Biomedical subjects

V K Weise

Publications and source records attributed to V K Weise.

At least 19 recordsLinked to original sources

PubMed1996

Effects of continuous and intermittent cold (SART) stress on sympathoadrenal system activity in rats.

We compared sympathoadrenal responses to intermittent cold (SART) stress (in which cold exposure is interrupted by 4-hourly intervals daily at room temperature) with those to continuous cold (-3 degrees C) stress. Plasma levels of dihydroxyphenylalanine (DOPA), catecholamines and their metabolites as well as tyrosine hydroxylase (TH) activities in sympathetically innervated tissues were examined in rats exposed to each stressor for 1 day or for 5 days. Neither SART nor continuous exposure to cold for 1 day or 5 days altered plasma epinephrine (EPI) levels. However, norepinephrine (NE) and dihydroxyphenylglycol (DHPG) levels increased markedly during exposure to these stressors. On the first day of SART or continuous cold stress, NE levels were increased similarly, but the increments in DHPG levels were greater during SART stress. Since DHPG is formed in neurons, neural reuptake of NE may be more enhanced on the first day of SART stress than on the first day of continuous cold stress. After 5 days of SART stress plasma NE levels were significantly higher than those found after 5 days of continuous cold exposure. Plasma levels of DHPG were elevated to the same extent in both 5 days SART- and continuously cold-stressed rats, whereas plasma levels of methoxyhydroxyphenylglycol (MHPG) increased only by 5 days SART stress. Even at 1 h after the removal from 5 days SART stress, increased plasma levels of NE, DHPG and MHPG were still evident. These results suggest that 5 days SART stress elevates extraneuronal O-methylation of DHPG, and that NE turnover is more greatly increased by SART stress than by continuous cold stress. Plasma levels of DOPA, dopamine, dihydroxyphenylacetic acid and homovanillic acid also increased after either SART or continuous cold stress for 1 day and 5 days. Adrenal TH activities were significantly increased in rats exposed to SART or continuous cold stress for 1 day and 5 days, but in brown fat TH activity was elevated only in rats exposed to 5 days of continuous cold. Both SART and continuous cold stress are selective and potent stimuli for activation of the sympathoneural system, apparently without significant adrenomedullary EPI release. The increase of TH activity in the brown fat pad as well as of plasma NE and its metabolites is probably a result of adaptation to cold. It appears that even short intervals of return to a normal environmental temperature, as in SART, are sufficient to diminish sympathetic adaptation to cold.

3-Methoxy-4-hydroxyphenylethanol↗

PubMed1994

Increase in rat adrenal phenylethanolamine N-methyltransferase mRNA level caused by immobilization stress depends on intact pituitary-adrenocortical axis.

The effects of a single and of repeated immobilization stress on the expression of the final enzyme involved in epinephrine biosynthesis, phenylethanolamine N-methyltransferase (PNMT), are described. A single immobilization (whether lasting 5 or 120 min) caused a severalfold increase of the adrenal PNMT mRNA level as measured 2 h after the beginning of the procedure. This elevation was of a transient nature, peaked 3-6 h after the 2-h immobilization, and returned to control values by 12 h after the stress. When the animals were immobilized for 2 h/day for seven consecutive days, an increase in content of PNMT mRNA of a similar magnitude was observed, which persisted for at least 2 days after the seventh immobilization. The immobilization-induced increase was completely abolished in hypophysectomized animals, whereas adrenal denervation failed to prevent it. These data suggest that the immobilization-induced increase in adrenal PNMT mRNA level depends primarily on pituitary-adrenocortical regulation.

Adrenal Cortex↗

PubMed1992

Regulation of tyrosine hydroxylase and dopamine beta-hydroxylase mRNA levels in rat adrenals by a single and repeated immobilization stress.

Adrenal catecholamines are known to mediate many of the physiological consequences of the "fight or flight" response to stress. However, the mechanisms by which the long-term responses to repeated stress are mediated are less well understood and possibly involve alterations in gene expression. In this study the effects of a single and repeated immobilization stress on mRNA levels of the adrenal catecholamine biosynthetic enzymes, tyrosine hydroxylase and dopamine beta-hydroxylase, were examined. A repeated 2-hr daily immobilization for 7 consecutive days markedly elevated both tyrosine hydroxylase and dopamine beta-hydroxylase mRNA levels (about six- and fourfold, respectively). In contrast, tyrosine hydroxylase but not dopamine beta-hydroxylase mRNA levels were elevated immediately following a single immobilization. The elevation in tyrosine hydroxylase mRNA with a single immobilization was as high as with seven daily repeated immobilizations. This elevation was not sustained and returned toward control values 24 hr later. Both tyrosine hydroxylase and dopamine beta-hydroxylase mRNA levels were elevated immediately following two daily immobilizations to levels similar to those observed after seven immobilizations and were maintained 24 hr later. The results indicate that both tyrosine hydroxylase and dopamine beta-hydroxylase mRNA levels are elevated by stress; however, the mechanism and/or timing of their regulation are not identical.

