Target sites for anticholinesterases on the ventral surface of the medulla oblongata: hypotension elicited by organophosphorus agents.

Sensitivity of the ventral surface of the medulla oblongata to organophosphorus agents, oxime reactivators, and muscarinic antagonists was examined in order to delineate sites of cholinergic activity in the central nervous system. The exposed ventral surface of the medulla oblongata in anaesthetized cats was treated with the organophosphorus anticholinesterase agents soman and (7-nitro-2-oxa-1,3-diazole) aminopentyl methylphosphonofluoridate (NBD-AP-MFP), a fluorescent active centre-selective probe of acetylcholinesterase. Topical application of soman (1-5 micrograms) or NBD-AP-MPF (5-120 micrograms) elicited a profound (80-90 mm Hg), long-lasting (0.5-3 h), dose-dependent vasodepression with only minor changes in heart rate and respiration. The vasodepression was rapidly reversed (7-10 min) upon topical application of muscarinic antagonists (atropine methylnitrate, atropine sulphate) and the bisquaternary oxime HI-6; systemic administration was without effect. Reversal of the hypotension by HI-6 occurred irrespective of whether the organophosphorus agent was NBD-AP-MPF, which forms conjugates with acetylcholinesterase that undergo no aging, or soman, which forms conjugates that undergo extensive aging rendering the enzyme refractory to oxime reactivation. Hence, oxime efficacy for reversal of the physiologic hypotension was not dependent solely on the fraction reactivatable enzyme. By virtue of the fluorescence distribution of NBD-AP-MPF the chemosensitive sites were estimated to reside no deeper than 50 microns into the medulla oblongata, providing a direct indication for localization of the chemosensitive cells on the superficial surface.

Yohimbine antagonism of the vasodepression elicited by organophosphates applied on ventral medulla oblongata.

The rostral ventral surface of medulla oblongata (RVMO) has been shown to constitute a selective target for organophosphate (op) cholinesterase inhibitors. The action of soman (S) as compared with (7-nitrobenz-2-oxa-1,3 diazole)aminopentyl methylphosphonofluoridate (NBD-AP-MPF), a fluorescent organophosphate has now been examined in anesthetized cats pretreated with atropine sulphate. Blood pressure (BP), electrocardiogram (ECG) and respiration (R) were recorded. In some animals a cannula was implanted into the right lateral ventricle. Chemicals were bilaterally applied on RVMO by means of a perspex cannula and removed after 5 min. The application of 2.5 micrograms S or 60 micrograms NBD-AP-MPF elicited severe fall of BP which recovered only after 2 h in the case of the former and up to 45 min in the latter. Smaller doses produced corresponding responses of lesser magnitude. Accompanying R changes consisted in most cases of increased rate and reduced amplitude whereas in others the opposite or mixed alterations occurred. Frequently, sigh-like movements intermingled at periodic intervals with regular R deflections. The sighs were interpreted as aiming to correct blood gases balance. After application of atropine on RVMO--but not by systemic administration--BP and R were restored whereas single repeated i.v. injection of 1 microgram/kg noradrenaline produced only transient reversals without influencing the course of long lasting vasodepression. In contrast, the intraventricular administration of 250-500 micrograms yohimbine considerably reduced both the magnitude and extent of the vasodepression elicited by topically applied organophosphates. It is postulated that central alpha 2-adrenoceptors in contrast to vascular sites are likely involved in the op-induced vasodepression. The present work provides an indication that effective antagonists might be developed considering blockade of these receptors.

Ciliary motility in brain ventricular system and trachea of hamsters.

Ciliary beat frequency (CBF) in various parts of brain ventricular system, as well as in trachea of hamsters, was examined. Coronal sections of brain and tracheal rings were maintained in a thermostatically controlled perfusion chamber and CBF measured by a photoelectric system equipped with a fiber-optic probe. CBF (Hz) values of lateral ventricle, aqueduct and fourth ventricle were 27.9 +/- 4.6; 30.7 +/- 7.7 and 31.9 +/- 7.8 Hz, respectively. CBF in the third ventricle--19.8 +/- 7.1 Hz--was significantly lower than in other segments of ventricular system. CBF in choroid plexus cilia was very slow, 5-10 Hz, whereas in tracheal rings amounted to 13.7 +/- 3.1 Hz. Bovine cervical mucus and mucus stimulant reversibly inhibited CBF in brain but not in trachea. Brain cilia in contrast to those in trachea were not capable of transporting particles. In addition to demonstrating differences between tracheal and ependymal cilia, this work suggests that cilial motility plays a functional role in local mixing of cerebrospinal fluid, but does not relate to the bulk flow within the ventricular system.

