Effects of intrathecal or intracerebroventricular pretreatment with pertussis toxin on antinociception induced by β-endorphin or morphine administered intracerebroventricularly in mice

We have previously demonstrated that -endorphin and morphine, when administered supraspinally, produce antinociception by activating different descending pain inhibitory systems in both rats and mice. However, the signal transduction mechanisms involved in the descending pain-inhibitory systems that are activated by -endorphin and morphine administered intracerebroventricularly (i.c.v.) have not been characterized. Therefore, in the present study, the effects of intrathecal (i.t.) and i.c.v. pretreatments with pertussis toxin (PTX) on antinociception induced by -endorphin or by morphine administered i.c.v. were studied in ICR mice. Antinociception was assessed by the tail-flick assay and by the hotplate assay. Intrathecal pretreatment with PTX (0.5 g) for 6 days effectively reduced the inhibition of the tail-flick response induced by -endorphin (1 g) or by morphine (1 g) administered i.c.v. However, i.t. pretreatment with PTX was not effective in reducing the inhibition of the hot-plate response induced by -endorphin or by morphine administered i.c.v. Intracerebroventricular pretreatment with PTX (0.5 g) for 6 days effectively reduced the inhibition of the tail-flick and hot-plate responses induced by morphine (1 g), but not that induced by -endorphin (1 g), administered i.cv. Our results suggest that there are PTX-sensitive G proteins coupled to the spinal descending pain inhibitory systems that are activated by -endorphin and morphine administered i.c.v. At a supraspinal level, i.cv. morphine- but not -endorphin-induced antinociception is mediated by PTX-sensitive G proteins. Correspondence to: Hong W. Suh at the above address     

A comparison of the analgetic potency of some analgesics as measured by the “flinch-jump” procedure

Summary The effects of various doses of morphine, dl-methadone, nalorphine, codeine, meperidine and saline on the flinch-jump thresholds of rats were measured by a procedure described previously. While none of the drugs influenced the flinch threshold, the group slopes of elevation of jump thresholds were significant for all drugs studied. In order of potency as revealed by this method, nalorphine ranked with morphine and methadone, while codeine and meperidine were less potent, suggesting that the procedure may be useful as a screening test for analgesic drugs.     

Some factors controlling oral morphine intake in rats

Rats were given the opportunity to drink morphine solution following stabilization at three levels of passive premedication. Compared to saline treated controls, premedicated rats consumed more morphine solution, but medication level did not significantly affect morphine intake. Premedicated rats adjusted to a reduction in morphine solution concentration by increasing fluid intake substantially, but nonpremedicated rats did not. When morphine was offered in a vehicle of isotonic saline oral consumption rose sharply in premedicated rats but not in their nonpremedicated counterparts. Drinker and nondrinker rats were identified on the basis of initial response to oral morphine. Premedication eliminated resistance to morphine drinking, but even at the expense of severe fluid deprivation, nonpremedicated nondrinkers refused morphine throughout the entire experiment.     

The effects of dexamphetamine on simulated driving performance

Rationale The number of road fatalities related to the presence of amphetamines in drivers has been relatively constant over the past 10 years. However, there remains uncertainty as to the extent that these drugs induce driving impairment, and whether any such impairments translate to an increase in road fatalities.Objectives To examine the acute effects of 0.42 mg/kg dexamphetamine on simulated driving performance, and to establish which, if any, simulated driving abilities become impaired following dexamphetamine administration.Methods A repeated-measures, counter-balanced, double-blind, placebo-controlled design was employed. Twenty healthy volunteers completed two treatment conditions—0.42 mg/kg dexamphetamine and placebo. Performance was assessed using a driving simulator task. Blood and saliva samples were obtained prior to the driving tasks and immediately after task completion (120 min and 170 min post-drug administration, respectively).Results Mean dexamphetamine blood concentrations were 83 ng/ml and 98 ng/ml at 120 min and 170 min, respectively. Results indicated a decrease in overall simulated driving ability following dexamphetamine administration during the day-time but not the night-time scenario tasks. Contributing to this performance reduction, incorrect signalling, failing to stop at a red traffic light and slow reaction times were the behaviours most strongly affected by dexamphetamine.Conclusions The decrease in simulated driving ability observed during the day-time driving tasks are consistent with the perceptual narrowing or tunnel vision that is associated with dexamphetamine consumption.     

