Imipramine-fentanyl antinociception in a rabbit tooth pulp model

Antinociception of imipramine (I) and its effect in combination with fentanyl (F) was evaluated in rabbits using electrically-induced lick chew responses via tooth pulp stimulation as the model of nociception. Acute i.v. injections of I elicited a graded dose response comparable to i.v. morphine (M) with I ED 50 = 4.35 mg/kg (2.31-8.14, 95% CL) and M ED 50 = 1.81 mg/kg (1.11-3.90), with no differences in the slopes between the two curves. The lethal dose of I was 10 mg/kg. An i.v. dose of I twice the ED 50 elicited an antinociceptive effect of more than 50% maximum possible effect (MPE) for 90 minutes with peak effect of 82% MPE occurring at 15 minutes. These effects of I were not reversed by a morphine-reversal dose of naloxone (0.1 mg/kg i.v.) but were reversed with a ten fold dose of naloxone. F ED 50 values (mcg/kg) were lowered from 11.35 to 2.70, 0.74 and 0.33 with increasing pretreatment doses of I (1.0, 2.1 and 3.2 mg/kg). These magnitudes of potency increases of F were 4.2, 15.3 and 34.4 fold respectively. A single i.v. ED 50 dose of I extended the time to 50% MPE of an ED 90 dose of F from 26 minutes to 77 minutes; of a 2 X ED 50 dose of F from 17 minutes to 28 minutes. Data points for three different combinations of I and F fell significantly within the synergistic field of an ED 50 isobologram and a polynomial equation described the curve best fitting the data points. F alone (i.v. ED 50 dose) increased the PaCO2 values to 74% above controls and three different combinations with I showed no increases in PaCO2 values above controls. I alone did not significantly cause any change in PaCO2 values from controls.     

Ionic fluxes induced by topical misoprostol in canine gastric mucosa

We studied the dose response of ionic fluxes in canine chambered gastric segment mucosa to increasing doses of topical misoprostol (0.1, 1, 10, 100, and 1000 micrograms). The fluxes were also correlated with the simultaneous changes in focal gastric mucosal blood flow measured by laser-Doppler flowmetry. After misoprostol administration, there was a dose-dependent increase in focal gastric mucosal blood flow (Emax = 8.23 +/- 3.25 V at 10 micrograms; ED50 = 1.05 micrograms), pH, and the outputs of ions (Na+, K+, Cl-, and HCO3-) and fluid (Emax for pH and fluxes greater than or equal to 1000 micrograms). ED50 values for these outputs ranged from 215.40 to 340 micrograms (mean +/- SE = 279.08 +/- 24.27 micrograms). H+ output showed a dose-dependent decrease to zero at the 10-micrograms dose, the dose at and after which net HCO3- secretion became obvious. The slopes of the dose-response curves for the fluxes of fluid, Na+, K+, Cl-, and HCO3- were significantly different (p less than 0.01) from the slope of the curve for mucosal blood flow changes. There were no correlations between the changes in these fluxes and blood flow changes. Na+ and Cl- were the predominant cation (98.84%) and anion (98.19%), respectively, in the misoprostol-induced secretion. Misoprostol stimulates a composite alkaline gastric nonparietal secretion, predominantly Na+ and Cl-, but also containing K+ and HCO3-. Our results suggest different mechanisms for the effects on nonparietal secretion and focal gastric mucosal blood flow.(ABSTRACT TRUNCATED AT 250 WORDS)     

Evaluation of the immunogenicity of meningococcal vaccines in experiments on mice]

The immunogenicity of 2 meningococcal vaccines, multicomponent vaccine produced at the Mechnikov Research Institute for Vaccines and Sera in Moscow and polysaccharide vaccine obtained from Merck Sharp & Dohme (USA), was evaluated on experimental meningococcal sepsis in mice, produced by the injection of meningococcal culture in mucin suspension. The protective effect of these 2 vaccines, expressed in terms of ED50, was 0.28 +/- 0.12 for the multicomponent vaccine and 0.25 +/- 0.24 for the polysaccharide vaccine; the challenge dose used in the test was 10 LD50 of the culture. The multicomponent vaccine gave the maximum immunological effect in a dose of 8 micrograms, while higher or lower doses induced a lesser increase in antibody titer and thus gave lower protection to mice against infection.     

