Ligands for opioid and sigma-receptors improve cardiac electrical stability in rat models of post-infarction cardiosclerosis and stress.

The effects of the extremely selective mu-opioid receptor agonist, [D-Arg2,Lys4]-dermorphin-(1-4)-amide (DALDA), the mu-opioid receptor agonist morphine, the mu/delta agonist D-Ala2, Leu5, Arg6-enkephalin (dalargin), the kappa-opioid receptor agonist spiradoline, and the sigma1-receptor antagonist DuP 734 on ventricular fibrillation threshold (VFT) was investigated in an experimental post-infarction cardiosclerosis model and an immobilization stress-induced model in rats. Both models produced a significant decrease in VFT. The postinfarction cardiosclerosis-induced decrease in VFT was significantly reversed by intravenous administration of dalargin (0.1 mg/kg), DALDA (0.1 mg/kg), or morphine HCl (1.5 mg/kg). Pretreatment with naloxone (0.2 mg/kg) completely eliminated the increase in cardiac electrical stability produced by DALDA. Both spiradoline (8 mg/kg, i.p.) and DuP 734 (1 mg/kg, i.p.) produced a significant increase in VFT in rats with post-infarction cardiosclerosis. This effect of spiradoline was blocked by nor-binaltorphimine. The immobilization stress-induced decrease in VFT was significantly reversed by administration of either DALDA, spiradoline or DuP 734. In conclusion, activation of either mu- or kappa1-opioid receptors or blockade of sigma1-receptors reversed the decrease in VFT in both cardiac compromised models. Since DALDA and dalargin essentially do not cross blood brain barriers, their effects on VFT may be mediated through peripheral mu-opioid receptors.     

DIFFERENTIATION OF DOPAMINERGIC AND NORADRENERGIC NEURONS IN RAT SPINAL CORD

Abstract— Norepinephrine (NE), dopamine (DM) and 3-methoxy-4-hydroxyphenylacetic acid (HVA) content have been measured in different parts of rat spinal cord and cerebellum by a gas chromatographic mass spectrometric method. In cerebellum, which does not contain dopaminergic neurons, the ratio of NE to DA content was 47, whereas in parts of the spinal cord this ratio varied between 11 and 19. In the cord after desipramine (25 mg/kg, i.p.) plus 6-hydroxydopamine (6-HDA, 100/jg intracisternally), there was a significant depletion of DM but not of NE. Conversely, after benztropine (25 mg/kg, i.p.) plus 6-HDA there was a significant depletion of NE but not of DM. Chlorpromazine (10 mg/kg, i.p.) or clozapine (25 mg/kg, i.p.) caused a significant increase in spinal cord HVA concentration 1 h after treatment. Evidence is presented which suggests that the increased HVA measured in the cord did not originate in the brain. After electrolytic lesion of the locus coeruleus there was a significant reduction of NE but not of DM. Spinal cord DM and NE were depleted by reserpine in a dose-dependent manner, the threshold dose for DM depletion being less than that for NE depletion. Seven days after cord transection at T₁₀ spinal cord DM was significantly reduced in the lumbar region. These results suggest that dopaminergic neurons exist in rat spinal cord independently of noradrenergic neurons and that the DM is likely to be present in the terminals of descending axons.     

Phencyclidine-induced stereotyped behavior and serotonergic syndrome in rat

Phencyclidine (50 mg/kg, i.p.) induced in rats a biphasic response consisting of serotonergic syndrome followed by stereotyped behavior. The initial serotonergic syndrome was significantly reduced by cinanserin (20 mg/kg, i.p.) and cyproheptadine (2.0 mg/kg, i.p.) but not influenced by haloperidol (0.5 mg/kg, i.p.). The later stereotyped behavior was significantly reduced by haloperidol (0.5 mg/kg, i.p.) but not influenced by cinanserin (20 mg/kg, i.p.) or cyproheptadine (2.0 mg/kg, i.p.). A lower dose of phencyclidine (5.0 mg/kg, i.p.) elicited only haloperidol-sensitive stereotyped behavior. These results indicate that serotonergic and dopaminergic mechanisms may mediate the behavioral effects of phencyclidine in rats.     

