Platelet adenylate cyclase and phospholipase C activity in posttraumatic stress disorder

Adenylate cyclase and phospholipase C activity were examined in platelet membranes obtained from 19 male subjects with combat-related posttraumatic stress disorder (PTSD) and 35 age- and gender-matched healthy controls. Basal and forskolin-stimulated adenylate cyclase activity were significantly lower in the PTSD group whereas aluminum chloride plus sodium fluoride (AlCl3/NaF)- and prostaglandin E1 (PGE1)-stimulated responses were normal. There was no difference in phospholipase C activity between the two groups. The lower basal and forskolin-stimulated adenylate cyclase responses replicate a previous report and suggest that PTSD may be associated with an abnormality of the catalytic subunit of the receptor-adenylate cyclase complex.     

The cyclic AMP second messenger system in man: the effects of heredity, hormones, drugs, aluminum, age and disease on signal amplification

The intracellular effects of a number of hormonal signals are mediated by the cyclic AMP second messenger system in man and the ubiquitous distribution of hormone-stimulated adenylate cyclase suggests the importance of this enzyme complex in normal aging and pathophysiological states. Various vectors including heredity, endogenous catecholamines, steroid hormones, and drugs affect the activity of hormone-stimulated adenylate cyclase in man. The effect of heredity was studied using lymphocytes obtained from monozygotic twin pairs and age and sex-matched sib pairs. Only for forskolin-stimulated activity is a significant proportion of individual variance attributable to heredity, suggesting the relative stability of the catalytic subunit. Beta-adrenergic and prostaglandin E-1 activity are "state" characteristics and their activities are controlled by environmental parameters. A significant reduction in isoproterenol-stimulated cyclic AMP accumulation between the menses and luteal phase of the menstrual cycle is observed in lymphocytes obtained from 11 female subjects. The lowest level of beta-adrenergic receptor activity is associated with the highest levels of progesterone and estradiol hormone levels in blood. Lithium at therapeutic concentrations markedly inhibits adenylate cyclase activity in platelet membranes. Moreover, marked individual differences are observed in sensitivity to lithium as determined by Dixon plot derived Ki values for 9 normal, healthy subjects. Human adenylate cyclase obtained from platelets and lymphocytes is activated by micromolar amounts of aluminum in the presence of NaF. Irreversible activation of adenylate cyclase by aluminum is suggested as a possible mechanism of this metal's neurotoxicity. The biochemical basis for the age-associated decline in beta-adrenergic responsiveness in man is discussed. Several investigations suggest a deficit at two levels in the adenylate cyclase complex: an impaired coupling of the receptor/N protein subunits and an additional lesion distal to the receptor at the level of N/C coupling. Perfusion studies with salbutamol suggest that the decline in beta-adrenergic sensitivity is general and not restricted to lymphocytes. Possible abnormalities in cyclic AMP signal amplification and recognition in various disease states is discussed. Increased prostaglandin E-1-stimulated cyclic AMP accumulation is observed in lymphocytes obtained from patients with Alzheimer's disease compared to age-matched controls and correlated with severity of the disease state.(ABSTRACT TRUNCATED AT 400 WORDS)     

Cyclic AMP signal transduction in posttraumatic stress disorder

Cyclic adenosine 3',5'-monophosphate (cAMP) signal transduction was examined in lymphocytes and platelets obtained from patients with posttraumatic stress disorder. Intact lymphocytes from the posttraumatic patients (N = 10) showed significantly lower basal, isoproterenol-, and forskolin-stimulated cAMP levels than those from 10 healthy control subjects. In platelet membrane preparations, basal, forskolin-, aluminum chloride plus sodium fluoride-, and prostaglandin E1-stimulated adenylate cyclase activity levels were all significantly lower in the posttraumatic group than in the control group. The authors discuss the potential role of their findings as a biological marker for posttraumatic stress disorder.     

