Specific and high affinity binding of perindoprilat, but not of perindopril to blood ACE

The bindings of perindopril and of its active metabolite perindoprilat to human serum, isolated proteins and to erythrocytes were studied by equilibrium dialysis. Within the therapeutic concentrations range, perindopril was 74% bound to serum involving a non-saturable process, NKa = 2.87. The main binders are serum albumin and alpha 1-acid glycoprotein. The serum binding of perindoprilat involved two successive steps. First, a saturable high-affinity binding (Ka: 2.8 x 10(9) M-1) occurred, involving probably the angiotensin converting enzyme (ACE). The second binding step was non-saturable with a very weak binding capacity, NKa = 0.15, quite superimposable to the HSA bound perindoprilat. Free fatty acids (FFA) did not alter the binding to HSA. The binding of both compounds to erythrocytes was low especially with perindopril, when measured in the presence of plasma. A significant correlation showed that the overall serum binding percentage of both drugs was essentially determined by HSA concentration. Serum binding was decreased in renal failure or cirrhosis, this result was principally linked to the hypoalbuminemia. Interactions with other drugs were limited to the binding of salicylate, tolbutamide and digitoxin to HSA.

Morphine place conditioning is differentially affected by CCKA and CCKB receptor antagonists

In the present study we have examined the interaction between the selective cholecystokinin (CCK)A and CCKB receptor antagonists, devazepide and L365-260 on morphine conditioned place preference (CPP). Using an unbiased procedure, morphine (1.5 mg/kg) produced a reliable CPP which was observed irrespective of the conditioning compartment type. Pretreatment with devazepide (0.001-0.01 mg/kg s.c.) produced a dose related attenuation of this response. At higher doses (0.1-1 mg/kg) this antagonism became variable and dependent on the training compartment with blockade only observed when conditioning was to the white/rough textured environment. This profile has also been reported for the serotonin (5-HT)3 receptor antagonist ondansetron. The CCKB antagonist L365-260 (0.000001-0.01 mg/kg) failed to antagonize the morphine CPP, if anything a mild potentiation was observed. To study this further we examined the interaction between L365-260 (0.01 mg/kg) and a subthreshold dose of morphine (0.3 mg/kg). At these doses neither drug elicited CPP, however when co-administered a significant CPP was recorded. Finally, L365-260 at 1 mg/kg induced a mild but significant CPP when administered alone. These results suggest a differential role of CCK receptor subtypes on reward-related behaviour and complement previous studies suggesting bimodal effects of CCK systems on mesolimbic dopamine function.

Effect of the 5-HT3 receptor antagonists, MDL72222 and ondansetron on morphine place conditioning

The purpose of the present study was to reassess the original findings of Carboni et al. (1988) who suggested that 5-HT3 receptor antagonists may block morphine-induced place conditioning in rats. These workers used a biased protocol with treatments allocated to compartments based on initial preference. In the present study we have adopted an unbiased approach with treatments randomly assigned to conditioning compartment in a counter-balanced fashion. Thus treatments were equally paired between distinct environmental cues. Using this protocol, morphine produced a dose-related place preference (0.3-3 mg/kg SC). Thirty-minute pretreatment with the selective 5-HT3 antagonists, MDL72222 (1 mg/kg SC) and ondansetron (0.01 mg/kg SC) before morphine (1.5 mg/kg SC), significantly antagonized the place conditioning to this treatment. However, with higher doses of ondansetron (0.1-1 mg/kg SC), the antagonism of morphine-induced place preference became variable and dependent on the conditioning compartment. This was probably a reflection of the fact that ondansetron when administered alone also appeared to produce an environmentally dependent place conditioning at these doses. Therefore it is concluded that at certain doses, 5-HT3 receptor antagonists may antagonize morphine place conditioning in a manner consistent with a blockade of the appetitive effects of this drug. However, at higher doses, at least with ondansetron, this antagonism became non-specific and dependent on the training environment. It is suggested that other animal models of opioid reinforcement (e.g., self-administration) are now needed to validate the hypothesis that 5-HT3 receptor antagonists may modify opioid reward.