Functional and histological changes in rat lung after boron neutron capture therapy

The motivation for this work was an unexpected occurrence of lung side effects in two human subjects undergoing cranial boron neutron capture therapy (BNCT). The objectives were to determine experimentally the biological weighting factors in rat lung for the high-LET dose components for a retrospective assessment of the dose to human lung during cranial BNCT. Lung damage after whole-thorax irradiation was assessed by serial measurement of breathing rate and evaluation of terminal lung histology. A positive response was defined as a breathing rate 20% above the control group mean and categorized as occurring either early (<110 days) or late (>110 days). The ED(50) values derived from probit analyses of the early breathing rate dose-response data for X rays and neutrons were 11.4+/-0.4 and 9.2+/-0.6 Gy, respectively, and were similar for the other end points. The ED(50) values for irradiation with neutrons plus p-boronophenylalanine were 8.7+/-1.0 and 6.7+/-0.4 for the early and late breathing rate responses, respectively, and 7.0+/-0.5 Gy for the histological response. The RBEs for thermal neutrons ranged between 2.9+/-0.7 and 3.1+/-1.2 for all end points. The weighting factors for the boron component of the dose differed significantly between the early (1.4+/-0.3) and late (2.3+/-0.3) breathing rate end points. A reassessment of doses in patients during cranial BNCT confirmed that the maximum weighted doses were well below the threshold for the onset of pneumonitis in healthy human lung.     

The effect of total body gamma-irradiation on mortality, egg production and egg weight of Japanese quails

Male and female Japanese quail 21 weeks old, that were given total body doses of 60Co gamma-rays ranging from 0 to 30 Gy, showed a peak in mortality at 6-8 days post-irradiation. The LD 50/30 was 22.5 Gy, and the LD 90/30 was 26.7 Gy. No differences were evident in mortality between males and females. The reduction in egg production by 30 days post-irradiation was related linearly to the dose, for doses above 6 Gy. The reduction in egg weight (30 days post-irradiation laying period) was also related linearly to the dose.     

Therapeutic evaluation of free and liposome-encapsulated atovaquone in the treatment of murine leishmaniasis

The use of drug delivery systems may reduce the toxicity and improve the activity of anti-leishmanial compounds. The activity of atovaquone (ATV)-loaded liposomes was compared by determination of median effective doses (ED(25) and ED(50)), with that of free ATV in a murine model of visceral leishmaniasis induced by Leishmania infantum. On day 0, mice were infected intravenously with 4.10(7) promastigotes and treated via the tail vein on days 15, 17 and 19 by free drug in a DMSO/cremophor/water solution (0.2 to 1.6 mg/kg body weight) or by liposomal drug (0.04 to 0.32 mg/kg body weight). Mice were killed and livers and spleens were removed and weighed on day 21 p.i. and liver parasite burdens evaluated using the Stauber method. Effective doses were determined using the Hill representation relating the percentage of parasite suppression to the dose. Liposomal ATV was significantly more effective than the free drug in reducing liver parasites (61.6% of parasite suppression at a dose of 0.32 mg/kg vs 34.9% at a dose of 1.6mg/kg). Liposomal ATV was 23 times more active than the free drug (ED(25) value=0. 02+/-0.01 mg/kg vs 0.46+/-0.15 mg/kg for free drug). It was not possible to obtain the ED(50) for free ATV because the dose-response curve reached a plateau around 33% of parasite suppression. Conversely, the ED(50) for liposomal ATV was 0.17+/-0.05 mg/kg. 100% efficacy of bound ATV could be obtained with a concentration of 1. 77+/-0.35 mg/kg. A significant decrease in spleen weights was also observed reflecting a leishmanicidal activity of ATV. These results suggest that liposome loaded ATV is more efficacious than the free drug against Leishmania infantum in this murine model.     

Choice of number of doses for maximum likelihood estimation of the ED50 for quantal dose-response data

We address the question of how to choose the number of doses when estimating the median effective dose (ED50) of a symmetric dose-response curve by the maximum likelihood method. One criterion for this choice here is the asymptotic mean squared error (determined by the asymptotic variance) of the estimated ED50 of a dose-response relationship with qualitative responses. The choice is based on an analysis of the inverse of the information matrix. We find that in many cases, assuming various symmetric dose-response curves and various design densities, choice of as many doses as possible, i.e., the allocation of one subject per dose, is optimal. The theoretical and numerical results are supported by simulations and by an example concerning choice of design in an adolescence study.     