alpha-Adrenergic receptor function in schizophrenia. Receptor number, cyclic adenosine monophosphate production, adenylate cyclase activity, and effect of drugs

alpha-Adrenergic receptor function was assessed in platelets from drug-free schizophrenic patients and control subjects. The number of alpha-receptors was similar in platelet membranes from schizophrenic patients and control subjects. In intact platelets from schizophrenic male, but not female, patients, prostaglandin E1 (PGE1)-stimulated cyclic adenosine monophosphate (cAMP) level was less than in control subjects. This defect may be due, at least in part, to decreased adenylate cyclase activity. In platelet lysates from schizophrenic patients, but not from normal control subjects, adenylate cyclase activity was diminished and PGE1-stimulated adenylate cyclase activity could be restored partially by the addition of guanosine triphosphate. Treatment with neuroleptic drugs or lithium carbonate did not change alpha-receptor number or cAMP production in platelets from schizophrenic patients, but high doses of propranolol hydrochloride increased cAMP production without affecting the number of alpha-receptors. If the production of cAMP in neurons is similar to that in platelets, diminished cAMP production may be associated with a vulnerability to schizophrenia.     

Mode of action of ticlopidine in inhibition of platelet aggregation in the rat.

Ticlopidine, when orally administered to rats, resulted in activation of basal and prostaglandin E1 (PGE1)-stimulated adenylate cylase activity through increase in affinity of the cyclase in platelet membrane to PGE1, although it failed to affect adenosine- or sodium fluoride-stimulated activity of the enzyme. In washed platelets, Ticlopidine also activated basal and PGE1-stimulated activity of the cyclase and prevented reduction in the cyclase activity caused by low concentrations of PGE2. Furthermore, Ticlopidine inhibited malondialdehyde formation in platelets induced by thrombin but failed to inhibit that caused by exogenous arachidonic acid. Adenosine 3',5'-cyclic monophosphate (c-AMP): phosphodiesterase activity of platelet lysate was not significantly affected by Ticlopidine treatment. These findings indicate that Ticlopidine inhibits platelet aggregation and prostaglandin synthesis from endogenous substrate through activating basal and PGE1-stimulated activity of the cyclase, preventing PGE2-induced depression of the cyclase activity and thus increasing platelet c-AMP level.     

Enhanced signal transduction by adenylate cyclase in platelet membranes of patients showing antidepressant responses to alprazolam: preliminary data

The triazolobenzodiazepine, alprazolam, was administered to 11 depressed patients over a period of six weeks, and six patients showed a favorable antidepressant response. There were no significant differences between responders and nonresponders in age, pretreatment Hamilton Depression Rating Scores, 4 p.m. postdexamethasone plasma cortisol levels, or platelet monoamine oxidase activities. Blood levels of alprazolam were not meaningfully different in responders and nonresponders when measured on treatment day 8. However, on treatment day 8, significantly enhanced prostaglandin D2-stimulated platelet adenylate cyclase activity, greater suppression of prostaglandin D2-stimulated platelet adenylate cyclase activity by epinephrine, and enhanced sodium fluoride-stimulated platelet adenylate cyclase activity were seen in the six patients who went on to respond to alprazolam, but not in the five nonresponders. In contrast, there were no significant changes in prostaglandin D2, (-)-isoproterenol, or fluoride ion-stimulated leukocyte adenylate cyclase activity in responders or nonresponders. No meaningful changes were observed in the mean densities of either the high-affinity platelet alpha 2-adrenergic receptor (for 3H-p-aminoclonidine) or the leukocyte beta-adrenergic receptor (for 3H-dihydroalprenolol) in responders or nonresponders. The present findings, taken in conjunction with findings from other recent studies, suggest that enhanced coupling between certain neurotransmitter or hormone receptors and adenylate cyclase through the guanine nucleotide regulatory proteins may help explain the antidepressant effects of alprazolam and possibly other forms of antidepressant treatment.     

Adenylate cyclase and phosphodiesterase activity in the platelet release abnormality.

