Evaluation of tissue ascorbic acid status in different hormonal states of female rat

Das, Piw; Das, Kaberi; Bagchi, Kalyan Kumar; Dey, C. D.

doi:10.1016/0024-3205(93)90111-f

Cited by 24 publications

(13 citation statements)

References 18 publications

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“…The AA concentration measured in the AP in the present study was 300 M, an extremely high value that is in agreement with an earlier study (7) and is greater than the concentration found in the hypothalamus (21). Incubation of APs with medium containing high [K ϩ ] resulted in increased release of AA into the medium by a factor of 3 without altering tissue concentration, but the release was not dose-dependent.…”

Section: Discussionsupporting

confidence: 91%

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Ascorbic acid stimulates gonadotropin release by autocrine action by means of NO

Karanth

Walczewska

et al. 2001

Proc. Natl. Acad. Sci. U.S.A.

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Because high concentrations of ascorbic acid (AA) are found in the adenohypophysis, we hypothesized that it might have an acute effect on the secretion of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) from the gland, particularly because we have reported that AA rapidly inhibits stimulated LH-releasing hormone (LHRH) release from medial basal hypothalamic explants. Incubation of anterior pituitary halves from adult male rats with graded concentrations of AA for 1 h induced highly significant release of both FSH and LH with a minimal effective concentration of 10 ؊5 M. Release remained on a plateau from 10 ؊5 to 10 ؊2 M. When both AA and an effective concentration of LHRH were incubated together, there was no additive response to LHRH and the response was the same as to either compound alone. The FSH and LH release in response to AA was blocked by incubation with N G -monomethyl-L-arginine (NMMA) (300 M), a competitive inhibitor of NO synthase. NMMA also inhibited LHRH-induced LH and FSH release and gonadotropin release in the presence of both LHRH and AA, whereas sodium nitroprusside, a releaser of NO, stimulated LH and FSH release. Membrane depolarization caused by incubation in high potassium (K ؉ ‫؍‬ 28 or 56 mM) medium stimulated release of FSH, LH, and AA that was blocked by NMMA. We hypothesize that AA is released with FSH and LH from secretory granules. AA is transported back into gonadotropes by the AA transporter and increases intracellular [Ca 2؉ ]-activating NO synthase that evokes exocytosis of gonadotropins and AA by cGMP .anterior pituitary gland ͉ follicle-stimulating hormone ͉ luteinizing hormone ͉ N G -monomethyl-L-arginine ͉ sodium nitroprusside A scorbic acid (AA) is a six-carbon ketolactone-synthesized from glucose (1, 2). It is an essential vitamin for humans, primates, guinea pigs, and bats, as they lack L-gulono-␥-lactone oxidase, the last enzyme involved in its synthesis from glucose (1, 3). AA is abundant in many endocrine tissues (4, 5) and plays a pivotal role in the control of adrenal and gonadal steroidogenesis (6). Several tissues in the body accumulate AA and its biologically active oxidized form, dehydroascorbic acid. The anterior pituitary gland, brain, adrenal gland, and gonads have high concentrations of AA (2, 7-10). The concentration of AA in the brain ranges between 1.1 and 1.7 mM and remains constant despite variation in AA ingestion (11,12). Intracellular AA concentration is much higher than extracellular AA concentration, and changes in neuronal activity were shown to have a profound influence on extracellular AA (13-18). AA is further concentrated in isolated nerve terminals, and synaptic vesicles concentrate AA by an active transport mechanism (19,20).Previously, we evaluated the effect of AA on basal and stimulated release of luteinizing hormone (LH)-releasing hormone (LHRH) from medial basal hypothalamic explants produced by high potassium medium and N-methyl-D-aspartic acid (NMDA). Sodium nitroprusside (NP), which spontaneously releases NO-stimulate...