Multifraction radiation response of mouse lung

The response of mouse lung to repeated doses of 60Co gamma-rays of as low as 115 cGy per fraction was measured using death from pneumonitis between 80 and 120 days after irradiation as the endpoint. A fractionation interval of 3 h was maintained for most regimens but in the longer experiments some 12 h intervals were introduced for logistic reasons. The longest overall duration (for a 43 fraction regimen) was 8 days. The total doses required to produce 50 per cent mortality increased continuously as dose/fraction was decreased, even from 160 to 115 cGy per fraction. Of clinical relevance, the steepness of the isoeffect curve over the dose range 115-500 cGy indicates that the lung shows greater sparing from dose fractionation than is characteristic of more rapidly-responding normal tissues, resembling, in this respect, other more slowly-responding tissues such as spinal cord. The plot of the reciprocal of the LD50 values as a function of dose per fraction was non-linear, suggesting that a linear quadratic dose response model may not be appropriate or that repair of cellular injury in lung is not complete in 3 h, or both.     

Nonstochastic effects of different energy beta emitters on pig skin

Circular areas of pig skin from 1- to 40-mm diameter were irradiated with beta emitters of high, medium, and low energies, 90Sr, 170Tm, and 147Pm, respectively. The study provides information for radiological protection problems of localized skin exposures. During the first 16 weeks after irradiation 90Sr produced a first reaction due to epithelial cell death followed by a second reaction attributable to damage to the dermal blood vessels. 170Tm and 147Pm produced the epithelial reaction only. The epithelial dose response varied as a function of beta energy. The doses required to produce moist desquamation in 50% of 15- to 22.5-mm fields (ED50) were 30-45 Gy from 90Sr, approximately 80 Gy from 170Tm, and approximately 500 Gy from 147Pm. A model involving different methods of epithelial repopulation is proposed to explain this finding. An area effect was observed in the epithelial response to 90Sr irradiation. The ED50 for moist desquamation ranged from approximately 25 Gy for a 40-mm source to approximately 450 Gy for a 1-mm source. The 5-, 9-, and 19-mm 170Tm sources all produced an ED50 of approximately 80 Gy, while the value for the 2-mm source was approximately 250 Gy. It is also suggested that the area effects could be explained by different modes of epithelial repopulation after irradiation. After high energy beta irradiation repopulation would be mainly from the field periphery, while after lower energy irradiation repopulation from hair follicle epithelium would predominate.     

General characteristics and comparative evaluation of the radioprotective properties of aryl alkyl amine adrenomimetics in experiments on mice]

The radioprotective effect (RPE) of some arylalkylamines (AAAs) was studied in experiments on mice. Mesaton and its close analogues were injected subcutaneously 15 minutes prior to irradiation at a dose of 800 rad. The protective effect is exerted by AAAs in low doses (25--50 mumole/kg), the compounds show stable and high RPE (80--80% survival, dose reduction factor being 1.3--1.4) and low toxicity (LD50 = 4--8 mumole/kg). AAAs studied are not less effective than aminothiols. Their pharmacological spectrum--K = LD50/ED50 (200--500) is superior to that of known aminothiols and indolylalkylamines.     

Effect of number of receptors for gonadotropin-releasing hormone on the release of luteinizing hormone

The relationship between number of receptors for gonadotropin-releasing hormone (GnRH) and the ability of the anterior pituitary gland to release luteinizing hormone (LH) was examined in ovariectomized ewes. A GnRH antagonist was used to regulate the number of available receptors. The dose of GnRH antagonist required to saturate approximately 50 and 90% of GnRH receptors in ovariectomized ewes was determined. Thirty min after intracarotid infusion of GnRH antagonist, ewes were killed and the number of unsaturated (i.e., those available for binding) pituitary GnRH receptors was quantified. Infusion of 10 and 150 micrograms GnRH antagonist over a 5-min period reduced binding of the labeled ligand to approximately 50 and 12% of controls, respectively. The effect of reducing the number of GnRH receptors on release of LH after varying doses of the GnRH agonist, D-Ala6-GnRH-Pro9-ethylamide (D-Ala6-GnRH) was then evaluated. One of four doses of D-Ala6-GnRH (0.125, 2.5, 50 and 400 micrograms) was given i.v. to 48 ovariectomized ewes whose GnRH receptors had not been changed or were reduced to approximately 50 or 12% of control ewes. In ewes with a 50% reduction in GnRH receptors, total release of LH (area under response curve) was lower than that obtained for controls (P less than 0.01) at the 0.125-micrograms dose of D-Ala (6.1 +/- 0.7 cm2 vs. 13.5 +/- 0.7 cm2) but was not different at the 2.5-, 50- or 400-micrograms doses of D-Ala6-GnRH.(ABSTRACT TRUNCATED AT 250 WORDS)     

An effective method for the estimation and comparison of the ED50 with small sample sizes

