Effects of a new TRH analogue,YM-14673 on the central nervous system

Summary The effects of a new TRH analogue, YM-14673 (N-[{(S)-4-oxo-2-azetidinyl}carbonyl]-L-histidyl-L-prolinamide dihydrate) on the central nervous system were compared with those of TRH. YM-14673 was 10–40 times more potent than TRH in antagonizing pentobarbital-induced sleep and hypothermia, and ethanol-induced hypothermia in mice. YM-14673 accelerated recovery from disturbed consciousness induced by concussive head trauma in mice and normalized the behavior and spontaneous EEG disturbed by electrolytic lesion of the hypothalamus in cats with 25 -100 times greater potency than that of TRH. In the tests on pentobarbital sleeping time and EEG disturbance, the cerebral activating activity of YM-14673 was 8 –36 times longer-lasting than that of TRH. These results indicate that YM-14673 possesses potent arousal effects on the central nervous system. The mode of action of YM-14673 was also discussed. Send offprint requests to M. Yamamoto     

Effects of a new TRH analogue,YM-14673 on a passive avoidance test as a possible criterion of improvement in cognitive disturbance in rodents

Summary Effects of a new TRH analogue, YM-14673 (N-[[(S)-4-oxo-2-azetidinyl carbonyl]-l-histidyl-L-prolinamide dihydrate) on cognitive disturbance of passive avoidance response were studied in rodents in comparison with those of TRH and CDP-choline. The latency for entering from the illuminated into the dark compartments was shortened in anoxia and scopolamine-treated rats, cycloheximidetreated mice and cerebral ischemic gerbils. The shortened latency in these models was prolonged by administration of both YM-14673 and TRH in doses without effect on spontaneous movement. YM-14673 was about 10 times more potent than TRH in ameliorating the cognitive disturbance, whereas CDP-choline showed no influence on the learning ability. These results suggest that YM-14673 and TRH possess facilitatory effects on cerebral function and that YM-14673 was distinct from CDP-choline in pharmacological profile. Send offprint requests to M. Yamamoto at the above address     

Comparative effects of thyrotropin releasing hormone,MK-771 and DN-1417 on morphine abstinence syndrome

The effect of thyrotropin releasing hormone (TRH) were compared with two of its analogs, l-N-(2-oxopiperidin-6-yl-carbonyl)-l-histidyl-l-thiazolidine-4-carboxamide (MK-771) and -butyrolactone-4-carboxyl-histidylprolineamide (DN-1417) on the abrupt and naloxone-precipitated abstinence symptoms in morphine-dependent male Swiss-Wester mice. Mice were made physically dependent on morphine by subcutaneous implantation for 3 days of a pellet containing 75 mg morphine free base. Control mice were implanted with placebo pellets. Intracerebral administration of TRH (10 ng-10 g per mouse) immediately after removal of placebo pellets had no effect on the basal temperature of mice. Mice implanted with morphine pellets exhibited a characteristic hypothermic response following the removal of the pellets. TRH at all doses employed prevented the hypothermia observed during abrupt withdrawal of morphine (pellet removal). DN-1417 and MK-771 (10 ng-10 g per mouse) on the other hand produced a short lived hyperthermic response in mice from which placebo pellets had been removed. However, both TRH analogs produced long-lasting antagonism of withdrawal hypothermia in mice from which morphine pellets had been removed. TRH and its analogs had no effect on the body weight loss observed during abrupt withdrawal of morphine. Intracerebral administration of 10 g TRH and its analogs inhibited the naloxone-induced jumping response as evidenced by increases in naloxone ED₅₀ values to elicit this response. It is concluded that TRH and its analogs may be useful in combating some of the withdrawal symptoms in opiate-dependent subjects.     

