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Biomedical subjects

S H Shin

Publications and source records attributed to S H Shin.

At least 55 records · Page 3Linked to original sources
PubMed1997

Dopamine D2 receptor mediates both inhibitory and stimulatory actions on prolactin release.

Dopamine is considered to be the major physiological tonic inhibitor of prolactin release, yet there is increasing evidence showing that it can also stimulate prolactin release from lactotrophs. In primary cultured lactotrophs, the major dopamine receptors responsible for inhibiting prolactin release are dopamine D2 receptors. A dopamine receptor subtype may be responsible for the stimulatory action, yet one cannot exclude the possibility that a dopamine D2 receptor can play dual roles. This study was therefore undertaken to investigate if dopamine both stimulates and inhibits prolactin secretion through activation of the same dopamine D2 receptor. GH4ZR7 cells, which have only one type of dopamine receptors--D2s, were perifused with different concentrations of dopamine, and the perifusate was assayed for prolactin; 10(-7) mol/L dopamine stimulated prolactin release (p < 0.05; n = 5), whereas 5 x 10(-4) mol/L dopamine inhibited prolactin secretion (p < 0.05; n = 5). In the pertussis toxin-treated cells, 10(-7) mol/L dopamine stimulated prolactin release (p < 0.05; n = 5), and 5 x 10(-4) mol/L dopamine did not significantly change the rate of prolactin release. These results indicate that both the stimulatory and inhibitory actions of dopamine are likely mediated by the same D2 receptor subtype, since GH4ZR7 cells express only D2s receptors. They also confirm that the inhibitory action of dopamine is mediated through a Gi protein; and the stimulatory action of dopamine is mediated through a PTX-insensitive pathway. These findings suggest that D2 receptors are coupled to both Gi and Gs proteins.

Animals↗
PubMed1997

Relationships between dopamine-induced changes in cytosolic free calcium concentration ([Ca2+]i) and rate of prolactin secretion. Elevated [Ca2+]i does not indicate prolactin release.

This study was undertaken to investigate the relationship between dopamine (DA) induced changes in the cytosolic calcium concentration ([Ca2+]i) and the rate of prolactin secretion using GH4ZR7, a rat pituitary cell line, which express only one subtype of D2 receptor. GH4ZR7 cells were loaded with Fluo-3, a fluorescent Ca2+ indicator, and then perifused with two different doses of DA (10(-7) mol/L and 5 x 10(-4) mol/L). We monitored changes in [Ca2+]i and rate of prolactin release simultaneously by attaching a spectrofluorometer to a dynamic perifusion system. DA has stimulatory and inhibitory effect on prolactin secretion in GH4ZR7 cells; 10(-7) mol/LDA slightly increased [Ca2+]i and stimulated prolactin release, whereas 5 x 10(-4) mol/LDA decreased [Ca2+]i and inhibited prolactin secretion. When the cells were pretreated with pertussis toxin (PTX), 10(-7) mol/L DA had no significant change in [Ca2+]i while stimulating prolactin release, and 5 x 10(-4) mol/L DA reduced [Ca2+]i without having any significant effect on the rate of prolactin secretion. The results of this study demonstrate that changes in [Ca2+]i do not always correlate with the rate of prolactin release from lactotrophs. The dissociation between [Ca2+]i and prolactin release is somewhat expected considering the diverse role of [Ca2+]i and post-[Ca2+]i events, which can change the rate of prolactin release.

Aniline Compounds↗
PubMed1997

Dopamine causes ultrastructural changes in prolactin cells of tilapia (Oreochromis niloticus).

This study was undertaken to examine ultrastructural changes induced by dopamine in fish prolactin cells. Tilapia adenohypophyses were incubated with dopamine and evaluated by electron microscopy. The quantities of rough endoplasmic reticulum (RER) in prolactin cells increased and the number of secretory granules were decreased by dopamine (10(-6) mol/l) treatment. Another set of adenohypophysial tissues was placed back into control medium for 10 min following a 3 h incubation period with dopamine (10(-6) mol/l) (RE10 min group). This group had significantly less RER than the 3 h dopamine-treated tissue, and the shape of many granules in the RE10 min group changed from spherical to rod-like. In addition, some of the granule content appeared to diffuse out of granules since some were not fully surrounded by membrane. It was therefore hypothesized that the rod-shaped granules might be the result of prolactin secretion by diffusion.

