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Biomedical subjects

W Z Potter

Publications and source records attributed to W Z Potter.

At least 91 records · Page 5Linked to original sources
PubMed1991

Lithium effects on noradrenergic-linked adenylate cyclase activity in intact rat brain: an in vivo microdialysis study.

The effects of chronic lithium treatment on adenylate cyclase activity in intact rat brain were examined using in vivo microdialysis. Basal extracellular cyclic adenosine monophosphate (AMP) increased in a dose-dependent manner after norepinephrine was added to the perfusate. Chronic lithium treatment increased basal brain extracellular fluid cyclic AMP levels, while decreasing the magnitude of the cyclic AMP response to stimulation with 100 microM norepinephrine.

Adenylyl Cyclases↗
PubMed1991

The mechanisms of action of lithium. I. Effects on serotoninergic and noradrenergic systems in normal subjects.

The effects of 2 weeks of lithium carbonate administration at therapeutic plasma levels were examined in 11 normal volunteers. Serotoninergic function before and after lithium administration was assessed using low-dose intravenous clomipramine hydrochloride challenge, while urinary and plasma metabolites of norepinephrine (NE) were used to assess noradrenergic systems. Long-term lithium administration in normal subjects did not significantly or consistently enhance serotonin-mediated neuroendocrine responses but did increase measures related to neuronal release of NE. No statistically significant effects of lithium on prolactin, corticotropin, or cortisol responses to serotoninergic challenge could be detected. The probability of a type II error was assessed, and a doubling of prolactin level was unlikely to have been missed, although more modest increases (less than 75%) could have been overlooked. After 2 weeks of lithium administration, there were significant increases in 24-hour urinary excretion of NE, normetanephrine, and fractional NE release, compatible with increased neuronal release of NE and a lithium-induced subsensitivity in alpha 2-adrenergic receptor function. These changes were not statistically significant after 1 week of administration, suggesting that increased NE release is characteristic of long- rather than short-term lithium administration. Since previous reports have demonstrated enhanced prolactin responses after short- but not long-term lithium use, the present study points to temporal specificity in lithium's effects on both serotoninergic and noradrenergic function. Lithium's effects on NE release were consistent but small (a 16% increase), while its effects on serotoninergic responses were larger (a 50% increase in prolactin responses) but quite inconsistent, suggesting that neither of these systems is the primary site of action of lithium.

Adrenocorticotropic Hormone↗
PubMed1991

The mechanisms of action of lithium. II. Effects on adenylate cyclase activity and beta-adrenergic receptor binding in normal subjects.

As part of a study of the effects of lithium carbonate on neurochemical function in man, platelet and lymphocyte adenylate cyclase activity and lymphocyte beta-adrenergic receptor binding characteristics were determined before and after 2 weeks of lithium treatment in 10 normal volunteers. Lithium had differential effects on platelet and lymphocyte adenylate cyclase activity. In platelets, basal and stimulated (guanyl imidodiphosphate [Gpp[NH]p] or cesium fluoride) adenylate cyclase activity was significantly augmented by lithium treatment. By contrast, in lymphocytes, Gpp(NH)p- and cesium fluoride-stimulated adenylate cyclase activity was unaffected, while basal activity was decreased modestly after lithium. These results are consistent with preclinical studies that suggest that lithium's effects on adenylate cyclase activity are specific with respect to tissue and brain region and that lithium may interfere with guanine nucleotide binding (G) protein function. Lithium treatment significantly increased the ratio of low- to high-affinity dissociation constants for agonist displacement of antagonist binding to lymphocyte beta-adrenergic receptors (thought to reflect coupling between the beta-adrenergic receptor and stimulatory G protein). Lithium had significant effects on measures associated with signal transduction that might be contrasted to its more subtle effects on neuronal function (norepinephrine release) and neuroendocrine systems (responses to serotoninergic challenge) in these same subjects (reported in a companion article). Lithium's primary site of action may be on signal transduction mechanisms. These effects subsequently may be manifested in changes in neurotransmitter function that may be important to lithium's mood-stabilizing actions.

Adenylyl Cyclases↗
PubMed1991

Pharmacokinetic and dynamic correlates of intravenous alprazolam challenge.