Central dopaminergic actions of YM-14673, a new TRH analogue, in rodents

The effects of a new TRH analogue, YM-14673 (N-[[(S)-4-oxo-2-azetidinyl]carbonyl]-L-histidyl-L-prolinamide dihydrate) on spontaneous movement, sniffing, climbing, licking, biting and circling behaviors were compared with those of TRH and methamphetamine, in rodents. YM-14673 in a dose of 1 mg/kg (i.p.) enhanced spontaneous motor activity in rats, and induced sniffing and climbing behaviors in mice. The licking and biting behaviors were not induced by administration of YM-14673 even in a high dose (30–100 mg/kg i.p.) to mice. In addition, ipsilateral circling did not follow the i.p. administration of YM-14673 in rats receiving cis-flupenthixol unilaterally into the striatum. YM-14673 was about 20–30 times more potent than TRH to induce sniffing and climbing behaviors and to increase spontaneous movement. The sniffing and climbing behaviors induced by administration of YM-14673 and TRH were antagonized by treatment with haloperidol and -methyl-para-tyrosine (-MT). Methamphetamine (0.5–10 mg/kg i.p.), unlike YM-14673, showed significant pharmacological effects in all behavioral experiments, so that the pharmacological profile of YM-14673 was different from that of methamphetamine. These results suggest that both YM-14673 and TRH induced behavioral changes, presumably due to facilitatory effects on the central dopaminergic system.     

Effect of YM-14673, a new thyrotropin releasing hormone analogue, on ataxic gait in cytosine arabinoside-treated mice

The effect of YM-14673, a new thyrotropin releasing hormone (TRH) analogue, on ataxic gait in mice treated with cytosine arabinoside was observed and compared with the effect of TRH. Ataxic gait was observed after administration of cytosine arabinoside in a dose of 40 mg/kg (s.c.) on the second and third postnatal days. The falling index, the ratio of the number of inversions to spontaneous motor activity, is regarded as an index of ataxia. YM-14673 significantly reduced the falling index. YM-14673 was about 30 times more potent than TRH in reducing the ataxic activity. These results suggest that YM-14673 ameliorates the ataxic gait of cytosine arabinoside-treated mice.     

Effects of a new TRH analogue, YM-14673, on disturbance of passive avoidance learning in senescence-accelerated mice

Effects of a new TRH analogue, YM-14673 (N alpha-[[(S)-4-oxo-2-azetidinyl]carbonyl]-L-histidyl-L-prolinamide dihydrate), on disturbance of passive avoidance behavior were observed in senescence-accelerated mice (SAM). Latency of step-through in SAM-P/8/Ta (SAM-P/8, senescence-prone substrain) was significantly shorter than that in SAM-R/1/Ta (SAM-R/1, senescence-resistant substrain). Successive oral administration of YM-14673 (1 and 10 mg/kg) and TRH (10 mg/kg) for 3 weeks prolonged the shortened latency of step-through. These results suggest that YM-14673 is more potent than TRH in antiamnesic activities.     

Anticonvulsive properties of YM-14673, a new TRH analogue, in amygdaloid-kindled rats

Effects of YM-14673 (N alpha-[( (S)-4-oxo-2-azetidinyl]-carbonyl]-L- prolinamide dihydrate), a new TRH analogue, on the development of kindling and the duration of afterdischarge (AD) were observed in amygdaloid-kindled rats in comparison with those of TRH. The right medial amygdaloid nucleus was electrically stimulated once a day for establishment of kindling. YM-14673 and TRH were administered intraperitoneally 15 and 30 min prior to electrical stimulation from 2 days after the first stimulation, respectively, and the number of stimulations required for the development of generalized seizures was measured. YM-14673 (1 mg/kg) showed tendency to suppress the development of kindling (p less than 0.1), but TRH even at high dose (10 mg/kg) showed little effect on it. In addition, the experiment for the AD duration was conducted in full-kindled rats from one day after at least 3 reproducible generalized seizures were elicited by electrical stimulation of the medial amygdaloid nucleus once a day. Both YM-14673 (1 mg/kg) and TRH (10 mg/kg) administered 15 and 30 min prior to electrical stimulation of the amygdala, respectively, significantly shortened the AD duration in full-kindled rats. At these doses, both drugs desynchronized spontaneous cortical electroencephalogram (EEG) in normal rats. These results indicate that YM-14673 seems to possess anticonvulsive property in rats.     