Enterostatin (VPDPR) has anti-analgesic and anti-amnesic activities

Enterostatin (VPDPR), an anorexigenic peptide derived from the amino terminus of procolipase, significantly inhibited analgesia induced by the mu-opioid agonist morphine (5 mg/kg, s.c.) after i.c.v. administration to mice at a dose of 100 nmol. On the other hand, VPDPR (approximately 200 nmol, i.c.v.) did not attenuate analgesia induced by the kappa-opioid agonist D-Phe-D-Phe-D-Nle-D-Arg-NH2 (100 microg/mouse, i.c.v.) or delta-opioid agonist DTLET (4 nmol/mouse, i.c.v.). VPDPR (100 nmol, i.c.v.) significantly improved amnesia induced by scopolamine (0.2 mg/kg, i.p.) in mice. However, VPDPR did not enhance memory in normal mice at the same dose.     

Endothelin-induced sudden death and the possible involvement of platelet activating factor (PAF)

Endothelin (5 nmol/kg, i.v.) caused a transient hypotension followed by a lasting hypertension in rats. However, an abrupt fall in the blood pressure was observed in most rats 6 to 30 min after the injection of endothelin and sudden death followed with lethality noted over 60 min. An abnormal electrocardiogram (ECG) (ventricular arrhythmias) was observed in rats injected with endothelin. Endothelin (i.v.) also caused sudden death in mice. Pretreatment (5 or 60 min) with specific PAF antagonists, CV-6209 (0.1-3 mg/kg, i.v.) and WEB 2086 (30 mg/kg, p.o.), and a calcium channel blocker, diltiazem (60 mg/kg, p.o.) prevented death and attenuated the ECG changes induced by endothelin, but CV-6209 did not prevent the blood pressure changes induced by endothelin. CV-6209 (0.5-3 mg/kg, i.v.), WEB 2086, diltiazem and dexamethasone (5 mg/kg, i.v.) protected mice against the death induced by endothelin. On the other hand, aspirin (cyclooxygenase inhibitor, 100 mg/kg, p.o.) did not protect mice from the death. Thus, endothelin is a highly toxic peptide with cardiotoxic effects, and PAF may be involved in the pathogenesis of the sudden death.     

Role of kappa- and delta-opioid receptors in the antinociceptive effect of oxytocin in formalin-induced pain response in mice

Oxytocin has been implicated in the modulation of somatosensory transmission such as nociception and pain. The present study investigates the effect of oxytocin on formalin-induced pain response, a model of tonic continuous pain. The animals were injected with 0.1 ml of 1% formalin in the right hindpaw and the left hindpaw was injected with an equal volume of normal saline. The time spent by the animals licking or biting the injected paw during 0-5 min (early phase) and 20-25 min (late phase) was recorded separately. Oxytocin (25, 50, 100 microg/kg, i.p.) dose dependently decreased the licking/biting response, both in the early as well as the late phases. The antinociceptive effect of oxytocin (100 microg/kg, i.p.) was significantly attenuated in both the phases by a higher dose of the non-selective opioid receptor antagonist naloxone (5 mg/kg, i.p.), MR 2266 (0.1 mg/kg, i.p.), a selective kappa-opioid receptor antagonist and naltrindole (0.5 mg/kg, i.p.), a selective delta-opioid receptor antagonist but not by a lower dose of naloxone (1 mg/kg, i.p.) or beta-funaltrexamine (2.5 microg/mouse, i.c.v.), a selective mu-opioid receptor antagonist. Nimodipine, a calcium channel blocker (1 and 5 mg/kg, i.p.) produced a dose-dependent analgesic effect. The antinociceptive effect of oxytocin was significantly enhanced by the lower dose of nimodipine (1 mg/kg, i.p.) in both the phases. Chronic treatment with oxytocin (100 microg/kg/day, i.p. daily for 7 days) did not produce tolerance in both the phases of formalin-induced pain response. The results thus indicate that oxytocin displays an important analgesic response in formalin test; both kappa- and delta-opioid receptors as well as voltage-gated calcium channels seem to be involved in the oxytocin-induced antinociception.     

