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Biomedical subjects

D L Wong

Publications and source records attributed to D L Wong.

At least 37 records · Page 2Linked to original sources
PubMed1998

Vitamin B-6 deficiency and level of dietary protein affect hepatic tyrosine aminotransferase activity in cats.

Total activity [pyridoxal 5'-phosphate (PLP) added in the assay] of hepatic tyrosine aminotransferase (TAT) measured in cats at 0300, 0900, 1500 and 2100h was 10.3 +/-1.1, 14.0 +/- 0.7, 9.8 +/- 1.3 and 11.0 +/- 0.7 nkat/g liver, indicating little diurnal variation. Activity after 18 h of food deprivation was 10.0 +/- 0.3 nkat/g liver, also not different from cats that were eating ad libitum. These findings support the idea that cats have only limited changes in the activity of hepatic TAT compared with rats. Total TAT activity was measured in cats fed high protein (550 g/kg) and low protein (180 g/kg) diets for 4 wk. Cats fed a high protein diet had activities significantly higher (about twice) than cats fed the low protein diet. Hepatic TAT activity of vitamin B-6-deficient cats (diet without pyridoxine for 9 wk) was compared with cats given the same diet with 8 mg pyridoxine/kg. Total hepatic TAT activity in deficient cats was significantly (P < 0.05) lower per gram soluble or total protein (but not per gram liver) than control cats; holoenzyme activity and percentage of active enzyme in deficient cats were also significantly lower by 75 and 64%, respectively. The apparent Km of TAT from cats for tyrosine (2.1 mmol/L) was similar to that for rats (1.9 mmol/L), but higher for PLP in cats (0.16 micromol/L) than rats (0.034 micromol/L). Part of the reason for the higher plasma tyrosine in vitamin B-6-deficient cats than rats is the higher Km of TAT for PLP in cats than rats.

Animals↗
PubMed1997

Adrenergic differentiation potential in PC12 cells: influence of sodium butyrate and dexamethasone.

The ability of sodium butyrate and dexamethasone to promote adrenergic differentiation in PC12 cells was examined using the gene encoding the epinephrine biosynthetic enzyme, phenylethanolamine N-methyltransferase (PNMT), as a marker. Sodium butyrate and dexamethasone independently stimulated expression of PNMT mRNA in PC12 cells, and the combined action of these drugs led to synergistic activation of the PNMT gene. Despite the induction of the PNMT gene, epinephrine is not produced in these cells, in part due to the absence of a corresponding induction in PNMT enzymatic activity. Another contributing factor appears to be a reduction in the precursor catecholamines, norepinephrine and dopamine, in the presence of sodium butyrate. Thus, while sodium butyrate and dexamethasone can induce PNMT gene expression, treatment of PC12 cells with these drugs appears insufficient for full acquisition of the adrenergic phenotype.

Adrenal Glands↗
PubMed1996

Brain specific proteins binding to the 3' UTR of the 5-HT2C receptor mRNA.

The 5-HT2C receptor2 is a prominent serotonin receptor that is uniquely expressed in the central nervous system and has been implicated in a variety of psychiatric diseases. While characterizing the 5-HT2C receptor gene, we observed that the mRNA contains a long 3' untranslated region that binds multiple brain proteins. Two proteins, molecular weights 55 and 58 kDa, were of particular interest because they were detected only in brain regions known to express the 5-HT2C receptor abundantly, namely, the hippocampus and cortex. These proteins bind with high affinity to the 5-HT2C receptor mRNA at its extreme 3' end (Kd = 1.8 nM), and binding can be specifically competed by selected regions of the 3' UTR. Furthermore, binding of the 55 and 58 kDa proteins to the mRNA is directionally specific and shows preference for an AU-rich loop containing 6 to 7 nucleotides. These results suggest the possibility that these two brain specific proteins may play a role in the post-transcriptional regulation of the 5-HT2C receptor, and that post-transcriptional control of 5-HT2C receptor expression may be an important regulatory mechanism which has not been previously reported for this serotonin receptor subtype.

Animals↗
PubMed1996

Expression of phenylethanolamine n-methyltransferase in the embryonic rat heart.

Phenylethanolamine N-methyltransferase (PNMT), the final enzyme in the pathway for epinephrine biosynthesis, serves as a marker for tissues and cells producing epinephrine. The present study examines the developmental expression of PNMT in the rat embryo. A transient burst in PNMT mRNA expression begins on embryonic day 9.5 (E9.5), peaks between E10.0 and E11.0, and declines to barely detectable levels by E13.0. Regional localization of PNMT mRNA and enzyme activity demonstrates that PNMT is concentrated in the heart. PNMT has not previously been reported to be expressed at these early stages of development, and its presence in the developing heart suggests that this embryonic tissue may produce epinephrine. Because this catecholamine is known to increase cardiac output and promote the growth of cardiomyocytes, local production of epinephrine by the heart could play an important role in the development of cardiac structure and function.