Effects of a new analog of thyrotropin-releasing hormone, N alpha-[(S)-4-oxo-2-azetidinyl) carbonyl]-L-histidyl-L-prolinamide dehydrate (YM-14673) on spinal reflex potentials and flexor reflexes in spinalized rats

Experiments were performed on spinalized rats, transected at the Cl level. The intravenous administration of TRH and its analog YM-14673 (N alpha-[(S)-4-oxo-2-azetidinyl) carbonyl]-L-histidyl-L-prolinamide dehydrate) produced marked increases in the amplitude of mono- and polysynaptic reflex potentials and those of the withdrawal flexor reflexes. The effects of YM-14673 were stronger and longer-lasting than those of TRH. The stimulant action of TRH and YM-14673 on the flexor reflexes was not antagonized by prazosin, chlorpromazine, haloperidol or cyproheptadine, suggesting no involvement of the release of catecholamines or serotonin in the stimulant effects of TRH and its analog. Therefore, YM-14673 may be beneficial for the treatment of several spinal motor neuron diseases.     

Role of nitric oxide in penile erection and yawning induced by 5-HT1c receptor agonists in male rats

The effect of the intracerebroventricular (i.c.v.) administration of N^G-nitro-l,-arginine methyl ester and N^G-monomethyl-l.-arginine, two inhibitors of nitric oxide (NO) synthase, on penile erection and yawning induced by 1-(3-chlorophenyl)-piperazine (m-CPP)- and N-(3-trifluoromethylphenyl)-piperazine (TFMPP), two selective 5HT_1c receptor agonists, was studied in male rats. Both NO synthase inhibitors (50–500 g i.c.v.) prevented dose-dependently the behavioural responses induced by m-CPP (0.5 mg/kg s.c.) or by TFMPP (I mg/kg s.c.), but N^G-nitro-l-arginine methyl ester was about 4–5 times more potent than N^G-monomethyl-l,-arginine. The D-isomer of N_G-monomethyl-l-arginine, which does not inhibit nitric oxide synthase, was ineffective. The inhibitory effect of N^G-nitro-l-arginine methyl ester on m-CPP- and TFMPP-induced responses was prevented by the administration of l-arginine (1 mg i.c.v.). In contrast, N^G-nitro-l-arginine methyl ester (20 g) was ineffective when injected in the paraventricular nucleus of the hypothalamus, a brain area that plays a key role in the expression of these behavioural responses. m-CPP- and TFMPP-induced penile erection and yawning was prevented also by the i.c.v. administration of LY 83583 (50–200 g) or methylene blue (50–400 g), two inhibitors of guanylate cyclase but not by reduced hemoglobin (50–400 g), a NO scavenger. The results suggest that central nitric oxide is involved in the expression of penile erection and yawning induced by 5-HT_1c receptor agonists.     

Effects of a new analogue of thyrotropin-releasing hormone on pentobarbital-induced sleeping time in rodents

The effects of a new analogue of TRH, YM-14673 (N-[[(S)-4-oxo-2-azetidinyl]carbonyl]-L-histidyl-L-prolinamide dihydrate) on pentobarbital-sleeping time were observed in comparison with those of TRH in rodents. The YM-14673 was administered intravenously, orally and intramuscularly. In all cases it reduced pentobarbital-sleeping time in rats and/or mice in a dose-dependent manner. The analeptic activity of YM-14673 was about 10 times greater than that of TRH. Analeptic action was also observed with successive intravenous injections of YM-14673, once daily for 5 and 14 days in mice, suggesting that the drug induced no tolerance. In addition, there was evidence that the pituitary-thyroid axis was not necessary for the analeptic effects of YM-14673. In particular, it was noted that hypophysectomy did not reduce the antagonism by YM-14673 of pentobarbital-induced sleep and intracerebrally administered YM-14673 produced analeptic actions in mice. Pretreatment with atropine and baclofen antagonized the ability of YM-14673 to reduce sleep, induced by pentobarbital in mice. However, the analeptic action of YM-14673 was not reduced by the administration of haloperidol and phentolamine. These results suggest that YM-14673 produced facilitatory effects on the central nervous system, independent of an effect on the pituitary gland, and that the antagonizing effects by YM-14673 on the actions of pentobarbital may be affected by activation of the central cholinergic system as well as by inhibition of the GABA-ergic system.     

