Paracrine interactions in the anterior pituitary

Endoscopic Endonasal Approach to Giant Pituitary Adenomas: Surgical Outcomes and Review of the Literature

OBJECTIVE

To present the outcomes of endoscopic endonasal surgery for giant pituitary adenomas and discuss the extent of resection to minimize morbidity and mortality.

METHODS

We retrospectively reviewed medical records of 44 patients with giant pituitary adenomas who underwent endoscopic endonasal surgery. Clinical presentation, laboratory results, imaging studies, clinical outcomes, extent of resection, and complications were collected and analyzed. Factors affecting long-term outcome according to surgical technique were identified and analyzed.

RESULTS

Radical resection (RR) was defined as either gross total resection or near-total resection (90%-100% of the tumor). There were 28 patients (63.6%) who underwent RR, 10 patients (22.7%) who underwent subtotal resection, and 6 patients (13.6%) who underwent partial resection. Visual improvement was achieved in 27 patients (81.8%). Thirteen patients (72.2%) with pituitary dysfunction had improvement in at least 1 preoperative endocrinological dysfunction. RR rates for dumbbell and multilobular tumors were 44.4% and 28.6%, respectively. Surgical complications were observed in 14 (31.8%) patients. Major vascular injury occurred in 3 patients (6.8%). Mean follow-up period was 38.5 months (range, 1-70 months). No patients with RR had recurrence or residual tumor progression. Ten patients (22.7%) received adjuvant radiation therapy after resection. Two patients were reoperated on for tumor regrowth, and 3 patients (including the 2 patients with tumor regrowth) were lost to follow-up.

CONCLUSIONS

Long-term follow-up results and low recurrence rate of tumors indicate that RR is effective to decrease morbidity and mortality.

Comparative aspects of GnRH-Stimulated signal transduction in the vertebrate pituitary - Contributions from teleost model systems

Gonadotropin-releasing hormone (GnRH) is a major regulator of reproduction through actions on pituitary gonadotropin release and synthesis. Although it is often thought that pituitary cells are exposed to only one GnRH, multiple GnRH forms are delivered to the pituitary of teleost fishes; interestingly this can include the cGnRH-II form usually thought to be non-hypophysiotropic. GnRHs can regulate other pituitary cell-types, both directly as well as indirectly, and multiple GnRH receptors (GnRHRs) may also be expressed in the pituitary, and even within a single pituitary cell-type. Literature on the differential actions of native GnRH isoforms in primary pituitary cells is largely derived from teleost fishes. This review will outline the diversity and complexity of GnRH-GnRHR signal transduction found within vertebrate gonadotropes as well as extra-gonadotropic sites with special emphasis on comparative studies from fish models. The implications that GnRHR transduction mechanisms are GnRH isoform-, function-, and cell-specific are also discussed.

Morphometric analysis of the folliculostellate cells and luteinizing hormone gonadotropic cells of the anterior pituitary of the men during the aging process

The aim of this research was to quantify the changes in the morphology and density of the anterior pituitary folliculostellate (FS) and luteinizing hormone (LH) cells. Material was tissue of the pituitary gland of the 14 male cadavers. Tissue slices were immunohistochemically stained with monoclonal anti-LH antibody and polyclonal anti-S100 antibody for the detection of LH and FS cells, respectively. Digital images of the stained slices were afterwards morphometrically analyzed by ImageJ. Results of the morphometric analysis showed significant increase of the FS cells volume density in cases older than 70 years. Volume density of the LH cells did not significantly change, whereas their area significantly increased with age. Nucleocytoplasmic ratio of the LH cells gradually decreased and became significant after the age of 70. Finally, volume density of the FS cell significantly correlated with LH cells area and nucleocytoplasmic ratio. From all above cited, we concluded that in men, density and size of the FS cells increase with age. Long-term hypertrophy of the LH cells results in their functional decline after the age of 70. Strong correlation between FS cells and LH cells morphometric parameters might point to age-related interaction between these two cell groups.

Inter-endothelial transport of microvectors using cellular shuttles and tunneling nanotubes

New insights into the intra- and intercellular trafficking of drug delivery particles challenges the dogma of particles as static intracellular depots for sustained drug release. Recent discoveries in the cell-to-cell transfer of cellular constituents, including proteins, organelles, and microparticles sheds light on new ways to propagate signals and therapeutics. While beneficial for the dispersion of therapeutics at sites of pathologies, propagation of biological entities advancing disease states is less desirable. Mechanisms are presented for the transfer of porous silicon microparticles between cells. Direct cell-to-cell transfer of microparticles by means of membrane adhesion or using membrane extensions known as tunneling nanotubes is presented. Cellular relays, or shuttle cells, are also shown to mediate the transfer of microparticles between cells. These microparticle-transfer events appear to be stimulated by environmental cues, introducing a new paradigm of environmentally triggered propagation of cellular signals and rapid dispersion of particle-delivered therapeutics. The opportunity to use microparticles to study cellular transfer events and biological triggers that induce these events may aid in the discovery of therapeutics that limit the spread of disease.

Effect of inspiration/expiration on height measurement

BACKGROUND

Growth parameters are a powerful screening tool in pediatric care. Accuracy assumes differing importance in different clinical settings. A small error is not clinically significant when height is obtained as a screening tool during annual well child visits. However, when assessing annual growth velocity using shorter interval visits, an error of equal magnitude might influence further management decisions. AIM AND HYPOTHESIS: To explore the effect of inspiration or expiration on height measurement. Our hypothesis was that height measurements obtained in inspiration would be greater than those obtained in expiration or without specific instructions as to status of respiration (unspecified).

METHODS

Heights of 99 individuals 8 years and older were measured in inspiration, expiration and unspecified respiratory status by two pediatric endocrinologists. Patients were measured three times in each mode. The p values were adjusted by Tukey procedure for multiple comparisons among three modes.