Periaqueductal gray matter involvement in the muscimol-induced decrease of morphine antinociception

Summary Microinjections of muscimol, a GABA receptor agonist, into the periaqueductal gray matter (PAG) counteracted the antinociceptive effect of morphine in rats, as measured by the tail-flick method. Muscimol's effect was partially reversed by bicuculline.     

Morphine attenuates ultrasonic vocalization during agonistic encounters in adult male rats

Ultrasonic vocalizations (USV) in rats may communicate affective states during pain, sex and aggression. This proposal was evaluated in an experiment with adult male Long-Evans rats during agonistic encounters; specifically, morphine and naltrexone effects were studied on different types of USV by intruder rats exposed to resident attacks and to threat of attacks (i.e., intruder residing within the home cage of the resident but prevented from physical contact by a wire mesh cage). Intruders readily emitted USV during agonistic encounters. These calls consisted primarily of two distinct distributions of pure tone whistles: 0.3–3 s, 19–32 kHz (low) calls and 0.02–0.3 s, 32–64 kHz (high) calls. Sonographic analysis revealed a considerable repertoire of frequency modulated calls. Different types of vocalizations proved to be differentially sensitive to the opiate treatments: morphine (1–10 mg/kg SC) dose-dependently decreased the rate, duration and pitch of both low and high frequency USV during the threat of attack; this decrease in rate and duration measures was naltrexone-reversible (0.1 mg/kg IP). Interestingly, audible vocalizations were also emitted but were unaffected by morphine in this dose range. Concomitant with the decrease in USV after morphine was a dose-dependent decrease in rearing, walking and nasal contact behavior with increases in submissive crouch behavior and tail flick analgesia. The decreases in rate and duration of both low and high USV and the pitch of specific frequency modulated calls after morphine administration may reflect an attenuation of affective aspects of pain, and the many characteristics of US (rate, duration, pitch, frequency modulation, pre-and suffix attributes and temporal structure) point to potentially diverse functions. Morphine's pervasive effects on ultrasonic but not audible vocalizations, in addition to reflexive and submissive responses, provides evidence for opioid influences on affective as well as somatomotor responses to socially aversive situations.     

Characterization of the discriminative stimulus effects of centrally administered morphine in the rat

The discriminative stimulus effects of centrally administered morphine were characterized in rats trained to discriminate 3.0 mg/kg SC morphine from saline in a two-choice discrete-trial avoidance paradigm. The intracerebroventricular (ICV) administration of 0.3–10 g morphine engendered morphine-appropriate responding, morphine administered ICV being nearly 1000 times as potent as morphine administered SC. Cannula implantation itself did not affect the sensitivity of the rats to the discriminative effects of morphine. The onset of the discriminative stimulus effects of ICV morphine was not immediate; stimulus generalization comparable to that produced by 3.0 mg/kg morphine occurred 30–60 min after the injection of 1.0 or 10 g ICV morphine and persisted for 90 and 150 min, respectively. Naltrexone blocked the discriminative stimulus effects of 10 g ICV morphine in a dose-related manner. Complete antagonism of the stimulus effects of this dose of morphine was obtained with 0.01–0.03 mg/kg SC naltrexone. When administered centrally, the relatively lipid insoluble naltrexone methobromide completely antagonized the discriminative effects of 3.0 mg/kg morphine at a median effective dose of 0.3 g. In contrast, when injected systemically at a dose of 1.0 mg/kg (approximately 500 g), naltrexone methobromide failed to block the discriminative stimulus effects of either 10 g ICV morphine or the SC training dose. Thus, periventricular brain sites appear to be involved in mediating the discriminative stimulus effects of morphine in the rat.     

