Prevention of physostigmine-induced lethality in rats. A pharmacological analysis.

A systematic study of a large number of compounds from various pharmacological classes was performed to better define their interaction with the cholinergic nervous system. An 'in vivo' test procedure called 'physostigmine antagonism' in rats was used; it involved the administration of the test compounds, measurement of the pupil diameter and recording of the survival time after injection of a lethal dose of physostigmine. Known peripherally acting anticholinergics, such as isopropamide and methylscopolamine did not protect from physostigmine lethality at doses up to more than 150 times the mydriatic dose. Known centrally acting anticholinergics, such as dexetimide and benztropine, protected from lethality at doses equal to or slightly higher than the mydriatic dose. Penetration into the brain of a muscarinic blocking agent thus appeared to be a sufficient condition to significantly reduce the cholinergic overstimulation of the CNS that results from inhibition of acetylcholine hydrolysis. Drugs of other pharmacological classes that are known to have anticholinergic activity in addition to their more characteristic action, were also active in the physostigmine test. They include most of the tricyclic antidepressants, some antihistamines such as diphenhydramine and cyproheptadine, some ganglion blocking agents such as mecamylamine and the neuroleptic clozapine. Drugs with hypnotic or anticonvulsant properties, sedative neuroleptics and high doses of some members of other pharmacological classes protected from physostigmine-induced lethality by a mechanism not based on anticholinergic activity. The results further show that a number of pharmacological actions: dopamine, histamine H1 and serotonin S2 antagonism, MAO-inhibition, alpha-adrenergic blockade etc. are all insufficient to produce physostigmine antagonism.

Delay of castor oil diarrhoea in rats: a new way to evaluate inhibitors of prostaglandin biosynthesis.

Forty-four non-steroidal anti-inflammatory compounds were tested for possible effects on castor oil-induced diarrhoea in rats. A small but significant delay of intestinal evacuations was found with all compounds. Quantitatively, the oral doses required to delay diarrhoea beyond the first hour after castor oil challenge reflected the acute anti-inflammatory potency of the tested compounds. Qualitatively, the evolution of the effective doses with increasing delay was linear for potent inhibitors of prostaglandin biosynthesis. The evolution for less potent compounds was markedly different and suggested the earlier occurrence of non-specific drug effects. Suprofen, the most potent of the series of compounds, produced the 1 h delay at an oral dose of 1.11 mg kg-1; the ED50 increased linearly to 115 mg kg-1 for a 4 h delay. Compared with other compounds the activity pattern of suprofen was consistent with that of a very potent, short-acting inhibitor of prostaglandin biosynthesis, which maintains its specific action over a wide dose range. It is concluded that delay of castor oil-induced diarrhoea in rats allows a detailed characterization of aspirin-like compounds, and that inhibition of prostaglandin biosynthesis is insufficient to suppress the intestinal effects of the oil.

Oxatomide, a new orally active drug which inhibits both the release and the effects of allergic mediators.

Oxatomide is a new potent inhibitor of anaphylactic and allergic reactions. After oral administration, the compound both inhibits the release of endogenous histamine and prevents the effects of exogensous histamine, at comparable doses. The combination of these effects appears to be the basis of the effectiveness of oxatomide in allergic reactions and may lead to clinical application different from classical antihistaminics and from cromoglycate.

Interaction of drugs with apomorphine, tryptamine and norepinephrine. A new 'in vivo' approach: the ATN-test in rats.

A new experimental test procedure is described for the 'in vivo' study of drug interactions with dopamine (DA), 5 hydroxy-tryptamine (5-HT) and norepinephrine (NE). The ultimate aim of this study is to provide an empirical evaluation of the relative specificity with which drugs may affect particular neurotransmitter systems, and to allow a classification of new drugs in this respect. The data indicate that, within certain dosage limits, compounds may modulate specifically a single component of the test procedure and may thus be considered as interacting specifically to modify one neurotransmitter system: i.e. DA in the apomorphine-test (e.g. pimozide), 5-HT in the tryptamine-test (e.g. pizotifen) and NE in the norepinephrine-test (e.g. phenoxy-benzamine). Higher doses of the same compounds may, however, excert effects on other neurotransmitter systems as well, and these actions may be classified as nonspecific. Thus the concept of drug specificity as applied in the present study, is not exclusive, but refers to the dissociation, in terms of doses, which exists between a drug's effect on one neurotransmitter system and its possible effects on other systems. The ATN-test separates and delineates, in terms of doses, the specific and nonspecific effects of drugs.

