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S H Shin

Publications and source records attributed to S H Shin.

At least 73 records · Page 4Linked to original sources
PubMed1993

Activation of the adrenergic beta-receptor stimulates prolactin release from primary cultured pituitary cells.

Prolactin release from primary cultured pituitary cells was investigated using a dynamic perifusion system. Although epinephrine (1 mumol/l) produced an elevation in the mean value of the prolactin concentration at the onset of the perifusion, the elevation was not statistically significant, and the overall effect of the epinephrine was to produce an inhibition of prolactin release. The alpha- and D2-receptors of the primary cultured cells were functionally removed by a pretreatment with phenoxybenzamine (0.1 or 1 mumol/l). Since phenoxybenzamine irreversibly inactivates both the adrenergic alpha- and the D2-receptors but does not block the beta-receptors, the enhanced stimulatory action of the epinephrine (1 mumol/l) on the phenoxybenzamine pretreated cells suggests the involvement of adrenergic beta-receptors in prolactin release. Perifusion of isoproterenol (1 mumol/l), a beta-receptor agonist, stimulated prolactin release. This stimulation was blocked by beta-receptor antagonism with propranolol (1 mumol/l) supporting the implication of the beta-receptor in prolactin release. In order to differentiate between beta 1- and beta 2-receptor involvement, we investigated the effects of ICI 118,551 (1 mumol/l) on isoproterenol-induced prolactin release. ICI 118,551, a selective beta 2-receptor antagonist, blocked the stimulatory action of isoproterenol on prolactin release indicating that the beta-receptor responsible for the stimulation of prolactin release belongs to the beta 2-receptor family. Moreover, the demonstration that salbutamol, a selective beta 2-receptor agonist, stimulated prolactin secretion offers further evidence in support of the role of the beta 2-receptor in the stimulation of prolactin release.(ABSTRACT TRUNCATED AT 250 WORDS)

Albuterol↗
PubMed1992

The effects of dopamine on prolactin mRNA levels in rat pituitary cells in culture.

Dopamine is known to be the prolactin-release inhibiting factor, but the effects of dopamine itself on regulation of prolactin messenger RNA have been little studied because of the instability of dopamine. We have compared the effects of dopamine and bromocriptine on the levels of prolactin mRNA and on the rates of synthesis, storage, and release of prolactin in primary cultured rat pituitary cells. The cells were incubated for 72 h with no secretagogue (control group) or in the presence of either dopamine (10 mumol/L) plus ascorbic acid (100 mumol/L) or bromocriptine (0.1 mumol/L). Prolactin mRNA was measured in cell extracts by means of slot blots, and newly synthesized prolactin was measured in similar incubations by the addition of [3H]leucine, followed by gel electrophoresis. The levels of total prolactin were measured by radioimmunoassay. Prolactin mRNA was reduced to 78 +/- 9% (mean +/- SEM) of control levels in bromocriptine-treated cells and to 59 +/- 7% in dopamine-treated cells, demonstrating that dopamine stabilized by ascorbic acid was able to reduce the levels of prolactin mRNA in rat pituitary cells in culture. Dopamine may act at sites in addition to the dopaminergic D2 receptor, since the level of prolactin mRNA was reduced more by a supramaximal dose of dopamine than by a supramaximal dose of bromocriptine. The results of the [3H]prolactin and prolactin measurements suggested that availability of mRNA was not a major factor in controlling the rate of prolactin synthesis.

Animals↗
PubMed1992

Differential inhibition of dopamine and bromocriptine on induced prolactin release: multiple sites for the inhibition of dopamine.

