PubMed Health⌕ Search

Biomedical subjects

G Rappay

Publications and source records attributed to G Rappay.

At least 37 records · Page 2Linked to original sources
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↗
PubMed1984

Responsiveness of intermediate lobe cells to neural mediators in culture.

Immunologically and biologically active ACTH, as well as biologically active alpha-MSH were secreted by monolayer cultures of rat pituitary intermediate lobe cells. The release of the immunoreactive ACTH and the bioactive alpha-MSH was inhibited by dopamine and by the dopamine agonist bromocriptine. The inhibition is probably mediated by specific dopaminergic receptors, since simultaneously added haloperidol prevented the dopamine induced hormone release inhibition. Pro-Leu-Gly-NH2, a potent inhibitor of the alpha-MSH secretion, had no effect on the release of ACTH. Synthetic ovine CRF stimulated the release of both immunoreactive ACTH and bioactive alpha-MSH in dose-dependent fashion. Corticosterone was without effect on hormone release in the cultures derived from both adrenalectomized and sham-operated animals.

Adrenocorticotropic Hormone↗
PubMed1983

Lysosomes in anterior pituitary corticotrophs of the rat. A combined immunocytochemical and enzyme cytochemical study.

E600 resistant non-specific esterase activity or acid phosphatase activity were localized in corticotrophic cells identified by postembedding immunocytochemistry (PAP of protein A-immunogold techniques). The lysosomal system of this cell type consists of dense bodies, of a population of small lysosomes mostly situated at the cell periphery in the vicinity of secretory granules as well as of tubular structures. These latter were located either in the central part of the cytoplasm and probably belonged to the Golgi apparatus or at the cell periphery, partly in the extensions. Small lysosomes occurred to be in continuity with enzyme-containing tubules. In a few structures lysosomal enzyme activity and ACTH immunoreactivity overlapped. Some autophagic vacuoles seemed to contain secretory granule matrix. It is suggested that the concept of crinophagy can be extended to the corticotrophs, though the lysosomal system may be involved in the specific function of this cell type by other mechanisms as well.

Acid Phosphatase↗
PubMed1983

Is there a direct correlation between the activities of various lysosomal enzymes and prolactin secretion in the rat anterior pituitary?

The degree of endocrine activity by rat pituitary lactotrophs was manipulated and the lysosomal involvement in the release and intracellular degradation of PRL was monitored by concomitant assays of acid phosphatase, beta-glucuronidase, dipeptidyl peptidases I and II, and nonspecific esterases in the anterior lobe. The in vitro release of PRL by cell cultures was inhibited by 0.5 or 1.5 microM bromocriptine during 24 or 72 h of incubation and by 0.75 microM for 4 h. Long term treatment caused a 40% reduction in the total PRL content of cells and media; however, after 4 h of bromocriptine treatment, no reduction in PRL content was found. TRH (10 ng/ml) in medium for 4 h increased PRL release, whereas it produced intracellular hormone depletion. In vitro treatment of anterior lobes of diestrous rats with 1 microM dopamine decreased PRL release by 50%. No changes in lysosomal enzyme activities were observed after the inhibition of release or stimulation of the in vitro secretion of PRL. Haloperidol (2.5 mg/kg BW) caused a 90% increase in serum PRL concentrations in diestrous rats 1 h after sc injection. alpha-Methyl-p-tyrosine (200 mg/kg BW, ip) stimulated in vivo PRL secretion, monitored 1, 4, and 24 h after drug administration. The administration of 100 micrograms/rat bromocriptine for 3 consecutive days, a single dose of 100 micrograms/rat polyestradiol phosphate, and their combination resulted in the expected changes in PRL production in female rats. These in vivo treatments failed to alter lysosomal enzyme activities in the anterior pituitary. These findings suggest that the release, intracellular accumulation, or depletion of PRL occurred without concomitant changes in lysosomal enzyme activity in the anterior pituitary. We suggest that the system of lysosome-dependent hormone degradation may involve more specific enzymes than those monitored to date.

Acid Phosphatase↗
PubMed1982

A serine-proteinase inhibitor (Boc-D-Phe-Pro-Arg-H) inhibits the secretion of adrenocorticotropin- and beta-endorphin-immunoreactive peptides in vitro.

The effects of a potent serine protease inhibitor, Boc-D-Phe-Pro-Arg-H, on the secretion and content of ACTH and beta-endorphin-like immunoreactivities of cultured rat anterior pituitary cells were studied. Basal release of the hormones was not affected by the drug but secretion in response to stalk-median eminence extracts was inhibited. The inhibitor did not effect the amount of ACTH or beta-endorphin in the medium plus the cells, nor did it change the ratio of the lipotropin and beta-endorphin-like immunoreactivities. Thus the compound seems to affect the release of ACTH and beta-endorphin, but not the processing of lipotropin to beta-endorphin.

Adrenocorticotropic Hormone↗
PubMed1982

Surface topography of cultured anterior pituitary cells of the rat.

