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

1990 ◽  
Vol 68 (9) ◽  
pp. 1226-1230 ◽  
Author(s):  
Seon H. Shin ◽  
Samia F. Hanna ◽  
Murray Hong ◽  
Khem Jhamandas
Keyword(s):  
Ascorbic Acid ◽  
Culture System ◽  
Monolayer Culture ◽  
Petri Dish ◽  
Inhibitory Effect ◽  
Male Rat ◽  
High Concentration ◽  
Prolactin Release ◽  
Inhibiting Factor ◽  
Perifusion System

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 μmol/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 μmol/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). We propose ascorbic acid as a major candidate for the supplementary factor for the PIF.Key words: dopamine, somatostatin, prolactin, cell cluster, perifusion.

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

1997 ◽  
Vol 273 (3) ◽  
pp. E593
Author(s):  
S H Shin ◽  
F Si ◽  
A Chang ◽  
G M Ross
Keyword(s):  
Ascorbic Acid ◽  
Inhibitory Action ◽  
D2 Receptors ◽  
Pituitary Cells ◽  
Control Medium ◽  
High Concentration ◽  
Prolactin Release ◽  
Receptor Downregulation ◽  
Inhibiting Factor ◽  
And Control

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.

Effect of Some Flavonic Compounds and Ascorbic Acid on Lactoferrin Stimulation of Erythrocyte Glycolysis and Na+/K+-ATPase Activity

2008 ◽  
Vol 63 (9-10) ◽  
pp. 773-779 ◽  
Author(s):  
Ana Maneva ◽  
Borislava Taleva
Keyword(s):  
Ascorbic Acid ◽  
Atpase Activity ◽  
Specific Binding ◽  
Lactate Production ◽  
Inhibitory Effect ◽  
High Concentration ◽  
Transport Chain ◽  
Strong Inhibitory Effect ◽  
Lactate Formation ◽  
Stimulation Of

The aim of the present study was to assess if some flavonic compounds (quercetin, piceatannol and apigenin) and ascorbic acid could interfere with the Lf stimulatory effect on the erythrocyte function. Quercetin (1.5 μm) and piceatannol (30 μm) showed an additive effect on Lf stimulation of Na+/K+-ATPase when used together with Lf. The enhancement of Lf stimulation on Na+/K+-ATPase in the presence of flavonoids was probably due to their antioxidative properties and/or to their involvement in the erythrocyte signaling. None of the estimated flavonoids showed an effect on Lf stimulation of the lactate production. Quercetin itself enhanced the ATPase activity but did not affect the lactate formation. Apigenin (1.5 μm) enhanced reliably the lactate generation, but it did not exert any effect on the ATPase activity. High concentration of ascorbic acid (60 mm) did not change the Lf stimulatory effect on Na+/K+-ATPase, but decreased the Lf-specific-binding. A significantly strong inhibitory effect on the Lf-specific binding exerted the electron acceptors NAD+ (2 mm) and FAD (2 mm). These effects concern most likely the competition with Lf for electron(s) which is (are) provided from the erythrocyte intercellular electron transport chain(s).

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

1989 ◽  
Vol 121 (3) ◽  
pp. 411-416
Author(s):  
S. H. Shin ◽  
M. C. Obonsawin ◽  
R. Stirling
Keyword(s):  
Blocking Agent ◽  
Male Rats ◽  
Male Rat ◽  
Prolactin Release ◽  
Inhibiting Factor ◽  
Inert Carrier ◽  
A Chain ◽  
Neurophysin Ii ◽  
Factor Release ◽  
Stimulation Of

Abstract. 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 μ-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.

Exogenous ascorbic acid or thiamine increases the resistance of sunflower and maize plants to salt stress

2009 ◽  
Vol 57 (3) ◽  
pp. 335-347 ◽  
Author(s):  
A. Hamada ◽  
A. Al-Hakimi
Keyword(s):  
Ascorbic Acid ◽  
Salt Stress ◽  
Net Photosynthetic Rate ◽  
Photosynthetic Rate ◽  
Membrane Integrity ◽  
Inhibitory Effect ◽  
Favourable Effect ◽  
High Concentration ◽  
Stimulatory Action ◽  
Salinity Levels

