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Biomedical subjects

A Uzan

Publications and source records attributed to A Uzan.

At least 37 records · Page 2Linked to original sources
PubMed1989

Mechanism of lipolytic action of a new alpha-2 adrenergic antagonist of the piperazinopyrimidine family: RP 55462.

The in vivo lipid mobilizing effect of alpha-2 adrenergic antagonist has been demonstrated previously. This has attracted attention to the putative interest of such compounds in a lipid-mobilizing strategy. RP 55462 [6-chloro-4-(isopropylamino)-5-(methyl)-2 piperazinopyrimidine], a piperazinopyrimidine derivative, has already been shown to exert alpha-2 adrenergic antagonist actions on fat cell function in vitro. Moreover, RP 55462 exhibits a direct in vitro lipolytic action which is independent of its alpha-2-blocking potency. When administered i.v. RP 55462 is also able to induce an increment in plasma nonesterified levels in dogs. The mechanism of action of RP 55462 was studied and the nature of its lipomobilizing effect was explored. RP 55642-dependent lipolysis was not affected by beta adrenergic blockers on rat fat cells and RP 55462 had no direct effect on adenylylcyclase activity on fat cell membranes. Moreover, RP 55462 did not compete with [3H]phenyl isopropyl adenosine binding (A1-adenosine receptor agonist) on fat cell membranes. In fact, RP 55462 inhibited, in a dose-dependent manner, the cyclic AMP (cAMP)-dependent phosphodiesterase (PDE) activity in rat adipose tissue. Several derivatives with the piperazinopyrimidine structure also inhibited cAMP-dependent PDE activity and exerted lipolytic effects. A short structure-activity study was performed with various derivatives. In dogs, by contrast with yohimbine, the in vivo lipid mobilizing effect of RP 55462 was not abolished by pretreatment with propranolol, and lasted longer. It is concluded that the in vivo lipolytic activity of RP 55462 is connected with its ability to inhibit cAMP-dependent PDE activity; a property of several piperazinopyrimidine derivatives. The lipid mobilizing effect induced in vivo by RP 55462 results from a combination of its alpha-2 adrenergic antagonist properties and its direct lipolytic action mediated by cAMP-dependent PDE inhibiting effects.

1-Methyl-3-isobutylxanthine↗
PubMed1989

Lipolytic action of a new alpha-2 adrenergic antagonist of the piperazinopyrimidine family: RP 55462.

Recent investigations have demonstrated the in vitro lipid mobilizing effects induced by alpha-2 adrenergic antagonist administration and have focused attention on the putative therapeutic interest of such compounds in the treatment of obesity as adjuvants in caloric restriction programs. We studied the impact of RP 55462 [6-chloro-4-(isopropylamino)-5-(methyl)-2, piperazinopyrimidine], a new alpha-2 adrenergic antagonist compound of the piperazinopyrimidine family, on fat cell function. The alpha-2-blocking properties of this agent, which had been defined initially on the brain were confirmed on adipocytes. RP 55462 competed with [3H]yohimbine binding sites on human fat cell membranes and inhibited the antilipolytic action of alpha-2-agonist compounds (UK 14304, clonidine and epinephrine) in human and hamster fat cells. It was also noticed that RP 55462 alone was able to activate lipolysis in isolated fat cells from various species (man, rat, hamster and dog). Moreover, the lipolytic response induced by isoproterenol or synacthene was largely amplified in the presence of RP 55462 in rat fat cells which are the least alpha-2 adrenergic responsive tested. RP-55462-dependent stimulation of lipolysis was not affected by the presence of other alpha-2 adrenergic antagonists (idazoxan, yohimbine or phentolamine). Intravenous administration of RP 55462 in alert dogs promoted an increment in plasma nonesterified acid concentrations reflecting its lipid mobilizing action. In summary this study focuses attention on a new alpha-2-antagonist compound which exhibits an in vivo lipid mobilizing action which could be attributable to its alpha-2 adrenergic antagonist properties. Inasmuch as the lipolytic activity of RP 55462, revealed in in vitro studies, seems to be independent from its alpha-2 adrenolytic properties; further studies are required to define the mechanism of such a lipolytic effect as well as its possible involvement in in vivo conditions.