Adrenal Glands↗

PubMed1992

Effects of handling or immobilization on plasma levels of 3,4-dihydroxyphenylalanine, catecholamines, and metabolites in rats.

In conscious animals, handling and immobilization increase plasma levels of the catecholamines norepinephrine (NE) and epinephrine (EPI). This study examined plasma concentrations of endogenous compounds related to catecholamine synthesis and metabolism during and after exposure to these stressors in conscious rats. Plasma levels of 3,4-dihydroxyphenylalanine (DOPA), NE, EPI, and dopamine (DA), the deaminated catechol metabolites 3,4-dihydroxyphenylglycol (DHPG), and 3,4-dihydroxyphenylacetic acid (DOPAC), and their O-methylated derivatives methoxyhydroxyphenylglycol (MHPG) and homovanillic acid (HVA) were measured using liquid chromatography with electrochemical detection at 1, 3, 5, 20, 60, and 120 min of immobilization. By 1 min of immobilization, plasma NE and EPI levels had already reached peak values, and plasma levels of DOPA, DHPG, DOPAC, and MHPG were increased significantly from baseline, whereas plasma DA and HVA levels were unchanged. During the remainder of the immobilization period, the increased levels of DOPA, NE, and EPI were maintained, whereas levels of the metabolites progressively increased. In animals immobilized briefly (5 min), elevated concentrations of the metabolites persisted after release from the restraint, whereas DOPA and catecholamine levels returned to baseline. Gentle handling for 1 min also significantly increased plasma levels of DOPA, NE, EPI, and the NE metabolites DHPG and MHPG, without increasing levels of DA or HVA. The results show that in conscious rats, immobilization or even gentle handling rapidly increases plasma levels of catecholamines, the catecholamine precursor DOPA, and metabolites of NE and DA, indicating rapid increases in the synthesis, release, reuptake, and metabolism of catecholamines.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1992

Hypercortisolemia inhibits yohimbine-induced release of norepinephrine in the posterolateral hypothalamus of conscious rats.

Chronic hypercortisolemia attenuates yohimbine (YOH)-induced increments in plasma levels of the sympathetic neurotransmitter norepinephrine (NE). The present study used in vivo microdialysis to study the effects of hypercortisolemia on YOH-induced release of NE in the brain. Cortisol (25 mg/kg.day) or saline was infused sc into rats for 7 days via an osmotic minipump. Microdialysate and plasma concentrations of NE and its metabolites dihydroxyphenylglycol and methoxyhydroxyphenylglycol were measured before and after YOH (1 mg/kg, iv) administration in conscious animals, with microdialysate and plasma collections beginning 20-24 h after probe implantation. Chronic cortisol treatment resulted in attenuated NE, dihydroxyphenylglycol, and methoxyhydroxyphenylglycol responses in both microdialysate and plasma. The results indicate that YOH increases central neural as well as peripheral release, reuptake, turnover, and metabolism of NE and that hypercortisolemia suppresses these responses.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1992

Plasma dopa responses during stress: dependence on sympathoneural activity and tyrosine hydroxylation.

Dihydroxyphenylalanine (dopa), the precursor of all the endogenous catecholamines, circulates in plasma at a concentration higher than that of the sympathetic neurotransmitter, norepinephrine (NE). Sources of dopa in plasma and the meaning of plasma dopa levels in terms of sympathoneural function have been unclear. Plasma concentrations of dopa, the catecholamines NE, epinephrine and dopamine, the deaminated catechol metabolites dihydroxyphenylglycol and dihydroxyphenylacetic acid, and the O-methylated metabolites methoxyhydroxyphenylglycol and homovanillic acid were measured during immobilization stress in conscious rats. Animals were pretreated with chlorisondamine to block ganglionic neurotransmission or with alpha-methyl-para-tyrosine to inhibit tyrosine hydroxylation. Immobilization produced rapid, sustained increases in plasma levels of dopa, catecholamines and catecholamine metabolites. Chlorisondamine decreased base-line plasma dopa and NE levels and abolished the increases in plasma dopa and NE levels during immobilization. alpha-Methyl-para-tyrosine administration produced sustained decreases in plasma dopa levels and markedly attenuated immobilization-induced increases in plasma dopa levels. Bilateral adrenalectomy augmented base-line plasma levels of dopa and NE and augmented dopa and NE responses during immobilization. The results indicate that during immobilization stress, increased postganglionic sympathoneural outflow stimulates the synthesis of dopa in sympathetic neurones and enhances release of dopa into the circulation. The data generally support the view that changes in plasma dopa levels during stress reflect in vivo changes in the rate of catecholamine biosynthesis in sympathetic nerve terminals.