Effects of dopamine and bromocriptine on TRH- or dibutyryladenosine 3',5'-cyclic monophosphate (dbcAMP)-induced prolactin release from primary cultured rat pituitary cells were studied using a perifusion system. TRH (100 nmol/l) stimulated prolactin release from basal concentrations of 33.8 +/- 0.5 to 151.2 +/- 28.0 ng/ml (net increase) or 447% increase. Dopamine inhibited the basal release of prolactin throughout the experiment, but TRH (100 nmol/l) was still able to stimulate prolactin release under the influence of dopamine. The increment in prolactin release was inversely proportional to the dopamine concentration. When TRH (100 nmol/l) was introduced during a perifusion period with bromocriptine 1 nmol/l, the prolactin concentration was increased to 110.9% of basal levels. The stimulatory effect of TRH under the influence of bromocriptine (1 nmol/l) was significantly lower than that without bromocriptine (control), although the higher concentrations of bromocriptine (10 and 100 nmol/l) did not further reduce the peak concentration of TRH-induced prolactin release. During a perifusion period with a low concentration of dopamine (1 nmol/l plus 0.1 mmol/l ascorbic acid), introduction of dbcAMP (3 mmol/l) stimulated prolactin release to 48% of basal concentration. A higher concentration of dopamine further reduced the stimulatory effect of prolactin release. Bromocriptine impeded the stimulatory effect of dbcAMP (3 mmol/l) on prolactin release in a similar manner as dopamine. Since a higher concentration of bromocriptine (10 and 100 nmol/l) did not further inhibit the TRH-induced prolactin release whereas a higher concentration of dopamine did, it is concluded that dopamine acts through additional mechanism(s) other than the D2 receptor transduction system.

Animals↗
PubMed1992

Phenoxybenzamine selectively and irreversibly inactivates dopaminergic D2 receptors on primary cultured rat lactotrophs.

Lactotrophs have several different kinds of receptors, such as dopaminergic D2, somatostatin, angiotensin II and thyrotropin-releasing hormone receptors, which stimulate or inhibit prolactin release. We have studied the specificity of phenoxybenzamine on receptors in lactotrophs. Phenoxybenzamine is a beta-haloalkylamine which alkylates chemically active radicals such as hydroxy, sulfhydryl, and amino groups. This alkylation is an irreversible chemical reaction in contrast to the receptor-secretagogue complex which is present in a state of dynamic equilibrium. Primary cultured rat adenohypophyseal cells were used in this study. A dose-response relationship was examined between concentrations of phenoxybenzamine pretreatment and prolactin release using a monolayer cell culture system. The inhibitory action of dopamine (10 mumol/l) on the control group (13.0 +/- 0.1 ng/ml or 86% inhibition relative to the control) was significantly higher than on the 0.1-mumol/l phenoxybenzamine-pretreated group (39.0 +/- 0.2 ng/ml or 58% inhibition relative to the control), but the stimulatory effect of thyrotropin-releasing hormone on prolactin release was not significantly affected up to a 10-mumol/l phenoxybenzamine pretreatment as compared with the control group. We thus selected a phenoxybenzamine concentration of 0.1 mumol/l for the next series of perifusion experiments in order to examine dynamic changes in prolactin release. The basal prolactin release was decreased to almost half by phenoxybenzamine pretreatment. The inhibitory action of dopamine (0.1 mumol/l containing 0.1 mmol/l ascorbic acid) was significantly less in the phenoxybenzamine-pretreated group (68% of the basal prolactin concentration) than in the control group (31% of the basal concentration).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

High concentrations of dopamine and epinephrine protect dopaminergic D2 receptors from inactivation by phenoxybenzamine on primary cultured rat lactotrophs.

The effect of a high concentration of catecholamines on phenoxybenzamine pretreatment was examined. The efficacy of the pretreatments was monitored by testing the inhibitory action of dopamine on prolactin release. Phenoxybenzamine is a beta-haloalkylamine which alkylates and irreversibly inactivates adrenergic alpha-receptors in smooth muscle. Dopaminergic D2 receptors share several common characteristics with the alpha-receptors. Primary cultured male rat pituitary cells were used. After phenoxybenzamine (0.1 mumol/l) pretreatment, the inhibitory action of dopamine on prolactin release was significantly reduced in a perifusion system. When the cells were pretreated with phenoxybenzamine in medium containing 0.1 or 1 mmol/l dopamine, the 0.1-mmol/l dopamine did not change the effect of phenoxybenzamine on inactivation of the receptors, but the 1-mmol/l dopamine eliminated the effect of phenoxybenzamine pretreatment. These observations were confirmed with a static monolayer culture system. The observations illustrate that a high concentration of dopamine forms a D2 receptor-dopamine complex and protects the D2 from inactivation by phenoxybenzamine. When the cells were pretreated with 0.1 mumol/l phenoxybenzamine in a medium containing 1 mmol/l epinephrine, the effect of the phenoxybenzamine was also eliminated, suggesting that a sufficient amount of D2 receptor-epinephrine complex was formed to protect the receptor from inactivation. The hormone release in response to a secretagogue depends on its affinity and intrinsic activity. It is, therefore, suggested that the intrinsic activity of epinephrine is much lower than that of dopamine on prolactin release, since the D2 receptor-epinephrine complex is as stable as the D2 receptor-dopamine complex, and the inhibitory action of epinephrine on prolactin release is less than 10% of that of dopamine.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

[A new analytical method for simultaneous measurement of iothalamate and iohexol].