Adenosine Deaminase↗
PubMed1989

Riluzole, a novel antiglutamate, prevents memory loss and hippocampal neuronal damage in ischemic gerbils.

The neuroprotective effects of riluzole, a novel antiglutamate, has been demonstrated in a model of ischemia induced in female Mongolian gerbils by transient bilateral carotid occlusion. Riluzole was administered at a dose of 4 mg/kg, i.p., just before, 4 hr after, and for the 14 d following the transient bilateral carotid occlusion (10 min). The functional sequelae of ischemic damage were assessed using a memory test (passive avoidance) and the extent of neuronal damage by histological examination and quantitative autoradiography of muscarinic cholinergic receptors in the hippocampus. The performance of the ischemic gerbils in the memory test was about half that of control animals. This memory deficit was completely reversed in animals treated with riluzole. This protective effect of riluzole was confirmed by histological and autoradiographic studies. The neuronal degeneration of CA1 pyramidal cells in the hippocampus observed in the ischemic group was not seen in the riluzole-treated animals, which resembled the control group. This neuronal degeneration in the CA1 area was confirmed by a quantitative measurement of muscarinic receptors: The binding was decreased by a third in the lacunosum moleculare, the stratum oriens, and the stratum radiatum. By contrast in riluzole-treated gerbils, this decrease was reversed by 50%. Finally, a clear-cut correlation was found between the deficit in the memory test and the decrease in muscarinic receptor binding in the CA1 fields. These results are compatible with the idea that glutamic acid may be involved in the neuronal degeneration of the hippocampus following ischemia, and could be foreseeable.(ABSTRACT TRUNCATED AT 250 WORDS)

Amnesia↗
PubMed1987

Binding in vitro of pipequaline (45319 RP) onto plasma proteins and blood cells in man.

Serum binding of pipequaline, a new anxiolytic drug, was studied in vitro by equilibrium dialysis. The percent binding in serum is high, 96.3%, and remains constant within the range of therapeutic concentrations. Investigations performed on isolated proteins with a wide range of concentrations showed one site with a high affinity constant (Ka = 450,000 M-1) for alpha 1-acid glycoprotein and two sites with a lower affinity constant (Ka = 58,000 M-1) for human serum albumin. Binding to lipoproteins was saturable, with an affinity constant of 22,000 less than or equal to Ka less than or equal to 35,000 M-1. Over the range of therapeutic concentrations, the ratio of pipequaline concentrations in serum and red blood cells remained constant (14.4%) and was shown to be dependent on the free fraction of pipequaline in serum.

Adult↗
PubMed1987

Binding sites for a peripheral type benzodiazepine antagonist ([3H]PK 11195) in human iris.

Peripheral-type benzodiazepine binding sites have been characterized on sections of 8 normal human iris/ciliary-body preparations. Saturability was determined at 25 degrees C with [3H] PK 11195 (1 nM) a specific ligand of peripheral type sites. The studies revealed a single class of binding sites for PK 11195 with a nanomolar range affinity (KD = 1.45 nM) and a maximal capacity (Bmax) of 35.5 fmol/mg protein. The displacement potency order of the benzodiazepines tested suggest that these sites belong to the peripheral type: PK 11211 (IC50 = 12 nM) greater than Ro 5-4864 (IC50 = 770 nM) greater than clonazepam (IC50 = 20,000 nM). The present data demonstrate that high affinity binding sites for peripheral type benzodiazepines are present in human iris/ciliary-body. This tissue is therefore a suitable tool for evaluation of the putative functional role of these binding sites.