Increasing NaCl levels retarded the net photosynthetic rate, biosynthesis of photosynthetic pigments and membrane integrity of maize and sunflower seedlings; a serious effect was exhibited when NaCl was applied at high concentration. On the other hand, the K + efflux increased at increasing NaCl levels. In addition, the various salt levels induced considerable variations in the concentrations of sodium, potassium, calcium and magnesium. The vitamins applied were generally effective in partially or completely countering the inhibitory effects of salt stress on net photosynthetic rate, pigments biosynthesis and membrane integrity, exerting a stimulatory action on these parameters, especially in plants subjected to moderate and low salinity levels. The leakage of K + was reduced by the application of both ascorbic acid (AsA) and thiamine (B 1 ). Soaking the seeds of salt-stressed plants in AsA or B 1 had a favourable effect on the accumulation of certain ions and antagonized or ameliorated the inhibitory effect of salt stress.

scholarly journals Chemical and Bioactivity Evaluation of Eryngium planum and Cnicus benedictus Polyphenolic-Rich Extracts

2019 ◽  
Vol 2019 ◽  
pp. 1-10 ◽  
Author(s):  
Gabriela Paun ◽  
Elena Neagu ◽  
Veronica Moroeanu ◽  
Camelia Albu ◽  
Simona Savin ◽  
...  
Keyword(s):  
Ascorbic Acid ◽  
Chlorogenic Acid ◽  
Ursolic Acid ◽  
Biological Activities ◽  
Sinapic Acid ◽  
Reducing Power ◽  
Inhibitory Effect ◽  
High Concentration ◽  
Standard Compound ◽  
Inhibitory Activities

This study evaluated the biological activities of Eryngium planum and of Cnicus benedictus extracts enriched in polyphenols obtained by nanofiltration. The HPLC-MS analysis showed that E. planum contains mainly flavonoids, especially rutin, while in C. benedictus extracts show the high concentration of the phenolic acids, principally the chlorogenic acid and sinapic acid. Herein, there is the first report of ursolic acid, genistin, and isorhamnetin in E. planum and C. benedictus. C. benedictus polyphenolic-rich extract showed high scavenging activity (IC50=0.0081 mg/mL) comparable to that of standard compound (ascorbic acid) and a higher reducing power (IC50= 0.082 mg/mL), with IC50 having a significantly lower value than IC50 for ascorbic acid. Both extracts were nontoxic to NCTC cell line. Among the investigated herbs, E. planum polyphenolic-rich extract showed the highest inhibitory activities with the IC50 value of 31.3 μg/mL for lipoxygenase and 24.6 μg/mL for hyaluronidase. Both polyphenolic-rich extracts had a higher inhibitory effect on α-amylase and α-glucosidase than that of the acarbose. The synergistic effect of ursolic acid, rutin, chlorogenic acid, rosmarinic acid, genistin, and daidzein identified in polyphenolic-rich extracts could be mainly responsible for the pharmacological potentials of the studied extracts used in managing inflammation and diabetes.

Ascorbic acid potentiates the inhibitory effect of dopamine on prolactin release in primary cultured rat pituitary cells

1988 ◽  
Vol 118 (2) ◽  
pp. 287-294 ◽  
Author(s):  
S. H. Shin ◽  
R. Stirling
Keyword(s):  
Ascorbic Acid ◽  
Cultured Cells ◽  
Inhibitory Effect ◽  
Physiological Effect ◽  
Biologically Active ◽  
Pituitary Cells ◽  
Prolactin Release ◽  
Minimum Effective Concentration ◽  
Isoascorbic Acid ◽  
Potentiation Effect

ABSTRACT The chemical structure of dopamine includes an ortho-catechol group which is labile to oxidizing agents. Ascorbic acid, a reducing agent, has in the past been added to the incubation medium in order to protect dopamine against oxidation. However, there has been no thorough examination of the biological effect of ascorbic acid on prolactin release. In this present study we have shown that ascorbic acid has neither a stimulatory nor an inhibitory effect on prolactin release but reduces by approximately two orders of magnitude the concentration of dopamine necessary to inhibit prolactin release from cultured anterior pituitary cells. The strong potentiation effect of ascorbic acid was reproduced using apomorphine. We compared the effect of ascorbic acid and isoascorbic acid on dopamine inhibition of prolactin release. Isoascorbic acid is an epimer of ascorbic acid, having the same reduction–oxidation potential as ascorbic acid, but is less biologically active. Isoascorbic acid was less effective in potentiating the dopaminergic effect than was ascorbic acid, which supports the notion that potentiation by ascorbic acid is not entirely due to its reducing property. In order to dissociate further the chemical protection of dopamine from the biological potentiation, the inhibitory effects of freshly made and 3-h-old dopamine solutions were compared. Neither one of the two solutions contained any ascorbic acid, yet the two solutions did not show any difference in their ability to inhibit prolactin release during the 3-h incubation period, indicating that no significant amount of dopamine was oxidized. The minimum effective concentration of ascorbic acid necessary to demonstrate potentiation was between 0·001 and 0·01 mmol/l. The potentiation effect was shown after 1, 2, or 3 h of exposure to dopamine, and was evident in both 2- and 6-day-old cultured cells. The effect of ascorbic acid can either be a pharmacological potentiation or a physiological effect on the primary cultured pituitary cells. However, it is quite clear that ascorbic acid is not a simple anti-oxidant but produces a strong potentiating effect on the dopaminergic inhibition of prolactin release by some other means. J. Endocr. (1988) 118, 287–294

