhibition could be overcome by increased estradiol concentrations. Tamoxifen and LY117018 increased the amount of prolactin mRNA per cell. These antiestrogens behave as partial agonists in the GH4C1 cells, but have two unusual features. Estrogens are approximately 10-fold more potent in stimulating cell number than in stimulating prolactin production, but the antiestrogens showed the same dose-response for both effects. The partial agonist activity was biphasic and at higher concentrations the antiestrogens showed more antagonist activity (GH4C1 cells, 17 beta-estradiol, tamoxifen).

Effect of diet or reproductive status on the histology of spontaneous pituitary tumors in female Wistar rats

Hypophyses of four groups of 50 female rats (F0--nulliparous, F0--multiparous, F1--standard diet, and F1--low protein) were examined by light microscopy and immunocytochemistry by the avidin-biotin complex method. In pituitary glands of rats fed a low protein diet, the incidence of neoplasms of the pars distalis, the number of multifocal tumors, and the degree of neoplastic cellular atypia were significantly reduced. Pituitary adenomata in rats fed a low protein diet also caused significantly less brain compression at the time of necropsy than in rats fed a standard diet. All but two neoplastic foci from the 83 tumors stained for prolactin, and 14 of these also stained for growth hormone. No differences were found in the frequency of hemorrhagic or solid patterns of tumor. These findings may reflect a reduction in pituitary tumor initiation, promotion, and/or progression in rats fed a low protein diet.

A possible differentiation of anterior pituitary cells in collagen gels into neurons

Dispersed cells from anterior pituitary glands of male rats were cultured embedded in collagen gels or on a plastic surface. After 6 or more days in culture, cells in collagen produced more prolactin than those on plastic. The cultures in collagen had fewer fibroblasts than those on plastic. Many cells cultured in collagen developed processes, and a few cells in every culture had long extended processes that sometimes branched and resembled those of neurons. About 60% of the cells in culture including cells with well developed processes bound the monoclonal antibody A2B5, an antibody that binds to neuronal cells in culture. Fibroblasts did not have detectable binding of A2B5. Some cells with short processes reacted with antiserum to prolactin or ACTH, but the cells with neuronlike processes did not. Collagen gels may provide a matrix in which cells from the anterior pituitary gland can differentiate into neuronlike cells.

Isolation and characterization of rat-mouse somatic cell hybrids secreting growth hormone and prolactin

Interspecific somatic cell hybrid clones have been isolated and characterized in order to study growth hormone (GH) and prolactin (PRL) gene expression. Rat pituitary tumor cells (GH3, 69 chromosomes) secreting rat GH and PRL were grown for 48 h together with nonhormone secreting, aminopterin-sensitive murine fibroblast cells (LMTK-, 55 chromosomes) and fused using polyethylene glycol. Resultant heterokaryons were selected in hypoxanthine-aminopterin-thymidine (HAT) medium and cloned. Five clones produced rat GH and PRL. Hormone-producing hybrids morphologically resembled the mouse parent fibroblast. Hybrids grew in monolayers and contained 80-142 chromosomes, and marker chromosomes for both rat (small submetacentric) and mouse (bi-armed and large true metacentric) were identified. The interspecific nature of the hybrids was further confirmed by the presence of both rat and mouse adenosine deaminase and superoxide dismutase isozymes. Using specific antisera and indirect immunoperoxidase staining, both hybrid clones and GH3 rat parental cells stained positively for rat GH and PRL, while the murine fibroblast parental cells were negative. Hormone production by the hybrids has been sustained for over twenty subcultures; secretion rates were initially 150 ng PRL and 321 ng GH/10(6) cells/24 h and are currently 100 ng PRL and 90 ng GH/10(6) cells/24 h. Parental GH3 rat cells secreted 720 ng PRL and 660 ng GH/10(6) cells/24 h. Exposure of hybrids to KCl (50 mM) resulted in acute stimulation of rat PRL, but not rat GH release, and long-term incubation with thyrotropin-releasing hormone (TRH, 80 nM) stimulated PRL secretion. Hormone-dependent modulation of PRL secretion was transferred to the hybrid cell thus enabling the model to be used in studying regulation of PRL gene expression.