RESULTS

Height measurement performed in inspiration, expiration or without specific instruction as to breathing (unspecified) did affect height measurement. Mean difference +/- SEM (95% CI) between height obtained in inspiration and expiration was 0.22 +/- 0.03 cm (95% CI: 0.15, 0.29); between inspiration and unspecified 0.31 +/- 0.04 cm (95% CI: 0.22, 0.40); and between expiration and unspecified 0.092 +/- 0.03 cm (95% CI: 0.03, 0.16).

CONCLUSIONS

Based on these results, we recommend multiple height measurements using uniform technique including inspiratory/expiratory status, especially when calculating 'annualized' height velocity over short intervals.

Pituitary cell lines and their endocrine applications

The pituitary gland is an important component of the endocrine system, and together with the hypothalamus, exerts considerable influence over the functions of other endocrine glands. The hypothalamus either positively or negatively regulates hormonal productions in the pituitary through its release of various trophic hormones which act on specific cell types in the pituitary to secrete a variety of pituitary hormones that are important for growth and development, metabolism, reproductive and nervous system functions. The pituitary is divided into three sections-the anterior lobe which constitute the majority of the pituitary mass and is composed primarily of five hormone-producing cell types (thyrotropes, lactotropes, corticotropes, somatotropes and gonadotropes) each secreting thyrotropin, prolactin, ACTH, growth hormone and gonadotropins (FSH and LH) respectively. There is also a sixth cell type in the anterior lobe-the non-endocrine, agranular, folliculostellate cells. The intermediate lobe produces melanocyte-stimulating hormone and endorphins, whereas the posterior lobe secretes anti-diuretic hormone (vasopressin) and oxytocin. Representative cell lines of all the six cell types of the anterior pituitary have been established and have provided valuable information on genealogy of the various cell lineages, endocrine feedback control of hormone synthesis and secretions, intrapituitary interactions between the various cell types, as well as the role of specific transcription factors that determine each differentiated cell phenotype. In this review, we will discuss the morphology and function of the cell types that make up the anterior pituitary, and the characteristics of the various functional anterior pituitary cell systems that have been established to be representative of each anterior pituitary cell lineage.

Recombinant human follicle-stimulating hormone: a controversial issue--without controversy

Recent developments in recombinant DNA technology have resulted in a rapidly expanding range of new diagnostic and therapeutic opportunities. This technology paved the way for identification, isolation, cloning and production of specific proteins. Recently, recombinant human gonadotropins became available for clinical use. Pharmacokinetics, receptor availability, pharmacodynamics and safety were extensively studied and the drugs were found to be identical, if not superior, to urinary gonadotropins that have been used in reproductive medicine for the last 40 years. It is currently apparent that the use of recombinant human gonadotropins is expected to provide improved batch-to-batch consistency, steady supply and most importantly, a purified compound with highly specific activity, which accounts for > 99% of the protein content of the preparation, making it possible to administer subcutaneously. The purpose of this report is to describe and evaluate recent developments in the use of recombinant human follicle-stimulating hormone.

From galactorrhea to osteopenia: rethinking serotonin-prolactin interactions

The widespread use of the selective serotonin reuptake inhibitors (SSRIs) has been accompanied by numerous reports describing a potential association with hyperprolactinemia. Antipsychotics are commonly known to elevate serum prolactin (PRL) through blockade of dopamine receptors in the pituitary. However, there is little awareness of the mechanisms by which SSRIs stimulate PRL release. Hyperprolactinemia may result in overt symptoms such as galactorrhea, which may be accompanied by impaired fertility. Long-term clinical sequelae include decreased bone density and the possibility of an increased risk of breast cancer. Through literature review, we explore the possible pathways involved in serotonin-induced PRL release. While the classic mechanism of antipsychotic-induced hyperprolactinemia directly involves dopamine cells in the tuberoinfundibular pathway, SSRIs may act on this system indirectly through GABAergic neurons. Alternate pathways involve serotonin stimulation of vasoactive intestinal peptide (VIP) and oxytocin (OT) release. We conclude with a comprehensive review of clinical sequelae associated with hyperprolactinemia, and the potential role of SSRIs in this phenomenon.

The influence of muscle action on the acute growth hormone response to resistance exercise and short-term detraining

The effects of resistance training with concentric or concentric-eccentric muscle actions on the acute hormonal response to a resistance exercise protocol was investigated. Thirty-two men completed a 19 week lower-body resistance training program (consisting of the leg press and leg extension exercises) in which they (1) performed concentric actions only (CON); (2) performed both concentric and eccentric actions (CON-ECC); (3) performed double concentric actions for each repetition (CON-CON); or (4) did not exercise. Following training each subject performed two exercise tests consisting of three sets of 30 isokinetic concentric (day 1) and eccentric (day 2) knee extensions separated by 48 h. The exercise tests were repeated following 4 weeks of detraining. Blood samples were obtained before and after each exercise test. Serum growth hormone (GH) was significantly (P< 0.05) greater for the concentric test in groups CON and CON-CON whereas GH was lower for the concentric test in CON-ECC compared with the eccentric test prior to detraining. Following detraining, GH was greater during the concentric test in CON-ECC than in the eccentric test, whereas no differences were observed between the concentric and eccentric tests in CON and CON-CON and the acute GH response to resistance exercise was attenuated. These data indicate that GH is sensitive to muscle action type with differential responses observed with resistance exercise after short-term detraining.