The NMDA antagonist dizocilpine (MK801) attenuates motivational as well as somatic aspects of naloxone precipitated opioid withdrawal

The non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist dizocilpine has recently been reported to antagonize certain overt withdrawal signs in morphine dependent rats. The purpose of the present study was to reassess this response and examine the effect of this drug in a model presumably reflective of the motivational impact of withdrawal using the place conditioning technique. Rats were made opiate dependent by the subcutaneous implantation of a 75 mg morphine pellet. Three-4 days later withdrawal was precipitated by naloxone 0.5 mg/kg. Dizocilpine (0.1-0.5 mg/kg) attenuated many of the subsequent behaviours elicited by naloxone, notably diarrhoea, mouth movements, paw shakes and ptosis. In a separate group of morphine dependent rats, naloxone (0.05 mg/kg) precipitated withdrawal produced a clear place aversion. This place aversion was blocked by dizocilpine (0.02-0.1 mg/kg) pre-treatment prior to conditioning. Therefore dizocilpine may modify both motivational and somatic aspects of opioid withdrawal.

Effects of 5-HT3 receptor antagonists on behavioural measures of naloxone-precipitated opioid withdrawal

The effect of the selective 5-HT3 receptor antagonists, ondansetron and MDL 72,222, against various behaviours elicited by naloxone-precipitated morphine withdrawal were examined. Rats made dependent upon morphine by the subcutaneous implantation of a 75 mg pellet, when challenged with naloxone (0.5 mg/kg SC), 3 or 4 days later exhibited a wide range of behaviours including wet dog shakes, paw shakes, salivation and a marked weight loss. Pre-treatment with ondansetron (0.01-1 mg/kg SC) or MDL 72,222 (1-3 mg/kg SC) failed to affect the incidence of these responses except weight loss, which was attenuated by both treatments. At doses similar to and below those required to elicit the withdrawal syndrome, naloxone produced a single-trial place aversion in morphine dependent rats. The place aversion produced by naloxone (0.05 mg/kg SC) was antagonized by pre-treatment of ondansetron (0.1-1 mg/kg SC) and MDL 72,222 (1 mg/kg SC) prior to conditioning. Chlordiazepoxide (10 mg/kg IP) but not gepirone (3-10 mg/kg SC) was similarly effective. It is concluded that 5-HT3 antagonists may attenuate some but not all behavioural signs associated with morphine withdrawal. Reasons for this apparent selectivity are discussed.

A re-evaluation of the HSA-piroxicam interaction

Piroxicam binding to HSA was studied using equilibrium dialysis and fluorescence methods. It was shown that this drug, like its analogs isoxicam and tenoxicam, binds to the apazone locus (site I area) and to a lesser extent to the diazepam site (site II). The piroxicam binding to HSA can be modulated by various specific ligands--apazone, warfarin, diazepam, ibuprofen--and these drug interactions have to be considered not only as potential displacement from the HSA binding sites but also in terms of induced allosteric effects.

Formation and reactivity of 1-pyrrolyl-2,2,2-trifluoroethyl cations

1-(1-Methyl-2-pyrrolyl)-2,2,2-trifluoroethyl p-nitrobenzoate (3) reacts by carbocation formation with an m value for the dependence of rate on the solvent polarity parameter YOTs of 0.56, and a rate 41 times slower than (1-methyl-2-pyrrolyl)methyl p-nitrobenzoate. The products from 3 include significant amounts of material derived from solvent attack at the 5-position of the pyrrole ring. The results indicate a high degree of charge delocalization by the strongly donating pyrrolyl group, resulting in a low k(H)/k(CF3) rate ratio and nucleophilic attack on the ring. 1,1, l-Trifluoro-2-(1-methyl-2-pyrrolyl)propan-2-ol (10) reacted with CF3CO2H via a tertiary carbocation, which led to dimeric products resulting from electrophilic substitution on the pyrrole ring. Keywords: pyrrole, trifluoromethyl substituents, carbocations.