Glomerular filtration rate (GFR) is believed to be the overall index of renal function, and the renal clearance of inulin (Cin) obtained during constant intravenous infusion has long been accepted as the gold standard of GFR measurement. Because of a number of technical difficulties inherent in the assay of inulin concentration in urine and plasma, its utility in clinical practice is limited. Iothalamate, urographic contrast medium, which behaves and is excreted in a fashion similar to inulin, has been accepted as a good filtration marker. We examined whether GFR could be estimated by ionic contrast media, "iothalamate" and non-ionic contrast media, "iohexol", when the high-performance liquid chromatography (HPLC) system was used as the analytic method. In our HPLC system, iothalamate and iohexol could be simultaneously determined. The assay results gave linearity within the wide range of concentrations tested. In seventeen subjects, the renal clearances of creatinine, iothalamate, and iohexol (Ccr, Ciot, and Cioh) were compared with that of inulin. The slopes with zero intercept of Ccr vs Cin, Ciot vs Cin, and Cioh vs Cin were 1.24 +/- 0.02, 1.06 +/- 0.02, and 0.83 +/- 0.02, respectively. In conclusion, an excellent correlation of renal clearance of iothalamate with that of inulin was obtained in patients with a wide range of renal function and normal volunteers. This justifies the use of the single injection of iothalamate and HPLC system as the analytic method in the measurement of GFR.

Chromatography, High Pressure Liquid↗
PubMed1991

Somatostatin partially impedes the stimulatory effects of thyrotrophin-releasing hormone and dibutyryl cyclic AMP on prolactin release: prolactin release through multiple routes.

Patterns of prolactin release were examined using stimulating and inhibiting agents. Primary cultured pituitary cells primed with oestrogens were used for perifusion experiments. TRH (100 nmol/l) increased the peak prolactin concentration to 360% of the basal concentration, while TRH, under inhibition by 1 nmol somatostatin/l, raised the peak prolactin concentration to 185% of the basal levels. When the somatostatin concentration was increased to 10, 100 and 1000 nmol/l, TRH still stimulated prolactin release to 128%, 121% and 140% respectively, indicating that concentrations of somatostatin of 10 nmol/l or higher did not further suppress the stimulatory effect of TRH. TRH (1 mumol/l) stimulated prolactin release under the influence of 0 (control), 1, 10, 100 and 1000 nmol dopamine/l (plus 0.1 mmol ascorbic acid/l) to 394, 394, 241, 73 and 68% of the basal concentration respectively, showing that the dopamine concentrations and peak prolactin concentrations induced by TRH have an inverse linear relationship in the range 1-100 nmol dopamine/l. The stimulatory effect of dibutyryl cyclic AMP (dbcAMP) on prolactin release was also tested. The relationship between dbcAMP and somatostatin was similar to that between TRH and somatostatin. When adenohypophyses of male rats were used for perifusion experiments, somatostatin (100 nmol/l) did not inhibit basal prolactin release from the fresh male pituitary in contrast with the primary cultured pituitary cells, but dopamine (1 mumol/l) effectively inhibited prolactin release. In conclusion, (1) oestrogen converts the somatostatin-insensitive route into a somatostatin-sensitive route for basal prolactin release, (2) TRH-induced prolactin release passes through both somatostatin-sensitive and -insensitive routes, (3) dopamine blocks both somatostatin-sensitive and -insensitive routes and (4) cAMP activates both somatostatin-sensitive and -insensitive routes.

Animals↗
PubMed1990

A high concentration of dopamine preferentially permitted release of newly synthesized prolactin.