Gender differences and the effect of different endocrine situations on the NOS expression pattern in the anterior pituitary gland

The presence of neuronal nitric oxide synthase (nNOS) in two populations of pituitary cells, gonadotrophs (LH) and folliculostellate (FS) cells, suggests that pituitary nitric oxide (NO) is involved in the control of hormone secretion. We have used single and double immunostaining and quantitative procedures to investigate possible gender-related differences in the nNOS expression pattern in the anterior pituitary lobe and its possible alterations in different endocrine situations. Our results reveal a sexual dimorphism in the pattern of nNOS expression. In males, nNOS is mainly found in FS cells, whereas only a few LH cells express nNOS. Conversely, in females, nNOS is mainly found in LH cells. After gonadectomy, paralleling an increase in LH cell size and serum luteinizing hormone (LH) levels, there is nNOS upregulation in LH cells and nNOS downregulation in FS cells. After testoterone replacement, LH cells become nNOS-immunonegative again. In lactating rats, LH cells overexpress nNOS, but LH cell size and serum LH levels are low. This suggests that, depending on its cellular source, pituitary NO can exert either an inhibitory or a stimulatory effect on hormone secretion. When released from FS cells, NO exerts a paracrine inhibitory effect, and when released from gonadotrophs it exerts an autocrine or paracrine stimulatory effect on LH or prolactin secretion, respectively.

Synaptoid contacts between gland cells of the anterior pituitary of the rat

BACKGROUND

There is evidence suggesting cross-talk among gland cells of the anterior pituitary. We had reported a rare form of synaptoid contact between corticotrophs in the anterior pituitary of the dog. We then found similar synaptoid contacts with different characteristics in the rat, as described in the present article.

METHODS

Male Sprague-Dawley rats were used. The anterior pituitaries were prepared for ultrastructural study of substance P immunoreactivity of the anterior pituitary. Routine preembedding immunohistochemical staining was conducted, the sections were embedded in Epon 812 (Serva Feinbiochemica, Heidelberg, New York), and ultrathin sections were prepared.

RESULTS

In the anterior pituitary of the rat, synaptoid contacts were found between corticotrophs and lactotrophs. They appeared very close to typical synapses in the central nervous system, aside from evident weakness of presynaptic density.

CONCLUSIONS

The presence of synaptoid contacts suggests a form of cross-talk between the gland cells in the anterior pituitary of the rat.

Enhancement by prolactin of the GnRH-induced release of LH from dispersed anterior pituitary cells of the bullfrog (Rana catesbeiana)

The response of enzymatically dispersed anterior pituitary cells of the bullfrog (Rana catesbeiana) to gonadotropin-releasing hormone (GnRH) was studied by monitoring the release of luteinizing hormone (LH) into the culture medium. The cells responded to GnRH by releasing LH according to the incubation time and to the GnRH concentration. The responsiveness to GnRH became less conspicuous as the cell density was reduced. Addition of prolactin (PRL) to the medium enhanced the responsiveness to the secretagogue, and addition of antiserum against PRL lowered the responsiveness to a certain extent. Immunohistochemical studies of sectioned pituitaries revealed that PRL cells most frequently located in contact with LH cells. The possibility that PRL acts directly on gonadotrophs to enhance their responsiveness to GnRH was suggested.

Effects of age and gender on the AII-induced stimulation of prolactin release and inositol phosphate accumulation in rat anterior pituitary cells in vitro

The stimulatory effects of Angiotensin II (AII) on prolactin secretion and inositol phosphate accumulation were examined in dispersed anterior pituitary cells collected from young (3-4 month), mature (7-8 month) and old (18-20 month) male and female rats. Physiological doses of AII (0.01-10 nM) stimulated prolactin release from cells collected from mature female rats only. This effect was antagonized by pretreatment with Saralasin, an AII receptor antagonist. Significant accumulation of the inositol phosphates was observed in cells obtained from the mature, female donors and this increase preceded the prolactin response. Although there was a small increase in total inositol phosphate accumulation in cells obtained from the old female rats, this was transient and did not coincide with a similar increase in prolactin release. These results indicate that pituitary sensitivity to AII stimulation is related to the age and the gender of the donor animal. The physiological role of pituitary AII needs to be examined in sexually mature female animals.

Neurotensin and tyrosine hydroxylase in the tuberoinfundibular system of the guinea pig hypothalamus with special emphasis to lactation status

Immunohistochemical methods allowed us to study the distribution of neurotensin immunoreactivity (NT-IR) in the infundibular area of the guinea pig and to obtain evidence of a clear increase of such immunoreactivity in females during lactation. By use of the double immunolabeling method we demonstrated the presence of NT in the tuberoinfundibular dopaminergic (TIDA) neuronal system, in the nerve terminals of the median eminence as well as in the arcuate perikarya. In addition, NT-IR was detected in anterior pituitary cells especially stained in the rostral part of the gland of lactating females. These cells were identified exclusively as gonadotrophs by use of the elution-restaining procedure. These results suggests that NT is able to participate in the modulation by TIDA of prolactin secretion. Moreover, NT production by gonadotrophs could be responsible for other unknown pituitary actions.

Localization of mRNA coding for the three subtypes of atrial natriuretic factor (ANF) receptors in rat anterior pituitary gland cells

Atrial Natriuretic Factor (ANF) action is mediated by highly selective and specific receptors. Three subtypes have been characterized and cloned: ANF receptor-A, -B and -C. These subtypes are all expressed in the anterior pituitary of the rat. In the present study, the mRNA for each subtype was detected by in situ hybridization. The amounts of ANFR-A and -B mRNA were found to be similar, and to be twice that of ANFR-C mRNA. At the ultrastructural level, the three types of ANFR mRNA were expressed in three anterior pituitary cell types, namely lactotrophs, corticotrophs, and gonadotrophs, identified by their hormonal content. No signal was revealed in somatotrophs or thyrotrophs. The different forms of mRNA were similar in terms of subcellular localization: in the cytoplasmic matrix and the nuclear euchromatin. These data indicate that the anterior pituitary is an important target tissue for ANF action.