11 patients with histories of clinical bleeding were selected as examples of platelet release abnormality. Mean bleeding time was 18 +/- 2.6 min (normal +/- SEM; 6 +/- 0.44); mean platelet adhesiveness was 9.9 +/- 4.3% (normal +/- SEM; 30 +/- 2.2). Clot retraction and platelet factor 3 were normal. Platelet aggregation with adenosine diphosphate (ADP), epinephrine and collagen was decreased, as was 14C-serotonin release. Electron microscopic studies of platelets exposed to epinephrine showed 2 subgroups: one which failed to aggregate or have centralization of organelles and a second which developed pseudopodia and centralization of organelles, but rarely aggregated or degranulated. Measurements of activity of adenylate cyclase and phosphodiesterase under basal conditions were performed on platelets from patients and control subjects. Adenylate cyclase activity was significantly lower and phosphodiesterase activity significantly higher in the patient group. Prostaglandin E1 was a potent stimulator of adenylate cyclase in both groups, as was NaF. It was concluded that the causative defects with "platelt release abnormality" do not reside in either the activity of adenylate cyclase or of phosphodiesterase. Changes in formation and destruction of cyclic adenosinemonophosphate (AMP) may instead be regarded as a compensatory response to a defect in another effector system.     

Relationship between platelet phospholipase activity and plasma in ischemic heart disease

Platelet phospholipase plays an important role in the metabolic responses of platelets to exogenous stimuli. The platelet phospholipase activity (PLA) was therefore studied in 38 patients with ischemic heart disease (IHD) and in 26 age-matched normal subjects who served as controls. The mean platelet PLA in the IHD group was 12.72 +/- 1.03 nmol/mg protein/30 sec which was significantly (p less than 0.005) higher than that of the normal controls (8.72 +/- 0.76). When they were classified into acute stage, such as unstable angina or acute myocardial infarction (AMI), and chronic stage, such as stable angina or old myocardial infarction (OMI), there was no significant difference between them. On the other hand, about two-fold activation of platelet PLA was observed in acute stage IHD, and 20-30% inhibition of it was demonstrated in chronic stage IHD following the addition of autologous plasma to washed platelet suspensions, suggesting that certain plasma factor(s) are responsible for such phenomena. In an attempt to identify these plasma factor(s), various substances such as serum albumin, high density lipoprotein, prostaglandin E1 (PGE1) and E2 (PGE2), and platelet activating factor were assessed by in vitro experiments. Only PGE1 and PGE2 revealed a significant effect on the platelet PLA. The relationship between plasma and platelet activity in terms of platelet PLA deserves attention since it varies according to the type and stage of IHD.     

Rapid antidepressant response to alprazolam in depressed patients with high catecholamine output and heterologous desensitization of platelet adenylate cyclase

The present study examined the relationship between 24-hr urinary catecholamine (norepinephrine and epinephrine) output and measures of platelet adenylate cyclase (AC) activity in depressed patients (n = 17) and control subjects (n = 10). In both groups, significant inverse correlations were observed when 24-hr urinary catecholamine levels were examined in relation to measures of both receptor-mediated (prostaglandin D2 and alpha 2-adrenergic) and postreceptor-mediated (NaF) platelet AC enzyme activities, suggesting that circulating catecholamines may regulate platelet AC by heterologous (agonist-nonspecific) desensitization of the AC enzyme complex. Depressed patients who had favorable antidepressant responses to alprazolam had significantly higher pretreatment urinary catecholamine output and lower receptor-mediated platelet AC enzyme activities than control subjects, whereas the nonresponders did not. After 8 days of treatment with alprazolam, urinary catecholamine levels declined significantly. In responders, receptor-mediated measures of platelet AC activity increased significantly by day 8 to values comparable to those in control subjects; but similar changes were not observed in nonresponders. Prior to treatment, responders showed a strict linear relationship between receptor-mediated (prostaglandin D2) and postreceptor-mediated (NaF) stimulation of platelet AC activity through the stimulatory guanine nucleotide regulatory protein (Ns), whereas nonresponders did not. This suggests the presence of two distinct coupling interactions between platelet prostaglandin D2 receptors and the stimulatory guanine nucleotide regulatory protein in responders and nonresponders to the antidepressant effects of alprazolam prior to treatment. The authors propose that catecholamines, possibly acting through prostaglandins, may regulate platelet AC enzyme activity by heterologous desensitization occurring through postreceptor mechanisms.     