Animals↗
PubMed1997

Dopamine requires ascorbic acid to be the prolactin release-inhibiting factor.

A high concentration of dopamine (10(-6) mol/l) inhibited prolactin release for < 60 min during a 2-h perifusion period by use of primary cultured pituitary cells. However, when dopamine (10(-6) mol/l) and control medium were alternately perifused, dopamine inhibited prolactin release for a longer period, indicating that the inability of dopamine to sustain an inhibitory action is likely caused by decreased sensitivity of the lactotrophs to dopamine. When 3 x 10(-7) mol/l dopamine was perifused, prolactin release was inhibited for only 15 min, and the rate of prolactin release was decreased to a nadir by addition of ascorbic acid (10(-4) mol/l) 15 min after the start of dopamine perifusion. Dopamine decreased density of dopamine D2 receptors, and ascorbic acid inhibited the receptor downregulation in GH4ZR7 cells. These results support our hypothesis that dopamine requires a supplementary agent to be the prolactin release-inhibiting factor and that the supplementary agent is ascorbic acid.

Animals↗
PubMed1996

Induction of IL-12 gene expression in the brain in septic shock.

Mental status changes are usually associated with septic shock. However, the molecular mechanisms underlying physiological changes of the central nervous system (CNS) remain speculative. We have investigated the expression of interleukin (IL)-12, one of the central cytokines in inflammatory and immune responses, in the brain from mice intraperitoneally (i.p.) injected with lipopolysaccharide (LPS). Transcripts of the IL-12 p40 gene are markedly induced in the brain, reaching its maximum level 6 h after LPS injection. Microglia-like cells are the primary producers of the p40 transcripts. In contrast, the IL-12 p35 gene is constitutively expressed in the brain at a very low level.

Animals↗
PubMed1996

Protective effect of nitric oxide in an endotoxin-induced septic shock.

BACKGROUND: Calcium ion (Ca++)-independent nitric oxide (NO) synthase activity in animals was markedly induced by treatment with endotoxin, but NO levels in various tissues removed from endotoxin-treated animals have not been reported. The role of NO during an endotoxin-induced septic shock remains controversial. METHODS: ICR mice, randomly divided into one of six treatment groups, received intraperitoneal injections as follows: phosphate-buffered saline; Escherichia coli LPS (LPS); N(omega)-nitro-L-arginine (L-NNA); N(omega)-nitro-D-arginine (D-NNA); LPS plus L-NNA; and LPS plus D-NNA. The mice were either monitored for mortality or killed for nitrite/nitrate assays and histologic analysis. RESULTS: NO levels in many tissues were markedly increased by injection of LPS, and administration of L-NNA increased mortality rates of LPS-treated mice, in association with an increase in tissue damage in the lung, liver, and kidney. CONCLUSIONS: The endogenous NO generated during LPS-mediated septic shock could be protective.

Animals↗
PubMed1996

Somatostatin does not inhibit prolactin synthesis in normal male rat pituitary cells but inhibits prolactin synthesis in estradiol-primed pituitary cells.

The effects of somatostatin (SRIF) on prolactin (PRL) synthesis and release were examined in primary cultured pituitary cells derived from normal and estradiol (E2)-primed male rat pituitaries. The cells were continuously incubated in a pulse medium containing [3H]leucine with or without 10(-6) mol/l SRIF for a period of 15, 30, 60, 180 or 360 min. Following incubation, the medium was recovered and the cells were fractionated into cytosolic and granular fractions. PRL was isolated by SDS-PAGE and newly synthesized PRL ([3H]PRL) was identified by coincident peaks of tritium activities and PRL contents. The specific activity (SA, c.p.m./ng), a ratio of [3H]PRL to total PRL, was determined for the granular, cytosolic and medium fractions. In control and SRIF-treated groups of non-primed pituitary cells, SAs of all three fractions significantly increased during the 6-h incubation. Cytosolic and granular SAs showed similar profiles of increasing rate in comparison to control. Medium SAs showed a significantly higher value in the SRIF-treated group than in the control group only at 180 min. These observations indicate that, in the non-primed condition, PRL synthesis is not inhibited by SRIF. Medium SAs in the E2-primed group were significantly higher than SAs in the non-primed control cells during the initial 3 h of incubation, and cytosolic and granular SAs were significantly higher than those of the non-primed control during the 3- to 6-h incubation period. These observations demonstrate that E2 enhances PRL synthesis and secretion of newly synthesized PRL. SRIF treatment of E2-primed lactotrophs resulted in a significant decrease in SAs of all three fractions as compared with those of the E2-primed control. Our results indicate that in normal male rat pituitary cells SRIF does not inhibit PRL synthesis but effectively inhibits PRL synthesis in E2-primed lactotrophs. This suggests that the inhibitory action of SRIF on PRL synthesis is estrogen dependent.