Nutritional parameters modify muricidal behavior of male Wistar rats: preventive effects of amino acids and 4' Cl diazepam.

In male Wistar rats fed a diet enriched in polyunsaturated fatty acids and starch (PUFA+S), the percentage of muricidal (Mu) rats increased to 82% within 60 days. Mu rats had higher serum triglyceride levels and lower cholesterol levels than non-Mu rats. Water intake decreased in all rats on the PUFA+S diet concurrently with the increase in the proportion of Mu rats; protracted water restriction in rats fed standard diet also increased the percentage of Mu rats. In the offspring of two Wistar females fed the PUFA+S diet, the proportion of young Mu rats was 67%. When the PUFA+S diet was replaced with standard diet, the induced Mu behavior was not reversed. PK11195 (6 mg/kg i.p.), clonazepam (0.2 mg/kg i.p.), and flumazenil (15 mg/kg i.p.) were ineffective in reversing the induced Mu behavior, whereas 4'-chlorodiazepam (5 mg/kg i.p.) or muscimol (0.5 mg/kg i.p.) caused reversals of 63% or 50%, respectively. A 5-hydroxytryptophan overload (60 mg/kg i.p.) also reversed Mu behavior by 71%. All reversal effects were temporary. Pretreatment with yeast for 7 days before the PUFA+S diet was given prevented induction for more than 90 days on the PUFA+S diet, while similar pretreatment 4'Cl-diazepam resulted in 71% prevention of induction. The results are analyzed in terms of the involvement of endozepin, vasopressin, and serotonin receptors, and of possible genetic parameters.     

Borapetoside C from Tinospora crispa improves insulin sensitivity in diabetic mice

Diabetes mellitus (DM) often leads to disability from vascular complications and neurological complications. Tinospora crispa has been widely used in Asia and Africa as a remedy for diabetes and other diseases. In this study, we investigated the hypoglycemic actions of borapetoside C isolated from T. crispa, and the mechanisms underlying its actions. Acute treatment with borapetoside C (5mg/kg, i.p.) attenuated the elevated plasma glucose induced by oral glucose in normal and type 2 DM (T2DM) mice. Compared to the effect of injected insulin (0.5 IU/kg), borapetoside C caused a more prominent increase of glycogen content in skeletal muscle of T2DM mice, but a less increase in type 1 DM (T1DM) mice. Combined treatment of a low dose borapetoside C (0.1mg/kg, i.p.) plus insulin enhanced insulin-induced lowering of the plasma glucose level and insulin-induced increase of muscle glycogen content. Continuous treatment with 5mg/kg borapetoside C (twice daily) for 7 days increased phosphorylation of insulin receptor (IR) and protein kinase B (Akt) as well as the expression of glucose transporter-2 (GLUT2) in T1DM mice. Combined treatment of a low dose borapetoside C (0.1mg/kg, twice daily) plus insulin for 7 days enhanced insulin-induced IR and Akt phosphorylation and GLUT2 expression in the liver of T1DM mice. This study proved that borapetoside C can increase glucose utilization, delayed the development of insulin resistance and enhanced insulin sensitivity. The activation of IR-Akt-GLUT2 expression and the enhancement of insulin sensitivity may contribute to the hypoglycemic action of borapetoside C in diabetic mice.     