The concentration-effect relationship of alprazolam plasma concentration and growth hormone changes was studied in six healthy volunteers by use of three different intravenous bolus doses of alprazolam (0.003, 0.007, and 0.02 mg/kg) in a random blind order. There was a linear increase in peak concentration (Cmax) and area under the curve (AUC) of alprazolam with increasing dose (r = 0.96). There was no significant correlation between alprazolam Cmax and effect on growth hormone measured as either maximum increase or maximum percentage change from baseline. There was, however, an overall positive correlation (r = 0.58) between the AUC values of alprazolam and growth hormone from 0 to 120 minutes, although the relative degree of increased AUC of growth hormone with increasing AUC of alprazolam varied greatly across individuals. The difficulties of interpreting the mechanisms underlying differential growth hormone responses even when concentration of stimulus is controlled are discussed.

Alprazolam↗
PubMed1991

Down-regulation of beta receptors by desipramine in vitro involves PKC/phospholipase A2.

Chronic treatment with a number of antidepressants results in a down-regulation and/or a desensitization of rat cortical beta-adrenergic receptors (beta ARs). Although these effects generally have been attributed to elevations in intrasynaptic norepinephrine via presynaptic mechanisms, the recent demonstration of similar changes in beta ARs following in vitro incubation of cultured cells with desipramine (DMI) suggests that direct, postsynaptic mechanisms may also be involved. To study these mechanisms, we incubated rat C6 glioma cells with 10 microM DMI for 1 or 5 days. DMI produced a significant reduction in beta AR density following chronic (but not acute) treatment (BMAX control = 1325 +/- 78 fmol/mg; DMI = 1179 +/- 96; p less than .05). Interestingly, the beta AR down-regulation was accompanied by an increase in KL/KH ratio (ratio of dissociation constants for the low- and high-affinity states of the receptor), suggesting that these drugs may stabilize the high-affinity complex. DMI treatment attenuated the cyclic adenosine monophosphate (cAMP) response to 1 microM isoproterenol (control = 540 +/- 82 pmol/mg/15 min; DMI = 335 +/- 64; p less than .05), but not to agents acting distal to the receptor (cholera toxin or forskolin). Coincubation of C6 cells with either the phospholipase A2 (PLA2) inhibitor mepacrine or the protein kinase C (PKC) inhibitor H7, during chronic treatment with DMI, blocked the down-regulation of beta ARs. Incubation of C6 cells with phorbol esters (PKC activators) also down-regulated beta ARs, effects that were nonadditive with those of DMI. Incubation with H7 alone resulted in an up-regulation of beta ARs, consistent with a tonic regulatory effect of PKC on beta ARs.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Signal transduction modulation by lithium: cell culture, cerebral microdialysis and human studies.

Considerable evidence suggests that signal transduction pathways are targets of lithium (Li) action. A number of investigators have reported that Li attenuates both adenylate cyclase (AC) activity and phosphoinositide (PI) turnover in rodents and in humans, thus "dampening" these systems. We have studied selected components of these second-messenger systems in a series of clinical and preclinical investigations. To overcome confounding effects of alterations in mood state, we examined AC activity and G-protein ribosylation in peripheral blood cells from 10 healthy volunteers, prior to and following 14 days of Li administration. Basal and postreceptor [cesium fluoride (CsF) or Gpp(NH)p] stimulated AC activity were unaffected in lymphocytes. In contrast, both basal and stimulated AC activity in platelets were significantly augmented, compatible with an attenuation of Gi function. Ribosylation of platelet Gs by cholera toxin was unchanged, whereas that of Gi by pertussis toxin (PT) was increased. Given that undissociated G protein is the preferred substrate for PT, our results suggest that Li interferes with subunit dissociation and the subsequent activation of Gi. To determine if Li has similar effects on Gi in the central nervous system, we measured extracellular (EC) cyclic adenosine monophosphate (cAMP) in rat brain by in vivo microdialysis, revealing a dose-dependent increase in cAMP by norepinephrine (NE) antagonized by propranolol. Chronic (4-week) Li doubled basal EC cAMP, while decreasing the fractional response to 100 microM NE. Thus, using in vivo microdialysis, we observed the reported reduction in NE-stimulated AC activity, but only as a function of elevated basal cAMP. Increased basal AC activity has been observed following chronic Li in both humans and rat tissues but generally has not been considered relevant. The PI generating system is another proposed major target for Li that we have studied using an in vitro cell culture model of peripheral blood cells. Chronic (6-day) exposure of neutrophil-like HL60 cells to 1 mM LiCl did not affect agonist fMet-Leu-Phe (fMLP) induced PI turnover. In contrast, Li attenuated both agonist and phorbol ester stimulated Na+/H+ exchange, suggesting reduced protein kinase C (PKC) function. Western blot analysis revealed altered levels of PKC in both membrane and cytosolic fractions. The functional consequences of these complex effects on the two major signal transduction pathways and their interactions in the intact living organism remain to be elucidated.