Animals↗
PubMed1995

Phosphoinositide-specific phospholipase C and mitogenic signaling.

The importance of PLC activation in cell proliferation is evident from the fact that the hydrolysis of PtdIns(4,5)P2 is one of the early events that follow the interaction of many growth factors and mitogens with their respective receptors. However, the importance of PLC activation is not restricted to proliferation; it is one of the most common transmembrane signaling events elicited by receptors that regulate many other cellular processes, including differentiation, metabolism, secretion, contraction, and sensory perception. It is also clear that cell proliferation signaling does not always require PLC, as indicated by the fact that growth factors such as insulin and CSF-1 do not appear to elicit the hydrolysis of PtdIns(4,5)P2, even though the intracellular domains of their receptors carry a PTK domain and the receptors show topologies very similar to those of the PLC-activating growth factors PDGF, EGF, and FGF. The growth factor-dependent activation of PLC is initiated by the formation of a complex between the receptor PTK and PLC-gamma; the formation of this complex is mediated by a specific interaction between a tyrosine phosphate residue on the intracellular domain of PTK and the SH2 domain of PLC-gamma. The receptor PTK subsequently phosphorylates PLC-gamma, of which two distinct isozymes, PLC-gamma 1 and PLC-gamma 2, have been identified. Proliferation of T cells and B cells in response to the aggregation of their respective cell surface receptors is also accompanied by the activation of PLC-gamma isozymes at an early stage. Unlike growth factor receptors, the T cell and B cell receptors lack intrinsic PTK activity but associate with several non-receptor PTKs of the Src and Syk families. Although the specific kinases are not known, one or more of these enzymes phosphorylate and activate PLC-gamma 1 and PLC-gamma 2. Transduction of growth signals by G protein-coupled receptors such as those for thrombin or bombesin also requires PtdIns(4,5)P2 hydrolysis, which, in this instance, is mediated by PLC-beta isozymes. The PLC-beta subfamily consists of four distinct members: PLC-beta 1, PLC-beta 2, PLC-beta 3, and PLC-beta 4. Agonist interaction with specific G protein-coupled receptors causes the dissociation of Gq proteins into G alpha and G beta gamma subunits and the exchange of GDP bound to G alpha for GTP. The resulting GTP-bound G alpha subunit then activates PLC-beta isoforms by binding to the carboxyl-terminal region of the enzyme.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

ANP secretion from small cell lung cancer cell lines: a potential model of ANP release.

Although atrial distension is widely accepted as the primary stimulus for atrial natriuretic peptide (ANP) release, a number of agonists are also known to induce its secretion. The mechanisms underlying these processes are not well understood. Studies of this nature are hampered by the inherent difficulty in culturing homogeneous populations of cardiac myocytes in sufficient quantities to perform molecular investigations. For this reason, we have examined the possibility of using other cell types as a model of ANP release. It has been reported that a number of tumor samples from small cell lung cancer (SCLC) patients express the ANP gene. Characterization of a large number of cell lines derived from SCLC tumor samples indicated that two of these cell lines, OS-A and SHP-77, secrete ANP at rates of approximately 10(-20) g.cell-1.min-1. This is a sufficient quantity to facilitate secretion studies using a perifusion system. We have demonstrated that ANP is released through regulated secretory pathways, as the Ca2+ ionophore A-23187, arginine vasopressin (AVP), and the sodium ionophore, monensin, were capable of modifying secretion rates. High-pressure liquid chromatography (HPLC) analysis indicated that the primary secretory product is ANP-(99-126), the circulating form of this hormone. Intracellularly, both ANP-(99-126) and ANP-(1-126) were present, suggesting the synthesis and appropriate cleavage of pro-ANP-(1-126). Because both of these cell lines have doubling times in the range of 3-5 days, they could serve as a rapidly proliferating and easily maintainable supply of homogeneous tissue for release studies.(ABSTRACT TRUNCATED AT 250 WORDS)

Arginine Vasopressin↗
PubMed1995

Neurophysin stimulates prolactin release from primary cultured rat pituitary cells.

