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S H Shin

Publications and source records attributed to S H Shin.

At least 19 recordsLinked to original sources
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↗
PubMed1979

Effect of ergocristine on prolactin secretion in the male rat with pituitaries grafted beneath the kidney capsule.

Male rats in which three pituitaries were grafted beneath the kidney capsule showed approximately a fourfold increase in circulating plasma prolactin concentration. The elevated plasma prolactin concentration did not remain at a constant level but fluctuated with time. The elevated prolactin concentration declined immediately after a single bolus injection of ergocristine (30 micrograms/kg). The slope of the prolactin decay curve, determined by sequential blood sampling, was parallel to a theoretical slope having a 7-min half-life. This result indicates that ergocristine blocked prolactin secretion immediately and completely as the decay curve (T 1/2 = 6.5 min, confidence interval 4.5--11.3) resulting from the administration of ergocristine is the same as the endogenous prolactin decay curve (T 1/2 = 7 min).

Animals↗
PubMed1979

Unsuppressed prolactin secretion in the male rat is pulsatile.

The pattern of prolactin (Prl) secretion was studied in several different situations. In normal and castrated male rats, the plasma Prl level gently fluctuated along the course of time. When the presumed hypothalamic Prl inhibitory factor was suppressed by treatment with a pharmacological agent, pimozide (Pim), the plasma Prl concentration was elevated and the elevated plasma level fluctuated in an irregular and pulsatile manner. Another situation was examined. First, baseline Prl concentration was elevated by implantation of estradiol, which also caused a moderate fluctuation of the circulating Prl level. The Prl level was then lowered from the elevated plateau level by administration of a dopaminergic receptor agonist, ergocristine. During this partial blockade, the plasma Prl level fluctuated in episodic bursts. It is suggested that the inherent, unsuppressed secretion of Prl is pulsatile in nature, but that this pulsatile pattern is normally suppressed under the inhibiting influence of the hypothalamus.

Animals↗
PubMed1979

Estradiol generates pulses of prolactin secretion in castrated male rats.

Unrestrained, freely moving rats implanted with an atrial indwelling cannula were used to inject estradiol and to take blood samples. The effect of estradiol on prolactin secretion was monitored by taking blood samples every 2 min. When a single bolus of estradiol (100 micrograms/kg) was injected, no response was seen for approximately 2 h. There then followed a pulsatile pattern of plasma prolactin and this lasted more than 24 h. The elevation of the prolactin concentration was not accomplished by a gradual change but through frequent pulsatile bursts of secretion. The major slopes of the decay curves of these bursts, plotted on a semilogarithmic scale, were parallel to a theoretical curve with a slope of 7 min half-life. Such consistency of decay slopes indicates that prolactin secretion is accomplished through discrete bursts of secretion.

Animals↗
PubMed1978

The effect of exposure to ether on prolactin secretion and the half-life of endogenous prolactin in normal and castrated male rats.

Normal and castrated male rats implanted with permanent right atrial cannulae were used, and sequential blood samples were taken every 2 min through the cannula. When the rats, both normal and castrated, were exposed to ether for 2 min, the prolactin (Prl) concentration in plasma was immediately and dramatically elevated. During 40 min of continuous ether anesthesia, plasma Prl concentration was not sustained. After the initial 'surge' of Prl secretion, which lasted about 15 min, the concentration returned to normal levels. Following the peak of the Prl 'surge', Prl disappeared from the circulation with a calculated half-life of 7 min (mean value: 6.9 min; confidence interval: 6.3-7.7).

Animals↗
PubMed1977

Evidence for the existence of LH-RH binding protein.

LH-RH in rat hypothalamic extract (HE) emerges in 2 peaks after gel filtration on Sephadex G-25 with pyridine acetate buffer (PAB), pH 5.8, 1 peak in the unretarded protein fraction and the other near the salt region. A synthetic LH-RH marker was found only in the peak near the salt region by elution with acid. Using a dialysis technique, a protein fraction, from which LH-RH and other small molecular weight material were dissociated by gel filtration on Sephadex G-25 with acid, showed affinity for synthetic LH-RH. Synthetic LH-RH in the hypothalamic protein solution was retained in the dialysis bags more effectively than other types of protein solutions. This binding protein is of relatively small molecular size according to gel filtration behavior on Sephadex G-75. Since the dialysis experiment showed extremely poor recovery of total LH-RH, we determined the rate of loss of LH-RH under several conditions. The rate of disappearance was significantly less in solutions containing protein derived from cerebellum and hypothalamus, compared to bovine serum albumin (BSA) solution or salt solution. The ability of the hypothalamic protein to retard the rate of disappearance of LH-RH is further evidence for a special affinity between LH-RH and the protein factor. It is concluded that the protein LH-RH complex is dissociated by lowering the pH and that the dissociated protein and synthetic LH-RH can be re-associated to form a protein-hormone (PrH) complex at neutral pH.

Animals↗