Anterior pituitary cells of the adult rat were studied by scanning electron microscopy after 3, 6 and 8 days in culture. Epithelial (parenchymal) cells and fibroblasts could be differentiated by their characteristic cell surface structures and by their associations with each other. The surface of solitary and grouped epithelial cells is uneven and rich in smaller or larger blebs, wrinkles and microvilli. A few solitary cilia were found on the surface of some cells. The individual cells forming epithelial cell groups adhere to each other with numerous, parallel, slender extensions. The fibroblasts found in monolayers have extensions with various lengths contacting other cells or the inert substratum. Microvilli arise in various frequency from their smooth surface. Transmission electron microscopy confirmed the presence of the surface structures detected in the scanning electron microscope.

Animals↗
PubMed1982

Calcium modifies the effects of thyroliberin and somatostatin on hormone release from cell cultures of the rat anterior pituitary.

Role of calcium (Ca2+) in the effects of thyroliberin (TRH) and somatostatin (SRIF) on the release of growth hormone (GH), prolactin (PRL) and thyroid stimulating hormone (TSH) from the rat adenohypophyseal cells in primary monolayer cultures has been studied. Decrease of extracellular Ca2+ diminished the stimulatory effects of TRH on TSH and PRL release. Ca2+ is also an important factor in the mechanism of SRIF action. Data obtained in the experiments with high Ca2+ levels in the medium indicate that some antagonistic interrelationship exists between Ca2+ and SRIF. These results suggest that the participation of cAMP alone is not sufficient for stimulus-secretion coupling. Another messenger, namely Ca2+, is necessary for the effects of hypothalamic hormones. On the other hand, the contribution of Ca2+ to the secretory process in mammotrophs, somatotrophs and thyrotrophs is not equal. PRL and TSH secretion is more dependent on the presence of extracellular Ca2+ than the release of GH.

Animals↗
PubMed1981

A quantitative approach to trace the corticotrophs in culture after adrenalectomy.

Anterior pituitaries of adrenalectomized and sham operated adult rats were dispersed by trypsin and cultured for 4 and 8 days. Adrenalectomy caused a moderate increase in number of corticotrophs in both zero-time cell suspensions and cultures. There was a pronounced elevation of immunoreactive ACTH content in both cells and media and an enhanced secretory response to stimulation of cultures with stalk-median eminence extract containing cortiocotropin releasing (CRF) activity. Some cells identified as corticotrophs by a specific immunostaining incorporated tritiated thymidine into their nuclei suggesting their ability to enter the cell cycle. The relatively smaller increase in number of ACTH cells and the considerably higher ACTH producing capacity of the corticotrophs after adrenalectomy seem to be inconsistent with the quantal response model of hormone secretion recently introduced by Rodbard.

Adrenal Glands↗
PubMed1981

Effects of paraventricular lesions on stimulated ACTH release and CRF in stalk-median eminence of the rat.

The effects of destroying the paraventricular nucleus (PVN) of the rat hypothalamus on pituitary-adrenal function were studied. Four days after PVN lesions were placed with a rotating knife, the basal plasma corticosterone level was normal, but the corticosterone response to electrical stimulation of the medial basal hypothalamus, surgical trauma, and ether-venesection stress was significantly inhibited. Four and 8 days after PVN lesioning and adrenalectomy, the basal plasma ACTH level was lower, and the rise of plasma ACTH level elicited by a 3-min ether inhalation was significantly smaller than in the adrenalectomized controls. Corticotropin-releasing factor (CRF) activity in the stalk-median eminence extracts from PVN-lesioned rats was significantly less than in the control extracts. The weight of the adrenals was decreased by both 2 and 4 wk after PVN destruction, and 2 wk after hemiadrenalectomy, the compensatory adrenal hypertrophy was inhibited. The plasma corticosterone response to ether-venesection stress was inhibited only temporarily because it returned to normal by the end of the 4th postoperative week. The results are consistent with the hypothesis that a substantial portion of CRF-containing fibers in the stalk-median eminence region either originate from or run though the PVN or its immediate vicinity.

Adrenal Glands↗
PubMed1981

Corticoliberin activity of rat neurohypophysis is distinct from vasopressin.

Electrical stimulation of the neural lobe of the pituitary resulted in an increase of corticosterone secretion in both normal and Brattleboro rats. Bioassaying the corticoliberin (CRF) activity of stalk-median eminence and neural lobe extracts obtained from normal and Brattleboro rats revealed that the endogenous vasopressin was not a prerequisite of ACTH-releasing potency. Arginine-8-vasopressin failed to potentiate the CRF activity of the different extracts. These data suggest that a nonvasopressin substance(s) with CRF activity can be released from the neurohypophysis of the rat, and it may contribute to activating the pituitary-adrenal axis under certain experimental conditions.

Adrenocorticotropic Hormone↗
PubMed1981

Effects of treatment with adrenocorticotrophin on the hypothalamo-pituitary-adrenal system.