Adrenalectomy↗

PubMed1991

Prolonged alterations in canine striatal dopamine metabolism following subtoxic doses of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and 4'-amino-MPTP are linked to the persistence of pyridinium metabolites.

Single toxic doses of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP).HCl (2.5 mg/kg i.v.) and 4'-amino-MPTP.2HCl (22.5 mg/kg) induce loss of striatal dopamine (DA) and tyrosine hydroxylase (TH) activity and of nigral DA neurons in the dog. To examine the subacute neurochemical changes induced by low doses of MPTP and 4'-amino-MPTP, dose-response studies of these compounds were carried out in the dog, using 6- and 3-week survival times for these two compounds, respectively. Low single doses of MPTP (1.0, 0.5, and 0.1 mg/kg i.v.) and 4'-amino-MPTP (15, 7.5, and 3.75 mg/kg i.v.) did not cause depletion of canine striatal DA or TH or a loss of nigral neurons. However, levels of the DA metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were decreased in a dose-related fashion, with significant loss of DOPAC being evident 6 weeks after the lowest administered dose of MPTP and 3 weeks after 4'-amino-MPTP. This selective loss of DA metabolites following nontoxic doses of MPTP and 4'-amino-MPTP led to a shift in the ratio of DA to DOPAC or HVA, which was characteristic for each compound. The measurement of striatal 1-methyl-4-phenylpyridinium (MPP+) and 4'-amino-MPP+ levels revealed that high concentrations (up to 150 microM) persist in the striatum for weeks following administration of a single nontoxic dose of MPTP or 4'-amino-MPTP. A causal relationship between the striatal concentration of MPP+ or 4'-amino-MPP+ and the change in DA metabolism as reflected in the DA/DOPAC ratio is suggested by a significant correlation between these measures. It is suggested that presynaptic sequestration and retention of MPP+ and 4'-amino-MPP+ by striatal DA terminals result in the inhibition of the monoamine oxidase contained within these terminals.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗

PubMed1989

Effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in the dog: effect of pargyline pretreatment.

Adult beagle dogs of either sex were injected with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-HCl (2.5 mg/kg, i.v.) alone or after pretreatment with pargyline (5.0 mg/kg, s.c., twice), with pargyline alone, or were uninjected. Groups were killed 2 h, 3 weeks, or 3 months after injection, and several brain areas were assayed for biogenic amines and their synthetic and degradative enzymes. MPTP caused a massive and permanent loss of striatal dopamine, tyrosine hydroxylase, and 3,4-dihydroxyphenylalanine decarboxylase activities and the loss of cells within the substantia nigra pars compacta. Dopamine and norepinephrine also were depleted to various degrees in cortex, olfactory bulb, and hypothalamus; however, dopamine beta-hydroxylase activity in cortex was normal. There was no cell loss in the ventral tegmental area or locus ceruleus. The activities of monoamine oxidase (MAO)-A and MAO-B in cortex and caudate were not affected by MPTP. Despite a permanent loss of the nigrostriatal system, the dogs exhibited only a transient hypokinesia lasting 1-2 weeks. Pargyline pretreatment prevented the loss of striatal dopamine and cells from the substantia nigra, but did not prevent a prolonged but reversible decrease in the concentration of dopamine metabolites. It is argued that this apparent inhibition of MAO is due not to suicide inactivation of the enzyme by MPTP, but to reversible inhibition by accumulation of the pyridinium metabolite, 1-methyl-4-phenylpyridinium, selectivity in aminergic terminals.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗

PubMed1987

A radiometric assay for phenylethanolamine N-methyltransferase and catechol O-methyltransferase in a single tissue sample: application to rat hypothalamic nuclei, pineal gland, and heart.

A simple and highly sensitive method for simultaneous assay of phenylethanolamine N-methyltransferase (PNMT) and catechol O-methyltransferase (COMT) is described. These enzymes are determined in a single tissue homogenate using S-[methyl-3H] adenosyl-L-methionine as methyl donor and sequentially incubating with the substrates phenylethanolamine and epinephrine. The radioactive products of the enzymatic reactions, N-methylphenylethanolamine and metanephrine, are extracted and then separated by thin-layer chromatography. The identity of the reaction products has been established chromatographically and the conditions for both enzymatic reactions in the assay procedure have been defined. Measurement of PNMT activity in the rat pineal gland or in minute fragments of other tissues (e.g., brain nuclei) has not been possible using previously described methods. Activities of PNMT and COMT in the rat pineal gland, various hypothalamic nuclei, and the auricular and ventricular myocardia are herein reported.

Animals↗

PubMed1987

Taurine biosynthesis in rat brain: a new specific and sensitive microassay of cysteine sulfinate decarboxylase (CSDI) activity through selective immunotrapping and its use for distribution studies.