Adult↗
PubMed1991

A survey of psychotropic medications not available in the United States.

The range of psychotropic medications available in the U.S. for the treatment of serious mental illnesses is limited. Many agents have been "me too" drugs, offering primarily side-effect differences, instead of new indications or mechanisms. As a result, patients refractory to the original drugs are not helped. Other patient populations (both mentally ill and addicted) have "fallen through the cracks" of the current U.S. psychotropic drug development process. The recent approval of chlorimipramine and clozapine demonstrates that real benefits for U.S. patients can be realized from judicious introduction of non-U.S. drugs. Many more psychotropic drugs developed and used in other countries are not available in the United States. Industrial and regulatory obstacles could be surmounted by the legislative innovation proposed. This survey identifies some specific non-U.S. drugs of interest.

Humans↗
PubMed1991

Gender differences in pharmacokinetics and pharmacodynamics of psychotropics: focus on women.

The animal literature provides many instances of gender differences in drug metabolism and/or response. However, there are inherent dangers in trying to generalize findings of either pharmacokinetic or pharmacodynamic gender differences to humans. The literature was searched for references to gender and pharmacokinetics of psychoactive drugs. Interest was primarily in whether sufficient data were available on humans to implicate a gender effect, given the large animal literature. There was a dearth of investigations to look for pertinent differences and many studies that examined gender differences appeared to do so incidentally. Some differences were identified that seemed hormonally influenced and age-related. The most compelling gender differences stem from data on research probes utilized to better understand psychiatric disease processes. The implications for women as psychoactive drug consumers are discussed.

Humans↗
PubMed1991

Dosage regimen design for cyclic antidepressants: a review of pharmacokinetic methods.

One of the difficulties in pharmacotherapy of depression is the frequent need to make several dosage titrations before reaching the optimal therapeutic dosage. This problem has led to several experimental approaches for predicting a stable antidepressant maintenance dose from plasma concentration data collected shortly following a test dose. The theoretical basis for these methods is reviewed along with the results of clinical trials. It is concluded that accurate steady-state concentrations of cyclic antidepressants can be predicted from kinetic analysis of plasma concentrations obtained early in therapy. The most applicable drug for prospective dosing methods is nortriptyline with its widely accepted therapeutic plasma concentration range. Other drugs that also have substantial evidence for predicting the optimal dose from an early point in therapy include desipramine and imipramine. Predictive dosing methods are easily applied in the inpatient setting. Multiple data points obtained between 12 and 48 hours after the first dose are likely to give accurate predictions and provide clinically useful information. More widespread application of predictive approaches to dosage regimen design of antidepressant pharmacotherapy may lead to reduced hospitalization and cost savings.

Antidepressive Agents, Tricyclic↗
PubMed1991

Acute noradrenergic effects of desipramine in depression.

As a probe of the noradrenergic system in depression, single oral doses of the tricyclic antidepressant desipramine (100 mg) and placebo were administered to unipolar and bipolar depressed patients and healthy volunteers. Plasma concentrations of norepinephrine (NE) were determined 2-3 hours after dosing, with subjects in supine and upright positions. On the placebo day plasma NE was low in a subset of bipolar patients; both groups of depressives demonstrated an exaggerated increase in plasma NE upon standing. After desipramine dosing, the orthostatic procedure resulted in even greater relative increments in plasma NE in both patient groups, with no change in volunteers. These data are consistent with noradrenergic dysregulation in depression.

Administration, Oral↗
PubMed1991

Acute cardiovascular effects of tranylcypromine: correlation with plasma drug, metabolite, norepinephrine, and MHPG levels.