Effect of lithium on the physostigmine-induced behavioral syndrome and plasma cyclic GMP.

Physostigmine has been reported to induce a syndrome of psychomotor retardation and in some cases a depressive syndrome. We attempted to investigate a possible mode of action of lithium's proven prophylactic value in depression by assessing the effect of pre-treatment with lithium on this physostigmine-induced behavioral response.A marked physostigmine response was observed in 5 lithium-treated, euthymic manic-depressive subjects as well as in 5 lithium-free, normal controls, with no diminution in the lithium-treated subjects. Plasma cyclic GMP, a possible product of cholinergic receptor activity, also showed no differential response in lithium-treated and lithium-free subjects.     

Alpha 2-adrenoceptor-mediated inhibition of platelet adenylate cyclase and induction of aggregation in major depression. Effect of long-term cyclic antidepressant drug treatment

The functional status of platelet alpha 2-adrenoceptors in patients with major depression has been assessed by simultaneously measuring both a biochemical mechanism of transduction of receptor activation (inhibition of adenylate cyclase activity) and a physiologic response of the receptor (induction of aggregation). The inhibitory effects induced by epinephrine and UK 14304 on adenylate cyclase activity were unchanged, while the aggregation responses induced by the same alpha 2-adrenoceptor agonists were potentiated, which indicated receptor supersensitivity. In depressed (n = 30) and euthymic (n = 11) patients as well as in control subjects (n = 66), there was a clear dissociation between inhibition of adenylate cyclase activity and induction of aggregation, indicating that the two responses represent different phenomena of alpha 2-adrenoceptor activation. alpha 2-Adrenoceptor-mediated platelet aggregation could represent a better marker than inhibition of adenylate cyclase to assess functional changes of the receptor in depression. Both of these functional responses are desensitized after long-term antidepressant treatment.     

Dysbalance of neuronal second messenger function in the aetiology of affective disorders: A pathophysiological concept hypothesising defects beyond first messenger receptors

Summary It is suggested that affective disorders arise from the dysbalance of the two major intraneuronal signal amplification systems, the adenylate cyclase and the phospholipase C system, with depression resulting from underfunction of cyclic adenosine 3,5-monophosphate-mediated effector cell responses associated with an absolute or relative dominance of the inositoltriphosphate/ diacylglycerol-mediated responses and mania resulting from the converse. The usefulness of this hypothesis is discussed with respect to (a) the mechanism of action of current therapeutic agents and (b) the development of novel therapeutic approaches.     

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.     

The role of adenylate cyclase in relaxation of brain arteries: studies with forskolin

The natural product, forskolin, which stimulates adenylate cyclase by a direct, non-receptor-mediated mechanism, was studied for its effect on the tension of isolated brain arteries and adenylate cyclase activity of cerebral arteries. Helical strips of bovine and porcine basilar arteries and bovine middle cerebral arteries, which had been precontracted with prostaglandin F2 alpha (PGF2 alpha) or KCl, relaxed potently to administration of forskolin with ED50 values, ranging from 22 to 69 nM. Incubation of forskolin with a broken cell preparation of bovine cerebral arteries resulted in an efficacious stimulation of adenylate cyclase, approximating 5 times basal activity at a forskolin concentration of 1 microM. The metal salts nickel chloride and manganese chloride decreased the potency of vasorelaxation by vasoactive intestinal peptide (VIP), which stimulates adenylate cyclase via the VIP receptor. In contrast, nickel chloride had little effect on vasorelaxation by forskolin. The endogenous nucleoside, adenosine, which acts via the adenosine receptor and adenylate cyclase, relaxed bovine basilar and middle cerebral arteries with ED50 values ranging from 0.26 to 0.94 microM. The data presented support a role for adenylate cyclase in mediating vasodilation of brain blood vessels.     