Beeinflussung der analgetischen Wirkung des Morphins durch Reserpin und Thiopropazat

Zusammenfassung Es wurde die Beeinflussung der Wirkungen von Morphin durch Thiopropazat und Reserpin an der Maus in verschiedenen Versuchsanordnungen verglichen.1. Thiopropazat verstärkte die analgetische Wirkung des Morphins an der Heißen Platte und bei mechanischer Reizung der Schwanzwurzel. Diese Wirkungskomponente war nach 30 min bereits optimal ausgeprägt und kann zu den Tests auf Sedation im Sinne von Courvoisier (1957) gerechnet werden.2. Thiopropazat antagonisierte die Hemmung eines polysynaptischen Reflexes (Wegziehen einer Hinterpfote bei Wärmereiz) durch Morphin. Diese Wirkungskomponente trat erst im Verlauf von 2 Std ein und ist ihrem Mechanismus nach der Katalepsie bei der Ratte vergleichbar.3. Reserpin schwächte die Wirkung von Morphin in allen Versuchsanordnungen ab. Seine sedierende Wirkung bei Mensch und Tier ist wahrscheinlich nicht mit der von Chlorpromazin zu vergleichen.

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Summary In mice, the influence of thiopropazate and reserpine upon the effects of morphine was compared in several tests.1. Thiopropazate enhanced the analgesic effect of morphine on the hot plate and on mechanical stimulation of the root of the tail. This component was optimally developped 30 min after the injection of thiopropazate and can be regarded as a test for sedation according to the definition of Courvoisier (1957).2. Thiopropazate antagonized the inhibition of a polysynaptic reflex (withdrawal of a hind foot upon irradiation) by morphine. This component could be demonstrated after 2 hours and is probably brought about by the same mechanism as the catatonia in rats.3. Reserpine inhibited the effects of morphine in all tests. Its sedative action in man and beast is probably not comparable to that of chlorpromazine.

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Herrn Prof. Dr. O. Schaumann, Innsbruck, zum 70. Geburtstag gewidmet.     

Stabilizing and Solubilizing Effects of Sulfobutyl Ether β-Cyclodextrin on Prostaglandin E1 Analogue

Purpose. Parent cyclodextrins are known to accelerate the degradations such as dehydration and isomerization of E-type prostaglandins in neutral and alkaline solutions. The objective of this study was to attempt the stabilization and solubilization of E₁-type prostaglandin analogue in aqueous solution by biocompatible cyclodextrin derivatives. Methods. The interaction of an E₁-type prostaglandin, methyl 7-[(1R,2R,3R)-3-hydroxy-2-[(E)-(3S)-3-hydroxy-4-(m-methoxymethylphenyl)1-butenyl]-5-oxocyclopentyl]-5-thiaheptanoate (MEester) with cyclodextrins (CyDs) was studied by spectroscopies and the solubility method. The degradation of MEester was monitored by high-performance liquid chromatography. Results. ¹H-nuclear magnetic resonance spectroscopic studies indicated that MEester forms 1:1 inclusion complexes with -, -, and -CyDs in solutions, where -CyD interacts with the -side chain containing methyl ester moiety of the drug, whereas - and -CyDs preferentially include around the five-membered ring and both side chains of the drug. Parent -CyD and hydrophilic derivatives, such as 2-hydoxypropyl-- and --CyDs, sulfobutyl ether -CyD (SBE--CyD) and maltosyl -CyD showed higher solubilizing abilities against MEester over parent - and -CyDs. SBE--CyD and 2,6-dimethyl--CyD (DM--CyD) significantly decelerated the degradation of MEester, particularly the base-catalyzed dehydration, in neutral and alkaline solutions, whereas other CyDs accelerated the degradation. The acid-catalyzed degradation of MEester (pH < 3) was decelerated by the addition of CyDs, especially -CyD. Conclusions. SBE--CyD with low hemolytic activity and low toxicity is useful as a pharmaceutical carrier for the preparation of injectable MEester, because of its higher stabilizing and solubilizing effects on MEester. Furthermore, SBE--CyD can be useful as a stabilizing agent for drugs, that are subject to base-catalyzed degradations, probably because of the electric repulsion between anionic charges of the sulfobutyl moiety and catalytic anionic species such as hydroxide ion.     