Division of labor among gonadotropes

This chapter has presented a somewhat complex view of the gonadotrope population, indicating that it consists of independent subsets. There may be regulatory cells that influence development and other ancillary processes needed for normal reproduction. For example, normal differentiation of PRL cells requires a functioning population of gonadotropes (Kendall et al., 1991). In addition, gonadotropes appear to be autoregulatory; subsets may produce inhibin or activin (in rats) and follistatin. Production of GnRH itself may serve as another regulatory tool. The gonadotrope population appears to be quite dynamic and convertible in the female rat. Cytological and cytochemical changes with the stage of the cycle are obvious. Increases in the numbers of immunoreactive gonadotropes parallel increases in GnRH target cells and culminate in peak expression of LH and FSH beta subunit mRNAs. The immunoreactive gonadotropes are greatly reduced after the surge activity, as though the cells had disappeared from the population. However, gonadotropes can still be detected by their content of gonadotropin mRNAs. This finding has led to the hypothesis that the gonadotropes recycle themselves. However, do they go through a resting phase? Is there a normal cycle of cell death and turnover? These are basic questions that must be answered in order to understand how the population is organized and renewed. Finally, we have returned to one of our original problems. Whereas it is clear that nonparallel release can be brought about by granules or cells with only one gonadotropin, the exact mechanisms that sort the gonadotropin molecules or turn off bihormonal expression are not known. A combination of autoregulatory events involving follistatin, activin, inhibin, and possibly steroids may play a role in modulating expression by a given subset. Delays in maturation may also prevent secretion of FSH and, hence, effect the delayed rise seen during late proestrus. The nonsecretory FSH cells seen in the studies by Lloyd and Childs (1988a) may be delayed maturers, requiring additional receptor types or changes in the calcium flux pattern to secrete their product. We also have a new question to address. What is the significance of the presence of GH in proestrous gonadotropes? Is GH a regulatory hormone, bound to receptors inside gonadotropes, or do subsets of somatotropes augment the population, producing a cocktail of GH and gonadotropins to aid ovulation? Either hypothesis is intriguing. Co-storage of GH and gonadotropins would be an efficient way of providing the hormones needed by the ovary. However, further work with in situ hybridization is needed to detect GH mRNA in such cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Internalization and nuclear localization of peptide hormones

The presence of neuropeptide receptors on the plasma membrane is well accepted, as is its internalization and down-regulation. The analysis of the fate of these peptides within their target-cells is difficult. Endogenous peptides or administered native peptides are visualized in these cells using immunocytology after cryoultramicrotomy. Labelled peptides can be injected and their internalization kinetics studied using ultrastructural autoradiography. The pituitary gland is a suitable model for the study of the neuropeptide mechanism, with the lactotroph function being taken as an example in the present case. Prolactin (PRL) release depends on two main neuropeptides: thyrotropin-releasing hormone (TRH) and somatostatin (SS). The TRH immunoreactivity obtained from endogenous as well as injected material was restricted to the plasma membrane, secretory granules, cytoplasmic matrix and nucleus. The internalization kinetics of exogenous native TRH showed an increase of immunoreactive material in all compartments including the nucleus. The endogenous SSs (SS14 and SS28) were detected in the same subcellular lactotroph compartments. Injection of 125I-SS showed a rapid binding of SS at the plasma membrane level before internalization. For 60 min of in vivo uptake, 125I-SS28, the large SS molecule, was detected in the cytoplasm only, while 125I-SS14 was found in the nuclear matrix. In vitro 125I-SS28 was restricted to the nuclear membrane. Under physiological conditions the endogenous neuropeptides were visualized in the nucleus, but after injection of labelled peptides only small molecules were found in the nucleus. The significance of the presence of these neuropeptides is discussed.

Bioactive peptides in anterior pituitary cells

The anterior pituitary (AP) has been shown to contain a wide variety of bioactive peptides: brain-gut peptides, growth factors, hypothalamic releasing factors, posterior lobe peptides, opioids, and various other peptides. The localization of most of these peptides was first established by immunocytochemical methods and some of the peptides were localized in identified cell types. Although intracellular localization of a peptide may be the consequence of internalization from the plasma compartment, there is evidence for local synthesis of most of these peptides in the AP based on the identification of their messenger-RNA (mRNA). In several cases the release of the peptide from the AP cell has been shown and regulation of synthesis, storage and release have also been described. Because the amount of most of the AP peptides is very low (except for POMC peptides and galanin), endocrine functions are not expected. There is more evidence for paracrine, autocrine, or intracrine roles in growth, differentiation, and regeneration, or in the control of hormone release. To demonstrate such functions, in vitro AP experiments have been designed to avoid the interference of hypothalamic or peripheral hormones. The strategy is first to show a direct effect of the peptide after adding it to the in vitro system and, secondly, to explore if the endogenous AP peptide has a similar action by using blockers of peptide receptors or antisera immunoneutralizing the peptide.

Effect of pulse frequency and amplitude of D-Trp6-luteinizing hormone-releasing hormone on the pulsatile secretion of prolactin and LH

This work analyzes the effect of the pulse amplitude and frequency of a potent LHRH analog, D-Trp6-LHRH, in a perfusion system of isolated rat pituitary cells. To this purpose, we studied the LH and PRL secretion in different conditions: basal secretion, secretion after increasing concentrations of D-Trp6-LHRL (0.001, 0.01, 0.1 and 1 nM) secretion in function of the pulses frequency (2,3, and 4 pulses per h) and amplitude (0.1, 1 and 10 nM). The principal findings were: 1. The basal LH and PRL secretions was pulsatile; 2. The stimulation of LH by the analog was not dose-dependent; 3. When more than 2 pulses per h were administered, a rapid desensitization of gonadotroph to release LH (at 20-30 min) occurred; 4. There was a loss of pulsatility of PRL secretion with an increase in the pulse frequency and amplitude of the D-Trp6-LHRH, which was produced parallelly to the desensitization of the gonadotroph to release LH. In summary, these findings suggest that a rapid loss of pulsatility of the PRL when the D-Trp6-LHRH pulse frequency and amplitude is increased might be due to the early desensitization of the gonadotroph to the analog.