Effects of YM-14673, a new thyroid-releasing hormone analogue, on neurological deficits in stroke-prone spontaneously hypertensive rats

The effects of YM-14673, a new thyroid-releasing hormone (TRH) analogue (N alpha-[[(S)-4-oxo-2-azetidinyl]carbonyl]-L-histidyl-L-prolinamide dihydrate), on neurological deficits were examined in stroke-prone spontaneously hypertensive rats (SHRSP). The neurological deficits were evaluated for more than 21 days after stroke. Administration of YM-14673 was started the day stroke was observed and repeated daily for 3 weeks. YM-14673 (0.1 and 0.3 mg/kg i.p.) improved the neurological deficits and reduced mortality. These results demonstrate that YM-14673 mitigates cerebral ischemic changes in SHRSP.     

Adenosine receptors mediating inhibitory electrophysiological responses in rat hippocampus are different from receptors mediating cyclic AMP accumulation

Summary Electrophysiological and biochemical techniques were used to characterize adenosine receptors in rat hippocampus. The site which mediates the inhibitory action of adenosine on excitatory synaptic transmission and on spontaneous interictal spiking had properties similar to the adenosine A1 receptor. Thus, the relative order of potency for adenosine analogs was l-PIACHA>NECA> 2CA (l-PIA = N⁶-phenylisopropyladenosine; CHA = N⁶-cyclohexyl-adenosine; NECA = adenosine 5-ethylcarboxamide; 2CA = 2-chloroadenosine), with EC50 values for the most potent analogs between 10–30 nM. The effect of the stable adenosine analog, particularly CHA and l-PIA, was slow in onset and very slowly reversible. This is suggested to be due both to a slow dissociation of these compounds from the receptors but particularly to the slow equilibrium between the concentration of the drug in the medium surrounding the slices and the biophase within the slices. Adenosine analogs bound specifically to membrane preparations of the rat hippocampus with the order of potency ³H-CHA³H-l-PIA>³H-NECA. Eadie-Hofstee plots of the binding data were curvilinear for each ligand, but only for ³H-l-PIA could the existence of two binding sites with different apparent K _d-values (0.27 and 11.8 nM) be confirmed by curve-fitting. The estimated K _d-values for CHA and NECA were 1.5 and 20 nM, respectively. The adenosine analogs also enhanced ³H-cyclic AMP accumulation in ³H-adenine-labelled hippocampal slices. The rank order of potency of adenosine analogs in increasing cyclic AMP (NECA>2CA>l-PIA>CHA) suggests that this effect is mediated by adenosine A2 receptors. The EC50 values for the accumulation of cyclic AMP were 10–1000 × higher than the EC50 values derived from electrophysiological experiments and the K _d-values from measurements of radioligand binding. Thus, on the basis of absolute as well as rank order potencies of drugs, the adenosine analog-induced electrophysiological responses appear to be related to actions at an A1 receptor site. By contrast, the adenosine receptor-mediated increases in cyclic AMP appears to involve an A2 receptor, the functional role of which is not clear.     

Calcium channel modulation by dihydropyridines modifies sufentanil-induced antinociception in acute and tolerant conditions