Glucocorticoids antagonize induction of prolactin-gene expression by calcitriol in rat pituitary tumour cells

Clonal strains of rat pituitary tumour (GH4C1) cells are known to possess specific intracellular binding sites for calcitriol (1,25-dihydroxycholecalciferol, 1,25-dihydroxyvitamin D3). GH4C1 cells respond to calcitriol by a selective increase in prolactin(PRL)-gene expression. The interaction between calcitriol and glucocorticoids was studied by using this cultured-cell model. It was found that cortisol potently antagonized the induction of PRL mRNA and PRL production by calcitriol. The effects were concentration-dependent and were evident at glucocorticoid concentrations that did not alter basal PRL production. Inhibition was half-maximal at 3.2 nM-cortisol and 0.4 nM-dexamethasone. Calcitriol-induced PRL mRNA fell by more than 50% at 25 h and reached the control level 50 h after treatment with cortisol. The inhibition by cortisol of calcitriol induction of PRL production was selective when compared with effects on other inducers of PRL-gene expression [thyroliberin, epidermal growth factor and phorbol myristate acetate ('12-omicron-tetradecanoylphorbol 13-acetate')]. Potent antagonism by glucocorticoids of vitamin D action on specific gene expression has been demonstrated. Further studies with this cultured-cell model may help to explain the mechanism of this hormonal interaction, which assumes particular importance at major sites of vitamin D action such as the intestine.

Demonstration and characterization of a 1 alpha,25-(OH)2D3 receptor-like macromolecule in cultured rat pituitary cells

Recent studies have demonstrated the importance of prolactin (PRL) and growth hormone (GH) in the regulation of 25-hydroxycholecalciferol-1 alpha-hydroxylase activity. We have previously shown that 1 alpha,25-dihydroxycholecalciferol (1 alpha,25-(OH)2D3) reduces PRL and GH production by a clonal strain of rat pituitary tumour cells (GH3). The biologically active form of vitamin D3, 1 alpha,25-(OH)2D3, acts via an initial binding to cytoplasmic receptor proteins in target cells, and we demonstrate in this study the presence of specific receptors for 1 alpha,25-(OH)2D3 in the GH3 cells. GH3 cell cytosol was incubated with [3H]1 alpha,25-(OH)2D3 at 0-4 degrees C. Maximal binding was obtained between 2 and 6 h, and Scatchard analysis showed one single class of binding sites with Kd of 0.33 +/- 0.05 nM (mean + SD) and a Bmax of 103 +/- 26 fmol/mg cytosol protein. Competitive binding experiments revealed the following potency order: 1 alpha,25-(OH)2D3 greater than 25-OHD3 greater than 1 alpha-OHD3, 24,25-(OH)2D3. In contrast, corticosterone, testosterone, progesterone and oestradiol showed negligible ability to displace [3H]1 alpha,25-(OH)2D3 from its receptor. Sucrose gradient ultracentrifugation in high salt concentration revealed that GH3 cell cytosol possessed at 3.7S [3H]1 alpha,25-(OH)2D3 receptor protein which was inactivated by heating and protease treatment, but not after incubation with DNase or RNase. The receptor protein aggregated in salt-free sucrose gradients since the 3.7S complex was shifted reversibly to a approximately 6S form. Isoelectric focussing localized most of the [3H]1 alpha,25-(OH)2D3 to a protein peak with an isoelectric point of approximately 6 (pI 5.8-6.2). Since this 1 alpha,25-(OH)2D3 receptor protein has similar properties as the corresponding 1 alpha,25-(OH)2D3 receptors found in normal rat tissues, we suggest that lactotropes and somatotropes represent true target cells for 1 alpha,25-(OH)2D3.

Hormonal and morphologic effects of bromocriptine on normal rat pituitary and GH3 tumor cells

Bromocriptine in concentrations up to 5 X 10(-4) mol/L was studied for any deleterious effects upon normal rat pituitary cells, as well as on the rat GH3 cell line. Normal rat pituitary glands were obtained by decapitation from 50-day-old female Wistar rats and dispersed with 0.25% trypsin. The cells (10(5) per plate) were then incubated in 60 by 15 mm plates (Falcon) that contained 3 ml of Dulbecco's modified Eagle's medium with 10% fetal calf serum. GH3 cells were plated in a similar fashion. Bromocriptine was added in concentrations of 5 X 10(-4) to 5 X 10(-9) mol/L, and aliquots of medium were obtained at 6, 24, and 48 hours for the determination of growth hormone and prolactin. Cell counts were performed at 24 and 48 hours. A significant reduction in concentrations of growth hormone and prolactin was observed with concentrations of bromocriptine of 5 X 10(-5) and 5 X 10(-4) mol/L at 24 and 48 hours (p less than 001). Although no significant changes in cell counts were observed in the normal rat pituitary cells, the GH3 cells showed complete disruption at 48 hours only in the plates that contained the highest concentrations of bromocriptine. Electron microscopy of normal rat cells and GH3 demonstrated selective cytotoxic effects only on the GH3 cells. In conclusion, bromocriptine has been demonstrated to have a direct effect on hormone release and on the morphologic characteristics of tumor cells but not normal pituitary cells.