In ED50 experiments the relationship between dose and probability of response is often modelled by the probit function. Standard statistical analysis estimates the parameters of this function by the maximum likelihood principle and derives the ED50 and its fiducial limits from these parameters. Bayesian analysis is more effective in two respects: It optionally includes prior information and in all but very few instances yields confidence intervals, whereas fiducial intervals often cannot be determined. Bayesian analysis of experiments with one substance has been treated in GRIEVE (1988). In the present article the mathematically interested reader is shown how to compare two substances. The probability of higher ED50 in the one substance as well as estimates of the ratio of the ED50's are obtained. The methods are easily extended to the effective dose for any other reasonable percentage of animals, e.g. ED90 or ED25. Experiments concerning lethal doses can be analysed by these methods as well. Both types of analysis are applied in two examples which compare new batches of vaccines with an established standard. In the first example both substances are nearly equivalent, while in the second example the new batch is considerably more efficient. An interactive FORTRAN program for a personal computer is available (cf. last section of 5.). It computes the maximum likelihood and the Bayesian solution, using approximate formulas in the latter case. Due to these approximations it was possible to develop a Bayesian program which is fast enough to run on a PC. Validation procedures have been performed. The output consists of a print file and, optionally, an ASCII file containing the coordinates of the posterior probability density and distribution functions.     

Significance of ED50 and therapeutic indexes of various radiation-protective agent groups]

Radioprotective agents are divided in 3 groups: (1) cystamine, AET, cystaphos, gammaphos, and thiogammaphos with ED50 (the dose that gives a half of the maximal protective effect) of 10(3)-10(1.6) mumol/kg and therapeutic index K = LD50/ED50 = 10(0)-10(1.6); (2) 5-methoxytryptamine, phenylephrine, serotonin, and norepinephrine with ED50 = 10(1)-10(0) mumol/kg and K = 10(1.8)-10(2,6); (3) clonidine and isoprenaline with ED50 = 10(-0.5)-10(-0.8) mumol/kg and K = 10(3)-10(4). Possible causes of these differences and advantages of low ED50 and high K are discussed.     

Changes in the sensitivity of mice to the action of gamma irradiation by Viscum album L. polysaccharides]

The influence of water-soluble polysaccharides of Viscum album L. on the survival of mice subjected to whole-body gamma-irradiation has been investigated. Polysaccharides were shown to exert a radioprotective effect which was a function of both the radiation dose and the drug dose and time of its injection. The maximum radioprotective efficacy of polysaccharides was observed after their injection 15 min before irradiation. A single intraperitoneal administration of polysaccharides (25 mg/kg) before irradiation with LD50/30 and LD100/10-12 increased the 60-day survival rate up to 95% and 27% respectively. The postirradiation injection of polysaccharides prevented death of 80% of mice given LD50 and increased the average life expectancy of animals irradiated with absolutely lethal doses.     

Alpha-chloralose as a capture and restraint agent of birds: therapeutic index determination in the chicken

The median effective dose for capture (ED50) and the median lethal dose (LD50) of alpha-chloralose given orally to domestic chickens (Gallus domesticus) were determined by probit analysis to be 45 mg/kg and 300 mg/kg, respectively. The therapeutic index (TI = LD50/ED50) was 6.7. This indicates that alpha-chloralose is only a marginally safe capture agent in domestic species and particularly in field applications involving other wild avian species in which the amount of the drug ingested by an individual bird is not controlled.     

Choice of quantitative characteristics of a radiation modifier affinity and the range of its pharmacological action (minireview)]

On the basis of the literature the necessity of using not only DMF and maximal protective or sensitizing effects, but also the affinity and the range of the pharmacological action of radiation modifiers is argued. The affinity is worth while to expressed as ED50 (the dose that produces a half of the maximal effect), and the range of the pharmacological action as a therapeutic index K = LD50/ED50.     

A single blind, placebo controlled, across groups dose escalation study of the safety, tolerability, pharmacokinetics and pharmacodynamics of the melatonin analog beta-methyl-6-chloromelatonin

