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G Rappay

Publications and source records attributed to G Rappay.

At least 19 recordsLinked to original sources
PubMed1992

Influence of oligopeptide aldehydes on intracellular Ca2+ concentration in rat pituitary cells.

We investigated the effects of some synthetic tripeptide aldehydes, earlier shown to influence pituitary hormone secretion and 45Ca2+ uptake, on the intracellular free Ca2+ concentration ([Ca2+]i) of rat anterior pituitary cells in suspension. Boc-D-Phe-Leu-Phenylalaninal or Boc-D-Phe-Leu-Prolinal in the tested range of 1-100 or 200 microM, respectively, were ineffective in influencing basal [Ca2+]i but caused a concentration-dependent inhibition in K+ (25 mM)-induced [Ca2+]i elevation. The IC50 of both effects was about 50 microM. In contrast, they did not interfere with the stimulation caused by the calcium channel agonist BAY K 8644 and were also ineffective in influencing the receptor-mediated stimulus of thyrotropin-releasing hormone on [Ca2+]i. On the basis of the present and foregoing results the possible involvement of calcium channels is discussed, but different mechanisms mediating the tripeptide aldehyde inhibition are also considered. A third tripeptide aldehyde, Boc-Gln-Leu-Lysinal (Boc-GLL), showed ionophore-like properties. This nontoxic substance caused a dose-dependent rise up to 400% (at 100 microM) in [Ca2+]i. Its effect is not mediated by voltage-dependent calcium channels, as it cannot be inhibited either by the classical calcium channel antagonists verapamil and nifedipine, or by the above-mentioned inhibitory tripeptide aldehydes. When we decreased the extracellular Ca2+ concentration by the addition of 4 mM EGTA, the effect was inverted and Boc-GLL caused a large fall in [Ca2+]i. We suggest that Boc-GLL may open cell membrane pores through which Ca2+ moves along the concentration gradient.(ABSTRACT TRUNCATED AT 250 WORDS)

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1991

Pituitary corticotrophs proliferate temporarily after adrenalectomy.

Relationship of corticotroph proliferation answer and survival time after adrenalectomy was examined. Corticotroph proliferation rates were detected by short-term 3H-thymidine radiolabeling, then ACTH immunostaining and autoradiography. Effect of adrenalectomy on corticotroph proliferation rate was examined in vivo and an elevation was demonstrated first on the second postoperative day, increasing on the third-fourth day postoperatively and then decreasing. Effects of different secretagogues on corticotroph proliferation were examined in short-term pituitary monolayer cultures taken from ADX rats. CRF and Forskolin treatment potentiated corticotroph proliferation in cultures taken from adrenalectomized rats, but not in the controls. We suggest that croticotroph proliferation is stimulated via the cAMP-proteinkinase A pathway, while adrenalectomy plays a permissive role.

Adrenalectomy↗
PubMed1990

Oligopeptides interfering with calcium channels inhibit prolactin and growth hormone release by cultured anterior pituitary cells of the rat.

A number of oligopeptides, protected at their N termini and possessing an aldehyde residue at their C terminal amino acids, are able to inhibit 45Ca2+ influx into anterior pituitary cells grown in monolayer culture and depolarized with high extracellular potassium concentration. In addition, the same oligopeptides interfere with hormone release, especially with that produced by lactotrophs. Our findings imply that oligopeptides may represent a new class of calcium channel ligands, and the pituitary cells are sensitive targets for them.

Animals↗
PubMed1989

Calcium ion uptake, somatotropin release, and fine structure of somatotrophs in cultures of the rat anterior pituitary upon the action of an oligopeptide (Boc-Gln-Leu-Lysinal).

Cultured cells from the anterior pituitary glands of adult rats were treated with the tripeptide aldehyde proteinase inhibitor, Boc-Gln-Leu-Lys-H. The oligopeptide had a profound releasing effect on growth hormone, whereas the prolactin release remained unchanged at 10(-3) mol/l drug concentration after an incubation for 2 h. In the presence of the oligopeptide a time- and dose-dependent calcium influx into cultured cells has been shown which was proved to be almost completely antagonized with magnesium ions but not with Nifedipine. In addition, radioactive calcium ions could be detected in a number of cells by light microscopic autoradiography when cultures were treated with Boc-Gln-Leu-Lys-H for short periods. The selective Gel action of the oligopeptide on growth hormone producing cells has been demonstrated also in fine structural investigations: multigranular and single exocytotic profiles have been observed. Accordingly, we have postulated that Boc-Gln-Leu-Lysinal mimics the effects of the known ionophores. Its mode of action needs, however, further studies especially on isolated somatotrophs.