Aged↗
PubMed1987

Labelling of peripheral-type benzodiazepine binding sites in human brain with [3H]PK 11195: anatomical and subcellular distribution.

The peripheral-type benzodiazepine binding site, erstwhile characterized in the rodent and feline brain, has now been characterized in post-mortem human brain using [3H]PK 11195. The kinetics and pharmacological properties of the binding of this ligand are similar to peripheral-type benzodiazepine binding sites elsewhere. The potency of RO5-4864 for this site in human brain is close to that seen in ruminant and carnivore tissues but considerably lower than in rodent tissues. The regional distribution of these binding sites would suggest a neuronal rather than a glial localization. [3H]PK 11195 bound in a similar fashion to slide-mounted sections of human brain, thus allowing quantitative studies of the regional distribution of peripheral-type benzodiazepine binding sites to be made. The binding sites were distributed heterogeneously, but were restricted to the grey matter. Highest densities of binding sites were found in forebrain structures. The localization was not limited to any functional system, nor did it resemble any previously described transmitter system. The similarities between peripheral-type benzodiazepine binding sites in human and in feline brain in terms of their pharmacological characteristics and their regional and subcellular distribution suggest that the cat, rather than the rat, may be the better model for studying a possible role for this site in human cerebral function.

Animals↗
PubMed1987

Quantitative autoradiographic determination of binding sites for a peripheral benzodiazepine ligand ([3H]PK 11195) in human iris.

Specific binding sites of peripheral-type benzodiazepines were investigated in human iris/ciliary body (8 eyes). Examination of color-coded prints and densitometric quantification of autoradiograms were performed on slides (20 micron) labelled with [3H]PK 11195 (1 nM) at 25 degrees C. Nonspecific binding was determined with PK 11211 (5 microM) or Ro 5-4864 (5 microM). Binding sites were present on all the slides, with equivalent density in the 3 regions of the preparation (ciliary body, iris, and pupil margin). The numbers of binding sites in ciliary body, iris, and pupil margin, respectively, were: 42.7 +/- 0.2, 30.1 +/- 0.5, and 37.4 +/- 0.4 femtomol/mg protein. Labelling on the pupil margin seemed to coincide with the iris sphincter muscle. The presence of peripheral benzodiazepine binding sites in iris muscular tissue, and particularly in the pupil margin, suggests that the iris preparation may be a valuable tool to detect putative physiological effects of peripheral benzodiazepines on muscular motility.

Aged↗
PubMed1987

Circadian rhythm in the membrane of circulating human blood cells: microviscosity and number of benzodiazepine binding sites. A search for regulation by plasma ions, nucleosides, proteins or hormones.

Circadian rhythms in both the number of peripheral type binding sites for benzodiazepines in platelet membranes and the microviscosity of the erythrocyte membrane were demonstrated in 7 healthy men. Neither variable appeared to be linked to each other, or regulated by the plasma concentrations of total or free cortisol, testosterone, potassium, magnesium, calcium, cAMP, cGMP or proteins or by the erythrocytic concentration of magnesium or potassium or by the plasma cAMP:cGMP ratio or by the ratio of intra-erythrocyte:plasma concentrations of potassium or magnesium. A highly significant negative correlation was found between the microviscosity of the erythrocyte membrane and the activity of the membrane-bound enzyme, methyltransferase I. Such a correlation was validated both on raw data and on 24 hr-means (r = 0.84; P less than 0.01). A circadian rhythm in the activity of this enzyme was also demonstrated. Moreover, a highly significant correlation was also found between plasma transcortin concentration (TRC) and microviscosity (r = 0.50, P less than 0.01), and between TRC and methyltransferase I activity (r = 0.61, P less than 0.01). Such findings may constitute clues towards the understanding of the regulation of the circadian rhythm in the fluidity of the red blood cell membrane in man and guide future steps with regard to the role of this rhythm upon the availability of drug binding sites at the cell surface.