Animals↗
PubMed1996

Role of Egr-1 in cholinergic stimulation of phenylethanolamine N-methyltransferase promoter.

The effects of the cholinergic agonist carbachol on phenylethanolamine N-methyltransferase promoter activity and Egr-1 mRNA expression in PC12-derived RS1 cells were examined to investigate the potential involvement of Egr-1 in the neural regulation of phenylethanolamine N-methyltransferase gene expression. Carbachol stimulated luciferase expression in cells transfected with a rat phenylethanolamine N-methyltransferase promoter-luciferase reporter gene construct and also elevated Egr-1 mRNA levels in untransfected cells. Maximum induction of Egr-1 mRNA by carbachol was rapid (0.5 h), whereas by comparison, peak luciferase activity was delayed (6 h). In addition, carbachol stimulation of both luciferase and Egr-1 mRNA expression could be completely inhibited by atropine but not hexamethonium. Furthermore, bethanechol but not nicotine could mimic the effects of carbachol, indicating that carbachol activation was mediated through muscarinic cholinergic receptors. Finally, carbachol failed to stimulate luciferase expression in cells transfected with a mutant construct, in which the Egr-1 binding element in the phenylethanolamine N-methyl-transferase promoter was mutated. These results suggest that carbachol activates the phenylethanolamine N-methyltransferase promotor through stimulation of Egr-1 expression, and are consistent with the potential involvement of Egr-1 in the cholinergic activation of the phenylethanolamine N-methyltransferase gene.

Animals↗
PubMed1996

Effects of botulinum toxin type A injections on aerodynamic measures of spasmodic dysphonia.

The effects of botulinum toxin type A (BOTOX) injections on aerodynamic measures of phonation were examined in 30 patients with adductor spasmodic dysphonia. Patients received bilateral injections of 2.5 U of botulinum toxin type A in each thyroarytenoid muscle. Measures of air pressure, average airflow, coefficient of variation (CV) of airflow, and laryngeal resistance were obtained before the injections and at 2 and 10 weeks after the injections. These measures were also obtained from 12 normal subjects. Compared with normal subjects, the spasmodic dysphonia patients had significantly higher preinjection values for air pressure, CV of airflow, and laryngeal resistance. At 2 and 10 weeks after the botulinum toxin type A injections, the spasmodic dysphonia patients showed a significant increase in the average airflow values and a significant decrease in the CV of airflow values and the laryngeal resistance values. At 10 weeks after the injections, the values for the three measures began to approach the preinjection values. It is concluded that these aerodynamic measures of phonation can provide useful measures of treatment outcome in adductor spasmodic dysphonia.

Adult↗
PubMed1996

Surgical anatomy of the epitympanic space.

A clear understanding of the surgical anatomy of the epitympanic space is crucial in modern otologic surgery. The tortuous facial nerve within the tight confines of this region presents important surgical challenges, especially when normal anatomy is obscured by disease. Microdissections of 20 human temporal bones were carried out with particular emphasis on the spatial relations of the facial nerve with various temporal bone landmarks. Measurements were made through a standard transmastoid approach to ensure clinical relevance. A high margin of safety can be achieved by observing consistent landmarks and relations in dealing with the facial nerve. We demonstrated the limitations of the transmastoid approach, particularly in accessing the labyrinthine segment of the facial nerve.

Ear, Inner↗
PubMed1996

Evaluation of vocal function in unilateral vocal fold paralysis following thyroplastic surgery.

Perceptual, acoustic, and aerodynamic measures of vocal function were examined, pre- and post-treatment, in nine patients who had received thyroplastic (type I) surgery for unilateral vocal fold paralysis. Following thyroplasty, the patients showed significant improvements in the following perceptual and acoustic measures of vocal function: perceived breathiness, maximum phonation time, s/z ratio, vocal shimmer, and signal-to-noise ratio. Significant post-treatment changes were also observed in the following aerodynamic measures of phonation: air pressure, average airflow, laryngeal resistance, and breath group duration. These findings suggest that a combination of perceptual, acoustic, and aerodynamic measures of vocal function may be useful for comparing the relative effectiveness of different treatment procedures (i.e., thyroplasty vs. Teflon injection) in unilateral vocal fold paralysis.