BACKGROUND: Recent case reports, small series, and uncontrolled, unblinded studies have suggested that tranylcypromine may produce pressor reactions in some patients. However, the physiologic mechanism underlying this cardiovascular change is unknown. METHOD: The authors studied the acute cardiovascular effects of tranylcypromine in 13 patients and attempted to correlate these changes with plasma measures of parent drug, possible pressor metabolites, norepinephrine, and 3-methoxy-4-hydroxyphenylglycol. RESULTS: Significant elevations in supine blood pressure occurred after administration of tranylcypromine and correlated with tranylcypromine dose. Similar changes were not observed in standing blood pressure measurements. In fact, an orthostatic decrease in blood pressure and increase in heart rate were observed. Amphetamine-like metabolites were not found. CONCLUSIONS: The authors speculate on possible mechanisms underlying these opposite cardiovascular effects.

Adult↗
PubMed1990

Chronic Li+ attenuates agonist- and phorbol ester-mediated Na+/H+ antiporter activity in HL-60 cells.

The effects of Li+ on signal transduction in dibutyryl cAMP-differentiated HL-60 cells were studied. Upon differentiation, these human promyelocytic leukemia cells express a chemotactic formyl peptide receptor, which is coupled through a guanine nucleotide-binding protein to phospholipase C. Stimulation with fMet-Leu-Phe results in changes in intracellular pH which are thought to be mediated by protein kinase C regulation of Na+/H+ antiporter function. Acute LiCl treatment (10 mM) was without any effect on Na+/H+ activity. However, pretreatment of HL-60 cells with 1 or 10 mM LiCl for at least 5 days resulted in a marked attenuation of fMet-Leu-Phe effects on Na+/H+ activity. In undifferentiated HL-60 cells, which lack fMet-Leu-Phe receptors, intracellular acidification induced by the proton ionophore nigericin generates an alkalinization response. Chronic (but not acute) Li+ treatment also resulted in an inhibition of the nigericin-mediated response. Furthermore, stimulation of the Na+/H+ antiporter by the phorbol ester, phorbol-12-myristate-13-acetate, was also markedly attenuated by chronic LiCl treatment, suggesting an impairment of protein kinase C activity. In contrast, fMet-Leu-Phe-induced increases in intracellular Ca2+ and phospho-inositide breakdown were unchanged in cells treated with Li+ for 5 days. These results indicate that chronic but not acute Li+ treatment alters intracellular pH regulation possibly at a site distal to the fMet-Leu-Phe receptor.

Calcium↗
PubMed1990

Effects of chronic exposure to ethanol alone and in combination with desipramine on beta-adrenoceptors of rat brain.

The effect of chronic ethanol exposure alone or in combination with desipramine on agonist and antagonist binding to beta-adrenoceptors was studied in membrane preparations from rat frontal cortex and hippocampus. Ten day exposure of animals to ethanol vapor (25 mg/l) in inhalation chambers had no effect on binding properties of antagonist iodocyanopindolol (ICYP) in either brain region. However, ethanol in combination with chronic desipramine treatment prevented the reduction of beta-adrenoceptor density in frontal cortex produced by desipramine administration. Similar to its effects on antagonist binding, chronic ethanol exposure did not change the agonist isoproterenol binding characteristics measured in membranes from either rat frontal cortex or hippocampus. However, the combination of ethanol plus desipramine reduced the dissociation constant of the low affinity state of the receptor (KL) in frontal cortex from 23.1 +/- 3.7 microM in controls to 11.2 +/- 1.7 microM. Moreover, ethanol plus desipramine produced a greater decrease in the percentage of cortical receptors in the high affinity state for agonist (%RH) than did desipramine alone. This suggests that ethanol enhances desipramine-induced desensitization of beta-adrenoceptors in frontal cortex in spite of the prevention of reduction in density of the receptors. In hippocampal membranes, ethanol together with desipramine prevented desipramine-induced changes in agonist binding characteristics, i.e. the decrease in KH (dissociation constant from high affinity state of the receptor) and the consequent enhancement in KL/KH ratio. Thus, chronic exposure to relatively low concentrations of ethanol partially prevents effects of desipramine on beta-adrenoceptors.