Unexpected effects of peptide and nonpeptide substance P receptor antagonists on basal prolactin and growth hormone release in vitro

The effect of peptide and nonpeptide substance P antagonists on prolactin (PRL) and growth hormone (GH) secretion was evaluated in three-dimensional rat anterior pituitary cell aggregates. [D-Arg1,D-Phe5,D-Trp7,9,Leu11]Substance P inhibited basal growth hormone (GH) release at a concentration range of 1-10 microM. At higher concentrations (50 microM), the analogue inhibited basal prolactin (PRL) release but provoked a tenfold stimulation of GH release. However, these latter two effects could neither be mimicked nor antagonized by the tachykinins substance P (10 microM), neurokinin A (10 microM), and neurokinin B (3.3 microM). The effects could also not be explained by agonism or antagonism at the level of other receptors (e.g., vasopressin, bombesin, angiotensin II, thyroid hormone-releasing hormone, vasoactive intestinal peptide, dopamine, adrenaline, acetylcholine). Remarkably the nonpeptide substance P antagonists R 30732 (10 microM), R 32602 (10 microM), and CP-96,345 (10 microM) showed a similar inhibition of PRL release and a stimulation of GH release. At a one hundredfold lower concentration, sufficient to block substance P receptors in other tissues. CP-96,345 did not affect PRL or GH release. It is concluded that substance P antagonists, when used at high concentrations, have profound intrinsic activities on PRL and GH release that are not mediated by substance P receptors. The failure of the more potent substance P antagonist, CP-96,345, to influence basal PRL or GH release when used at lower concentrations suggests that endogenous substance P in the anterior pituitary does not play a tonic paracrine role on GH or PRL secretion.

Partial dopamine D2 receptor agonists antagonize prolactin-regulating D2 receptors in a transfected clonal cell line (GH4ZR7)

(-)-(3-Hydroxyphenyl)-N-n-propylpiperidine ((-)-3-PPP) and transdihydrolisuride (terguride, TDHL) are partial dopamine D2 receptor agonists displaying low intrinsic activity at normosensitive postsynaptic dopamine D2 receptors in brain while activating prolactin-regulating dopamine D2 receptors in male rats with an efficacy close to that of full dopamine D2 receptor agonists. In the present study we examined the effects of these partial dopamine D2 receptor agonists on prolactin release in vitro. For this purpose prolactin-producing tumour cells which have been transfected with the dopamine D2 receptor cDNA and hence which express a dopamine D2 receptor (short isoform) that is functionally active with respect to inhibition of adenylate cyclase and prolactin release (GH4ZR7; Albert et al., J. Biol. Chem. (1990) 265, 2098) were used. While the full dopamine D2 receptor agonists, quinpirole, (+)-(3-hydroxyphenyl)-N-n-propylpiperidine ((+)-3-PPP) and dopamine induced a dose-dependent suppression of vasoactive intestinal peptide (VIP)-induced prolactin release from GH4ZR7, both (-)-3-PPP and terguride were inactive. Furthermore, the prolactin-suppressive effects of dopamine and quinpirole were significantly antagonized by pretreatment with (-)-3-PPP and terguride. It is concluded that partial dopamine D2 receptor agonists, which activate male lactotroph dopamine D2 receptors in vivo, may antagonize dopamine D2 receptors on GH4ZR7 cells. There were similar results from an experiment using monolayers of anterior pituitary cells from male rats. Thus, in this in vitro preparation (+)-3-PPP suppressed spontaneous prolactin release while (-)-3-PPP again was inactive.(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation of pituitary gonadotropins and prolactin secretion by testosterone in vitro

Investigations were undertaken to study the differential modulation of LH, FSH and PRL secretion by testosterone (T) using whole pituitary (PI) or pituitary-hypothalamus coincubates (PHC) as in vitro constructs. PI and PHC from intact and castrated rats were incubated with or without T thrice, for 24 h each, (24 h x 3, total incubation period 72 h). The spent media was replenished every 24 h. At the end of 72 h, a few of the pituitary glands were challenged with 10 nM LHRH for 4 h. The spent media and pituitary glands were analyzed for LH, FSH and PRL using specific RIAs. Incubation of PI or PHC from intact rats with T stimulated the release of LH and FSH but inhibited the release of PRL. T had no effect on the intrapituitary contents of LH but inhibited intrapituitary contents of FSH and PRL, as compared to controls incubated without T. Castration increased intrapituitary contents of LH and FSH with concomitant decrease in PRL levels. Incubation of PI or PHC from castrated rats with T inhibited intrapituitary contents of LH to intact pituitary levels, while PRL levels were further reduced instead of being ameliorated. It is concluded that PI or PHC can be used as convenient in vitro models to monitor the effect of castration or of T modulation of pituitary and hypothalamus functions. T does not affect the synthesis of LH at the gonadotroph level but facilitates the regulation of intracellular LH and FSH levels. It is postulated that T inhibits the synthesis of FSH/PRL at the gonadotroph/lactotroph levels.