Adult↗
PubMed1996

Neural stimulation of Egr-1 messenger RNA expression in rat adrenal gland: possible relation to phenylethanolamine N-methyltransferase gene regulation.

Metrazole, which reflexively activates the splanchnic nerve to the adrenal medulla, was used to investigate the physiological role of Egr-1 in the neural regulation of phenylethanolamine N-methyltransferase (PNMT) gene transcription in the rat adrenal gland. A single dose of this drug (70 mg/kg s.c.) rapidly and transiently induced Egr-1 mRNA, with a maximum 22.0-fold increase at 30 min after treatment, followed by a 3.7-fold increase in PNMT mRNA at 8 hr. In contrast, cocaine (15 mg/kg i.p.), which activates the hypothalamic-pituitary-adrenal axis, increased Egr-1 mRNA only 3-fold at 30 min, although it elevated PNMT mRNA comparably. Consistent with their mechanisms of activation, cocaine increased corticosterone levels 7.7-fold at 30 min, whereas metrazole modestly elevated this endogenous corticosteroid 2.5-fold. The cholinergic agonists nicotine (2 mg/kg l.p.) and muscarine (0.1 mg/kg i.p.) also elevated Egr-1 mRNA, with a peak 12- to 15-fold increase being apparent at 30 min after treatment, followed by a 1.7-to 2.0-fold rise in PNMT mRNA at 8 hr. In vitro, metrazole did not increase Egr-1 mRNA above levels observed with carbachol alone (100 microM) in PC-12-derived RS1 cells pretreated with this cholinergic agonist. Finally, splanchnic denervation partially blocked the metrazole-induced rise in Egr-1 mRNA (50% control), while having no effect on cocaine-induced changes in Egr-1 mRNA. These results provide further support for the involvement of Egr-1 in the neural regulation of PNMT gene expression in the rat adrenal gland.

Adrenal Glands↗
PubMed1995

Differential activation of the rat phenylethanolamine N-methyltransferase gene by Sp1 and Egr-1.

The rat phenylethanolamine N-methyltransferase (PNMT) gene contains overlapping consensus elements for the Sp1 and Egr-1 transcription factors located at -45 bp and -165 bp in the PNMT promoter. In the present study, we show that Sp1 and Egr-1 can specifically bind to these overlapping elements, that this binding appears to be mutually exclusive, and that binding site occupancy is dependent upon the concentration of each factor and its binding affinity for each site. Egr-1 binds to the -165 bp site with relatively high affinity (IC50 = 14 nM) and to the -45 bp site with relatively low affinity (IC50 = 1360 nM), whereas Sp1 binds to both sites with intermediate affinities (IC50 = 210 and 140 nM, respectively). Consistent with the DNA-binding data, Egr-1 stimulates PNMT promoter activity primarily through interaction with the -165 bp site, while Sp1 stimulates PNMT promoter activity by interacting with both the -45 bp and the -165 bp sites. These results show that Sp1 and Egr-1 are capable of differentially activating PNMT gene expression, thereby suggesting that different stimuli may control the activity of the PNMT gene by selectively regulating Sp1 and/or Egr-1.

Animals↗
PubMed1995

Role of transcription factor Egr-1 in phorbol ester-induced phenylethanolamine N-methyltransferase gene expression.

Transfection of PC12-variant RS1 cells with an Egr-1 expression construct has previously been shown to stimulate phenylethanolamine N-methyltransferase (PNMT) promoter activity, thus suggesting a putative role of Egr-1 as a factor regulating PNMT gene expression. To elucidate the physiological implication of this finding, the effects of phorbol 12-myristate 13-acetate (PMA) on PNMT promoter activity and Egr-1 expression were examined. PMA stimulated luciferase expression in RS1 cells transfected with a rat PNMT promoter-luciferase reporter gene construct, and also elevated both Egr-1 mRNA and Egr-1 protein levels in the untransfected cells. Further study on the concentration dependence of PMA action showed that the stimulation of luciferase expression correlated with the elevation of Egr-1 mRNA level. Finally, the stimulatory action of PMA on luciferase expression was dramatically diminished in the cells transfected with a mutant construct in which the Egr-1 binding site in PNMT promoter was mutated. These findings suggest that PMA-stimulated PNMT gene expression requires the enhancement of Egr-1 expression, thus providing further evidence for the physiological role of Egr-1 in the regulation of PNMT gene expression in the adrenergic cell.

Animals↗
PubMed1995

Hormonal control of rat adrenal phenylethanolamine N-methyltransferase. Enzyme activity, the final critical pathway.