Adenylyl Cyclases↗
PubMed1990

Cerebrospinal fluid monoamine metabolites, aggression, and impulsivity in disruptive behavior disorders of children and adolescents.

Cerebrospinal fluid levels of 5-hydroxyindoleacetic acid, a metabolite of serotonin, were measured in relation to aggression, impulsivity, and social functioning in 29 children and adolescents with disruptive behavior disorders. The cerebrospinal fluid 5-hydroxyindoleacetic acid level was low compared with that of age-, sex-, and race-matched patients with obsessive-compulsive disorder. Within the disruptive group, significant negative correlations with age-corrected 5-hydroxyindoleacetic acid level were seen for the child's report of aggression toward people and the expressed emotionality of the child toward his or her mother; other correlations of age-corrected 5-hydroxyindoleacetic acid level with measures of aggression were in the expected negative direction but did not reach statistical significance. Impulsivity per se and socioenvironmental factors were not significantly related to cerebrospinal fluid 5-hydroxyindoleacetic acid concentration.

Adolescent↗
PubMed1990

Cerebrospinal fluid and plasma monoamine metabolites and their relation to psychosis. Implications for regional brain dysfunction in schizophrenia.

The relationship between central (cerebrospinal fluid [CSF]) and peripheral (plasma) monoaminergic metabolites and psychotic symptoms was examined in 22 drug-free schizophrenic inpatients. The CSF homovanillic acid levels did not differ significantly between patients and normal controls (n = 33). The CSF homovanillic acid levels, however, were negatively correlated with ratings of psychosis and positive symptoms, and the CSF homovanillic acid and 5-hydroxyindoleacetic acid levels correlated negatively with individual deficit symptoms. Stepwise and hierarchical multiple-regression analysis revealed that among monoaminergic measures, only the CSF and plasma homovanillic acid levels contributed significantly to the total Brief Psychiatric Rating Scale and positive symptom variance with negative and positive partial correlations, respectively. Levels of CSF 3-methoxy-4-hydroxyphenylglycol, but not of CSF norepinephrine, were significantly elevated in the schizophrenic patients compared with controls, and plasma 3-methoxy-4-hydroxyphenylglycol levels were positively correlated with negative symptoms. We discuss the potential implications of these findings for a model of dopaminergic dysfunction in schizophrenia involving distinct cortical and subcortical contributions.

Adult↗
PubMed1990

Abnormal neuroendocrine responsivity to acute i.v. clomipramine challenge in depressed patients.

The neuroendocrine responsivity to an acute serotonergic challenge with low-dose i.v. clomipramine was studied in seven drug-free depressed patients and seven age-matched healthy control subjects. The depressed patients had higher baseline prolactin concentrations than the healthy subjects, and their prolactin response to clomipramine, assessed as either the percent of baseline or the log-transformed concentration, was significantly different (delayed and blunted peak response) compared to healthy controls. The growth hormone response was exaggerated in the depressed patients, and there were also trends toward blunting in their cortisol and adrenocorticotropic hormone responses. These results are consistent with previous findings of altered neuroendocrine responses to a variety of putative serotonin agonists in depressed patients.

Adrenocorticotropic Hormone↗
PubMed1990

Stimulant drug treatment of hyperactivity: biochemical correlates.

To compare the effects of the stimulant drugs dextroamphetamine and methylphenidate on urinary and plasma monoamines and metabolites within the same clinical sample, thirty-one children with attention-deficit disorder with hyperactivity were treated with dextroamphetamine (up to 1.5 mg/kg/day), methylphenidate (up to 3.0 mg/kg/day), and placebo in an 11-week double-blind crossover trial. As expected, both drugs showed striking clinical efficacy, and within a subsample of the group, earlier findings were confirmed, that dextroamphetamine but not methylphenidate lowered urinary and plasma 3-methoxy-4-hydroxyphenylglycol and whole body norepinephrine turnover, and that urinary and plasma concentration of homovanillic acid was unaltered by either drug. Methylphenidate but not dextroamphetamine increased plasma norepinephrine. Urinary epinephrine and metanephrine were increased with both drugs, but this increase did not correlate significantly with clinical improvement.

3,4-Dihydroxyphenylacetic Acid↗