Summary The study was aimed at elucidating the possible participation of l-type Ca²⁺ channel in the acute analgesic effect of an opiate and the development of tolerance to this action. Sufentanil, a selective p agonist, and two dihydropyridines, the Ca²⁺ antagonist nimodipine and the Ca²⁺ agonist Bay K 8644, were selected. The tail-flick test was used to assess the nociceptive threshold. In naive rats, nimodipine (200 g/kg) potentiated the analgesic effect of sufentanil reducing the ED₅₀ from 0.26 to 0.08 g/kg. Similar results were observed with its (–)-enantiomer Bay N 5248, while the (+) enantiomer Bay N 5247 was ineffective. Tolerance to the opiate was induced by chronic subcutaneous administration of sufentanil with minipumps (2 g/h, 7 days). In these conditions the dose-response curve to sufentanil was displaced to the right and the ED₅₀ was increased to 1.49 g/kg. In tolerant rats, nimodipine preserved its potentiating ability and prevented the displacement to the right of the sufentanil dose response-curve (ED₅₀ = 0.48 g/kg). When nimodipine was pumped (1 g/h, 7 days) concurrently with sufentanil, the development of tolerance to the opioid was not disturbed. However, the expression of tolerance was abolished and even the effect of acutely administered sufentanil was markedly potentiated (ED₅₀ = 0.03 g/kg). Similar experiments were performed with Bay K 8644. In naive rats, Bay K 8644 at a low dose (20 g/kg) that behaves as a calcium agonist, antagonized the analgesic effect of sufentanil (ED₅₀ = 0.58 g/kg), whereas at a high dose (200 g/kg) it potentiated this action (ED₅₀ = 0.15 g/kg). In tolerant rats, Bay K 8644 (20 g/kg) preserved its antagonizing ability inducing a displacement to the right of the sufentanildose-response curve (ED₅₀ = 4.2 g/kg). When Bay K 8644 was pumped (1 g/h, 7 days) concurrently with sufentanil, it enhanced the expression of tolerance to the opiate (ED₅₀ = 3.8 g/kg). These results suggest that the calcium fluxes through the l-type channel in neurones are functionally linked to the activation of the opiate receptor: the blockade of the channel increased the potency of sufentanil, whereas its activation reduced the potency of the opiate. In chronic experiments, DHPs concurrently administered with sufentanil did not affect the development of tolerance to the opiate. However, nimodipine prevented the expression of this phenomenon. Even more, the animals became hypersensitive to the opiate suggesting that the adaptative mechanisms induced by chronic opiate could be affected by chronic nimodipine.This work was supported by grants from Universidad de Cantabria-Caja Cantabria (1988) and Bayer AG, Wuppertal, FRGPredoctoral Fellow: Fondo de Investigaciones Sanitarias de la Seguridad Social.Send offprint requests to: M. A. Hurlé at the above address     

Growth hormone-releasing activity of hexarelin in humans

Hexarelin is a new hexapeptide (His-d-2-methyl-Trp-Ala-Trp-d-Phe-Lys-NH₂) that stimulates the release of growth hormone both in vitro and in vivo. In this double-blind, placebo-controlled, rising-dose study we evaluated the growth hormone releasing activity of hexarelin in healthy human subjects. Twelve adult male volunteers received single intravenous boluses of 0.5, 1 and 2 ·g·kg^–1 hexarelin as well as placebo. For safety, drug doses were given in a rising-dose fashion with placebo randomly inserted into the sequence. Plasma growth hormone concentrations increased dose-dependently after the injection of the peptide, peaking at about 30 min and then decreasing to baseline values within 240 min with a half-life of about 55 min. The mean peak plasma growth hormone concentrations (C_max) were 3.9, 26.9, 52.3, 55.0 ng·ml^–1 after 0, 0.5, 1 and 2 g·kg^–1, respectively. The corresponding areas under the curve of growth hormone plasma levels from drug injection to 180 min (AUC_0–180) were 0.135, 1.412, 2.918 and 3.695 g·min·ml^–1. The theoretical maximum response (E_max) and the dose that produces half of the maximum response (ED₅₀) were estimated using logistic regression. The calculated ED₅₀ values were 0.50 and 0.64 g·kg^–1 for C_max and AUC_0–180, respectively. The corresponding E_maxs were 55.1 ng·ml^–1 and 3936 ng·min·ml^–1, thus indicating that the effect after the 2 g·kg^–1 dose is very close to the maximal response. Plasma glucose, luteinising hormone, follicle-stimulating hormone, thyroid-stimulating hormone and insulin-like growth factor I were unaffected by hexarelin administration, while the peptide caused a slight increase in prolactin, cortisol and adrenocorticotropic hormone levels. Hexarelin was well tolerated in all subjects. The results of this study indicate that intravenous administration of hexarelin in man produces a substantial and dose-dependent increase of growth hormone plasma concentrations.     