Animals↗
PubMed1989

Proteinases and their inhibitors in cells and tissues.

A large body of evidence has been assembled to indicate the substantial importance of proteolytic processes in various physiological functions. It has recently become clear too that endo-acting peptide bond hydrolases provisionally characterized and classified at present as serine, cysteine, aspartic and metallo together with unknown catalytic mechanism proteinases sometimes act in cascades. They are controlled by natural proteinase inhibitors present in cells and body fluids. In the first part of the present monograph the author was concerned to present an overview on the morphological and physiological approach to localization, surveying reaction principles and methods suitable for visualization of proteolytic enzymes and their natural and synthetic inhibitors. In the second part the roles played by proteinases have been summarized from the point of view of cell biology. The selection of earlier and recent data reviewed on the involvement of proteolysis in the behavior of individual cells reveals that enzymes, whether they be exogeneous or intrinsic, can be effective and sensitive modulators of cellular growth and morphology. There exists a close correlation between malignant growth and degradation of cells. It appears likely that as yet unknown or at least so far inadequately characterized factors that influence the survival or the death of cells may turn out to be proteinases. The causal role of extracellular proteolysis in cancer cell metastases, in stopping cancer cell growth and in cytolysis remains for further investigated. Ovulation, fertilization and implantation are basic biological functions in which proteolytic enzymes play a key role. The emergence of new approaches in reproductive biology and a growing factual basis will inevitably necessitate a reevaluation of present knowledge of proteolytic processes involved. The molecular aspects of intracellular protein catabolism have been discussed in terms of the inhibition of lysosomal and/or non-lysosomal protein breakdown. Peptide and protein hormone biosynthesis and inactivation are still at the centre of interest in cell biology, and a number of proteinases have been implicated in both processes. A number of conjectures partly based on the author's own work have been discussed which suggest the possibility of the involvement of proteolysis in exocytosis and endocytosis. The author's optimistic conclusion is that through the common action of biochemists, cell biologists, cytochemists, and pharmacologists the mystery of cellular proteolysis is beginning to be solved.

Animals↗
PubMed1988

The tripeptide aldehyde, Boc-DPhe-Phe-Lysinal, is a novel Ca2+ channel inhibitor in pituitary cells.

The effect of Boc-DPhe-Phe-Lysinal (Boc-DPPL) on the 45Ca2+ uptake of rat anterior pituitary monolayer cultures was investigated. The compound decreased the basal Ca2+ uptake at 3 x 10(-4) mol/l. The 45Ca2+ uptake stimulated by potassium-induced depolarization was more sensitive to Boc-DPPL inhibition, a slight decrease was seen with 3 x 10(-6) mol/l and there was a half maximal inhibition at 3 x 10(-5) mol/l. Boc-DPPL is known to inhibit pituitary hormone release in similar concentrations, an effect might also be due to its calcium antagonist property.

Animals↗
PubMed1988

Cationic ferritin uptake by cultured anterior pituitary cells treated with the proteinase inhibitor, BOC-DPhe-Phe-Lys-H.

Cultured cells from the anterior pituitary glands of adult rats were treated with the tripeptide aldehyde proteinase inhibitor, BOC-DPhe-Phe-Lys-H. The addition of this tripeptide aldehyde decreased the in vitro release of prolactin to 25% of the control value, while the release of growth hormone in the same cultures decreased to 33% of the control value. Prolactin immunostaining was stronger in semithin sections of proteinase-inhibitor-treated cultures than in control sections. After 2 h treatment with the inhibitor, prolactin- and growth hormone-containing secretory granules were numerous, and the number of crinophagic vacuoles had increased. In the presence of the inhibitor, the overall cytoarchitecture of parenchymal cells was well preserved, and the pathway of the uptake of cationic ferritin appeared to be unaffected.

Animals↗
PubMed1987

Is calcium or cyclic AMP involved in the inhibitory effect on pituitary hormone secretion of the tripeptide aldehyde proteinase inhibitors?

