A risk model for thrombocytopenia requiring platelet transfusion after cytotoxic chemotherapy.

Severe thrombocytopenia is a rare but life-threatening side effect of cytotoxic chemotherapy for which risk factors are not well known. Our objective was to delineate a risk model for chemotherapy-induced thrombocytopenia requiring platelet transfusions in cancer patients. Univariate and multivariate analysis of risk factors for chemotherapy-induced thrombocytopenia requiring platelet transfusions were performed on the cohort of the 1,051 patients (CLB 1996) treated with chemotherapy in the Department of Medicine of the Centre Léon Bérard (CLB) in 1996. In univariate analysis, performance status (PS) greater than 1, platelet count less than 150, 000/microL at day 1 (d1) before the initiation of chemotherapy, d1 lymphocyte count < or = 700/microL, d1 polymorphonuclear leukocyte count less than 1,500/microL, and the type of chemotherapy (high risk v others) were significantly associated (P < .01) with an increased risk of severe thrombocytopenia requiring platelet transfusions. Using logistic regression, d1 platelet count less than 150,000/microL (odds ratio [OR], 4.3; 95% confidence interval [CI], 1.9 to 9.6), d1 lymphocyte counts < or = 700/microL (OR, 3.37; 95% CI, 1.77 to 6.4), the type of chemotherapy (OR, 3.38; 95% CI, 1.77 to 6.4), and PS greater than 1 (OR, 2.23; 95% CI, 1.22 to 4.1) were identified as independent risk factors for platelet transfusions. The observed incidences of platelet transfusions were 45%, 13%, 7%, and 1.5% for patients with > or = 3, 2, 1, or 0 risk factors, respectively. This model was then tested in 3 groups of patients treated with chemotherapy used as validation samples: (1) the series of 340 patients treated in the CLB in the first 6 months of 1997, (2) the prospective multicentric cohort of 321 patients of the ELYPSE 1 study, and (3) the series of 149 patients with non-Hodgkin's lymphoma treated in the CLB within prospective phase III trials (1987 to 1995). In these 3 groups, the observed incidences of platelet transfusions in the above-defined risk groups did not differ significantly (P > .1) from those calculated in the model. This risk index could be useful to identify patients at high risk for chemotherapy-induced thrombocytopenia requiring platelet transfusions.

Electrophysiological and electrochemical analysis of the secretion of ATP and noradrenaline from the sympathetic nerves in rat tail artery: effects of alpha 2-adrenoceptor agonists and antagonists and noradrenaline reuptake blockers.

The aim of this study was to investigate whether or not nerve impulses release ATP and noradrenaline in parallel from the sympathetic nerve terminals of the rat tail artery. The extracellularly recorded excitatory junction current (EJC) was used to study, pulse by pulse, the release of ATP. An electrochemical method was used to study online the nerve stimulation-induced rise in the extracellular concentration of endogenous noradrenaline at the probe, a carbon fibre electrode (CF). This parameter, which does not directly represent noradrenaline release, but reflects release minus clearance, has been termed delta[NA]CF. The effects of a number of pharmacological agents on the EJCs were examined both at 0.1 and 2 Hz, and the effects on the EJC response to 100 pulses at 2 Hz compared with that on the delta[NA]CF response. Clonidine and xylazine were used as alpha 2-agonists, yohimbine and idazoxan as alpha 2-antagonists and desipramine and cocaine as blockers of noradrenaline reuptake. Most of these agents had unwanted side effects, especially at higher concentrations. However, clonidine and xylazine depressed at lower concentrations the EJC and delta[NA]CF responses to about the same extent; these effects were partially or completely reversed by yohimbine. Yohimbine or idazoxan did not affect the EJCs at 0.1 Hz but enhanced the EJC and delta[NA]CF responses to 100 pulses at 2 Hz to the same extent. All effects of desipramine (1 microM) seemed explainable as a result of block of noradrenaline reuptake, while cocaine (10 microM) in addition exerted an 'unspecific' depressant (probably local anesthetic) effect. Under control conditions, both agents depressed the EJC but dramatically enhanced the delta[NA]CF response to 100 pulses at 2 Hz. Addition of yohimbine prevented the depressant effect of desipramine on the EJCs completely and reduced that of cocaine, but increased their effects on the delta[NA]CF response. These results are compatible with the view that ATP and noradrenaline are released in parallel from the sympathetic nerve terminals of this tissue. The different, and under some conditions even opposite, effects of desipramine or cocaine on the EJC and delta[NA]CF responses are explainable in terms of the known post-secretory effects of these agents.