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Section: Discussionsupporting

confidence: 91%

“…Several tissues in the body accumulate AA and its biologically active oxidized form, dehydroascorbic acid. The anterior pituitary gland, brain, adrenal gland, and gonads have high concentrations of AA (2,(7)(8)(9)(10). The concentration of AA in the brain ranges between 1.1 and 1.7 mM and remains constant despite variation in AA ingestion (11,12).…”

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confidence: 99%

Ascorbic acid stimulates gonadotropin release by autocrine action by means of NO

Karanth

Walczewska

et al. 2001

Proc. Natl. Acad. Sci. U.S.A.

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“…The highest concentrations of ascorbic acid occur in the pituitary, adrenal gland, and gonads (Chinoy 1972, Das et al 1993. Ascorbic acid is required for collagen synthesis and its role in steroid and peptide hormone production.…”

Section: Discussionmentioning

confidence: 99%

Effects of polychlorinated biphenyl (Aroclor 1254) on steroidogenesis and antioxidant system in cultured adult rat Leydig cells

Palaniappan¹,

Balaganesh²,

Balasubramanian³

et al. 2007

Journal of Endocrinology

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Polychlorinated biphenyls (PCBs) are ubiquitous and persistent environmental contaminants that disturb normal endocrine functions, including gonadal functions in humans and mammals. In the present study, we examined the direct effects of PCB on rat Leydig cells in vitro. Adult Leydig cells were purified by Percoll gradient centrifugation method and the purity of Leydig cells was also determined by 3b-hydroxysteroid dehydrogenase (3b-HSD) staining method. Purified Leydig cells were exposed to different concentrations (10 K10-10 K7 M) of PCB (Aroclor 1254) for 24 h under basal and LH-stimulated conditions. After the experimental period, cultured media were collected and used for the assay of testosterone and estradiol. The treated cells were used for the quantification of cell-surface LH receptors and activities of steroidogenic enzymes, such as cytochrome P 450 side-chain cleavage enzyme (P 450 scc), 3b-HSD, and 17b-hydroxysteroid dehydrogenase (17b-HSD). Leydig cellular enzymatic antioxidants, such as superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, g-glutamyl transpeptidase, glutathione-S-transferase, and nonenzymatic antioxidants, such as vitamins C and E, were assayed. Lipid peroxidation (LPO) and reactive oxygen species (ROS) were also estimated in Leydig cells. In addition, total RNA was isolated from control and Aroclor 1254-exposed Leydig cells to monitor the steady-state mRNA levels by reverse transcription(RT)-PCR for steroidogenic acuteregulatory (StAR) protein, cytochrome P 450 scc, 3b-HSD, and 17b-HSD. Our results indicated that Aroclor 1254 (10 K9 , 10 K8 , and 10 K7 M) treatments significantly inhibit basal and LH-stimulated testosterone and estradiol production. In addition, the activities of steroidogenic enzymes, enzymatic and nonenzymatic antioxidants were significantly diminished in a dose-dependent manner. However, LPO and ROS were elevated in a dose-dependent manner under basal and LH-stimulated conditions. RT-PCR analysis of StAR mRNA level showed a decrease only in 10 K7 M dose of Aroclor 1254 treatment, while cytochrome P 450 scc, 3b-HSD, and 17b-HSD mRNAs were drastically decreased in both 10 K8 and 10 K7 M Aroclor 1254 treatment. These findings suggest that PCBs can act directly on Leydig cells to diminish testosterone production by inhibiting gene expression of steroidogenic enzymes and antioxidant system.

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“…The explants (8 -12 mg) were incubated in vitro as previously reported (34). In brief, one MBH per tube was placed in 0.5 ml of Krebs-Ringer bicarbonate buffer (KRB, pH 7.4, 5.5 mM K ϩ ) supplemented with 20 M bacitracin (Sigma) in an atmosphere of 95% O 2 and 5% CO 2 and incubated in a Dubnoff shaker (50 cycles per minute) for 60 min. After this preincubation, the tissues were incubated with 0.5 ml of KRB or KRB ϩ K ϩ (28 or 56 mM) for 30 or 60 min.…”

Section: Methodsmentioning

confidence: 99%

Ascorbic acid acts as an inhibitory transmitter in the hypothalamus to inhibit stimulated luteinizing hormone-releasing hormone release by scavenging nitric oxide

Karanth

Yu²,

Walczewska³

et al. 2000

Proc. Natl. Acad. Sci. U.S.A.