The mechanism by which tripeptide aldehyde proteinase inhibitors decrease prolactin (PRL) and growth hormone (GH) secretion was studied. Agents known to modify the intracellular levels of cyclic adenosine monophosphate (cAMP) or cytosolic free calcium were used in monolayer cultures of the rat anterior pituitary gland. The phosphodiesterase inhibitor isobutyl-methylxanthine (IBMX), 8-bromo-cAMP and forskolin all stimulated PRL release. Boc-D-Phe-Pro-arginal (Boc-DPPA) at 1 mmol/l concentration was a potent inhibitor of basal PRL release and significantly decreased the effect of 8-Br-cAMP, forskolin or IBMX (0.5 mmol/l). Forskolin (1 mumol/l) stimulated ACTH, PRL and GH release and all these effects were decreased by 100 mumol/l of Boc-D-Phe-Phe-lysinal (Boc-DPPL). Neither tripeptide aldehyde affected the forskolin-induced rise in intracellular cAMP. Growth hormone releasing factor (hpGRF, 1 nmol/l) stimulated both GH release and intracellular cAMP generation; Boc-DPPL (100 mumol/l) significantly decreased stimulated GH release without affecting cAMP accumulation. Increasing medium K+ to 10 times normal level stimulated PRL release presumably by enhancing Ca2+ entry into the cells and 1 mmol/l Boc-DPPA decreased high potassium-stimulated PRL release. The ionophore A-23187 stimulated PRL release at 10 mumol/l but not at 1 mumol/l. At 1 mumol/l A-23187 prevented the Boc-DPPA-induced inhibition of PRL release. These findings suggest that the tripeptide aldehyde proteinase inhibitors inhibit PRL and GH release at a site beyond cAMP formation.

1-Methyl-3-isobutylxanthine↗
PubMed1987

Proteinase inhibitors while influencing hormone release do not affect cell morphology of hypophyseal cultures.

Cultured cells from adult rat anterior pituitaries and intermediate lobes were treated with proteinase inhibitor substrate analogues (Boc-DPhe-Pro-Arginal [BOC-DPPA], DPhe-Pro-Arginal [DPPA], BOC-DPhe-Leu-Lysinal [BOC-DPLL], BOC-DPhe-Phe-Lysinal [BOC-DPPL]) to elucidate their effect on cell morphology. It was established that BOC-DPPA and DPPA (which in previous studies stimulated alpha-MSH release [6]) caused a slight decrease in the number of immunoreactive secretory granules in melanotrophs. BOC-DPLL, which inhibited growth hormone and prolactin release, did not alter the fine structural features of cultured cells. No difference was observed in the membrane turnover traced by cationic ferritin when cells were treated with BOC-DPPL. We suggest that substrate analogues used are harmless to pituitary cells.

Animals↗
PubMed1986

Dissimilar responsiveness of cultured corticotrophs and melanotrophs to tripeptide aldehydes.

Cultured cells from adult rat anterior pituitaries or intermediate lobes were treated with the proteinase inhibitor tripeptide aldehydes BOC-DPhe-Pro-Arg-H (Boc-fPRH) and DPhe-Pro-Arg-H (fPRH), ovine corticotropin-releasing factor (oCRF), and bromocriptine. One millimolar fPRH stimulated basal, and slightly enhanced oCRF-induced ACTH release by melanotrophs in short-term experiments. The basal release of alpha-MSH was also stimulated by the drug. In long-term experiments, fPRH elevated markedly both the release and the intracellular level of ACTH; BOC-fPRH caused an increased alpha-MSH release. Tritiated fPRH had no preference for POMC-producing cells and BOC-fPRH or fPRH were harmless to the cell morphology. In anterior pituitary cell cultures, fPRH diminished slightly basal and oCRF-induced ACTH release. Bromocriptine was ineffective on corticotrophs, however, in melanotrophs it inhibited ACTH release markedly with or without fPRH in the medium. The dissimilar responsiveness of the corticotrophs and melanotrophs to the peptide aldehydes may be interpreted in terms of their differing membrane receptors or intracellular mechanism of stimulus-secretion coupling.

Adrenocorticotropic Hormone↗
PubMed1986

Mechanism of restoration of ACTH release in rats with long-term lesions of the paraventricular nuclei.