To examine whether glucocorticoids control rat adrenal phenylethanolamine N-methyltransferase (PNMT) through gene transcription, the effects of hypophysectomy and acute and chronic glucocorticoid replacement on PNMT mRNA and enzymatic activity were determined. Glucocorticoid depletion through hypophysectomy did not alter PNMT mRNA, whereas PNMT activity declined to approximately 25% of normal. A single dose of ACTH (4 IU SC) rapidly induced PNMT mRNA, with a six-fold peak at 6 hours postinjection. The short-term rise in PNMT mRNA was accompanied by an increase in corticosterone and elevated levels of glucocorticoid receptor mRNA. Ribosomal loading experiments suggested that available PNMT mRNA was fully utilized for protein synthesis. However, PNMT activity did not increase commensurately. Chronic ACTH treatment (4 IU SC daily for 7 days) sustained elevated levels of glucocorticoid receptor mRNA but returned corticosterone to hypophysectomized levels and decreased PNMT mRNA to 50% of normal. Despite the decline in PNMT mRNA and its partial utilization for protein synthesis, PNMT enzymatic activity was fully restored. These findings indicate that glucocorticoids exert marked but complex influences on PNMT gene transcription. In addition, corticosteroids appear to posttranscriptionally regulate PNMT protein expression, underscoring the uncoupling between the expression of PNMT mRNA and active enzyme. Thus, glucocorticoid control of gene transcription and protein synthesis do not fully account for changes in PNMT expression, consistent with the previous observation that glucocorticoid control of PNMT proteolysis is also important in PNMT regulation and the potential for epinephrine biosynthesis.

Adrenal Glands↗
PubMed1995

Laryngeal image analysis following botulinum toxin injections in spasmodic dysphonia.

The injection of botulinum toxin (BT) into laryngeal muscles has proven to be an effective treatment for spasmodic dysphonia (SD), a neurologic disorder characterized by intermittent vocal spasms during speech. BT treatment has reduced abnormal laryngeal muscle hyperactivity in SD patients, when measured by subjective visual rating scales. This paper utilizes images obtained from endoscopic laryngeal video recordings to quantify changes in pre- and post-injection parameters of 17 patients following bilateral BT injections. A previous study, utilizing perceptual, acoustic, and laryngeal aerodynamic measures, showed significant improvements following treatment with BT. In addition, post-injection vocal rest, rather than vocalization, enhanced therapeutic responses. Results of these measures are compared with data from the image analyses and those parameters that proved to be the most useful are highlighted.

Adult↗
PubMed1995

Effect of neuromuscular activity on the response to botulinum toxin injections in spasmodic dysphonia.

Spasmodic dysphonia (SD), a neurologic disorder characterized by involuntary vocal spasms during speech, has been effectively treated by injections of botulinum toxin (BT) into the laryngeal muscles. The aim of the present study was to determine if the therapeutic response to BT is enhanced by immediate and continuous activation of the injected muscles. Twenty SD patients were randomized into two groups following bilateral injections: vocal rest for 30 minutes and continuous vocalization for 30 minutes. Evaluations consisted of voice ratings by expert observers, acoustic measurements using computer analyses, and laryngeal aerodynamic measurements. The findings suggest that vocal rest, rather than vocalization, produces a superior and longer lasting response in SD patients receiving BT injections. It is recommended that SD patients refrain from post-injection vocalization to maximize the therapeutic effects of BT.

Adult↗
PubMed1995

Comparison of botulinum toxin injection procedures in adductor spasmodic dysphonia.

This study compares the effects of unilateral and bilateral thyroarytenoid muscle injections of botulinum toxin in 50 patients with adductor spasmodic dysphonia. Patients were randomly assigned to two treatment groups of 25 patients each and a group of 15 normal control subjects was also included. Using a standard electromyographic guidance procedure, one patient group received unilateral thyroarytenoid muscle injections of 15 units of botulinum toxin, while the second patient group received bilateral thyroarytenoid muscle injections of 2.5 units of botulinum toxin on each side. Follow-up data were obtained at 2- and 6-week intervals. Acoustic and perceptual measures of vocal performance included maximum phonation time, fundamental frequency, standard deviation of fundamental frequency, jitter, shimmer, signal/noise ratio, voice break frequency, spasm severity rating, and vocal breathiness rating. Unilateral and bilateral group comparisons at 2-weeks postinjection revealed no significant difference on any of the measures examined. At 6-weeks postinjection, maximum phonation time was significantly lower in the bilateral group. All other measures failed to differentiate the two patient groups. These results suggest that standard unilateral and bilateral botulinum toxin injections provide equivalent degrees of improvement in the symptoms of spasmodic dysphonia. However, bilateral injections appear to be associated with a longer period of excessive phonatory airflow than do unilateral injections.