GnRH antagonists suppress prolactin release in non-human primates

GnRH antagonists, such as Antide, are being evaluated for potential contraceptive applications. Although their contraceptive efficacy clearly results from their rapid inhibitory effects on gonadotropin release, there remains the possibility of other incidental effects. Under certain physiological conditions, the release of prolactin (Prl) appears to be temporally related to the secretion of luteinizing hormone (LH) and hence by inference to the secretion of GnRH. Here, we examined the effects of the GnRH antagonist Antide on the release of LH and Prl. Under agonadal conditions, a remarkable concordance was seen between LH and Prl pulses with up to 100% of pulses being coincident. Administration of Antide resulted in a rapid parallel decline in both LH and Prl with LH levels falling by 50% within 2 h and Prl levels falling by 30-40%. At this dose of Antide (1.0 mg/kg, sc), pulsatile release of LH and Prl continued albeit at a much reduced amplitude. The administration of a bolus of exogenous GnRH in the face of GnRHant-induced suppression resulted in prompt release of LH and Prl in all 3 monkeys. Since Antide inhibits the release of LH and Prl in a parallel fashion, and GnRH re-stimulates the release of both hormones in a parallel fashion, we conclude that the synchronous pulsatile release of LH and Prl observed in the agonadal monkey is due to a direct action of GnRH. What this action is for Prl release, and how it relates to the control of dopamine or other neuroendocrine mechanisms normally controlling the release of Prl remains unclear. It also remains to be seen whether this GnRH antagonist-induced suppression of Prl will have physiologic significance.

Contrasting effects of pituitary adenylate cyclase activating polypeptide (PACAP) on in vivo and in vitro prolactin and growth hormone release in male rats

Pituitary adenylate cyclase activating polypeptide (PACAP) is produced by hypothalamic neurons which terminate within the median eminence suggesting that it may be a hypophysiotropic hormone. However, little endocrine activity has been ascribed to the peptide. Therefore we studied the effects of PACAP on prolactin (Prl) release from dispersed cultivated rat pituitary cells in vitro using conventional cultures as well as the reverse hemolytic plaque assay (RHPA). Furthermore the effects of the peptide on in vitro GH release were assessed. In addition, the activity of the peptide on in vivo release of Prl and GH was studied in hypothalamus-lesioned animals. PACAP dose dependently inhibited Prl release form dispersed pituitary cells in both, monolayer cell cultures and the RHPA, whereas GH secretion was not affected. In hypothalamus-lesioned rats which have high Prl levels due to the absence of hypothalamic dopamine, PACAP further stimulated Prl release. Serum GH increased more than 20 fold in response to the intravenous PACAP infusion. Thus in vitro (inhibition of Prl release, no effect on GH release) and in vivo (stimulation of both hormones) experiments yielded contradicting effects of PACAP on pituitary hormone release. We suggest that PACAP may stimulate the release of a paracrine, yet unknown factor which in the intact pituitary overrides the direct inhibitory action of PACAP on the lactotropes. The same or another paracrine factor may also enhance in vivo GH release. In cell culture the paracrine factor is diluted by the medium. Therefore the peptide never reaches effective concentrations which are present within the intact pituitary tissue.

In vivo and in vitro evidence of growth hormone-releasing factor-like produced locally in the adenohypophyseal cells of the rat

In order to characterize immunocytochemically the existence of GRF in the rat adenohypophysis and the origin of this hormone, an immunocytochemical and morphometric study was made of r-GRF-immunoreactive cells from the adenohypophysis of untreated adult rats, adult rats treated intraventricularly with colchicine and in primary cultures of adult rat adenohypophyseal cells that had been incubated with serum devoid of GRF. r-GRF immunoreactive cells were observed in untreated rat pituitaries, both male and female, although the numbers of positive cells were greater in the males (p less than 0.05) and were found to increase in number following treatment with colchicine (p less than 0.01). These cells appeared dispersed throughout the anterior lobe, without forming clusters, and were often close to blood vessels. Additionally, immunoreactive cells appeared in the cultures at 7 days of incubation. The presence of GRF-immunoreactive cells in the adenohypophysis of rats previously treated with colchicine suggests the existence of a non-hypothalamic origin for r-GRF; this is confirmed by the findings obtained in the in vitro studies which would corroborate the hypothesis that the origin of the neuropeptide is in the rat adenohypophysis itself.

Identification of a D1 dopamine receptor, not linked to adenylate cyclase, on lactotroph cells

1. We studied the lactotroph cells of the rat by both in vivo and in vitro pharmacological techniques for the presence of D1-receptors. Both approaches revealed the presence of D2-receptor, stimulated by quinpirole (resulting in an inhibition of prolactin secretion) and blocked by domperidone. 2. Administration of fenoldopam, the most selective D1-receptor agonist currently available, resulted in a dose-dependent decrease of prolactin secretion in vivo (after pretreatment with alpha-methyl-p-tyrosine) and in vitro (cultured pituitary cells). This increase was dose-dependently blocked by the selective D1-receptor antagonist, SCH 23390, and although the effect of fenoldopam was less than that obtained by D2-receptor stimulation, these data suggest that a D1-receptor also controls prolactin secretion. 3. In order to detect the location of these dopamine receptors, autoradiographic studies were performed by use of [3H]-SCH 23390 and [3H]-spiperone as markers for D1- and D2-receptors, respectively. Specific binding sites for [3H]-SCH 23390 were demonstrated. Fenoldopam dose-dependently reduced [3H]-SCH 23390 binding, but had no effect on [3H]-spiperone binding. Immunocytochemical labelling of prolactin cells after incubation with [3H]-SCH 23390 revealed that the granulae and hence, D1 binding sites were present on the lactotroph cells. 4. Radioligand binding studies performed on membranes from anterior pituitary cells revealed the presence of the D2-receptor (54 fmol mg-1 protein) with a Kd of 0.58 nM for [3H]-spiperone, but failed to detect D1-receptors. 5. Finally, we studied the effect of dopamine and of fenoldopam on the adenosine 3':5'-cyclic monophosphate (cyclic AMP) content of anterior pituitary cells. Although cyclic AMP increased upon prostacyclin administration, indicating an intact adenylate cyclase system, fenoldopam failed to increase the cyclic AMP production. 6. It is tempting to speculate that fenoldopam reduces prolactin secretion through interaction with a non-cyclase-linked D1-receptor on the lactotroph cells.