Activity of novel aminocannabinoids in baboons.

The axial and equatorial isomers of 7-(methylamino)hexahydrocannabinol (1 and 2) and 7-(dimethylamino)hexahydrocannabinol (3 and 4) were prepared by reductive amination of the corresponding cannabinoid aldehydes. The amines caused some tranquility in baboons but did not evoke the typical cannabimimetic syndrome caused by psychoactive cannabinoids. However the axial amines (1 and 3) but not the equatorial ones (2 and 4) caused bouts of scratching and yawning. The latter is a rare pharmacological effect hitherto not observed with other cannabinoids.

Disposition of phencyclidine after intramuscular administration.

The disposition of radioactive phencyclidine (PCP) in various rat tissues, after single or repeated intramuscular injections for 23 days, have been investigated. Peak levels of radioactivity appeared 45-90 min after a single administration. The pancreas, salivary glands and mesenteric fat contained 4 to 6-fold higher radioactivity than brain, muscles, tendons, and bones. After repeated 3H-PCP injections, radioactivity levels showed a similar pattern as to that of the peak levels after a single administration, but at notably higher values. On the other hand, the percentage of depletion, within 48 h after the final injection, was the highest in the pancreas, salivary glands and mesenteric fat. It is possible that despite the low retention capacity of PCP radioactivity per unit weight of muscle, tendon and bone, they may be considered important reservoirs for either PCP, or its metabolites or both because of their large relative mass in the body.

Pyrenebutyl-methylphosphonofluoridate: a fluorescent anti-cholinesterase in vivo.

In vivo properties of pyrenebutyl-methylphosphonofluoridate (PBMPF) have been studied. The LD50 (i.v.) for mice was 15 mg/kg and toxic symptoms were typical of cholinesterase (ChE) inhibition but central signs were absent. After intraventricular injection of PBPMPF in unanaesthetized rabbits, continued walking in bizarre circular fashion together with peripheral vascular dilation and tachypnoea were observed. Recovery occurred 3 h post-injection. Fluorescent particles of unabsorbed material juxtaposed on lining ependyma were observed up to 14 days of administration. In addition, a large number of hippocampal cells showed vivid fluorescence, particularly in the cytoplasm, which was attributed to ChE inhibition. It is concluded that PBMPF seems promising as an organophosphate marker of nerve cells.

Models to predict cannabinoid-induced disturbances.

The most commonly used animal models to evaluate the psychoactivity of cannabinoids have been reviewed. The need for suitable models is acute considering the present interest to develop drugs based on the cannabinoid moiety but preferably dissociated from psychoactivity. Conceivably, a satisfactory assay should show features of cannabinoid-induced disturbances relevant to man as well as sensitivity, specificity and simplicity. These requisites seemed better fulfilled in the monkey model. Various lines of evidence have demonstrated the close pattern of the behavioural response to psychoactive and inactive cannabinoids in man and monkeys. Rhesus monkeys showed development of tolerance and withdrawal symptoms, which have been frequently reported in humans after prolonged exposure to cannabinoids. The exposure was reported also to cause in monkeys alterations of electrical activity and organic damage in deep brain structures. The monkey model has been particularly useful to determine the relative potency of naturally occurring cannabinoids and metabolites, which was adequately compared to that in man, and to establish the structural requirements for psychoactivity in large series of synthetic new compounds. In addition it appeared that rhesus monkeys react similarly to man with respect to proposed antidotes against cannabinoids. Four newly synthetized amino-cannabinoids were tested in baboons. All these compounds were virtually void of typical cannabinoid psychoactivity but two trans-analogs differed from the cis-analogs in that they provoked bouts of vigorous scratching and yawning. This unusual drug-effect, at difference from scratching alone has not been previously observed after administration of cannabinoids. In this presentation some terms of cannabis terminology have been discussed.