The effects of lesions in the paraventricular nucleus (PVN) on the adrenocortical response to ether stress were investigated in neurohypophysectomized and intact rats. During the first 4 days after placement of lesions in the PVN, the corticosterone response to ether stress was almost completely inhibited. It then gradually increased and, within 4-6 weeks of surgery, was restored to about 60% of that in sham-operated rats. Basal plasma concentrations of corticosterone were low in rats after placement of lesions in the PVN and/or after neurointermediate lobectomy (NILX). Corticosterone responses to ether stress were similar in groups submitted to PVN lesions and/or NILX, and lower than those in the appropriate sham-operated groups. In all lesioned groups, plasma ACTH concentrations after a combination of stressors (ether plus laparotomy) were also lower than those in the sham-operated groups. Six weeks after lesioning of the PVN, immunoreactive rat corticotrophin-releasing factor-41 (rCRF-41) concentrations in stalk-median eminence (SME) extract fell to about 5% of that in sham-operated rats, while immunoreactive arginine vasopressin (AVP) concentrations did not change. Immunohistochemistry revealed a substantial decrease in rCRF-41 immunostaining of the median eminence 6 weeks after lesioning of the PVN, though randomly located clusters of stained terminals were still seen in the whole rostro-caudal extent of the median eminence. A mixture containing synthetic rCRF-41 and AVP, in proportions similar to those in SME extracts from sham-operated rats, caused significantly less release of ACTH from anterior pituitary cell cultures than did SME extracts from sham-operated rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Cortex↗
PubMed1986

[Lysosomal activity in prolactin cells under the effect of a dopamine agonist].

The influence of bromoergocryptine, a dopamine agonist used in clinical praxis, on hormone degradation by the lysosomal system was studied in the pituitary mammotrophs of female rats. Immunocytochemistry of prolactin (protein A-gold technique) combined with the electron-microscopic visualization of the lysosomal system by its non-specific esterase activity (gold thiol-acetic acid method) revealed that bromoergocryptine administration increases the spatial extent of both the lysosomal and the hormone storage compartments with a considerable overlap and interaction between them. This change in compartmentalization may be effective in eliminating hormone excess and preserving cell integrity after release inhibition.

Animals↗
PubMed1985

Various proteinase inhibitors decrease prolactin and growth hormone release by anterior pituitary cells.

Proteinase inhibitors were tested for their ability to inhibit prolactin (PRL) and growth hormone (GH) release by cultured anterior pituitary cells of the rat. Inhibitors of microbial origin (chymostatin, elastatinal, leupeptin) had either no or a moderate effect on hormone release while some tripeptide aldehydes, especially those with lysine at their C terminus, inhibited markedly PRL and to a lesser extent GH release. Boc-DPhe-Phe-lysinal was the most effective on lactotrophs inhibiting PRL release more than 50% at 10(-4) M. The site(s) of action of tripeptide aldehydes remain to be elucidated.

Animals↗
PubMed1985

DNA synthesis in lactotrophs of primary rat anterior pituitary cell cultures. Effects of thyroliberin, bromocriptine and somatostatin.

Prolactin immunostaining in combination with thymidine autoradiography was used to characterize changes in the DNA-synthesizing activity of lactotrophs in primary monolayer cultures of the rat anterior pituitary gland treated for 3 days with thyroliberin (TRH), somatostatin (SRIF) and bromocriptine (CB 154). The number of lactotrophs labelled with 3H-thymidine within the total pool of labeled pituitary cells was used to estimate DNA synthesis in prolactin-producing cells. TRH (10 ng/ml) stimulated DNA synthesis in the whole population of cultured cells but not in lactotrophs. TRH only weakly counteracted the noticeable inhibitory effect of CB 154 (0.75 microM/l) on thymidine incorporation into lactotrophs. SRIF (20 ng/ml) inhibited DNA synthesis in lactotrophs to a lesser extent than CB 154. The combination of methods used in this paper may be useful for studying the selective effects of regulators on the proliferative activity of various pituitary cell types in vivo and in culture.

Animals↗
PubMed1985

Tripeptide aldehyde protease inhibitors may depress in vitro prolactin and growth hormone release.