Differential antagonism of endomorphin-1 and endomorphin-2 supraspinal antinociception by naloxonazine and 3-methylnaltrexone

To determine if different subtypes of mu-opioid receptors were involved in antinociception induced by endomorphin-1 and endomorphin-2, the effect of pretreatment with various mu-opioid receptor antagonists beta-funaltrexamine, naloxonazine and 3-methylnaltrexone on the inhibition of the paw-withdrawal induced by endomorphin-1 and endomorphin-2 given intracerebroventricularly (i.c.v.) were studied in ddY male mice. The inhibition of the paw-withdrawal induced by i.c.v. administration of endomorphin-1, endomorphin-2 or DAMGO was completely blocked by the pretreatment with a selective mu-opioid receptor antagonist beta-funaltrexamine (40 mg/kg), indicating that the antinociception induced by all these peptides are mediated by the stimulation of mu-opioid receptors. However, naloxonazine, a mu1-opioid receptor antagonist pretreated s.c. for 24h was more effective in blocking the antinociception induced by endomorphin-2, than by endomorphin-1 or DAMGO given i.c.v. Pretreatment with a selective morphine-6 beta-glucuronide blocker 3-methylnaltrexone 0.25mg/kg given s.c. for 25 min or co-administration of 3-methylnaltrexone 2.5 ng given i.c.v. effectively attenuated the antinociception induced by endomorphin-2 given i.c.v. and co-administration of 3-methylnaltrexone shifted the dose-response curves for endomorphin-2 induced antinociception to the right by 4-fold. The administration of 3-methylnaltrexone did not affect the antinociception induced by endomorphin-1 or DAMGO given i.c.v. Our results indicate that the antinociception induced by endomorphin-2 is mediated by the stimulation of subtypes of mu-opioid receptor, which is different from that of mu-opioid receptor subtype stimulation by endomorphin-1 and DAMGO.     

Rubiscolin-6, a delta opioid peptide derived from spinach Rubisco, has anxiolytic effect via activating sigma1 and dopamine D1 receptors

Rubiscolin-6 (Tyr-Pro-Leu-Asp-Leu-Phe) is a delta opioid peptide derived from the large subunit of spinach d-ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). We previously reported that rubiscolin-6 had an analgesic effect and stimulated memory consolidation. Here we show that intraperitoneally (i.p.) or orally administered rubiscolin-6 has an anxiolytic effect at a dose of 10 mg/kg or 100 mg/kg, respectively, in the elevated plus-maze test in mice. The anxiolytic effects of rubscolin-6 after i.p. (10 mg/kg) and oral (100 mg/kg) administration were blocked by a delta opioid receptor antagonist, naltrindole (1 mg/kg, s.c.), suggesting that the anxiolytic activity of rubiscolin-6 is mediated by delta opioid receptor. The anxiolytic effect of rubiscolin-6 (10 mg/kg, i.p.) was also blocked by a dopamine D(1) antagonist, SCH23390 (30 microg/kg, i.p.), but not by a dopamine D(2) antagonist, raclopride (15 microg/kg, i.p.). The anxiolytic effect of rubiscolin-6 (10 mg/kg, i.p.) was blocked by sigma(1) receptor antagonist, BMY14802 (0.5 mg/kg, i.p.) or BD1047 (10 mg/kg, i.p.). Taken together, the anxiolytic effect of rubiscolin-6 is mediated by sigma(1) and dopamine D(1) receptors downstream of delta opioid receptor.     

Roles of 5-HT3 and opioid receptors in the ethanol-induced place preference in rats exposed to conditioned fear stress.