Long-term treatment with adrenocorticotrophin (ACTH) inhibited the stress-induced response of the hypophysial-adrenocortical system 24 h after the final ACTH injection. The mechanism of this phenomenon was studied in both normal and adrenalectomized rats, the latter receiving corticosterone at various doses. The effect of electrical stimulation of the medial basal hypothalamus on the concentration of corticosterone in plasma (an indicator of ACTH secretion), the corticotrophin releasing factor (CRF) content of the stalk median eminence (SME), the ACTH content of the pituitary gland and the in-vitro release of ACTH by the pituitary gland incubated with or without addition of SME extract were investigated. Electrical stimulation of the medial basal hypothalamus failed to induce a rise in concentrations of corticosterone in plasma of normal rats treated with ACTH; moreover the levels of hypothalamic CRF and hypophysial ACTH were significantly decreased. Hemipituitary glands of ACTH-treated rats released markedly less ACTH in vitro in response to SME extract than did the control glands. This indicated that long-term hormone administration caused a serious impairment of the responsiveness of the corticotrophic cells toward CRF. Pituitary ACTH content and in-vitro responsiveness of pituitary glands obtained from ACTH-treated, adrenalectomized rats receiving corticosterone replacement seemed to be dependent on the amount of exogenous corticosteroid, but not on that of exogenous ACTH. Our previous and present findings suggest that long-term treatment with ACTH elicits repeatedly increased secretion of endogenous corticosterone, impairing the stress-induced CRF-ACTH release at both the hypothalamic and hypophysial levels. Our data challenge the view that ACTH itself is able to inhibit its own secretion.

Adrenalectomy↗
PubMed1981

Growth hormone releasing activity persists in the deafferented medial-basal hypothalamus of the rat.

The possible role of the neural connections of the medial-basal hypothalamus (MBH) in the maintenance of GH releasing activity of the pituitary stalk median eminence (SME) was investigated. Male rats, subjected to sham-operation and to complete and anterolateral cuts around the MBH were used 7-8 days after surgery. Electrical stimulation of neural structures within the MBH caused an increase of plasma GH in pentobarbitone- as well as in urethane-anaesthetized animals. In sham-operated rats the rise of plasma GH levels was apparent only after completion of 10 min of electrical stimulation, while in animals with complete or anterolateral cuts an increase was already evident during electrical stimulation. The results suggest that depolarization of somatostatin secreting fibres in the median eminence may be responsible for the delay in the rise of GH levels in sham-operated rats, while the increment can be attributed to a GH releasing principle in the hypothalamus. Acidic extracts of the SME of rats with complete or anterolateral cuts stimulated the release of GH by primary cultures of rat anterior pituitary cells. Microinjection of 0.05 SME equivalents of SME extract into the anterior pituitary gland of urethane-anaesthetized rats produced a rise in plasma GH levels within 3 min of injection. These data favour the existence of a GH releasing factor, and suggest that the ventromedial and arcuate hypothalamic nuclei are major sites of production of this releasing hormone.

Afferent Pathways↗
PubMed1981

Ba2+ affects growth hormone and prolactin secretion as well as cell morphology in rat anterior pituitary cultures.

The effects of barium ions (Ba2+) on the release of growth hormone (GH), and prolactin (PRL) and ultrastructural changes accompanying altered hormone secretion in primary cultures of the rat anterior pituitary gland were studied in the presence or absence of calcium ions (Ca2+) in the medium. In four days old cultures previously labelled with 14C-L-leucine radiolabelled PRL release was stimulated in the presence of both Ba2+ and Ca2+, while GH release remained unchanged. In the absence of Ca2+, Ba2+ caused a more marked PRL and a significant GH release. In seven days old cultures, Ba2+ stimulated immunoreactive GH release in the presence of Ca2+ three-fold and a dramatic GH release occurred when Ca2+ was omitted from the incubation medium. Many parenchymal cells contracted profoundly in the presence of Ba2+ without Ca2+ in the incubation medium and the discharge of secretory material was frequent in a number of granular cells that did not contract. The observation on contraction suggests that Ba2+ may activate the microtubular-microfilamentous system in pituitary parenchymal cells.

Animals↗
PubMed1980

Effect of electrical stimulation of the neurohypophysis on ACTH release in rats with hypothalamic lesions.

Electrical stimulation of the neural lobe (NL) of the pituitary induces a rise in plasma corticosterone indicating the release of adrenocorticotropin (ACTH) in rats pretreated with dexamethasone, morphine and pentobarbitone. 7-8 days after placing an anterolateral cut around the medial basal hypothalamus (MBH), the rats failed to respond with ACTH release to electrical stimulation of the NL; the number of nerve fibers and terminals in the NL decreased to less than 5% of the normal; and ACTH releasing activity of acid extracts of the NL was undetectable using both in vivo and in vitro tests, which are insensitive to vasopressin. After lesions of the paraventricular nuclei the stimulation of the NL elecited a rise of plasma corticosterone that was significantly less than that in the controls. These results suggest that the NL of the pituitary contains electrically excitable fibers capable of releasing corticotropin-releasing factor (CRF; distinct from vasopressin) and that these fibers probably originate from outside the MBH, with a portion of them coming from or through the paraventricular nuclei or their immediate vincinity.

Adrenocorticotropic Hormone↗