Cocaine-induced cocaine craving

In nine experienced users of cocaine, we examined the urge to use cocaine or other drugs following a 40 mg dose of intravenous (IV) cocaine with and without oral pretreatment with 2.5 mg bromocriptine. The urge to use cocaine was assessed with a questionnaire constructed to assess both wanting and craving for cocaine or other drugs. Fifteen minutes after the administration of cocaine (but not after placebo), subjects' ratings for both drug wanting and drug craving were significantly increased. Our results provide a laboratory demonstration of cocaine-induced increases in the urge to use drugs in humans. The findings, stressing the role of internal stimuli associated with drug administration, suggest the possibility of distinguishing among related, but perhaps distinct, components of the fluctuating levels of motivation to reuse drugs.     

Anti-nociceptive effect of morphine,opioid analgesics and haloperidol injected into the caudate nucleus of the rat

Summary The effect of intracaudate (i.c.) microinjections of morphine, opioid analgesics and haloperidol was determined on the tail-flick response evoked by radiant heat in rats. Bilateral injections (0.2 l on each side) into the caudate nuclei of morphine 5 g, pethidine 50 g, levorphanol 4 g, dextrorphan 10 g and haloperidol 5 g significantly increased the reaction time of the tail-flick response. The antinociceptive effect of an i.c. injection of morphine or levorphanol was abolished by an intraperitoneal (i.p.) injection of naloxone 0.2 mg/kg or apomorphine 2 mg/kg. The anti-nociceptive effect of pethidine, dextrorphan and haloperidol was reduced but not abolished by an i.p. injection of naloxone 0.2 mg/kg. An i.p. injection of apomorphine 2 mg/kg abolished the effect of an i.c. injection of haloperidol. A bilateral i.c. injection of naloxone 5 g or apomorphine 10 g reduced the anti-nociceptive effect of an i.p. injection of morphine 2 mg/kg or haloperidol 2 mg/kg, but did not abolish it. It is concluded that (1) an anti-nociceptive effect can be achieved by an action on the caudate nucleus of the drugs tested; (2) the anti-nociceptive effect exerted by morphine and levorphanol in the caudate nucleus is due to a specific action mediated by opiate receptors, whilst that produced by pethidine and dextrorphan is due to a specific and/or unspecific action; (3) the anti-nociceptive effect of haloperidol in the caudate nucleus is due to an impairment of dopaminergic impulse transmission, which is also involved in the effect of morphine and levorphanol.Supported by the Sonderforschungsbereich 38 Membranforschung     

The influence of learning on morphine analgesia and tolerance development in rats tested on the hot plate

The influence of learning on the development of tolerance to the analgesic effect of morphine in rats was examined employing the hot plate procedure. A tested-reinforced (Tr) group and its yoked-control, a tested-non-reinforced (Tnr) group, received identical exposure to the testing procedure; the Tr group was reinforced daily for its behavior on the heated plate whereas the Tnr group was reinforced only on the last day of the experiment. Paired statistical comparisons between these two groups on the last day of the experiment revealed that: 1. premorphine control reaction times on the heated plate were significantly lower in Tr than in Tnr animals; and 2. post-morphine increases in reaction time did not differ between Tr and Tnr animals. It was concluded that whereas some learning does occur in this testing procedure, learning does not influence the behavioral tolerance to morphine which develops in this analgesiometric method. An hypothesis which accommodates this behavioral tolerance and a mechanistic scheme is offered.     

Potentiation of catalepsy induced by narcotic agents during Haffner's test for analgesia

Potentiation of morphine catalepsy in the mouse during Haffner's (tail-clip) test for analgesia has been investigated. Very marked potentiation occurred in the presence of the clip. Both native and clip catalepsy were antagonised by nalorphine. Atropine antagonised morphine native catalepsy in a dose-dependent fashion, but produced a parallel increase in both analgesia and clip catalepsy at higher doses. Haloperidol catalepsy was abolished in the presence of the clip but reappeared on its removal. It is suggested that morphine must have at least two sites of action in producing catalepsy to account for these results.     