Adolescent↗
PubMed1994

Egr-1 activation of rat adrenal phenylethanolamine N-methyltransferase gene.

The immediate early gene transcription factor Egr-1 increases luciferase reporter gene activity 3-4-fold when a rat phenylethanolamine N-methyltransferase (PNMT) promoter-luciferase construct and an Egr-1 expression construct are cotransfected into transformed PC12 cells (RS1). Egr-1 also stimulates endogenous PNMT mRNA expression in the RS1 cells. Furthermore, when transfected RS1 cells are treated with dexamethasone, both luciferase and endogenous PNMT mRNA rise an additional 2-fold although dexamethasone does not independently activate transcription from the PNMT promoter. While both Egr-1 sites (-45 and -165 base pairs) in the PNMT promoter appear necessary for maximum luciferase reporter gene expression, the -165 site appears to be the more important for mediating the Egr-1 response. When the upstream site is deleted or either or both sites are mutated in PNMT-reporter gene constructs, Egr-1-induced luciferase activity from the PNMT promoter is significantly reduced. In addition, the incremental activation by dexamethasone is lost when sequences containing the glucocorticoid response element are deleted or when the Egr-1 sites are mutated. In the transfected RS1 cells, a rise in nuclear Egr-1 protein accompanies the rise in endogenous PNMT mRNA. Similarly, reserpine-treated rats (10 mg/kg, intraperitoneally), which show an 8-fold elevation in adrenal PNMT mRNA at 6 h postdrug administration, also show a marked rise in Egr-1 protein in adrenal medullary cell nuclei. These studies provide the first direct evidence that a transcription factor, Egr-1, can activate PNMT gene expression and identify PNMT as a novel target gene for Egr-1. Finally, the incremental enhancement of the Egr-1 response by glucocorticoids suggests a potential interaction between Egr-1 and another transcription factor, the glucocorticoid receptor.

Adrenal Medulla↗
PubMed1994

Neural control of dopamine beta-hydroxylase in vivo: acute and chronic effects.

Reserpine treatment was used to examine whether short- and long-term neural stimulation regulates rat adrenal medullary dopamine beta-hydroxylase (DBH, EC 1.14.17.1) through transcriptional activation and to examine the extent of coordinate control of DBH and phenylethanolamine N-methyltransferase (PNMT, EC 2.1.1.28). A single dose of reserpine (10 mg/kg i.p.) elevates DBH mRNA 1.5-fold by 6 h post-injection. Chronic treatment (10 mg/kg i.p., 4 alternate day injections) continues the rise in DBH mRNA, with a peak of 3.4-fold control values after 2 doses of reserpine and a plateau at this level thereafter. Even though DBH mRNA is elevated 6 h after a single injection of reserpine, DBH activity does not change in parallel. A 1.3-fold rise in activity occurs at 24 h post-injection. In contrast, chronic reserpine treatment concomitantly increases DBH activity and mRNA. As observed for DBH mRNA, enzyme activity peaks and plateaus after 2 injections on alternate days. However, the rise in enzymatic activity is less than the rise in mRNA (2.4-fold versus 3.4-fold). Ribosomal loading experiments demonstrate that the DBH mRNA pool is fully utilized for protein synthesis with an apparent decrease in the number of ribosomes loaded per molecule of mRNA. Western analysis and thermal denaturation studies indicate that an altered form of DBH may be expressed. With a single dose of reserpine, the enzyme shows a decline in specific activity while repeated treatment leads to an enzyme with higher specific activity. In both cases, the protein appears to be more stable. Reserpine treatment also markedly elevates adrenal glucocorticoids. A 1.5-fold increment in glucocorticoid receptor mRNA accompanies the corticosteroid rise, with the receptor mRNA peaking at 6 h and remaining at this level thereafter. The up-regulation of glucocorticoid receptor mRNA expression, together with the presence of a putative glucocorticoid response element in the 5' flanking region of the DBH gene, suggests that neural and hormonal regulatory mechanisms may work in concert to control DBH gene transcription. Finally, by comparison to PNMT, activation of DBH appears to require sustained stimulation of the neural axis, since acute changes in mRNA lead to only minor changes in enzyme expression. Similar to PNMT, continuous neural stimulation increases both DBH mRNA and enzymatic activity. However, the discordance in the magnitude of these indices suggests that other regulatory controls may be important in setting the ultimate limits on DBH expression, glucocorticoids perhaps being one such influence.

Animals↗