Measurement of the Platelet Response to Laser- induced Microvascular Injury

1974 ◽  
Vol 32 (02/03) ◽  
pp. 704-713 ◽  
Author(s):  
F. N McKenzie ◽  
K.-E Arfors ◽  
N. A Matheson
Keyword(s):  
Inhibitory Effect ◽  
Microvascular Blood Flow ◽  
Platelet Response ◽  
High Concentration ◽  
Platelet Activity ◽  
Microvascular Injury ◽  
Arterial Blood ◽  
Proximal Site ◽  
Adenosine Phosphates

SummaryA study has been made of the biochemical factors underlying the platelet response to laser-induced microvascular injury. A platelet aggregating substance is produced at sites of laser-induced injury which markedly stimulates platelet activity at a site of injury inflicted a short distance downstream. Distal sites of injury are not similarly influenced if the distance between the injuries is increased or if the proximal site no longer shows platelet-stimulating activity. The stimulating effect of an adjacent proximal injury on platelet activity at a distal site is inhibited by local intra-arterial infusion of adenosine. Measurements of arterial blood pressure and microvascular blood flow velocity during adenosine infusion showed that its inhibitory effect on platelet activity is largely independent of its vasodilator properties. The effect of infusion of different adenosine phosphates (AMP, ADP, ATP) was also studied. Very small amounts of ADP markedly stimulated platelet activity and the emboli formed were similar to those normally produced at sites of laser injury. At high concentration AMP inhibited while ATP stimulated platelet activity in vivo. The results emphasise the fundamental role of ADP as a mediator of the platelet response at sites of laser- induced microvascular injury.

Inhibitory Effect of Ascorbic Acid 2-O-.ALPHA.-Glucoside on the Pigmentation of Skin by Exposure to Ultraviolet Light.

1996 ◽  
Vol 58 (3) ◽  
pp. 439-443 ◽  
Author(s):  
Eriko MIYAI ◽  
Itaru YAMAMOTO ◽  
Jun-ichi AKIYAMA ◽  
Mitsuhiro YANAGIDA
Keyword(s):  
Ascorbic Acid ◽  
Ultraviolet Light ◽  
Inhibitory Effect

scholarly journals Inhibitory effect of the Ascorbic Acid on photodegradation of pharmaceuticals compounds exposed to UV-B radiation

2021 ◽  
pp. 100035
Author(s):  
Consuelo León ◽  
Claudio Henríquez ◽  
Nicolás López ◽  
Georgina Sanchez ◽  
Bárbara Pastén ◽  
...  
Keyword(s):  
Ascorbic Acid ◽  
Inhibitory Effect

Somatostatin inhibits insulin-stimulated amino acid uptake into cultured rat myoblasts

1987 ◽  
Vol 114 (4) ◽  
pp. 470-474 ◽  
Author(s):  
G. S. G. Spencer ◽  
D. J. Hill ◽  
G. J. Garssen ◽  
J. P. G. Williams
Keyword(s):  
Amino Acid ◽  
Nutrient Uptake ◽  
Monolayer Culture ◽  
Amino Acid Uptake ◽  
Inhibitory Effect ◽  
Isobutyric Acid ◽  
Acid Uptake ◽  
Newborn Rat ◽  
Amino Isobutyric Acid

Abstract. The effects of somatostatin on the acute metabolic actions of insulin on newborn rat myoblasts in culture has been examined during monolayer culture. Somatostatin significantly inhibited the insulin-stimulated uptake of [3H]leucine and [3H]amino-isobutyric acid into myoblasts but had no effect on basal (unstimulated) uptake of these two substances. The lowest concentration of somatostatin to have a significant effect was 10 μg/l, and this was apparent in all the experiments undertaken. The inhibitory effect of somatostatin was seen at all effective concentrations of insulin used (0.3–1 U/l). These findings lend support to the concept of an endocrine role for somatostatin in vivo and suggest that a peripheral antagonism may exist between circulating insulin and somatostatin on anabolic processes such as nutrient uptake into cells.

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