The effect of the selective 5-HT3 receptor antagonist ondansetron on the ethanol-induced place preference in rats exposed to conditioned fear stress, which stimulates the release of endogenous opioid peptides (beta-endorphin and enkephalins), was investigated using the conditioned place preference paradigm. In addition, we also examined the effect of ondansetron on the ethanol-induced place preference enhanced by the administration of mu- and delta-opioid receptor agonists (exogenous opioids). The administration of ethanol (300 mg/kg, i.p.) induced a significant place preference in rats exposed to conditioned fear stress. Pretreatment with ondansetron (0.01 and 0.1 mg/kg, s.c.) effectively attenuated this ethanol-induced place preference. When the mu-opioid receptor agonist morphine (0.1 mg/kg, s.c.) or the selective delta-opioid receptor agonist 2-methyl-4a(alpha)-(3-hydroxyphenyl)-1,2,3,4,4a,5,12,12a(alpha)-octah ydroquinolino [2,3,3-g] isoquinoline (TAN-67; 20 mg/kg, s.c.) was administered in combination with 75 mg/kg ethanol (which tended to produce a place preference), the ethanol-induced place preference was significantly enhanced. The selective mu-opioid receptor antagonist beta-funaltrexamine at a dose of 10 mg/kg significantly attenuated the enhancement of the ethanol-induced place preference produced by morphine. Ondansetron (0.1 mg/kg, s.c.) also significantly attenuated the enhancement of the ethanol-induced place preference produced by morphine. Furthermore, the selective delta-opioid receptor antagonist naltrindole at a dose of 3 mg/kg significantly attenuated the enhancement of the ethanol-induced place preference produced by TAN-67. Ondansetron (0.1 mg/kg, s.c.) slightly, but significantly, attenuated the enhancement of the ethanol-induced place preference produced by TAN-67. These results suggest that 5-HT3 receptors may be involved in the rewarding mechanism of ethanol under psychological stress, and may play an important role in the rewarding effect of ethanol through the activation of mu- and delta-opioid receptors.     

Dual action on central dopamine function of transdihydrolisuride,a 9, 10-dihydrogenated analogue of the ergot dopamine agonist lisuride

Transdihydrolisuride (TDHL), a 9, 10-dihydrogenated analogue of the ergot dopamine (DA) agonist lisuride (LIS), was investigated for its influence on central dopaminergic functions in rats and mice after single i.p. administration. TDHL (0.39–25 mg/kg) unexpectedly induced catalepsy and antagonized apomorphine-induced stereotypes in rats; it was approx. 3–5 times less potent than the DA antagonist haloperidol. TDHL (0.025–6.25 mg/kg) caused hypokinesia and antagonized the apomorphine-induced hyperactivity in rats. Pre-treatment with TDHL (0.78–12.5 mg/kg) which per se did not alter thermoregulation at room temperature, antagonized the hypothermia induced by the DA agonist apomorphine (5 mg/kg i.p.) in mice. These DA antagonistic properties contrasted with the prolactin (PRL) lowering effect of TDHL (0.01–10 mg/kg p.o.) in reserpinized female rats thus indicating DA agonist function. PRL inhibition tended to be longer lasting (>8h) than after LIS (0.01–1 mg/kg p.o.) with comparable potency. In healthy volunteers TDHL (0.2–1 mg p.o.) effectively lowered PRL levels with similar potency but with a markedly longer duration of action than LIS (>24h after 0.5 mg TDHL). In contrast to the side effects after acute LIS treatment, no comparable adverse reactions such as nausea, emesis or postural hypotension typical for DA agonists could be observed with effective PRL lowering doses of TDHL. The unique profile of TDHL on DA functions suggests its usefulness as a potent, longlasting PRL inhibitor with less unwanted effects. The behavioural findings indicate the potential usefulness of TDHL as a neuroleptic, which due to its partial DA agonistic action, should lack typical extrapyramidal or neuroendocrine side effects of classic DA receptor blocking agents. Possible implications of the dual function of TDHL upon central DA receptors are discussed with regard to the incidence of side effects or selectivity of action for other conceivable therapeutic indications.     

Effects of novel 5-HT1A receptor antagonists on measures of postsynaptic 5-HT1A receptor activation in vivo