The interferon family stimulates the secretions of prolactin and interleukin-6 by the pituitary gland in vitro

The effects of interferon-alpha, interferon-beta 1 and interferon-gamma on the secretions of prolactin (PRL) and interleukin-6 by primary cultured rat anterior pituitary cells were examined. These three interferons caused dose-dependent increases in PRL secretion within 30 min, and dose-dependent stimulation of interleukin-6 were weaker than the effects of interleukin-1 and tumor necrosis factor-alpha. These results suggest that interferons regulate PRL secretion from the pituitary gland, and that there may be a pathway in which interferons stimulate PRL secretion through interleukin-6 release.

Mechanisms that subserve estradiol's induction of increased prolactin concentrations: evidence of amplitude modulation of spontaneous prolactin secretory bursts

Estradiol stimulates hyperprolactinemia in human beings and in experimental animals by mechanism(s) that remain largely undefined. We have tested the hypothesis that estrogen modulates episodic and rhythmic prolactin release. To this end we studied six postmenopausal women by repetitive venous sampling basally and on days 1, 5, 10, and 30 after intravaginal placement of an estradiol-impregnated polymeric silicone (Silastic) ring. Computerized analysis of episodic prolactin pulsatility revealed that estrogen amplified prolactin pulse amplitude threefold without changing prolactin pulse frequency. Fourier analysis disclosed heightened amplitudes of specific ultradian rhythms, and deconvolution analysis demonstrated a sevenfold increase in the mass of prolactin secreted per pulse with no change in its half-life. We conclude that estradiol selectively augments the amplitude of episodic prolactin pulsatility, amplifies ultradian rhythms, and increases the mass of prolactin released per secretory burst.

Prolactin, human nutrition and evolution, and the relation to cystic fibrosis

Cystic fibrosis (CF) is a lethal, genetically transmitted disease of Caucasian populations. Its prevalence is highest (ca 1:2000 live births) among Western and Central Europeans and their descendants. Major clinical symptoms are chronic, obstructive, pulmonary disease, impaired intestinal digestion and absorption and elevated concentration of salt in sweat. The last is important, not only for diagnosis, but because it is an example of an electrolyte transport defect present in other epithelial tissues. Numerous other clinical manifestations are generally present. The history of prolactin (PRL), especially its role in osmoregulation, is outlined and related to the symptomatology and electrolyte defect of CF. Data are presented showing the relation of PRL to regulation of sweat electrolytes and its presence and probable synthesis in the coil of the human sweat gland. The basic biochemical defect of CF has not yet been elucidated, but recent research has shown that it is probably an abnormality of a regulatory factor. We propose that PRL is a likely candidate. The large variety of functions of PRL, in particular the regulation of the transport of sodium and chloride across epithelial membranes, and the regulation of mucus production, can be matched to the major disease symptomatology. Additionally, every other one of the multiple abnormalities of CF can be associated with described activities of PRL. In lower vertebrates epithelial tissues regulated by PRL are phylogenetic progenitors of affected tissues in CF. In the human, these tissues contain cells of the Diffuse Neuroendocrine System, or APUD cells, that show PRL-like immunoreactivity, or overt synthesis of the hormone. Thus, the regulatory activity of these tissues could be paracrine. The geographic distribution and the dietary habits of early Caucasians are examined. It appears that the Neolithic revolution, with the necessity of adapting to agriculturally produced foods, i.e. milk and wheat, could have brought about the genetic selection of post-translational variants of PRL. It is suggested that the combination of two or more of these mutations in the same individual may be responsible for CF. This is illustrated with proposed models of CF inheritance. We conclude by postulating that PRL acts at the level of the target cell by triggering (in conjunction with a steroid) the gene expression of unique proteins; these act as intermediaries of PRL activity; two or more abnormalities of these proteins when present in an individual produce CF; the protein abnormalities are the consequence of nutritional and ecological pressure.

Prolactin-inhibiting activity of GnRH associated peptide in cultured human pituitary cells

The 56-amino-acid extension of GnRH in the human GnRH precursor (pHGnRH 14-69 or GAP) has previously been shown to inhibit PRL secretion from cultured rat pituitary cells. We have studied the effect of GAP and shorter sequences on prolactin secretion from human and rat pituitary cells. Bacterially synthesized GAP inhibited PRL secretion from human pituitary cells. At 10(-6) M GAP inhibition of prolactin release was 67.7% which was similar to that observed in rat pituitary cells (65.5%). A series of shorter peptide sequences (pHGnRH 14-26, pHGnRH 14-36, pHGnRH 14-37.NH2, pHGnRH 28-36, pHGnRH 38-49 and pHGnRH 51-66) which are potentially processed from GAP at basic amino acid residues had no effect on prolactin secretion from human or rat pituitary cells at doses up to 10(-5) M.

Use of semipermeable polyurethane hollow fibers for pituitary organ culture

A new model for organ culture of endocrine tissue is described. Rat anterior pituitary fragments were cultured for 4 wk within semipermeable polyurethane isocyanate hollow fibers. Growth hormone and prolactin, two of the anterior pituitary hormones, were released into the medium during the entire culture period. Electron microscopy of the pituitary fragments after 2 wk in culture showed a rim of viable tissue in all specimens examined. Individual cells, from this outer rim, exhibited excellent organelle preservation and numerous secretory granules. Experiments involving potassium depolarization and 10(-6) M dopamine provided evidence for the normal responsiveness of the cultured pituitary tissue to both stimulatory and inhibitory factors. These studies illustrate the potential utility of the described organ culture system for further investigations of endocrine physiology.