Clinical investigation of melatonin agonists has been hampered by side effects such as hypothermia, hypotension and bradycardia. The availability of a melatonin agonist devoid of these side effects would improve our understanding of the mechanisms by which melatonin agonists affect sleep. This study investigated the pharmacokinetics, pharmacodynamics and safety of the melatonin agonist beta-methyl-6-chloromelatonin at doses up to 100 mg in healthy volunteers. The design was a single blind, across subjects, placebo controlled, group wise dose escalation using doses of 20, 35, 50 and 100 mg beta-methyl-6-chloromelatonin. Eight subjects received one dose of study drug or placebo. Pharmacokinetic analysis showed a consistent Tmax across all doses with a mean of 1.12 +/- 0.11 hr for all groups (mean +/- SD). The half-life was also consistent across dose, with a mean of 1.04 +/- 0.04 hr. Maximum plasma concentrations increased with increasing dose with values of 44.83 +/- 29.79, 100.3 +/- 41.08, 79.84 +/- 26.36 and 410.3 +/- 129.4 ng/ml at doses of 20, 35, 50 and 100 mg, respectively. Area under the curve showed similar increases. No consistent changes in vital signs occurred as a function of dose or time after study drug. The incidence of all adverse events, the severity of the event or the event's relationship to treatment did not increase with higher doses of beta-methyl-6-chloromelatonin. Sleepiness was reported after all doses of beta-methyl-6-chloromelatonin. beta-methyl-6-chloromelatonin appears safe and well tolerated at doses up to 100 mg. These doses are not associated with hypothermia, bradycardia or hypotension. A melatonin agonist lacking these side effects should allow investigation of the direct soporific effects of melatonin agonists.     

A comparison of N-methyl-N-nitrosourea-induced chromatid aberrations and micronuclei in barley meristems using FISH techniques

Individuals can be exposed to high doses (more than 5Gy) during radiation accidents. It is, of course, helpful to the physician to have biological indicators also for such high doses. The problem with most cytogenetic indicators is, that the response levels off at doses starting around 5-7Gy of low LET radiation and that the dose-response curve even declines after doses exceeding about 10Gy. Thus, it may be difficult to decide, whether the dose was, for example, 8 or 14Gy. We studied how the micronucleus assay can be used to give information also in the high dose range. It turned out that micronucleus frequency itself cannot be used for the estimation of doses exceeding about 5-7Gy. There are, however, at least three other endpoints that can be determined in the cytochalasin B assay that can assist the decision in the high dose range: (1) the number of mononucleated cells; (2) the ratio of tri- to tetranucleated cells; (3) the average micronucleus frequency in micronucleus positive binucleated cells.     

Doxycycline in the prevention of experimental plague induced by plague microbe variants]

A comparative study was performed on the efficacy of doxycycline in experimental plague infection induced in albino mice by strain 231 of the plague microbe and its variant 231 Fra- deprived of the ability to produce the fraction I antigen. It was shown that the LD50 for strain 231 during animal treatment with doxycycline was significantly higher than that for variant 231 Fra-. Prophylaxis of the plague infection caused by the Fra- forms of the plague microbe required significantly higher doses of doxycycline (ED50) than that of the infection caused by the Fra+ forms. The use of the daily maximum permissible doses of doxycycline (50 to 100 mg/kg a day) for 10 days in treatment of albino mice infected with the strain Fra- did not provide animal survival at the level higher than 60 to 70 per cent while the survival rate in the animals infected with the strain Fra+ of the plague microbe and treated according to the same scheme amounted to 90-100 per cent. The lower therapeutic efficacy of doxycycline in the treatment of the infection caused by the fractionless variant of the plague microbe should be considered in development of rational schemes for prophylaxis and treatment of plague.     

Acute creatine ingestion in human: consequences on serum creatine and creatinine concentrations

The aim of the study was to explore the effect of an acute dose of creatine (Cr) ingestion on serum Cr and serum creatinine (Crn) concentrations. Sixteen healthy subjects ingested a single dose of Cr (20 g) followed by the measurement of serum Cr and Crn concentration for 3 h up to a maximum of 6 h (n=6). In response to Cr ingestion a large rise in serum Cr concentration was observed (by 50 folds) occurring approximately 2 1/2h after the ingestion (peak value of 2.17 +/- 0.66 mmol x l(-1)). We also found a moderate but significant rise in serum Crn concentration averaging 13 % after 3 h (peak value at 99.5 +/- 10.5 micromol x l(-1)). A dose response curve obtained in two case studies, in whom different doses of Cr were ingested (0, 2.5, 5, 10, 15, 20 g and 0, 10, 20, 30 g), showed that serum Cr concentration as well as the peak time increased linearly with Cr ingestion. In addition, acute Crn ingestion (5 g) resulted in a substantial increase in serum Crn concentration (by 10 folds) but led to a minor rise in serum Cr concentration (by 2 folds). These results suggest that when acute doses of Cr are ingested in humans, the degree of conversion of exogenous Cr to Crn in the stomach and the gut can be considered as negligible following the first 6 h of ingestion. However, further studies are required to explore the prolonged effect of Cr on Crn metabolism.