促甲状腺素释放激素类似物YM14673对小鼠学习记忆的影响

采用小鼠跳台法评价促甲状腺素释放激素类似物YM14673(ip 1 mg·kg^-1) 对正常成年小鼠被动回避学习记忆成绩的影响. 结果表明YM14673对东莨菪碱， 氯霉素和乙醇造成的小鼠记忆获得,巩固及再现障碍均有明显的改善作用.     

Neuroleptic properties of cis-N-(1-benzyl-2-methylpyrrolidin-3-yl)-5-chloro-2-methoxy-4-methylaminobenzamide (YM-09151-2) with selective antidopaminergic activity

A new benzamide, cis-N-(1-benzyl-2-methylpyrrolidin-3-yl)-5-chloro-2-methoxy-4-methylaminobenzamide (YM-09151-2) exhibited more potent and longer-lasting inhibitory effects on apomorphine-induced behaviours (stereotyped behaviour, emesis and hypothermia), and methamphetamine-induced stereotyped behaviour, conditioned avoidance response and open field behaviour than either structurally similar benzamides (YM-0850 and sulpiride) or calssical neuroleptics [chlorpromazine(CPZ) and haloperidol(HPD)]. Such inhibitory effects of YM-09151-2 relative to cataleptogenicity were greater than those of CPZ and HPD. In contrast, sulpiride elicited few of the neuroleptic effects described above. YM-09151-2, a potent inhibitor for dopamine-sensitive adenylate cyclase (Ki: 3.0 nM) reduced, in a selective manner, the binding of [³H]dopamine to the dopamine D₁ receptor (Ki: 4.8 nM) associated with adenylate cyclase rather than to the dopamine D₂ receptor (Ki: 0.98 M) independent of adenylate cyclase. Sulpiride, on the contrary, inhibited only the binding to the dopamine D₂ receptor. CPZ and HPD antagonized [³H]dopamine non-selectively at the two distinct dopaminergic receptors. These results suggest that YM-09151-2 is a potent and long-lasting neuroleptic with a highly selective blocking action on the dopamine D₁ receptor.     

The selective P2X purinoceptor agonist, β,γ-methylene-L-adenosine 5′-triphosphate,discriminates between smooth muscle and neuronal P2X purinoceptors

The effects of the putative selective P_2X purinoceptor agonist, ,-methylene-l-adenosine 5-triphosphate (me-l-ATP), were determined at rat neuronal and smooth muscle P_2X purinoceptors.Me-l-ATP had no effect on the extracellularly recorded membrane potential of the rat isolated vagus nerve preparation at concentrations up to 300 M. In contrast, the archetypal P_2X purinoceptor agonist, , methylene ATP (meATP;1–100 M), produced concentration-related depolarisation responses with a mean EC₅₀ value of 10.8 M. The depolarising effects of meATP were not attenuated by me-l-ATP (100 M). In voltage clamp experiments on single nodose ganglion neurones, ATP (100 M), but not me-l.-ATP (1–300 M), evoked rapid ( < 20 ms onset) inward currents when applied using a concentration-clamp method. In receptor binding studies to rat brain membranes, me-d-ATP and meATP competed with high affinity for [³H]Lx meATP binding sites, with mean pIC₅₀ values of 7.7 and 8.3, respectively. However, me-l-ATP possessed low affinity for these sites and competed only at concentrations in excess of 10 M (mean pIC₅₀ value 4.1).In prostatic segments of the rat vas deferens, me-l-ATP (1–100 M) and meATP (0.3–100 M) each produced concentration-related contractile responses with mean EC₅₀ values of 17.1 and 3.6 M, respectively. Me-l-ATP (1–10 M) evoked fast inward currents in freshly dispersed vas deferens smooth muscle cells, indicative of an action at ligand-gated ion channels. Binding sites in vas deferens membranes labelled using 1 nM [³H]meATP exhibited high affinity for me-l-ATP, meATP and me-d-ATP with mean PIC₅₀ values of 7.7, 8.4 and 7.3, respectively.These results indicate that me-l-ATP exhibits neither agonist nor antagonist properties at P_2X purinoceptors on rat vagal neurones and possesses only very low affinity for [³H]meATP binding sites in rat brain. In contrast, me-l-ATP is a potent, high affinity agonist at smooth muscle P_2X purinoceptors of the rat vas deferens. This selective agonist action of me-l-ATP suggests that P_2X purinoceptors in smooth muscle and neurones are different and represent distinct P_2X purinoceptor subtypes.     