Decrease in epinephrine-induced attenuation of platelet adenylate cyclase activity in depressed patients: relation with plasma electrolytes.

We have measured the alpha 2-adrenoceptor-mediated inhibition of platelet membrane adenylate cyclase in depressed patients and control subjects. The results showed a decrease in the forskolin-stimulated adenylate cyclase inhibition of depressed patients compared to the healthy subjects. This suggests a subsensitivity of alpha 2-adrenoceptor in depression. However, this subsensitivity was not correlated to the severity of depression as both severely and moderately depressed patients exhibited the same percent of adenylate cyclase inhibition. The antidepressant drugs treatment induced an increase in the percent of adenylate cyclase inhibition with a trend towards the control values. However, this increase did not equal control value, and moreover both remitted and unremitted patients presented a similar change in their alpha 2-adrenoceptor-mediated adenylate cyclase inhibition. This result raises the question about a simple and direct relation between the clinical status of depression and the power of alpha 2-adrenoceptor-mediated adenylate cyclase inhibition. Plasma magnesium and sodium yielded correlations to this alpha 2-adrenoceptor-mediated adenylate cyclase inhibition suggesting a relation between the platelet adrenergic function and plasma electrolytes.     

Elevated thyrotropin in bipolar youths prescribed both lithium and divalproex sodium

OBJECTIVE: To examine the effect of combined lithium and divalproex sodium on thyroid-stimulating hormone (TSH) levels in children and adolescents with bipolar disorders and to identify risk factors for lithium-induced hypothyroidism. METHOD: Bipolar youths aged 5 to 17 years participating in an open-label clinical trial received treatment with lithium and divalproex sodium for up to 20 weeks. TSH levels were measured at baseline and at the end of the study. Subjects were divided into two groups for analysis: group 1 had TSH levels of less than 10.0 mU/L at the end of the study and group 2 had TSH levels of 10.0 mU/L or more at end of the study. RESULTS: Twenty of the 82 subjects (24.4%) showed TSH elevations of at least 10 mU/L within an average exposure of less than 3 months. The mean baseline TSH level for group 2 was significantly higher than for group 1 (2.97 [SD = 1.48] versus 2.05 [SD = 0.89], p <.05). Mean lithium levels at the end of the study were 1.00 mEq/L for group 2 compared to 0.76 mEq/L for group 1 (t = -2.41, p =.019). CONCLUSIONS: Lithium is associated with significant rates of thyrotropin elevation in bipolar youths. Factors associated with elevation in TSH in lithium-treated subjects include a higher baseline TSH level and a higher lithium level. Close monitoring of thyroid function in children and adolescents taking lithium is recommended.     

The effect of cholera toxin on choroid plexus carbonic anhydrase activity in vitro

The effects of the adenylate cyclase agonists cholera toxin and prostaglandin E2 on carbonic anhydrase activity in vitro was measured in choroid plexuses isolated from Sprague-Dawley rats. Choroid plexuses were incubated in buffer at 38 degrees C (pH 7.4) with either cholera toxin or prostaglandin E2 (PGE2) at a concentration and for a time period that had been shown in earlier studies to result in maximal stimulation of cyclic AMP production. Cholera toxin (10 micrograms/ml) caused a twofold increase (p < .001) in choroid plexus carbonic anhydrase activity when cholera toxin treated plexuses [20.92 +/- .46 mol CO2/(min)(mg protein X 10(-8)] were compared with plexuses exposed to heat inactivated cholera toxin (10.92 +/- .43). When choroid plexuses were homogenized and separated into a 10,000 g pellet and a supernatant fraction, the supernatant carbonic anhydrase was unresponsive to cholera toxin stimulation. In the pellet fraction, which contained all the cellular adenylate cyclase, challenge with cholera toxin produced a significant increase in carbonic anhydrase activity (p < .01). Control activity was 10.9 +/- 1.2 mol CO2/(min)(mg protein X 10(-8), while carbonic anhydrase activity in fractions exposed to cholera toxin was 28.4 +/- 0.8. PGE2 had no effect, however, upon choroid plexus carbonic anhydrase activity. Since both PGE2 and cholera toxin stimulate cyclic AMP production in vitro, a compartmental model of secretory control is proposed.     