The effects of novel nontoxic tripeptide aldehyde inhibitors of proteolytic enzymes were examined in order to investigate the possibility that serine-thiol protease(s) may be involved in PRL and GH secretion. Rat anterior pituitary cells maintained in culture for 7-8 days or freshly taken pituitary quarters were treated with BOC-DPhe-Pro-Arg-H (BOC-dPPA), DPhe-Pro-Arg-H (dPPA), BOC-DPhe-Leu-Lys-H (BOC-dPLL), or BOC-DPhe-Phe-Lys (BOC-dPPL). Newly synthetized [3H]PRL and [3H]GH as well as immunoreactive (i) hormones (iPRL, iGH) were measured in the incubation media and cell homogenates. Four hours of incubation in the presence of 0.1 mM dPPA resulted in a 30% decrease of [3H]PRL and iPRL release by cell cultures; the inhibition by BOC-dPPA was 60% and 48%, respectively. [3H]PRL biosynthesis was unchanged or slightly decreased. The effect of these tripeptide aldehydes on [3H]GH and iGH release was less pronounced but statistically significant. Pituitary quarters treated with 1.0 or 3.0 mM BOC-dPPA release 20% and 57% less [3H]PRL than the controls. In the same system BOC-dPPA in a 1.0 mM concentration did not effect GH secretion, and 3.0 mM BOC-dPPA inhibited [3H]GH output by 27%. Forty micromolars of BOC-dPPL decreased by 47%, 0.2 mM by 79%, and 1.0 mM by 94% [3H]PRL release from pituitary quarters. GH secretion was not influenced. A similar selectivity was observed when BOC-dPLL was used. It is clear that by serine-thiol protease inhibitors whose effects are sequence and dose dependent, PRL and GH release are decreased. The relative inhibiting potency on PRL release was BOC-dPPL greater than BOC-dPLL greater than BOC-dPPA greater than dPPA. The biosynthesis of [3H]PRL was reduced only in the presence of the highest tripeptide aldehyde concentrations or long (8 h) exposure, and only 1.0 mM Boc-dPPL reduced [3H]GH biosynthesis by 30%. The data suggest that proteolysis may be involved in the process of PRL and GH release and the enzyme(s) in question may be serine-thiol protease(s).

Aldehydes↗
PubMed1984

Inhibition of growth hormone and prolactin secretion by a serine proteinase inhibitor.

The action of the tripeptide aldehyde t-butyloxycarbonyl-DPhe-Pro-Arg-H (boc-fPR-H), belonging to a family of serine proteinase inhibitors, on the release of immunoreactive prolactin (iPRL) and growth hormone (iGH) has been studied. In rat anterior pituitary cell cultures and pituitary quarters 1 mM boc-fPR-H inhibited basal iPRL and iGH release. Thyroliberin-induced iPRL release by cultured cells was also markedly inhibited with a concomitant accumulation of intra-cellular iPRL. During the short- and long-term exposure of cells to boc-fPR-H there no changes in total cell protein contents and in activities of some lysosomal marker enzymes. A wide scale of unchanged parameters characteristic for cellular metabolism indicated that the tripeptide aldehyde has no cytotoxic effect. The marked inhibition of basal as well as stimulated hormone release in the presence of the enzyme inhibitor might suggest that at least a portion of the hormones is released via a proteolytic enzyme-dependent process.

Animals↗
PubMed1984

Lysosomal enzyme activities in hypo- and hypersecretory anterior pituitary cells. A combined immunocytochemical and enzyme cytochemical study.

The involvement of lysosomes in ACTH and prolactin secretion was studied. Lysosomes were visualized in the anterior pituitary by their non-specific esterase (gold thioacetic acid technique) or acid phosphatase (Gomori technique) activity. Corticotrophs and mammotrophs were identified by postembedding immunocytochemistry for their respective hormones. Corticotrophs were rendered hypersecretory by bilateral adrenalectomy (7 or 12 days prior to examination), hyposecretory by dexamethasone administration. Prolactin secretion was enhanced by 17-beta-estradiol, prolactin release was inhibited by bromoergocriptine administration. Long-term hypersecretion of ACTH was accompanied by the presence of numerous autophagic vacuoles often containing secretory granules in the corticotrophs. Lysosomal enzyme-containing tubules and small lysosomes were abundant in the cytoplasm near the cell membrane, among the mature secretory granules. Feed-back inhibition of ACTH release by dexamethasone resulted in the extension of enzyme-containing tubules, continuous with cisternae and small lysosomes anywhere in the cytoplasm and in the appearance of numerous crinophagic vacuoles. A higher frequency of tubular lysosomes was described at the periphery of mammotrophs stimulated by 17-beta-estradiol. Bromoergocriptine caused a high incidence of characteristic crinophagic vacuoles in the prolactin cells. The concept of crinophagy has been extended to the corticotrophs. Morphological phenomena were attributed to the traffic and increased turnover of membranes, ligands and cytoplasmic organelles during stimulated secretion.

Acid Phosphatase↗