The neurohypophysial hormones, oxytocin and vasopressin, are present as non-covalently bound complexes with their designated neurophysin in the secretory granules of the posterior pituitary. The neurophysins are generally considered to be biologically inert carrier proteins for oxytocin and vasopressin. We have examined the actions of bovine neurophysin-I (bNP-I), bovine neurophysin-II (bNP-II), rat neurophysin (rat NP) and oxytocin on prolactin release using primary cultured rat pituitary cells. A dynamic perifusion system was chosen to test their stimulatory actions. The rat NP and bNP-II stimulated prolactin release. It is a new observation that rat NP and bNP-II stimulate prolactin release from primary cultured rat pituitary cells. The maximum sensitivities, the lowest concentration which stimulate prolactin release, of rat NP, bNP-II, bNP-I and oxytocin in primary cultured cells were 1 nmol/1, 1 nmol/l, 1000 nmol/1 and 1 nmol/1 respectively. The maximum sensitivities of rat NP and bNP-II were within the physiologically relevant concentrations.

Animals↗
PubMed1994

Stimulation of poliovirus proteinase 3Cpro-related proteolysis by the genome-linked protein VPg and its precursor 3AB.

Purified recombinant poliovirus polypeptide 3AB interacts with 3CDpro and 3Dpol as shown by coimmunoprecipitation with anti-3Dpol antibodies. A consequence of this interaction is an accelerated autoprocessing of 3CDpro to produce 3Cpro and 3Dpol. The activation of 3Dpol polymerase activity by cleavage of 3CDpro, a polypeptide that has no polymerase activity, can be shown by template- and primer-dependent poly(U) synthesis. Anti-VPg antibodies (VPg = 3B) added to HeLa translation extracts programmed with poliovirion RNA inhibit cleavage of 3CDpro whereas addition of purified 3AB or VPg to these translation reactions increases 3CDpro processing. 3AB stimulates also 3Cpro-related proteolysis of 2BC, a poliovirus-specific, nonstructural processing intermediate. In contrast, 3CDpro-specific cleavage of the structural precursor P1 is inhibited by the addition of 3AB as shown by a decrease in the production of VP0 and VP3. These data shed new light on a phenomenon in the regulation of expression of poliovirus genetic information: whereas the proteinase 3CDpro is needed for processing of the capsid precursor, the cleavage product of this relatively stable precursor is required for RNA replication.

3C Viral Proteases↗
PubMed1994

N-nitroso compounds in two nitrosated food products in southwest Korea.

Gastric cancer is the commonest malignant neoplasm in Southwest Korea. The possibility of carcinogenic dietary factors led to the investigation of exposure to N-nitroso compound precursors among residents of the City of Chonju and of two outlying rural townships in North Cholla Province. Two traditional and widely consumed home-prepared food products, salted pickled cabbage (kimchi) and salted seafood sauce (chut-kal) were analysed (a) for nitrite, nitrate, total secondary amines and pH in these food products prior to nitrite incubation and (b) for volatile nitrosamines and total N-nitroso compounds before and after incubation with nitrite in simulated human stomach conditions. Nitrate levels were significantly higher in kimchi (median 1550 mg/kg) than in chut-kal (median 140 mg/kg) (P < 0.001). Secondary amine levels in non-nitrosated samples of kimchi (median 5.5 mg/kg) were significantly lower than secondary amine levels in non-nitrosated chut-kal (median 56 mg/kg) (P = < 0.001). Analyses of nitrite-incubated kimchi revealed high levels of total N-nitroso compounds (median 1173 micrograms/kg); the increase with nitrosation was significant (P = 0.001). The concentration of N-nitroso compounds in nitrite-incubated kimchi was significantly greater than that found in nitrite-incubated chut-kal (P = 0.015). The combination of high levels of nitrate in the kimchi, the demonstration of high levels of total N-nitroso compounds in this food after nitrosation, and the volume of kimchi consumed in the traditional diet suggest that salted pickled cabbage may play a role in gastric carcinogenesis in Southwest Korea.