Does rilmenidine act in vivo on central alpha 2-adrenoceptors modulating noradrenaline release?

Noradrenaline release evoked by electrical stimulation was recorded in the rat hypothalamus by in vivo electrochemistry. Rilmenidine (0.3-10 mg kg-1 i.v.) did not diminish this evoked release while clonidine induced a dose-dependent decrease. These results further suggest that the antihypertensive action of rilmenidine is not mediated by central alpha 2-adrenoceptors and might explain why, unlike clonidine, rilmenidine does not have sedative effects.

Selectivity of rilmenidine for the nucleus reticularis lateralis, a ventrolateral medullary structure containing imidazoline-preferring receptors.

Neuronal metabolic activity was studied by in vivo electrochemistry in two brain areas of the anesthetized rat: the nucleus reticularis lateralis (NRL) region of the ventrolateral medulla oblongata - site of the hypotensive action of clonidine-like imidazolines - and the locus coeruleus (LC), which is involved in the sedative effect of these drugs. Hypotensive doses of i.v. rilmenidine (0.3 and 1.5 mg/kg), which is structurally related to clonidine, induced a dose-related inhibition of the metabolic activity of catecholaminergic neurons in the NRL region whereas higher doses (50-fold) were required to inhibit the activity of the catecholaminergic neurons in the locus coeruleus. On the other hand azepexole, another centrally acting antihypertensive drug that is not structurally related to the imidazolines failed to inhibit the neuronal metabolic activity of the NRL region when administered i.v. in hypotensive doses (1 mg/kg). Taken together, these findings suggest that the central hypotensive action of clonidine-like drugs requires the imidazoline structure or pharmacologically compatible compounds like rilmenidine. Our results also show that rilmenidine is twice as selective as clonidine for the NRL region, which contains imidazoline-preferring receptors, compared with the LC, which contains mainly alpha 2-adrenoceptors. In conclusion, this study provides a functional confirmation of the dissociation between the therapeutic (hypotensive) and untoward (sedative) effects of rilmenidine.

Effect of clonidine on catechol metabolism in the rostral ventrolateral medulla: an in vivo electrochemical study.

The dose-dependent reduction in catechol metabolism induced by an imidazoline with alpha 2-adrenoceptor agonist specificity, clonidine, was assessed (ED50 = 7 micrograms.kg-1 i.v.) with in vivo voltammetry in the rostral ventrolateral medulla of rats kept under halothane anesthesia and strictly controlled circulatory and ventilatory conditions. This reduction in catechol metabolism was observed in intact as well as in barodeafferented rats.

A new predictive equation for the solubility of drugs based on the thermodynamics of mobile disorder.

The thermodynamics of mobile disorder rejects the static model of the quasi-lattice for liquids. Because cause of the perpetual change of neighbors, during the observation time of thermodynamics of the order of seconds, each molecule of a given kind in a solution has experienced the same environment and had at its disposal the same mobile volume. This domain is not localizable and not orientable. Each molecular group perpetually "visits" successively all parts of this domain. The highest entropy is obtained when the groups visit all the parts of the domain without preference. H-bonds are preferential contacts with given sites of the neighbors that cause deviations with respect to such "random" visiting, thereby decreasing the entropy. The quantitative development of these ideas leads to equations describing the effect of solvent-solvent, solute-solvent, and solute-solute hydrogen bonds on the chemical potential of the solute. A universal equation predicting the solubility of drugs in a given solvent is derived. The effect of H-bonds is governed not by "solubility parameters" but by stability constants from which the order of magnitude can be estimated. From the sole knowledge of the solubility of methylparaben in pentane, the method predicts correctly the order of magnitude of its solubility in 26 other solvents, including alcohols and water.

Significance of partial and total cohesion parameters of pharmaceutical solids determined from dissolution calorimetric measurements.

The total and partial adhesion-derived cohesion parameters of three solid pharmaceutical substances (caffeine, theophylline, and phenylbutazone) were determined from dissolution calorimetric measurements, a new technique devised for this purpose. Calorimetry has the advantage of leading directly to enthalpies, from which the solute cohesion parameter(s) is(are) deduced. An equation was developed that relates partial molar enthalpies of mixing (obtained by subtracting enthalpies of fusion from enthalpies of dissolution) to the cohesion parameters of the solute and of the solvents. Solvents were selected on the basis of their known cohesion parameters by applying the experimental research methodology.

An imidazoline-specific mechanism for the hypotensive effect of clonidine: a study with yohimbine and idazoxan.