Blood distribution of tenoxicam in humans: a particular HSA drug interaction

Blood binding of tenoxicam was studied in vitro by equilibrium dialysis. Isolated human plasma proteins and blood cells were checked, and the distribution of the bound form was then calculated. The results showed that tenoxicam is mainly bound to HSA and that binding percentages are not different when measured in plasma (98.4%) and in an HSA solution at physiological concentration (704 microM, 98.15%). In these conditions, within the range of 1-150 microM, the tenoxicam binding percentage remained constant, evidence of a nonsaturable process. When a lower HSA concentration (10 microM) was used, the binding parameters of the tenoxicam interaction were calculated by using the same equilibrium dialysis data, by 3 methods of analysis- a stoichiometric method and site-oriented methods, fixing or not the number of HSA binding sites (n) as integer values. The best fit was observed with the first method, suggesting that two main interactions occurred. The site-oriented method gave lesser fits, the better being observed when n was not fixed. Its value, 1.77, suggest the possibility of two binding sites, one of them not preformed. The effects of known markers of site I, warfarin and apazone, of site II, diazepam and ibuprofen and of palmitic acid showed that tenoxicam is bound simultaneously to both sites I and II. The binding capacity of site I for tenoxicam is enhanced by diazepam: as this compound alone is bound to site II, this result suggests that the two HSA binding sites are not independent.

Evidence for isoxicam binding to site I as a primary site and to site II as a secondary site of human serum albumin

Isoxicam binding to HSA was studied using equilibrium dialysis and fluorescence methods. It was shown that this drug binds to or near site I (warfarin or azapropazone site) and to site II (the diazepam site) as a secondary site, although it is generally considered that their respective drug structural requirements are often exclusive. The binding parameters were calculated with different mathematical models; a site oriented model with or without fixing the number of binding sites as integer values and a stoichiometric model. The relevant results are in good agreement under the selected experimental conditions. The stoichiometric method indicates that no positive cooperativity occurred during the binding process but other interactions between the two sites cannot be excluded.

Prolonged exposure of neutrophils to saline or bronchoalveolar lavage fluid does not alter superoxide anion generation

The role played by neutrophils (PMNs) in the genesis of lung injury in diverse clinical situations, such as bronchial asthma, idiopathic pulmonary fibrosis, and the adult respiratory distress syndrome, is an area of intensive investigation. Functional studies of PMNs, particularly those obtained from the alveoli by bronchoalveolar lavage, should shed light on their contribution to lung injury. However, it has not been demonstrated whether procedures used to harvest cells from the lung (bronchoalveolar lavage), particularly the potentially prolonged exposure to saline, commonly used to perform lavage, and other components of lavage fluid, can alter the functional characteristics of PMNs. In this report we demonstrate that a 2- to 3-hour exposure of neutrophils to saline from both humans and sheep in vitro does not alter the functional characteristics of PMNs as determined by superoxide anion generation after activation with phorbol myristate acetate (PMA; 6.96 +/- 0.44 vs. 7.60 +/- 0.32 nmol O2-/250,000 PMNs for control and saline-treated human cells, respectively, after a 45-min incubation with 10(-7) M PMA, and 4.73 +/- 0.30 vs. 4.50 +/- 0.42 nmol O2-/250,000 PMNs for control and saline-treated sheep cells). In a second series of experiments, we studied the effect of exposure of human PMNs to bronchoalveolar lavage fluid supernatants obtained from normal volunteers on superoxide anion generation by neutrophils.(ABSTRACT TRUNCATED AT 250 WORDS)

Reduction of enucleation-induced metastasis in intraocular melanoma by periorbital irradiation

The optimum treatment of malignant choroidal melanoma remains controversial. Some authors have hypothesized that enucleation promotes metastatic disease. This hypothesis has been demonstrated in the B16F10 melanoma mouse model. The present study used this model to examine the effect of external beam irradiation as a means of reducing metastases induced by enucleation. The results show a dose-dependent reduction in the DNA synthesis of irradiated melanoma cells. Administration of 800 cGy (800 rad) of radiation produced a 90% reduction in DNA synthesis; however, higher levels of radiation failed to produce further depression of cell proliferation. Irradiation of melanoma cells before intravenous injection resulted in a significant dose-dependent reduction in the number of lung metastases. While there was no effect with 100 cGy (100 rad) of radiation, 1000 cGy (1000 rad) produced a 95% reduction in metastases. In the animal model of enucleation-induced metastasis, 2000 cGy (2000 rad) delivered to the orbit either before or after enucleation produced a significant reduction in the number of lung tumors, compared with animals that did not undergo irradiation; 1000 cGy (1000 rad) delivered before enucleation did not have such an effect. These studies provide evidence that periorbital external beam irradiation is useful in reducing metastases following enucleation of a malignant melanoma in this animal model.