Adult↗
PubMed1987

Partial purification and pharmacology of peripheral-type benzodiazepine receptors.

This report describes the results obtained with a new photoaffinity ligand for the "peripheral-type" benzodiazepine binding site (PBS), using a digitonin solubilized preparation from rat heart or adrenals. The specific binding activity of the solubilized adrenal preparation is higher than 50 pmol/mg protein, with binding properties and pharmacological specificity identical to the membrane bound PBS. The apparent molecular weight of the solubilized PBS, determined by gel filtration is 215 KDa. The photoaffinity ligand (PK 14105) is a nitrophenyl derivative of PK 11195, which attaches covalently and specifically to all the PBS when cardiac membranes are irradiated with this compound under ultraviolet light. After photolabelling with [3H]PK 14105 and solubilization in SDS of heart or adrenal membranes, gel electrophoresis indicates the existence of a single protein band whose molecular weight (18 KDa) is unaltered by incubation with sulphydryl-reducing or protein cross-linking agents. This molecule seems to be a low molecular weight, acidic protein. Diethylpyrocarbonate decreases partially (60%) the binding of [3H]PK 11195 without affecting [3H] RO5-4864 binding, which implies a vital histidine residue in the binding domain of [3H]-PK 11195. Treatment with phospholipase A2 or mellitin, a stimulant of endogenous PLA2, led to a selective loss of [3H] RO5-4864 binding with no change in the binding of [3H]PK 11195. Such differences between a benzodiazepine ligand and an isoquinoline ligand suggest that these compounds may induce, on binding, different conformational changes in the PBS, which is compatible with the hypothesis that RO5-4864 and PK 11195 may be an agonist and an antagonist respectively at the PBS.

Adrenal Glands↗
PubMed1987

Photoaffinity labeling of peripheral-type benzodiazepine-binding sites.

The use of a novel photoaffinity label for the peripheral-type benzodiazepine-binding site is described. This compound, PK 14105, has high affinity (4 nM) and selectivity for cardiac benzodiazepine-binding sites. Under ultraviolet light, PK 14105 couples covalently to an 18,000-Da membrane protein which apparently corresponds to the (or a part of the) cardiac benzodiazepine-binding site. Since covalent attachment of PK 14105 totally precludes the binding of other ligands to this binding site, it is suggested that, during ultraviolet irradiation, this compound inserts covalently into the binding domain of the peripheral-type benzodiazepine-binding site.

Affinity Labels↗
PubMed1986

Stereoselective inhibition of the binding of [3H]PK 11195 to peripheral-type benzodiazepine binding sites by a quinolinepropanamide derivative.

The specific binding of [3H]PK 11195 to the peripheral-type benzodiazepine binding site is inhibited by the l-enantiomer of N,N-diethyl-alpha-methyl-2-phenyl-4-quinolinepropanamide ((-)Q1) but not by its d-enantiomer ((+)Q1). (-)Q1 inhibited [3H]PK 11195 binding to several rat tissues with an IC50 of less than 10 nM whereas (+)Q1 was at least 500 times less potent. This stereoselectivity was observed in all the tissues tested (brain, heart, kidney and adrenals). The same stereoselectivity was found for the displacement of the binding of [3H]PK 11195 in vivo, where (-)Q1 had an ID50 between 4-15 mg/kg and (+)Q1 was completely inactive at all doses tested (i.e. up to 40 mg/kg). Neither isomer had appreciable affinity for central-type benzodiazepine binding sites ([3H]diazepam) nor for voltage-sensitive calcium channels ([3H]PN 200210 and [3H]verapamil).

Adrenal Glands↗
PubMed1986

PK 11195, an antagonist of peripheral type benzodiazepine receptors, modulates Bay K8644 sensitive but not beta- or H2-receptor sensitive voltage operated calcium channels in the guinea pig heart.