Our previous in vivo electrochemical studies in the normotensive rat have shown that there was a positive correlation between the hypotensive effect of low doses of clonidine (8-40 nmol/kg i.v.) and the inhibition of the metabolic activity of catecholaminergic neurons within the nucleus reticularis region in the brain stem. Higher doses of the drug (200 nmol/kg i.v.) were required to decrease the metabolic activity in the locus ceruleus, which is involved in the sedative effect of clonidine. To investigate further the pharmacological mechanism involved in the hypotensive effect of imidazolines, low doses of antagonists were injected centrally in the cisterna magna (5 nmol/kg intracisternal): idazoxan, an imidazoline that labels nonadrenergic imidazoline-preferring sites and yohimbine, which is a classical alpha-2 adrenergic antagonist. Our results show that idazoxan very potently antagonizes both the hypotensive effect of clonidine and neuronal inhibition on the nucleus reticularis lateralis region but not in the locus ceruleus. The opposite effect is observed with yohimbine, i.e., neither the hypotensive effect nor the neuronal inhibition produced by clonidine on the nucleus reticularis lateralis region were affected but it prevented the inhibitory effect of clonidine on locus ceruleus neuronal metabolic activity. In conclusion, we confirm the hypothesis that the hypotensive action of imidazoline is due to an interaction of these substances with imidazoline-preferring receptors in the ventrolateral medulla oblongata whereas its sedative effect is related to an action on alpha-2 adrenoceptors.

On-line electrochemical monitoring of the local noradrenaline release evoked by electrical stimulation of the sympathetic nerves in isolated rat tail artery.

A treated carbon fibre electrode was used to measure by differential normal pulse voltammetry or differential pulse amperometry the release of noradrenaline from the sympathetic nerve terminals innervating the smooth muscle in rat tail artery. On calibration in vitro with exogenous noradrenaline in phosphate-buffered saline solution the electrode recorded an oxidation current at +0.1 V, the oxidation potential of noradrenaline. This signal was proportional to the noradrenaline concentration in the solution. When the electrode was apposed to the wall of the artery there was no oxidation current at +0.1 V under resting conditions, but electrical nerve stimulation for 1-100 s at 1-10 Hz induced a current with a peak at this potential. This signal was suppressed by tetrodotoxin, guanethidine or cadmium, or by omission of calcium; it was strongly enhanced by tetraethylammonium and potentiated by the noradrenaline uptake blockers desipramine or cocaine. The results indicate that the carbon fibre electrode method described here may be used to monitor on-line the nerve stimulation-induced increase in the local noradrenaline concentration at the surface of the muscle layer in a blood vessel such as the rat tail artery.

Electrically evoked noradrenaline release in the rat hypothalamic paraventricular nucleus studied by in vivo electrochemistry: characterization and facilitation by increasing the stimulation frequency.

The hypothalamic paraventricular nucleus is densely innervated by noradrenergic terminals mainly originating in the A1 group within the ventrolateral medulla. An oxidation signal corresponding to extracellular catechols was recorded from the paraventricular nucleus of urethane anaesthetized rats every 1 s by differential pulse amperometry at + 105 mV combined with carbon fiber electrodes. In basal conditions, both extracellular noradrenaline and DOPAC, which are synthesized by noradrenergic terminals, contributed to this oxidation signal. Electrical stimulations of the rostral part of the A1 group were applied for 10 or 20 s every 10 min at physiological frequency (3-20 Hz). They induced an immediate increase in the oxidation signal which lasted as long as the stimulation. This increase was due to the evoked noradrenaline release since it was enhanced by pargyline, desipramine and amphetamine and it was attenuated by alpha-methyl-p-tyrosine and reserpine. The amplitude of the evoked noradrenaline release depended non-linearly on the frequency of the stimulation (from 3 to 20 Hz). When expressed per pulse, noradrenaline release was facilitated four-fold as the frequency increased from 3 to 20 Hz. Central noradrenergic neurons exhibit a tonic activity in a single spike discharge pattern with a mean frequency below 5 Hz but they respond to physiological stimuli by short bursts of action potentials at 20 Hz. Therefore, the present data show that noradrenergic terminals convert physiological impulse flow into noradrenaline release as a high pass filter which enhances the signal-to-noise ratio in response to phasic stimuli.

Presynaptic receptors and modulation of noradrenaline and ATP secretion from sympathetic nerve varicosities.