A new apparatus for measuring diameter changes of the rat paw and tibiotarsal joint.

A new apparatus for the study of hind-limb inflammation in the rat is described. It measures with high precision the diameters of the hind paws and tibiotarsal joints at anatomically well defined reference points. Inflammation induced by subplantar carrageenin injection and by inoculation of adjuvant in the tail is accompanied by readily detectable and pronounced increases in diameters. Results obtained with this rapid and simple method are reliable and the method offers practical advantages over volume measurements.

The antipyretic effect of suprofen in rats with yeast-induced fever.

The antipyretic activity of alpha-methyl--4-(2-thienylcarbonyl)benzeneacetic acid (suprofen) was studied in rats with comparable hyperthermia after s.c. injection of brewer's yeast. The lowest dose effectively reducing fever is 5 mg/kg and restoration of normal body temperature is obtained with 40 mg/kg. Hypothermia is not observed even after treatment with 160 mg/kg. The ED50 (with confidence limits), which reduces fever below 39 degrees C in 50% of the animals, at the time of peak hyperthermia is 10.0 (6.6--15.2) mg/kg. ED50's of simultaneously studied reference compounds are 5.7 (3.9--8.3) mg/kg for indometacin, 38 (24--61) mg/kg for tolmetin, 76 (47--121) mg/kg for phenylburazone and 113 (75--170) mg/kg for acetyl-salicylic acid. Two to four times higher doses of these compounds restore normal body temperature but further increase of the dose induces hypothermia, which is particularly pronounced for acetyl-salicylic acid and phenylbutazone. Suprofen is a potent antipyretic agent, devoid of hypothermic activity even at 32 times the lowest effective dose.

The activity of suprofen on nystatin-induced paw oedema in rats.

Subplantar injection of nystatin into the rat paw induces acute paw oedema of long duration. In this test the anti-inflammatory activity of alpha-methyl-4-(2-thienylcarbonyl)benzeneacetic acid (suprofen) has been studied using doses from 1.25 up to 160 mg/kg. The lowest dose significantly reducing paw diameter increases was 2.5 mg/kg; more intense and longer lasting reductions appeared progressively with increasing doses. The dose producing 50% inhibition of diameter increase was 2.70 mg/kg 1 h and 1.5 h after administration (lowest ED50). Comparative lowest ED50-values for simultaneously tested reference compounds were 6.2 mg/kg for indometacin, 34 mg/kg for phenylbutazone and 38 mg/kg for acetyl-salicylic acid. Within the first 2 h after administration suprofen exhibited anti-inflammatory activity from 2 to 14 times as potent as did the reference compounds.

The effects of suprofen in rats with Mycobacterium butyricum-induced arthritis.

The activity of alpha-methyl-4-(2-thienylcarbonyl)benzeneacetic acid (suprofen) was studied in rats with established Mycobacterium butyricum-induced arthritis. The arthritic response was evaluated by measuring the diameter changes of the hind paws and tibiotarsal joints, using a new apparatus. Treatment once daily by gavage during 14 days revealed activity at the dose of 1.25 mg/kg and above. The lowest ED50 was 6.2 mg/kg. In comparison with simultaneously studied reference compounds, this corresponded approximately to the activity of phenylbutazone. In the higher dose range, 10 to 40 mg/kg, the reduction of external arthritic symptoms was associated with marked reversal of multiple bone deformations. A treatment schedule with 4 administrations of 2.5 mg/kg/day was significantly more effective than a single daily administration of 10 mg/kg and comparable to that of 10 mg/kg once daily. Mixing of suprofen with the diet, to give the low daily dose of 1.28 mg/kg confirmed the high activity expected from the maintenance of a practically constant compound level in the treated rats. In a comparative study involving suprofen, acetyl-salicylic acid, indometacin, phenylbutazone and tolmetin, all administered over 14 days with the diet in a dose range up to toxic dose levels, dose-related anti-inflammatory and toxic effects were obtained. The potency order and ED50's of the compounds were: indometacin (0.31 mg/kg) greater than suprofen (1.48) greater than tolmetin (18.0) = phenylbutazone (18.2) greater than acetyl-salicylic acid (440). Suprofen had by far the largest safety margin (48), followed by phenylbutazone (20), tolmetin (16), indometacin (8) and acetyl-salicylic acid (2). In conclusion, three major symptoms of adjuvant arthritis: joint inflammation, impaired growth and bone erosion, were markedly reduced by different doses of suprofen, which revealed to be a safe compound when compared to several reference compounds.