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Because ascorbic acid (AA) is concentrated in synaptic vesicles containing glutamic acid, we hypothesized that AA might act as a neurotransmitter. Because AA is an antioxidant, it might therefore inhibit nitric oxidergic (NOergic) activation of luteinizing hormonereleasing hormone (LH-RH) release from medial basal hypothalamic explants by chemically reducing NO. Cell membrane depolarization induced by increased potassium concentration [K ؉ ] increased medium concentrations of both AA and LH-RH. An inhibitor of NO synthase (NOS), N G -monomethyl-L-arginine (NMMA), prevented the increase in medium concentrations of AA and LH-RH induced by high [K ؉ ], suggesting that NO mediates release of both AA and LH-RH. Calcium-free medium blocked not only the increase in AA in the medium but also the release of LH-RH. Sodium nitroprusside, which releases NO, stimulated LH-RH release and decreased the concentration of AA in the incubation medium, presumably because the NO released oxidized AA to dehydro-AA. AA (10 ؊5 to 10 ؊3 M) had no effect on basal LH-RH release but completely blocked high [K ؉ ]-and nitroprusside-induced LH-RH release. N-Methyl-D-aspartic acid (NMDA), which mimics the action of the excitatory amino acid neurotransmitter glutamic acid, releases LH-RH by releasing NO. AA (10 ؊5 to 10 ؊3 M) inhibited the LH-RH-releasing action of NMDA. AA may be an inhibitory neurotransmitter that blocks NOergic stimulation of LH-RH release by chemically reducing the NO released by the NOergic neurons.is present in high concentrations in the hypothalamus (1-3) but its role in the modulation of hypothalamic hormone release is obscure. The brain accumulates AA from the blood and maintains a relatively high concentration (1.1-1.7 mM), independent of AA ingestion (4-7). Neuronal intracellular AA concentrations are 10 times greater than extracellular AA concentration (6, 7). Neuronal activity was shown to increase extracellular AA in vitro (6,(8)(9)(10)(11)(12) and in vivo as determined by voltametry (13). AA is further concentrated in isolated nerve terminals (14). Synaptic vesicles concentrate AA by active transport (15). AA is present in high concentrations in synaptic vesicles of glutamergic neurons (13) and in adrenal medullary catecholamine secretory granules (16,17).The presence of high concentrations of AA in synaptic vesicles and the evidence that it could be released into the extracellular space by neuronal activity suggested to us that AA might be a neurotransmitter. Since high concentrations of AA are already known to be present in the hypothalamus, we hypothesized that AA might control luteinizing hormone-releasing hormone (LH-RH) release, possibly by its antioxidant properties. LH-RH release is controlled by release of nitric oxide (NO) from NOergic interneurons that release the soluble gas in juxtaposition to the LH-RH terminals (18,19). In the terminals, NO activates guanylyl cyclase, leading to an increase in cyclic guanosine monophosphate (cGMP), cyclooxygenase, resulting in increased concentrations of prostagla...

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Evaluation of tissue ascorbic acid status in different hormonal states of female rat

Cited by 24 publications

References 18 publications

Ascorbic acid stimulates gonadotropin release by autocrine action by means of NO

Ascorbic acid stimulates gonadotropin release by autocrine action by means of NO

Effects of polychlorinated biphenyl (Aroclor 1254) on steroidogenesis and antioxidant system in cultured adult rat Leydig cells

Ascorbic acid acts as an inhibitory transmitter in the hypothalamus to inhibit stimulated luteinizing hormone-releasing hormone release by scavenging nitric oxide

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