Our results in the model tissues examined show (1) that alpha 2 agonist(s) depressed the secretion of NA and ATP caused by nerve stimulation at low frequency, (2) that the secretion of both NA and ATP was moderately autoinhibited, under conditions when endogenous NA was shown to accumulate extracellularly, (3) that a K+ channel blocking agent increased much more strongly than alpha 2-adrenoceptors block the secretion of both NA and ATP, and also amplified enormously the NA-mediated neurogenic contraction, (4) that, therefore, a high K+ efflux is likely to be much more important than alpha 2-adrenoceptor-mediated autoinhibition for maintaining a low release probability in sympathetic nerve varicosities, and (5) that the alpha 2-adrenoceptor agonist, clonidine, or the Ca2+ channel blocking agent, Cd2+, inhibited transmitter secretion, at least in part, via targets "upstream" of the varicosity.

Electrically evoked noradrenaline release in the rat hypothalamic paraventricular nucleus studied by in vivo electrochemistry: autoregulation by alpha-2 receptors.

Evoked noradrenaline release was monitored every 1 s in vivo from the hypothalamic paraventricular nucleus by differential pulse amperometry at +105 mV combined with carbon fiber electrodes. Noradrenaline release was evoked by electrical stimulations of the ventrolateral medulla for 20s every 10 min at a physiological frequency (3-20 Hz) (see accompanying paper). The evoked noradrenaline release was dose-dependently attenuated by clonidine (10-100 micrograms/kg, i.v.) and strongly enhanced by alpha-2 antagonists: yohimbine (2 mg/kg), piperoxane (2 mg/kg) and idazoxan (0.05-1 mg/kg). Moreover, the effect of clonidine (50 micrograms/kg) was prevented by yohimbine (5 mg/kg) or idazoxan (1 mg/kg). Haloperidol (50 micrograms/kg) or propranolol (10 mg/kg) did not affect evoked noradrenaline release while prazosin (0.05-1 mg/kg) induced a moderate increase. However, prazosin did not prevent the effect of clonidine (50 micrograms/kg). Reserpine (5 mg/kg) pretreatment for 1 h induced a pronounced decrease in the evoked noradrenaline release and abolished the effect of yohimbine (2 mg/kg). Pretreatment by desipramine 30 min before injection abolished the effect of clonidine (50 micrograms/kg) but not of yohimbine (2 mg/kg). The amplitude of the yohimbine (2 mg/kg) effect depended on the frequency of the stimulation: it was maximal between 3 and 7 Hz and gradually declined from 10 to 20 Hz. These results show that noradrenaline release is presynaptically controlled by an alpha-2 adrenoreceptor and suggest that, in physiological conditions, endogenous extracellular noradrenaline inhibits its own phasic release. In conclusion, noradrenergic terminals act as a high pass filter which converts impulse flow into noradrenaline release and the features of this filter are modulated by extracellular noradrenaline via an alpha-2 adrenoreceptor.

Correlation between the inhibitory effect on catecholaminergic ventrolateral medullary neurons and the hypotension evoked by clonidine: a voltammetric approach.

Neuronal activity was monitored in vivo by differential voltammetry, an electrochemical technique measuring the metabolism of catecholamines. This technique was used to determine the influence of low doses of clonidine (starting from 2 micrograms/kg i.v.) on the activity of the catecholaminergic neurons of the nucleus reticularis lateralis region, site of its hypotensive action, and of the locus ceruleus, which is involved in its sedative effect. There was a correlation between the hypotensive effect of low doses of clonidine (2, 5 and 10 micrograms/kg i.v.) and the decrease of the neuronal metabolic activity within the ventrolateral medulla, whereas only higher doses of clonidine (50 micrograms/kg i.v.) decreased the metabolic activity in the locus ceruleus. Thus, we demonstrate in vivo differences in sensitivity toward the same drug of two different neuronal structures that are involved in the regulation of the cardiovascular and wakefulness functions, respectively. The present study also shows that clonidine has a preferential action on a medulla oblongata region that contains imidazoline-preferring receptors, namely the nucleus reticularis lateralis region, rather than on the locus ceruleus region, that contains mainly alpha-2 adrenoceptors.

Ether stress stimulates noradrenaline release in the hypothalamic paraventricular nucleus.