We used continuous labelling ([3H]leucine) of cultured adenohypophysial cells to investigate the relationship between the storage and release of newly synthesized and stored prolactin in response to dopamine (1 mumol/l) and thyrotropin-releasing hormone (TRH) (0.1 mumol/l) challenge. Newly synthesized prolactin was identified by the tritium radiation activity incorporated in prolactin. A maximal dose of dopamine (1 mumol/l) could not completely block prolactin release from a primary culture of lactotrophs. During 3 h of continuous labelling under maximal dopaminergic inhibition, newly synthesized prolactin was released which was of a significantly higher specific activity than control groups. In contrast, TRH stimulation produced results consistent with previous observations of the release of predominantly old, stored hormone. However, the absolute amount of the newly synthesized prolactin was increased by the TRH administration, and the increased release of the newly synthesized prolactin could be accounted for by increased levels of synthesis. Our results are consistent with the concept of the existence of a regulated route and a dopamine-insensitive constitutive route of prolactin release which predominantly encompasses newly synthesized hormone. However, the possibility that cellular heterogeneity or that non-dopaminergic prolactin-release inhibiting factor(s) (PIF) is responsible for this observed release cannot be ruled out.

Animals↗
PubMed1990

Reexamination of dopamine as the prolactin-release inhibiting factor (PIF): supplementary agent may be required for dopamine to function as the physiological PIF.

A large number of studies have been performed concerning dopamine's inhibitory effect on prolactin release, but many of these studies have examined the effect of dopamine dissolved in a solution containing ascorbic acid. Ascorbic acid, routinely used to protect dopamine from oxidation, alone does not stimulate or inhibit prolactin release, but it can potentiate the inhibitory effect of dopamine in a static monolayer culture system by approximately 100 times. We have closely examined the inhibitory effect of dopamine on prolactin release in the absence of ascorbic acid using a perifusion system. Male rat adenohypophyses were dispersed with trypsin and cultured in a Petri dish to form cell clusters. Inhibition of prolactin release by dopamine (1 mumol/L) in the absence of ascorbic acid was sustained for only 63 min during the 2-h perifusion period. Following a 2-h period of incubation of dopamine in the same experimental solution, the dopamine concentration was reduced from 1 to 0.18 mumol/L, yet this "2-h-old dopamine" was still effective in inhibiting prolactin release (approximately 30 min). This result suggests that the lactotrophs may be desensitized by chronic exposure to a high concentration of dopamine in the absence of ascorbic acid. In contrast, when a low concentration of dopamine (3 nmol/L) containing ascorbic acid (0.1 mmol/L) was perifused, inhibition of prolactin release was sustained for the entire 2-h perifusion period. Although there may be a large number of explanations for dopamine's transient inhibitory effect on prolactin release, the present results suggest that dopamine may require supplementary agent(s) to effectively inhibit prolactin release and thus function as the prolactin release inhibitory factor (PIF).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Ascorbic acid potentiates the inhibitory effect of dopamine on prolactin release: a putative supplementary agent for PIF.

Dopamine has a catechol group which can be easily oxidized by mild oxidizing agents. Ascorbic acid has been routinely added to a dopamine solution in order to protect it from oxidation. We have examined the effect of ascorbic acid on dopaminergic inhibition of prolactin release. Male rat pituitary cells were dispersed using trypsin and cultured for 5-7 days before experiments. Ascorbic acid did not stimulate nor inhibit prolactin release in both static monolayer culture and dynamic perifusion systems, but potentiated by approximately 100 times the inhibitory effect of dopamine on prolactin release. In order to differentiate chemical protection from potentiation, we tested the potentiation effect of isoascorbic acid which is an epimer of biologically active L-ascorbic acid but is biologically less active. Our results indicated that isoascorbic acid caused less potentiation of the dopaminergic effect on prolactin release than did ascorbic acid. In a perifusion system, a high concentration of dopamine (100 nmol/l) was unable to inhibit prolactin release for a 1 h experimental period, but a low concentration of dopamine (10 nmol/l) plus ascorbic acid (10 mumol/l) inhibited prolactin release for the entire 1 h perifusion period. There is a strong possibility that ascorbic acid may be a physiological supplementary agent for the prolactin-release inhibiting factor (PIF) since the blood concentration of ascorbic acid is rather high (23-85 mumol/l).

Animals↗
PubMed1989

Localization of acid phosphatase in lysosomes of pituitary folliculo-stellate cells following estrogen withdrawal from primed male rats.

Acid phosphatase was localized in lysosomes of non-granulated, folliculo-stellate pituitary cells 72 h after estrogen was withdrawn from primed male rats. The appearance of lysosomes and the accumulation of lipid droplets in folliculo-stellate cells coincide with the clearance of lipid from pituitary mammotropes. Positive identification of lysosomes supports our proposal in a previous study that folliculo-stellate cells are phagocytic.

Acid Phosphatase↗
PubMed1989

Prolactin crinophagy is induced in the estrogen-stimulated male rat pituitary.