Behavioural effects of selective μ-, κ-, and δ-opioid agonists in neonatal rats

The behavioural effects of selective -, - and -opioid agonists in 5-, 10- and 20-day-old rats were investigated by observational analysis. The predominant response to -agonists was behavioural depression. High doses (10 mg/kg IP) of morphine and DAGO (d-Ala², NMe-Phe⁴, Glyol⁵-enkephalin) produced overt sedation in all the age groups and also induced catalepsy which was particularly apparent in the 5- and 10-day-old animals. These compounds did not produce any signs of behavioural activation in the neonatal rats. In contrast, rat pups treated with the -agonists U50,488H and PD 117,302 (1,10 mg/kg IP) exhibited marked hyperactivity with increases in wall-climbing and locomotion. Sedative effects of the highest dose of the -agonists began to emerge, however, as the animals grew older, resulting in significant decreases in behaviours such as gnawing and grooming at 20 days of age. The -agonist (+)-tifluadom (0.1–10 mg/kg), but not its corresponding (-)-isomer, produced an increase in activity in 5-day-old rats, thus extending the observations made with U50,488H and PD 117,302 and establishing the stereoselective nature of the response. The involvement of -receptors in opioid-induced hyperactivity was further substantiated by using a variety of opioid antagonists. In this context, the increase in activity induced by U50,488H (10 mg/kg) in 5-day-old neonates was attenuated by naltrexone (1 mg/kg IP) but not by larger doses (10 mg/kg) of either M8008 (which has low affinity for -receptors) or the selective -receptor antagonist ICI 174,864. Finally, DPDPE (d-Pen², d-Pen⁵-enkephalin) which acts selectively at -opioid receptors, did not exert any behavioural effects in either the 5-, 10- or 20-day-old rat pups at doses of up to 10 mg/kg. These results demonstrate behavioural effects of - and -but not -agonists in neonatal rats. There is a clear differentiation between - and -receptor effects and both - and -mediated behaviours show dissimilarities from the adult profile.     

Differential modulation by muscimol and baclofen on antinociception induced by morphine, β-endorphin,d-Pen2,5-enkephalin and U50,488H administered intracerebroventricularly in the mouse

The present study was designed to investigate the modulatory effects of stimulation of GABA_A and GABA_B receptors at supraspinal sites on antinociception induced by supraspinally administered -, -, -, and -opioid receptor agonists. The effects of the GABA_A and GABA_B receptor agonists, muscimol and baclofen respectively, on the antinociception induced by morphine (a -receptor agonist), -endorphin (an -receptor agonist), D-Pen^2,5-enkephalin (DPDPE, a -receptor agonist) and U50,488H ({trans-3,4-di-chloroN-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl] benzeocetamide}; a -receptor agonist) injected intracerebroventricularly (i.c.v.) were studied. The anti-nociception was assayed using the tail-flick and hot-plate tests. Muscimol at doses of 25–200 ng, administered i.c.v. alone did not affect the latencies of tail-flick and hot-plate thresholds, but attenuated dose-dependently the inhibition of the tail-flick and hot-plate responses induced by i.c.v. administered morphine (2 g), -endorphin (1 g), DPDPE (10 g), and U50,488H (60 g). Baclofen (1.25–10 ng) administered i.c.v. alone did not affect the latencies of the tail-flick and hot-plate responses, but attenuated dose-dependently the inhibition of the tail-flick and hot-plate responses induced by -endorphin and U50,488H, without affecting morphine-or DPDPE-induced responses. Our results indicate that activation of GABA_A receptors at the supraspinal sites by i.c.v. injection of muscimol antagonizes antinociception induced by supraspinally administered -, -, -, and -opioid receptor agonists. On the other hand, activation of GABA_B receptors at supraspinal sites by i.c.v. baclofen antagonizes antinociception induced by i.c.v. administered - and -opioid agonists, but not - or -opioid agonists.     

Effects of depletion of brain catecholamines during the development of morphine dependence on precipitated withdrawal in rats

Summary The significance of long term depletion of brain catecholamines (CAs) for the development of morphine dependence and for the expression of morphine withdrawal was studied in rats which were implanted with morphine pellets for 10 days. CAs were depleted by inhibition of tyrosine-hydroxylase with alpha-methyl-tyrosine (AMT) or by destruction of catecholaminergic nerve terminals with 6-hydroxydopamine (6-OHDA). In the acute experiments these drugs were applied within 24 hrs before precipitation of withdrawal; in the chronic experiments drug administration was started before the first implantation and in the case of AMT, continued repeatedly thereafter.With either method, acute depletion of brain CAs resulted in reduced intensity of withdrawal. When CAs were kept low through the whole time of morphine exposure and also at the time of withdrawal, the intensity of withdrawal was normal in the case of 6-OHDA administration and only slightly decreased in the case of AMT. When AMT administration was discontinued 40 hrs before precipitation of withdrawal the withdrawal pattern occurred with unchanged intensity.Our experimental data are compatible with the assumption that long lasting depletion of brain CAs is compensated for by induction of neuronal supersensitivity for noradrenaline (NA) and dopamine (DA). While both CAs play an important role in the full expression of the withdrawal syndrome their possible involvement in mechanisms leading to dependence seems to be unlikely although final statements cannot be made by the presented experiments.     