Amines↗
PubMed1993

Activation of phospholipase C-beta 2 mutants by G protein alpha q and beta gamma subunits.

The beta- but not the gamma- and delta-type isozymes of inositol phospholipid-specific phospholipase C (PLC) are activated by G protein alpha q and beta gamma subunits. The beta-type PLC isozymes differ from other isozymes in that they contain a long carboxyl-terminal region downstream of the Y catalytic domain and a region rich in acidic amino acids between the two separated X and Y catalytic domains. To determine the sites on PLC-beta 2 that participate in the interaction of the enzyme with alpha q and beta gamma subunits, we introduced specific truncations and substitutions in the PLC-beta 2 cDNA at positions corresponding to the carboxyl-terminal and acidic amino acid-rich regions, respectively. After transient expression of these cDNA clones in CV-1 cells, the mutant enzymes were partially purified and their capacity to be activated by alpha q and beta gamma subunits determined. Substitution of glutamine residues for three or all seven of a stretch of consecutive glutamic acids in the acidic domain of PLC-beta 2 affected neither alpha q- nor beta gamma-dependent activation significantly. Carboxyl-terminal truncation to residue Gly-934 or to residue Ala-867 resulted in enzymes that were activated by beta gamma but not by alpha q. This result suggests that the carboxyl-terminal region of PLC-beta 2 is required for activation by alpha q, and that beta gamma subunits interact with a different region of the enzyme. Thus, alpha q and beta gamma subunits may independently modulate a single PLC-beta 2 molecule concurrently.

Amino Acid Sequence↗
PubMed1993

Ultrastructural changes in rat mammotropes following incubation with dopamine.

Cultured mammotropes incubated with dopamine for one hour exhibited changes in ultrastructure indicative of actively depressed biosynthetic and secretory activity. Peripheral relocation of rough endoplasmic reticulum appeared to create a barrier to secretory granule release by exocytosis. A decrease in the numbers of secretory granules indicated a decrease in prolactin production and enhanced lysosomal activity.

Animals↗
PubMed1993

A cytoplasmic 57-kDa protein that is required for translation of picornavirus RNA by internal ribosomal entry is identical to the nuclear pyrimidine tract-binding protein.

Initiation of translation of the RNA genomes of picornaviruses such as poliovirus and encephalomyocarditis virus is cap-independent and results from interaction of ribosomes with a segment of the 5' noncoding region of these mRNAs termed the internal ribosomal entry site. Genetic and biochemical studies have previously shown that a 57-kDa cytoplasmic RNA-binding protein (p57) plays an essential role in this translation mechanism. We have now found that p57 shares physical, biochemical, and antigenic properties with the pyrimidine tract-binding protein (PTB), a nuclear protein that has been implicated in various processes involving pre-mRNA. These data indicate that p57 and PTB are the same protein. Purified recombinant PTB bound specifically to a bulged hairpin within the internal ribosomal entry site of encephalomyocarditis virus and had a much lower affinity for a mutated derivative of this hairpin and for unrelated RNAs. Immunodepletion of p57/PTB from a HeLa cell-free lysate inhibited translation of poliovirus and encephalomyocarditis virus mRNAs but had no effect on translation of beta-globin mRNA, confirming the essential role of p57 in translation by internal ribosomal entry.

Base Sequence↗
PubMed1993

Measurement of prolactin release and cytosolic calcium in estradiol-primed lactotrophs.

We have developed a perifusion system that can measure both changes of cytosolic free calcium concentration [Ca2+]i and prolactin release simultaneously from cultured lactotrophs. This model incorporated a commonly-used perifusion system to a spectrofluorometer. Indo-1 loaded cells were injected into Sephadex G-150 matrix in the cuvette at a site where the emitting light of the fluorometer projects. During perifusion periods, the perifusate was collected in a fraction collector, while optical density of the emitting light at 405 nm was recorded. The [Ca2+]i was calculated based on an ionomycin and Mn2+ quenching technique. As expected, TRH (1 mumol/l) stimulated prolactin release from cultured lactotrophs in this system. We further observed that prolactin releases as induced by TRH and ionomycin were not proportional with changes of the [Ca2+]i, suggesting that changes of [Ca2+]i is not the sole final pathway of intracellular transduction systems for prolactin release.

Animals↗