In cow anterior pituitary, growth hormone and prolactin can be packed in separate granules of the same cell

The ultrastructural localization of growth hormone and prolactin in cow anterior pituitary was studied by double immunocytochemical labeling using specific antibodies and protein A-gold particles of different sizes. The two hormones were found in specific somatotrophs and mammotrophs as well as in somatomammotropic cells which were multinucleated and predominantly arranged in clusters in the central area of the lobules. In these mixed cells the two hormones were packaged (a) in different granules of the same cell, (b) in the same granules where they were segregated in different portions of the granule content, or (c) in the same granules but evenly intermixed. The relative proportion of these three types of granules varied in somatomammotrophs of different animals. A single large Golgi complex was generally present in somatomammotrophs. Small, immature granules containing either growth hormone or prolactin or both hormones were found randomly distributed along Golgi stacks. This suggests that in these cells the two hormones are processed in the same Golgi cisternae and that mechanism(s) exist(s) to sort out the two hormones from each other.

Perturbation of differentiated functions during viral infection in vivo. I. Relationship of lymphocytic choriomeningitis virus and host strains to growth hormone deficiency

Disordered growth and glucose metabolism secondary to growth hormone deficiency is associated with persistent lymphocytic choriomeningitis virus (LCMV) infection. C3H/St, BALB/WEHI, and SWR/J mice infected at birth with LCMV:ARM carried virus in their blood and organs throughout life but only C3H/St mice developed growth hormone insufficiency. BALB/WEHI and SWR/J infected mice contained normal amounts of growth hormone in their pituitaries and a relatively small proportion of the cells containing growth hormone replicated the virus. In susceptible C3H/St mice, the disease-causing viral strains (LCMV:ARM, E-350, and Pasteur) replicated to higher titers and infected the vast majority of cells producing growth hormone in the anterior lobe of the pituitary. In contrast, LCMV strains Traub and WE replicated in far fewer growth hormone-producing cells and failed to disorder growth hormone synthesis. In another paper (Y. Riviere, R. Ahmed, P. Southern, and M. B. A. Oldstone (1985), Virology 142, 175-182) these findings are used to make reassortants between LCMV:ARM (disease positive) and LCMV:WE (disease nil) and the pathogenic effect is mapped to the small RNA segment of LCMV:ARM. Peptides cleaved by trypsin and chymotrypsin from growth hormone molecules isolated from infected cells or control cells were equivalent when examined by two-dimensional electrophoresis. Further, transfer of antibody to interferon failed to alter the growth hormone insufficiency in these mice, although it corrected LCMV-induced liver disease of BALB mice, suggesting that interferon did not play a dominant role in this disease. The selective tropism of LCMV:ARM for cells containing growth hormone over cells that contain prolactin was observed in both infected animals and in cultured GH-3 cells.

Diethylstilbestrol inhibits tumor growth and prolactin production in rat pituitary tumors

Treatment of rats bearing transplantable MtT/W15 tumors with 10 mg of diethylstilbestrol (DES) for 3 weeks led to inhibition of tumor growth. The inhibition of tumor growth was reversible after removal of the DES. Histologic examination revealed decreased mitotic activity; however, DES did not produce cell necrosis. Concomitantly, the anterior pituitary glands of animals treated with DES became hyperplastic, with an increased number of prolactin (PRL)-producing cells. DES resulted in a decreased number of PRL cells in the tumor and decreased serum PRL/tumor weight, compared with that of control rats. There was also an increase in the number of growth hormone (GH) tumor cells and an increased serum GH/tumor weight. 17 beta-Estradiol had an effect similar to that of DES, while progesterone did not inhibit tumor growth or cause pituitary cell hyperplasia. Ovariectomy resulted in a decrease in the tumor growth rate, compared with that of control animals, suggesting that the MtT/W 15 tumors are relatively dependent on estrogens for optimal growth. These results indicate that DES inhibition of MtT/W 15 tumor growth is an excellent model for study of the mechanism of the inhibition of tumor growth and the modification of GH and PRL expression by the tumor cells.

Isolated ACTH deficiency with transitory GH deficiency

A nine-year-old girl, who presented with a severe hypoglycemic coma, proved to have isolated ACTH deficiency, a finding previously reported in only two children. On the initial evaluation, before any treatment, GH did not respond to provocative stimuli. On replacement therapy with hydrocortisone, normal linear growth was observed. Repeated testing while on glucocorticoids replacement four years after the initial attack revealed normal GH response to stimulation test. It is suggested that cortisol deficiency was responsible for the severe hypoglycemic coma and subnormal GH response. A similar mechanism is speculated for the normal growth observed in some patients with apparent deficiency of anterior pituitary hormones, including GH. The possibility of permanent ACTH deficiency and transitory GH deficiency following hypophysitis is discussed.