The phenomenon of crinophagy in rat pituitary mammotrophs, or lysosomal uptake of prolactin secretory granules, was confirmed by means of double-label immunogold electron microscopy, and shown to be induced in estrogen-stimulated male rats. Rabbit antibodies to rat cathepsin D were used to label lysosomes, and to rat prolactin to label secretory granules. The pituitaries were fixed in 4% formaldehyde and 1% glutaraldehyde, embedded in Lowicryl K4M, and thin sections were exposed successively to primary antibodies, biotin-labelled second antibodies, and streptavidin-gold, with an amplification procedure for cathepsin D. Cathepsin D and prolactin were detected separately on opposite sides of the sections, using 5-nm and 15-nm gold particles. Lysosomal uptake of prolactin secretory granules was not observed in untreated control rats. It was detected in about 26% of lysosome-containing mammotroph cell sections in estrogen-stimulated rats and at 7 h after estrogen withdrawal, but fell to 14% at 24 h and to 2% at 72 h after estrogen withdrawal.

Animals↗
PubMed1989

Crystalloid inclusions in folliculostellate cells of adenohypophysis following estrogen withdrawal from primed male rats.

Crystalloid inclusions were observed within nongranulated, folliculostellate pituitary cells 72 after estrogen was withdrawn from primed male rats. Like crystalloid inclusions in macrophages reported by others, those observed in this study were associated with structures that appeared to be lysosomes. We suggest that crystalloid inclusions may be the result of phagocytosis, a function of folliculostellate cells proposed by us in a previous study.

Animals↗
PubMed1989

Bovine neurophysin-II stimulates prolactin release without involvement of dopaminergic prolactin-release inhibiting factor receptor in the estradiol-primed male rat.

Neurophysins have been considered to be physiologically inert carrier proteins for the neurohypophysial hormones, oxytocin and vasopressin. We have observed that bovine neurophysin-II indirectly stimulates prolactin release in estradiol-primed male rats. The release of prolactin is regulated by a dual hypothalamic control system, the prolactin-release-inhibiting factor and the prolactin-releasing factor. We have tried to clarify whether neurophysin-II is acting through stimulation of prolactin-releasing factor by eliminating the possibility of dopaminergic prolactin release-inhibiting factor release. Male rats were primed with estradiol and functional dopaminergic prolactin release-inhibiting factor receptors were completely blocked by pretreatment with a large dose of pimozide (3 mg/kg), a dopaminergic receptor blocking agent. The neurophysin-II stimulated prolactin release in the rats which did not have any functional dopaminergic prolactin release-inhibiting factor receptors suggesting that neurophysin-II likely initiates a chain of events which eventually stimulates prolactin-releasing factor release since the possibility of involvement of the dopaminergic prolactin release-inhibiting factor system is eliminated. Opioids are known to be one of a chain of events which transmit external stress into a stimulation of prolactin release. Naloxone, a mu-receptor antagonist, was injected 20 min before neurophysin-II administration into rats which were primed with estradiol and pretreated with pimozide (3 mg/kg), but the naloxone administration did not block the prolactin release stimulated by neurophysin-II injection. This result indicates that opioids are not one of the chain of events between initiation of stimulation by neurophysin-II and prolactin release.

Animals↗
PubMed1988

Morphine can stimulate prolactin release independent of a dopaminergic mechanism.

Prolactin release is controlled by prolactin-release inhibiting factor (PIF), possibly dopamine, and an unidentified putative hypothalamic prolactin-releasing factor (PRF). Morphine and related opioids may indirectly stimulate prolactin release by inhibiting PIF release and (or) by stimulating putative PRF release. In the present study, we have completely blocked the dopaminergic receptors in normal male rats by pretreatment with a large dose of pimozide (3 mg/kg) to demonstrate if putative PRF has a role in morphine-induced prolactin release. Morphine sulfate (10 mg/kg) was still able to stimulate prolactin release in the rat without any functional dopaminergic PIF receptors. When naloxone (3 mg/kg) was injected 20 min before the morphine in the pimozide-treated rat, plasma prolactin concentration was not affected by morphine indicating that the stimulatory effect of this opioid on prolactin release in the pimozide-pretreated rat was mediated by mu-receptors. We can conclude that morphine can stimulate prolactin release through a mechanism apparently independent of dopaminergic receptors, one possible route being through a putative PRF.

Animals↗