Gastrointestinal effects and acute toxicity of suprofen.

The acute effects of orally administered, high doses of alpha-methyl-4-(2-thienylcarbonyl)benzeneacetic acid (suprofen) were studied in various tests, related to gastrointestinal functions. A decrease of the diarrheal stools in the castor oil test in rats was the first effect noted; the ED50 in this test was 40 mg/kg. This dose is 540 times higher than the ED50 of suprofen in the acetic acid-induced writhing test in rats (ED50 = 0.074 mg/kg). Temporarily decreased food consumption in rats was first noted after administration of 80 mg/kg. This is more than 1000 times the ED50 in the rat anti-writhing test. The appearance of gastrointestinal lesions was also studied in rats and a direct quantitative comparison was made with indometacin, acetyl-salicylic acid and ketoprofen. The dose of suprofen that produced lesions in 50% of the rats was 200 mg/kg, viz. 2700 times the ED50 in the rat anti-writhing test. Similarly obtained safety margins are 9.0 for indometacin, 78 for acetyl-salicylic acid and 102 for ketoprofen. The mortality after a single oral administration of suprofen was studied in mice, rats, guinea-pigs and dogs. LD50-values, based on mortality 7 days after administration, were 590 mg/kg, 353 mg/kg, 280 mg/kg and more than 160 mg/kg, respectively. Comparative LD50's in mice and rats were 14 and 19 mg/kg for indometacin, 280 and 70 mg/kg for ketoprofen. Therefore the safety margin in rats, with respect to the ED50 in the acetic acid-induced writhing test, is 4770 for suprofen, 156 for ketoprofen and 17.3 for indometacin. In guinea-pigs the safety margin of suprofen is 1470 with respect to the ED50 in UV-erythema and in dogs more than 250 with respect to the ED50 in urate-induced arthritis. From these data we may conclude that suprofen is comparatively safer than the reference compounds studied and that its effects on the gastrointestinal tract appear at doses far above those required for effectiveness in tests related to pain, fever and inflammation.

Clopimozide (R 29 764), a new highly potent and orally long-acting neuroleptic of the diphenylbutylpiperidine series.

Clopimozide (R 29 764), 5-chloro-1-(4-[4,4-bis(p-fluorophenyl)butyl]-4-piperidyl)-2-benzimidazolinone, is a new member of the potent and long-acting series of diphenylbutylpiperidine neuroleptics of which pimozide is the prototype, In animals the pharmacological profile of R 29 764 resembles that of typical neuroleptic compounds. R29 764 is very potent by oral route and has an extremely long duration of action. The onset of action of clopimozide is relatively fast, it is already very potent after 4 h and, in the procedures described, reaches its peak effect 24 h after administration. In spite of the high potency and long duration of action clopimozide is relatively atoxic. The safety margin, calculated as the ratio between the acute LD50 value and the lowest ED50 value is larger than or equal to 15.000 in rats and greater than 7.250 in dogs. Qualitatively, R 29 764 is more closely related to haloperidol, pimozide and penfluridol than to chlorpromazine. The side effect liability is expected to be very low, when hypotensive, autonomic and undesirable neurological side effects are concerned.

A critical study on RO-4-1284 antagonism in mice.

Ro-4-1284 is found to produce ptosis, hypothermia, sedation and miosis in mice, and the antagonsim to these symptoms is investigated. The study reports the differential effects of various pharmacologically distinct classes of compounds. The relevance of this type of experiments to possible antidepressant drug activity is discussed.