Comparative study of antiplatelet drugs in vitro: distinct effects of cAMP-elevating drugs and GPIIb/IIIa antagonists on thrombin-induced platelet responses.

Among various categories of antiplatelet drugs, cAMP-elevating agents and GP IIb/IIIa antagonists have been reported to inhibit platelet aggregation stimulated by a wide variety of platelet agonists. To clarify the qualitative difference between these two agents, their effects on various platelet responses in washed platelets evoked by thrombin (0.05 U/mL) were compared in vitro. Two types of cAMP-elevating drugs, cilostazol (a phosphodiesterase III inhibitor) and prostaglandin E1 (an adenylate cyclase activator), both inhibited platelet aggregation, thromboxane A2 formation, and platelet factor 4 release in a concentration-dependent manner. In addition, both agents suppressed intracellular Ca++ elevation induced by thrombin. However, two classes of GP IIb/IIIa antagonists, abciximab (Fab fragment of antibody) and tirofiban (a synthetic compound), showed no inhibitory effects against thromboxane A2 formation and platelet factor 4 release, although these drugs inhibited platelet aggregation. Essentially the same results were obtained in platelet-rich plasma stimulated with high concentration (100 microM) of thrombin receptor activating peptide. In contrast to these different profiles on thromboxane A2 formation and release reaction, both cAMP-elevating agents and GP IIb/IIIa antagonists potently suppressed procoagulant activity in thrombin-stimulated platelets. These results suggest that the development of platelet procoagulant activity induced by thrombin is exclusively dependent on platelet aggregation or aggregation-dependent processes. These observations also indicate that cAMP-elevating agents possess wider inhibitory effects on platelet responses evoked by strong agonists than GP IIb/IIIa antagonists.     

Effect of platelet activity of inhibition of adenylate cyclase

SQ22536 (9-[tetrahydro-2-furyl]-adenine), an inhibitor of adenylate cyclase, blocks the inhibition of platelet function by substances that stimulate this enzyme, including PGE₁, PGI₂, PGD₂, and adenosine. SQ22536 enhances platelet aggregation and serotonin release induced by prostaglandin endoperoxides and their analogs but does not consistently affect the platelet response to ADP or other agonists. SQ22536 reduced platelet cyclic AMP and inhibits the effect on this nucleotide of PGE₁ and adenosine. The elevation of cyclic GMP induced by ADP is prevented by SQ22536.     

Kinematics of fast wrist movements in manic-depressive illness chronically treated with lithium carbonate

Abstract

Lithium salts have been shown to impair kinematics of fast voluntary movements during acute intoxication. The aim of the present study was to determine whether lithium carbonate affected the kinematics of fast movements in patients chronically treated and who did not exhibit signs of neurotoxicity. We analysed fast wrist flexion movements in 6 healthy subjects, in 5 patients presenting a manic-depressive illness without treatment, and in 8 patients receiving lithium carbonate for a manic-depressive disease. The mean duration of treatment was 3.9±4.1 years, the mean daily dose 837±341 mg and the mean serum level 0.95±0. 15 mEq/l. Although mean movement amplitudes were similar in the 3 groups, the variability of fast movements was increased in patients receiving lithium salts. The ratio of maximum to average velocities (VmNaveJ was significantly higher in patients treated, and their movements were temporally asymmetrical, with a ratio ofacceleration duration divided by deceleration duration being lower than in the 2 other groups. These kinematic abnormalities show that a chronic treatment with lithium salts is associated with an impairment of the cerebellar control of fast single-joint movements. [Neural Res 1998; 20: 320-326]