Involvement of the kidney in catabolism of human leukocyte interferon.

The metabolic fate of human leukocyte interferon (HuIFN-alpha) was studied after intravenous injection into rats and cynomolgus monkeys. At various intervals the animals were sacrificed and the HuIFN-alpha content determined in serum and various tissues. HuIFN-alpha quickly disappeared from the circulation and was found mainly in the kidneys, in which levels were at least 7- to 10-fold higher than in the liver, spleen, lungs, heart, brain and muscles. No interferon was detected in urine. Subcellular fractionation of kidney revealed that the mitochondrial-lysosomal fraction (15 000 g) had a high HuIFN-alpha content. It was also found that HuIFN-alpha was rapidly inactivated by two types of proteinases found in the lysosomal fractions of rat, monkey and human kidneys, with an optimal pH of 3 to 4. The inactivation was partially inhibited by either pepstatin or leupeptin. Inactivation was totally prevented by a mixture of both inhibitors. Since it is known that interferon is scantily excreted in urine, our findings suggest that the kidney serves as a main site for its degradation.

Stereochemical requirements for cannabinoid activity.

Several pairs of cannabinoid isomers were synthesized and tested for psychotropic activity in rhesus monkeys. Two regularities were observed: (a) In the absence of the other substituents, the equatorial stereochemistry of the substituent at C-1 determines activity. (b) Two groups of THC-type cannabinoids which differ only in that the chemical groupings in one of them at C-1, C-2 are situated at C-1, C-6 in the other (but retain their stereochemistry) have almost equivalent psychotropic activity.

Blood kinin system in renal hypertensive patients administered with SQ 20881.

The i.v. administration of 0.25 mg/kg SQ 20881 to eight renal hypertensive patients caused blood pressure fall and in five of them also reduced heart rate. The latter was attributed to increase in vagal tone. Peripheral and renal blood samples taken at the nadir of the hypotensive response showed considerable inhibition of plasma kininase activity, rise in free kinin level and reduced kininogen content. This reduction was not due to increased consumption as shown by in vitro experiments. PGE2 and PGF2 alpha levels in kidney blood of three patients remained practically unchanged. Plasma renin activity was augmented to a larger extent in blood of kidney with stenotic artery than in the one with patent vessel. It is concluded that the action of SQ 20881 on human blood kinin system, besides inhibition of kininase, involves also reduction of kininogen, the mechanism of which remains to be clarified.

Sugar-oximes, new potential antidotes against organophosphorus poisoning.

In attempt to improve distribution and transport qualities of antidotes against organophosphorus poisoning, a new series of pyridine aldoximes linked to glucose moiety were synthesized and studied both in vivo and in vitro. Preliminary results describing the biological activity of the new compounds are presented and discussed in this report.

Administration of obidoxime tablets to man. Plasma levels and side reactions.

Twenty-four male volunteers were given obidoxime tablets in quantities ranging from 1.84-3.58 g in a single dose, or 7.36 g divided into 4 equal doses. With the lowest dose, average peak plasma level of the drug was 1.9 mug/ml and after the highest single dose it was 5.6 mug/ml, both attained 1.5 h after administration. In the multiple-dosed individuals, plasma levels of the oxime increased gradually following each additional dose, reaching a peak of 3.5 mug/ml after the last dose. Thirteen individuals complained of one or more of the following side effects: pallor, nausea, pyrosis, headache, generalized weakness, sore throat, and paresthesia of the face muscles. Activities of blood cholinesterase, glutamic oxalacetic transaminase, glutamic pyruvic transaminase, as well as hematocrit values, heart rate, and blood pressure were not affected. It is postulated that due to the undesirable side effects, the general use of obidoxime tablets should not be recommended. However, prophylactic oral treatment with obidoxime could be considered for persons at high risk of organophosphate poisoning or when parenteral administration might not be feasible.

An improved preparation for determination of bradykinin.

The cat isolated jejunum kept either in an organ-bath or under superfusion can be rendered extremely sensitive to bradykinin after exposure to chymotrypsin. Treated preparations responded to as little as 100 pg/ml of the peptide. Use has been made of sensitized preparations to determine bradykinin-like material of dog blood extracts obtained in experimental "dumping syndrome".