Neuroendocrine significance of vasoactive intestinal polypeptide

The new data reported here, and available in the literature, are interpreted to indicate that acute release of PRL in stress is probably mediated by secretion of VIP and PHI arising from a subpopulation of paraventricular cells in the tuberoinfundibular system, and that this secretion is under serotonergic control, presumably by way of the raphe nuclear projection to the hypothalamus. The acute PRL response to suckling response is only partially under VIP/PHI control, and may be regulated by an as yet unidentified neural lobe hormone. In addition to the hypothalamic component of PRL regulation, there is a well-defined population of VIP cells within the pituitary, representing the only known example of VIP expression outside of nerve cells. This population of VIP cells is exquisitely responsive to thyroid status, and in common with the thyrotrope cell, is activated by hypothyroidism. Since VIP secretion is enhanced in the hypothyroid pituitary, and VIP release is stimulated by TRH, it is reasonable to postulate that paracrine VIP secretion may play a role in the reasonable to postulate that paracrine VIP secretion may play a role in the hyperprolactinemia prolactinemia that occurs in the hypothyroid human, although this is clearly not the case for the rat in whom hyperprolactinemia was not demonstrable. The role of VIP/PHI in human pituitary disease is unknown. We have been unable to identify any tumors that contain immunoreactive material using tissues prepared by standard methods. It may be that the demonstration of VIP/PHI is more demanding and will require better techniques for staining. The role of tuberoinfundibular VIP hypersecretion remains to be established but the evidence for stress-induced PRL hypersecretion in man encourages us to believe that at least some cases may be due to excessive hypothalamic activity. Additional potential neuroendocrine actions of VIP are in the secretomotor control of the ovary and thyroid, and in the regulation of somatostatin secretion and synthesis. In dispersed cell cultures (but not in whole hypothalamic slices from adult animals), VIP stimulates somatostatin secretion and independently stimulates the formation of somatostatin mRNA, an effect that can be duplicated in mixed cultures by treatment with forskolin, a postreceptor cAMP stimulator. In work carried out by Montminy and colleagues, the cAMP action has shown to be mediated by formation of a soluble protein that appears to activate the somatostatin gene promotor through interaction with a specific gene sequence.

Fine structural cytology of the adenohypophysis in rat and man

The present review deals with the use of electron microscopy in the identification of pituitary cell types as well as the assessment of their functional state, in rat and man. Application of immunoelectron microscopy, especially immunogold techniques, utilizing multiple labeling in establishing differentiation and hormone content of cell types, is emphasized. Recent evidence of plurihormonality in various pituitary cell types indicates that the once axiomatic one cell-one hormone theory is untenable and that the present perception of pituitary cell types and their function requires modification. Detection of hormonal and nonhormonal substances in pituitary cell types, not associated with their known endocrine function, suggests that hypophysial cells may have yet unknown roles, possibly in the realm of paracrine and autocrine regulation.

Modulating actions of estradiol on gonadotropin-releasing hormone-stimulated prolactin secretion in postmenopausal individuals

The temporal aspects of estrogen treatment on serum prolactin concentrations basally and in response to a 10 micrograms intravenous injection of gonadotropin-releasing hormone were assessed in eight postmenopausal women. The response of prolactin to gonadotropin-releasing hormone stimulation was compared with that of follicle-stimulating hormone and luteinizing hormone obtained simultaneously. Basal serum prolactin increased significantly (p less than 0.001) in response to estrogen treatment, and a positive correlation was found between the serum concentrations of estradiol and prolactin (r2 = 0.266; p = 0.0011). Gonadotropin-releasing hormone induced a significant increase in serum prolactin concentrations, which was greater after 5 to 10 days of estrogen treatment compared with that in the estrogen-depleted state (p = 0.031). No correlation was found between gonadotropin-releasing hormone-stimulated prolactin and luteinizing hormone or follicle-stimulating hormone release. These data demonstrate that estrogen treatment of previously hypoestrogenemic postmenopausal women potentiates gonadotropin-releasing hormone-stimulated prolactin release. Furthermore, our data suggest that the previously described paracrine interaction between the gonadotropins and lactotropes exerted by gonadotropin-releasing hormone does not appear to be mediated via increased gonadotropin release.

Effect of [D-Trp6]LHRH infusion on prolactin secretion by perifused rat pituitary cells

The effect of a superactive agonistic analog of luteinizing hormone-releasing hormone (LHRH), [D-Trp6]LHRH on prolactin (PRL) secretion by perifused rat pituitary cells was investigated. Constant infusion of [D-Trp6]LHRH (0.5 ng/min) for 2-3 h elicited a significant decrease in PRL secretion by these cells. This decrease in PRL release started ca. 30 min after the beginning of the infusion with the LHRH analog and lasted up to 1.5-2 h. [D-Trp6]LHRH significantly stimulated luteinizing hormone (LH) secretion during the first 30 min of peptide infusion; thereafter, LH levels began to return to control values. In animals pretreated in vivo with 50 micrograms of [D-Trp6]LHRH (s.c.) 1 h before sacrifice, PRL secretion by the rat pituitary cell perifusion system was significantly lower than vehicle-injected controls throughout the entire [D-Trp6]LHRH infusion period. On the other hand, thyrotropin-releasing hormone (TRH)-stimulated PRL secretion was slightly, but significantly imparied by [D-Trp6]LHRH infusion, while dopamine (DA) inhibition of PRL release was unaffected by this same treatment. These results reinforce previous observations of a modulatory effect of [D-Trp6]LHRH, probably mediated by pituitary gonadotrophs, on PRL secretion by the anterior pituitary. In addition, our findings suggest that basal PRL secretion by the lactotroph may be dependent on a normal function of the gonadotroph. The collected data from this and previous reports support the existence of a functional link between gonadotrophs and lactotrophs in the rat pituitary gland.