Differential normal-pulse voltammetry was combined with treated carbon fibre electrodes for monitoring in vivo extracellular catechols synthesized by noradrenergic terminals innervating the paraventricular hypothalamic nucleus. From urethane-anaesthetized rats, pretreated with a monoamine oxidase inhibitor, pargyline, we were able to monitor a catechol signal which unequivocally corresponded to extracellular noradrenaline, and we observed that ether inhalation for 2 min induced an immediate increase in this signal. Electrical stimulation of the ventral noradrenergic pathway (10 Hz for 40 s) induced a similar effect. On the other hand, from freely moving rats which were not treated with pargyline, we recorded a catechol peak which mainly corresponded to 3,4-dihydroxyphenylacetic acid which was synthesized by noradrenergic terminals. However, electrochemical and biochemical evidence strongly suggested that the increase in this signal induced by a 2-min ether stress does not correspond to 3,4-dihydroxyphenylacetic acid, but to an increase in the extracellular noradrenaline concentration. In both experimental situations the time course of the effects was identical: ether stress induced an immediate and pronounced increase in norepinephrine release, and this effect lasted as long as the stimulus duration. This effect appeared specific for noradrenergic terminals, since no effect on dopamine release was observed when recorded from the striatum or behind the paraventricular hypothalamic nucleus from the A13 dopaminergic group. In conclusion, our data are consistent with those which suggest a facilitatory action of norepinephrine on neurosecretory neurons whose cell bodies are located in the paraventricular hypothalamic nucleus and which play a major role in the hormonal response to stress.

In vivo voltammetric monitoring of noradrenaline release and catecholamine metabolism in the hypothalamic paraventricular nucleus.

The paraventricular hypothalamic nucleus receives a dense noradrenergic innervation. Electrochemically treated carbon fibre electrodes were implanted in the paraventricular nucleus of anaesthetized rats and their locations were histologically controlled after each experiment. Differential normal pulse voltammograms showed an oxidation peak at +50 mV. This peak was mainly due to 3,4-dihydroxyphenylacetic acid synthesized by noradrenergic terminals since: it appeared at the same oxidation potential as 3,4-dihydroxyphenylacetic acid in vitro; it was rapidly suppressed after inhibition of tyrosine hydroxylase by alpha-methyl-p-tyrosine or monoamine oxidase by pargyline; blockade of dopamine-beta-hydroxylase by FLA 63 induced a marked increase in this signal, whereas this drug was without effect in dopaminergic terminals fields (striatum, zona incerta); stimulation of alpha 2 noradrenergic receptors by clonidine (50 micrograms/kg) decreased the peak height and this effect was reversed by piperoxane (30 mg/kg). This oxidation peak corresponded to a 3,4-dihydroxyphenylacetic acid concentration of 2 microM. On the other hand, when recorded from rats which were treated with pargyline 3 h before recording, a small peak appeared at +100 mV. This signal was attributed to the oxidation of extracellular noradrenaline on the basis of the following arguments: it appeared at the same potential as noradrenaline in vitro; desipramine (25 mg/kg) induced a 4-fold increase in this peak height; piperoxan (2 mg/kg) enhanced this signal and reversed the decrease induced by clonidine (50 micrograms/kg); electrical stimulations (bipolar electrode, square pulses, 0.3 ms, 200 microA, 15 Hz for 40 s) in the rostral part of the A1 group were followed by an immediate, short-lasting 4-fold increase in the signal.

In vivo voltammetric monitoring of catecholamine metabolism in the A1 and A2 regions of the rat medulla oblongata.

Catecholaminergic metabolism was estimated in A1 and A2 noradrenergic nuclei of the rat medulla oblongata using differential normal pulse voltammetry combined with electrochemically treated carbon fiber microelectrodes. In both areas an oxidation peak appearing at +50 mV was recorded. Electrochemical data and pharmacological experiments indicated that 3,4-dihydroxyphenylacetic acid (DOPAC) synthesized by noradrenergic neurons was the major contributor to this signal. Indeed, alpha-methyl-p-tyrosine, by inhibiting tyrosine hydroxylase, and pargyline, by inhibiting monoamine oxidase, both totally suppressed the peak appearing at +50 mV in A1 and A2 areas. Conversely, FLA-63, an inhibitor of dopamine-beta-hydroxylase, increased it. Moreover, a local and unilateral injection of catecholaminergic neurotoxin (6-hydroxydopamine) in the vicinity of A1 induced a 60% decrease in the peak height. This effect was prevented by pretreatment with desipramine, an inhibitor of noradrenaline reuptake, which is known to protect noradrenergic neurons against the action of 6-hydroxydopamine. Finally, specific drugs acting on alpha-2-noradrenergic receptors (clonidine and piperoxane) modulated the peak height recorded from both structures. Thus, as previously shown in the locus ceruleus, the variations in the extracellular DOPAC levels reflect the metabolic activity of A1 and A2 noradrenergic neurons.