Presynaptic dopamine DA2-receptors in rabbit jejunal arteries

Summary Excitatory junction potentials (e.j.ps) evoked by nerve stimulation with 15 pulses at 1 Hz were recorded from muscle cells of rabbit isolated jejunal arteries. LY 171555 1 mol/l, SKF 38393 10 mol/l, dopamine 10 ol/l and clonidine 0.1 mol/l depressed all e j.ps in the train. The percentage inhibition was inversely related to the number of pulses. S- and R-sulpiride, 10 mol/l, domperidone 1 mol/l, SCH 23390 1 mol/l and rauwolscine 1 mol/l did not change, or even depressed the first e j.ps. Of these compounds only S- and R-sulpiride, 10 mol/l and rauwolscine 1 mol/l facilitated the late e.j.ps. The percentage facilitation increased with the number of pulses until a maximum was reached; rauwolscine 1 ol/l had the largest effect. S- and R-sulpiride, 10 mol/l, as well as domperidone 1 ol/l antagonized the action of LY 171555 1 mol/l. S-Sulpiride was more potent than its R-isomer. SCH 23390 1 mol/l and rauwolscine 1 mol/l blunted the effect of SKF 38393 10 mol/l. Rauwolscine 1 mol/l slightly reduced the inhibition by dopamine 10 mol/l; S-sulpiride 10 mol/l was antagonistic only in the presence of rauwolscine 1 mol/l. When rauwolscine 1 mol/l, prazosin 0.1 mol/l, propranolol 1 mol/l and cocaine 10 mol/l was added to the medium, dopamine 10 mol/l continued to produce the same depression of e j.ps, as in the absence of these compounds. Under such conditions S-sulpiride 10 mol/l also counteracted dopamine 10 gmol/l. Rauwolscine 1 mol/l prevented the effect of clonidine 0.1 mol/l. The antagonists were not absolutely selective against only one type of agonist. We suggest that both presynaptic DA₂- and postsynaptic DA₁-receptors are present in rabbit jejunal arteries. The activation of either receptor-type may depress the e j.ps. Dopamine interferes with neuroeffector transmission due to ₂-adrenoceptor agonist properties; its DA₂-effect is unmasked only after ₂-adrenoceptor blockade. There was no evidence for a co-transmitter function of dopamine. Send offprint requests to P. Illes at the above address     

β-funaltrexamine antagonizes the discriminative stimulus effects of morphine but not naltrexone in pigeons

Antagonistic actions of the irreversible, -selective antagonist -funaltrexamine (-FNA) were evaluated in pigeons trained to discriminate among intramuscular injections of morphine (5.6 mg/kg), saline, and naltrexone (10.0 mg/kg). -FNA administered alone (1.0 or 10.0 mg/kg) failed to mimic the discriminative stimulus effects of morphine or naltrexone. -FNA attenuated the discriminative stimulus effects of morphine. A three-fold larger dose of morphine was required for complete generalization when pigeons were pretreated with a dose of 1.0 mg/kg -FNA. A dose of 10.0 mg/kg -FNA completely antagonized the morphine discriminative stimulus, so that pigeons responded predominantly on the saline key up to doses of morphine that suppressed responding. Doses of -FNA that attenuated the effects of morphine had no effect on the discriminative stimulus effects of naltrexone. These results demonstrate that, like naltrexone, -FNA attenuates the discriminative stimulus effects of morphine in pigeons and, at sufficiently large doses, antagonizes morphine in an unsurmountable manner. -FNA does not, however, share discriminative stimulus properties with naltrexone in these pigeons, and fails to attenuate the discriminative stimulus effects of naltrexone, lending support to the suggestion that naltrexone exerts discriminative stimulus effects under these experimental conditions predominantly by a non-mu opioid mechanism.     