Binding of 8-methoxypsoralen to human serum proteins and red blood cells

Serum binding of 8-methoxypsoralen (8-MOP) was studied by equilibrium dialysis. In therapeutic concentrations, 8-MOP binding in serum was high, 91.4%, and constant, indicating concentration-independent kinetics. This binding involved the two main proteins, human serum albumin and alpha 1-acid glycoprotein, in a saturable process with one class of binding sites (n) and affinity constants (Ka) of 1.295 X 10(4) mol/l and 2.115 X 10(4) mol/l, respectively. Binding to lipoproteins and gamma globulins was negligible and non-saturable in therapeutic concentrations, with nKa values of 0.35, 0.024, 0.013 and 0.0004 mumol/l for VLDL, LDL, HDL and gamma globulins, respectively. Inhibition of 8-MOP serum binding was observed with salicylic acid and indomethacin, but not with diazepam, warfarin or erythromycin. Over a range of therapeutic concentrations, the ration of 8-MOP concentration in red blood cells (RBCs) and in serum was constant at 20.3% and three times higher than would be expected if a simple diffusion of the 8-MOP plasma free fraction (fu) occurred. According to the measured and calculated parameters, simulations of 8-MOP blood binding in pathological states (hypoalbuminaemia with or without inflammation) showed variations of fu which were partially 'buffered' by RBCs. Simulation of 8-MOP protein binding at cutaneous interstitial fluid level showed that fu is approximately 30% and permitted prediction of a decrease of fu available to the epidermis in case of local or systemic inflammation. This may imply an increase in the minimum phototoxic dose relevant for PUVA and explain some cases of 'poor' responsiveness of psoriatic patients to PUVA therapy.

Intrathecal diazepam suppresses nociceptive reflexes and potentiates electroacupuncture effects in pentobarbital-anesthetized rats

Using noxious heat-evoked tail flick in rats anesthetized with pentobarbital infusion, we studied the effects of diazepam applied intrathecally. This drug caused a marked suppression of nociceptive reflexes in a dose-dependent manner. In addition, a small non-suppressive dose of diazepam potentiated electroacupuncture effects. These results are discussed in terms of gamma-aminobutyric acid (GABA) since it is known that diazepam enhances binding of GABA to its receptor and hence potentiates inhibitory effects of GABA in the spinal cord. The possible synergism of diazepam and pentobarbital is also discussed.

Management of anti-thrombin III deficiency during pregnancy without administration of anti-thrombin III

We report a patient with hereditary antithrombin III deficiency who was successfully treated with heparin throughout pregnancy. Functional antithrombin III levels fell to 0.32 U/ml during heparin treatment, but it was possible to achieve a heparin effect, measured by the activated partial thromboplastin time, thrombin clotting time and heparin assay with subcutaneous heparin in doses of 30,000 U to 35,000 U/24 hours. This achieve an long term heparin effect was obtained without the need for antithrombin III infusions.

Stability of thiamin in parenteral nutrition solutions

Since the vitamin thiamin is sensitive to degradation in the presence of stoichiometric concentrations of sulfite ions, the stability of thiamin in parenteral nutrition solutions containing sulfite as an antioxidant and preservative has been questioned. The usual clinical practice of mixing amino acids, dextrose, and other solutions for administration in total parenteral nutrition significantly dilutes the concentration of sulfite. We have measured the thiamin concentration in total parenteral nutrition solutions sampled from containers after administration to patients. We have also determined the time course of thiamin degradation in solutions containing two concentrations of sulfite. Thiamin content exceeded labeled amounts in total parenteral nutrition bags containing amino acid, dextrose, and multivitamin solutions. However, when multivitamins were added directly to amino acid solutions containing 0.1% (9.6 mM) sulfite, significant degradation occurred by 5 hr. Thiamin was stable for at least 22 hr when added to total parenteral nutrition solutions containing less than 0.05% (4.8 mM) sulfite.