Species differences in the relative analgesic potencies of some classical opiates and opioid peptides

The analgesic ED₅₀ values of some classical morphine congeners (morphine, methadone, fentanyl, azidomorphine) in the rat and mouse tail-flick tests were found to be similar. However, several synthetic derivatives of the natural enkephalins were more potent in mice than in rats. (These analogs contain d-amino acid in position 2 and d- or l-sulfonic (or phosphonic) acid residue in position 5). -Endorpin, d-Met², Pro⁵-enkephalinamide and two partial agonists showed intermediate interspecies relative potencies. According to the data obtained, similar opiate receptors might mediate the analgesic action of classical opiates in rats and in mice. However, the opiate receptors responsible for the antinociceptive effects of the above mentioned enkephalin analogues must be dissimilar in the two species examined. The results are discussed in terms of the role of - and -receptors in mediation of the analgesic effect induced by different types of opioids.     

Increase by NO synthase inhibitors of acetylcholine release from guinea-pig myenteric plexus

The effects of nitric oxide (NO) synthase inhibitors on the electrically evoked release of [³H]acetylcho-line were studied in guinea-pig myenteric plexus preparations preincubated with [³H]choline. N^G-monomethyl-l-arginine (EC₅₀ 5.3 mol l^–1) and N^G-nitro-l-arginine (EC₅₀ 1.3 mol l^–1) concentration-dependently increased the evoked release of [³H]acetylcholine without affecting the basal outflow. The facilitatory effect of N^G-monomethyl-l-arginine was prevented by l-arginine but not by d-arginine. The results suggest that endogenous NO inhibits the depolarisation-evoked release of acetylcholine. Correspondence to: H. Kilbinger at the above address     

The Potential Use of the South African River Crab,Potamonautes warreni,as a Bioindicator Species for Heavy Metal Contamination

In 1995, preliminary water and sediment analyses of the river bed and burrow sediments from 9 locations along the Mooi River, NW Province, South Africa had shown cadmium concentrations up to 0.009 mg l^–1±0.003 and up to 0.33 and 0.89 weight % with scanning electron microscopy (SEM) and x-ray microanalysis. Samples of the adult river crab (Potamonautes warreni) were collected from the Mooi River at Noordbrug (26°40S/27°05E), 1 km north of Potchefstroom Town, and exposed to 0.2 or 2.0 mg Cd²⁺ l^–1 in situ to determine tolerance, uptake and bioaccumulation of cadmium. Using flame atomic absorption spectroscopy (FAAS) the gills, haemolymph and digestive gland of naturally exposed P. warreni showed wet mass values of 0.74±0.27 g Cd²⁺ g^–1, 0.007±0.007 g ml^–1 and 0.12±0.09 g g^–1 respectively. The tolerance of crabs to aqueous Cd reached its limit (ET₅₀=42 hours) at 2.0 mg l^–1 aqueous Cd exposure. At an exposure to 0.2 mg Cd²⁺ l^–1 for 21 days, the greatest Cd (n=11; 9.99±5.09 g g^–1 wet mass) and Cu concentrations (n=11; 17.90±4.66 g g^–1 wet mass) were associated with the gills, and to a lesser extent the digestive gland (n=11; 0.38±0.20 g g^–1 wet mass), whereas concentrations of Zn were variable in both organs. In the haemolymph Cd levels were relatively small (n=11; 0.012–0.006 g ml^–1) with exposure and time and Cu, Zn concentrations varied. Changes in the uptake of Cd in P. warreni indicated that transport, storage and possibly regulatory mechanisms are likely to operate in adult crabs. The potential of P. warreni as a bioindicator species of pollution is also discussed.