Cysteine sulfinate decarboxylase (CSD), the putative biosynthetic enzyme for taurine, has been shown to exist in two forms in rat brain, respectively CSDI and CSDII, one of which (CSDII) is considered to be in fact glutamate decarboxylase (GAD). CSDI assay after immunotrapping was made possible by using an anti-CSD antiserum raised in sheep immunized with a partially purified CSD fraction from liver. This antiserum immunoprecipitated both liver CSD and brain CSDI activities with the same affinity but did not inhibit their enzymatic activities. The immunotrapping of CSDI was selective without any contamination by GAD/CSDII activity. The immunotrapped CSD activity, which corresponded exactly to the amount of CSD not precipitated by a GAD/CSDII antiserum, was not inhibited by a specific irreversible GAD inhibitor. A quantitative, selective and sensitive assay was thus developed by measuring CSD activity on the solid phase after immunotrapping. Kinetic parameters of the immunotrapped enzyme remained unchanged. CSDI activity represented only a fraction, around 20% with saturating concentration of substrate, of the total CSD activity in rat brain homogenate. This indicates that most studies on total CSD activity dealt essentially with CSDII activity that is indeed GAD. Regional and subcellular distributions of CSDI have been determined. CSDI activity was about threefold higher in the richest (cerebellum) compared to the poorest (striatum) region without any correlation with GAD/CSDII distribution. Subcellular distribution showed a fourfold enrichment of CSDI activity in the synaptosomal fraction. The precise role of CSDI and CSDII in the biosynthesis of taurine in vivo remains to be elucidated.

Animals↗

PubMed1985

Effect of ventral noradrenergic bundle transection and locus coeruleus lesions on urinary 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG) excretion in the rat.

Urinary 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG) excretion was determined in rats after central noradrenergic pathway interruption by ventral bundle transection or by locus coeruleus (LC) lesions. The transection prevented an increase in urinary MHPG that occurred in sham-operated animals, an effect that was presumed to be due to loss of cerebrospinal fluid (CSF). Electrolytic lesioning of the LC, which was not attended by loss of CSF, had no effect on baseline MHPG excretion but diminished the response to subsequent administration of the alpha-adrenergic blocking agent, phenoxybenzamine (PBZ). Since the contribution of brain MHPG to total urinary MHPG is small, the observed effects of these procedures are most likely due to disrupted central regulation of peripheral sympathetic nerve activity.

Animals↗

PubMed1983

Glutamate decarboxylase immunoreactivity and gamma-[3H] aminobutyric acid accumulation within the same neurons in dissociated cell cultures of cerebral cortex.

In order to evaluate the reliability of high affinity [3H]GABA accumulation as a marker for GABAergic neurons, murine cerebral cortical neurons were studied in dissociated cell culture. Cultures which had been incubated in [3H]GABA were stained immunohistochemically for the GABA-synthesizing enzyme, glutamate decarboxylase, fixed with paraformaldehyde, and subsequently processed for radioautography. In mature cultures, there was an 84 to 94% correlation between the presence of the enzyme and [3H]GABA uptake within the same cortical neurons. These data provide direct evidence that those neurons which synthesize GABA are the same neurons which are labeled by high affinity [3H]GABA uptake.

Animals↗

PubMed1982

Central GABAergic innervation of neurointermediate pituitary lobe: biochemical and immunocytochemical study in the rat.

Activity of glutamic acid decarboxylase GluDCase, the biosynthetic enzyme of gamma-aminobutyric acid (GABA) was measured in low-speed homogenate supernatant of the neural and intermediate (neurointermediate) lobe (28--30 pmol of CO2 per microgram of protein per hr) and of the anterior lobe (2--4 pmol of CO2 per microgram of protein per hr). In the neurointermediate lobe, stalk transection reduced the GluDCase activity by more than 95%. By using an antiserum to rat brain GluDCase and the unlabeled antibody--peroxidase method of Sternberger, GluDCase immunoreactivity was localized in many terminals within the neurointermediate lobe of the hypophysis. In pars intermedia, immunoreactive terminals occurred in apposition to secretory cells and to glial cells and were near nonimmunoreactive axonal profiles; in pars neuralis they were apposed to pituicytes and to unlabeled axons including the neurosecretory terminals and were along fenestrated portal capillaries. GluDCase immunoreactive axons terminals exhibited diverse morphological features and would not have been identified as a distinct population without the GluDCase antiserum. No GluDCase-immunoreactivity was found in the anterior pituitary lobe. Stalk transection abolished GluDCase immunoreactivity in the neurointermediate lobe. These data provide biochemical and morphological evidence for a central GABAergic innervation of neural and intermediate lobes of the hypophysis.

Animals↗

PubMed1982