In a partially depolarized guinea pig papillary muscle preparation, BAY K8644 stimulated voltage-operated calcium channels, promoting slow action potentials; this effect was dose-dependent over a concentration range of 3 X 10(-7) M to 3 X 10(-6) M. Isoproterenol and histamine also induced slow action potentials by stimulating beta or H2 receptors, respectively. PK 11195, the antagonist of peripheral type benzodiazepine receptors, inhibited the effect of BAY K8644, but not those of histamine or isoproterenol. Moreover, PK 11195 "dose-dependently" antagonized the ability of RO5-4864 to inhibit the slow action potentials elicited by barium chloride. Thus, in the heart, PK 11195, an antagonist of peripheral type benzodiazepine receptors, can modulate voltage-operated calcium channels when they are activated directly, but not when they are activated by stimulation of neurotransmitter receptors.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1986

4-Amino-6-chloro-2-piperazinopyrimidines with selective affinity for alpha 2-adrenoceptors.

A series of 4-amino-6-chloro-2-piperazinopyrimidines were synthesized and evaluated for their ability to interact with alpha 1- and alpha 2-adrenoceptors in vitro in binding assays using [3H]WB-4101, [3H]clonidine, and [3H]idazoxan as radioligands. Some compounds were also tested as inhibitors of [3H]spiroperidol binding. Several members of this series showed high and selective affinity for alpha 2-adrenoceptors. The nature of the 4-amino substituent seems to be the most critical factor in determining the potency at these receptors.

Animals↗
PubMed1985

Dihydropyridine and peripheral type benzodiazepine binding sites: subcellular distribution and molecular size determination.

Electrophysiological and pharmacological studies have shown that peripheral-type benzodiazepine receptors modulate voltage-sensitive calcium channels in the heart. We have compared these binding sites with binding sites for [3H]dihydropyridines, which are believed to label such channels. Although no direct or allosteric interaction could be demonstrated between the two sites, their subcellular distribution--sarcolemma and ryanodine-sensitive sarcoplasmic reticulum--was parallel. Size determination of the two sites suggests that the receptors for these two classes of compounds are separate molecules packaged in the same membrane compartment.

Animals↗
PubMed1985

PK 11195, an antagonist of peripheral benzodiazepine receptors, reduces ventricular arrhythmias during myocardial ischemia and reperfusion in the dog.

PK 11195, an antagonist of peripheral type benzodiazepine receptors, in doses from 5 to 25 mg/kg i.d. protected in a dose-dependent manner dogs against both early and delayed ventricular arrhythmias induced by 20 min ischemia and against ventricular fibrillation following reperfusion. Thus, peripheral-type benzodiazepine receptors might represent a novel target in the treatment of angina and cardiac ischemia.

Animals↗
PubMed1985

Comparative effects of heparin and PK 10169, a low molecular weight fraction, in a canine model of arterial thrombosis.

The comparative properties of heparin and PK 10169, a low molecular weight fraction, were studied using an antithrombotic test in anaesthetized dogs. The antithrombotic properties of the two compounds were evaluated by measuring inhibition of thrombus formation following transluminar stimulation of coronary artery with anodal current and by measuring anticoagulant properties, anti Xa and anti IIa activities. The results show that PK 10169 displayed significant antithrombotic activities above 0.625 mg/kg and was equipotent at 2.5 mg/kg s.c. with heparin 10 mg/kg s.c. No correlation could be observed between antithrombotic/anti Xa ratio of both compounds. Moreover it was shown that, unlike heparin, PK 10169 s.c. was devoid of obvious anticoagulant properties and induced a negligible anti IIa activity contrasting with a high anti Xa level. A similar dissociation between anti Xa and anti IIa activities was observed following i.v. administration of 2.5 mg/kg of PK 10169 but not with heparin. This low molecular weight heparin fraction might thus be regarded as a potential arterial antithrombotic agent devoid of appreciable anticoagulant effect.

Animals↗