The involvement of central cholinergic system in the pressor effect of intracerebroventricularly injected U-46619, a thromboxane A2 analog, in conscious normotensive rats

The aim of this study was to determine the involvement of the central cholinergic system in the rise in blood pressure evoked by the thromboxane A2 (TxA2) analog, U-46619, given centrally. Intracerebroventricular (i.c.v.) injections of U-46619 (0.5, 1.0 and 2.0 g) caused dose- and time-related increases in blood pressure and decreased heart rate in awake rats. U-46619 (1 g; i.c.v.) also produced an approximately 65% increase in posterior hypothalamic extracellular acetylcholine and choline levels. Pretreatment with SQ-29548 (8 g; i.c.v.), selective TxA2 receptor antagonist, completely inhibited both the cardiovascular responses and the increase in acetylcholine and choline levels to subsequent injection of U-46619 (1 g; i.c.v.). Atropine (10 g; i.c.v.), nonselective muscarinic receptor antagonist, pretreatment did not affect the cardiovascular responses observed after U-46619 (1 g; i.c.v.). Pretreatment with the nonselective nicotinic receptor antagonist, mecamylamine (50 g; i.c.v.) attenuated the pressor effect of U-46619 (1 g; i.c.v.). Higher doses of mecamylamine (75 and 100 g; i.c.v.) pretreatments did not change the magnitude of the blockade of pressor response to U-46619; however, they abolished the bradycardic effect of U-46619 dose-dependently. Interestingly, pretreatment of rats with methyllycaconitine (10 g; i.c.v.) or -bungarotoxin (10 g; i.c.v.), selective antagonists of 7 subtype of nicotinic acetylcholine receptors (7nAChRs), partially abolished the pressor response to i.c.v. injection of U-46619 (1 g). Similar to the mecamylamine data, the use of higher doses of methyllycaconitine (25 and 50 g; i.c.v.) produced the same magnitude of blockade that was observed after the 10 g methyllycaconitine pretreatment, but it completely abolished the bradycardic effect of U-46619 (1 g; i.c.v.) at the dose of 25 g. The present results show that central administration of U-46619 produces pressor and bradycardic effect and increase in hypothalamic acetylcholine and choline levels by activating central TxA2 receptors. The activation of central nicotinic receptors, predominantly 7nAChRs, partially mediates the cardiovascular responses to i.c.v. injection of U-46619.     

Effect of hexachlorobenzene on enzymes of the steroid metabolism in rat liver

Adult female Wistar rats were fed with a diet containing 0.05% hexachlorobenzene. On the 60th day of this treatment the specific activities of NADPH: ⁴-3-oxosteroid-5-reductase and the 3-hydroxysteroid dehydrogenases in rat liver microsomes were diminished compared to control rats. The cytoplasmatic 5-reduction was higher in HCB treated rats than in control rats. These alterations of the steroid metabolism lead to increased formation of 5-H-steroids which are known to be inducers of the porphyrin biosynthesis.

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Zusammenfassung Erwachsene weibliche Wistar-Ratten wurden mit 0.05% Hexachlorbenzol enthaltendem Futter ernährt. Am 60. Tag dieser Behandlung waren die spezifischen Aktivitäten der NADPH: ⁴-3-oxosteroid-5-Reduktase und der 3-Hydroxysteroid-Dehydrogenasen in Lebermikrosomen, verglichen mit Kontroll-Ratten, vermindert. Die cytoplasmatische 5-Reduktion war bei HCB-behandelten Ratten höher als bei Kontroll-Ratten. Diese Veränderungen des Steroidmetabolismus führen zu vermehrter Bildung von 5-H-Steroiden, von denen bekannt ist, daß sie Induktoren der Porphyrin-Biosynthese sind.

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Abbreviations HCB Hexachlorobenzene - 5-DHT 5-Dihydrotestosterone (17-hydroxy-5-androstan-3-one) - 5-DHT 5-dihydrotestosterone (17-hydroxy-5-androstan-3-one) Dedicated to Prof. Dr. Hj. Staudinger on occasion of his 65th birthday