The effects of two putative 5-HT_1A antagonists, 4-(2′-methoxyphenyl)-1-[2′-[N-(2″-pyridinyl)-p-iodobenzamido]ethyl]piperazine (p-MPPI) and 4-(2′-methoxyphenyl)-1-[2′-[N-(2″-pyridinyl)-p-flourobenzamido]ethyl]piperazine (p-MPPF), were examined in vivo in two tests of postsynaptic 5-HT_1A receptor activation, hypothermia and reciprocal forepaw treading, in the rat. Both p-MPPI (10 mg/Kg, I.p.) and p-MPPF (10 mg/Kg, I.p.) antagonized the hypothermia induced by the 5-HT_1A receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) (0.5 mg/Kg, S.c.). Neither p-MPPI nor p-MPPF administered alone at a dose of 10 mg/kg (i.p.) induced hypothermia. Similarly, both p-MPPI (10 mg/Kg, I.p.) and p-MPPF (2.5 mg/Kg, I.p.) completely antagonized 8-OH-DPAT (2 mg/Kg, S.c.)-induced forepaw treading in rats pretreated with reserpine (1 mg/Kg, S.c., 18–24 hours prior to the experiment). p-MPPI and p-MPPF, at doses of 10 mg/kg (i.p.) did not induce forepaw treading in reserpine pretreated animals. The results of the present study demonstrate that p-MPPI and p-MPPF act as 5-HT_1A receptor antagonists in these measures of postsynaptic 5-HT_1A a receptor activation.     

Effect of humanin analogues on experimentally induced impairment of spatial memory in rats.

Humanin and its analogues have been shown to protect cells against death induced by various Alzheimer's disease genes and amyloid-beta-peptides in vitro: the analogue [Gly14]-humanin has also been shown to be potent in reversing learning and memory impairment induced by scopolamine in mice in vivo. It is important to validate these results by using other behavioral methods. In this study, the effect of [Gly14]-humanin and des-Leu-PAGA, another analogue (0.2 micromol kg(-1), i.p.) on the 3-quinuclidinyl benzilate-induced (2 mg kg(-1), i.p.) impairment of spatial memory in the multiple T-maze in rats has been evaluated. Both peptides reversed the impairment of spatial memory. These results indicate the potential of humanin analogues in modulation of the cholinergic system.     

Solanum paniculatum L. (Jurubeba): potent inhibitor of gastric acid secretion in mice.

Solanum paniculatum L. is used commonly in Brazilian folk medicine for the treatment of liver and gastrointestinal disorders. The freeze-dried aqueous extracts (WEs) obtained from distinct parts of the plant (flowers, fruits, leaves, stems and roots) were tested to determine their antiulcer and antisecretory gastric acid activities using mice. The aqueous extracts of roots, stems and flowers inhibited gastric acid secretion in pylorus-ligated mice with ED50 values of 418, 777 and 820 mg/kg body wt. (i.d.), respectively. Extracts of leaves (0.5-2 g/kg body wt., i.d.) did not affect gastric secretion, whereas fruit extracts (0.5-2 g/kg body wt., i.d.) stimulated gastric acid secretion. The stimulatory effect of the fruit extract was inhibited by pretreatment with atropine (5 mg/kg body wt., i.m.) but not with ranitidine (80 mg/kg body wt., i.p.) suggesting that the fruit extract activates the muscarinic pathway of gastric acid secretion. In contrast, administration of the root extract into the duodenal lumen inhibited histamine- and bethanechol-induced gastric secretion in pylorus-ligated mice. In addition, the aqueous extract of roots (ED50 value, 1.2 g/kg body wt., p.o.) protected the animals against production of gastric lesions subsequent to the hypersecretion induced in mice by stress following cold restraint. This effect was not reproduced when the lesions were induced by blockade of prostaglandins synthesis via subcutaneous injection of indomethacin. Thus, antiulcer activity of the plant extracts appears to be related directly to a potent anti-secretory activity. No toxic signs were observed following administration of different extracts up to 2 g/kg body wt., p.o. Collectively, the results validate folk use of Solanum paniculatum L. plant to treat gastric disorders.     

Possible involvement of 5-HT and 5-HT2 receptors in acceleration of gastrointestinal transit by escin Ib in mice

We have reported previously that escin Ib accelerated gastrointestinal transit (GIT) in mice, and that its effect may be mediated by the release of endogenous prostaglandins (PGs) and nitric oxide (NO). In this study, the possible involvement of 5-HT and 5-HT receptors in the GIT acceleration of escin Ib was investigated in mice. The acceleration of GIT by escin Ib (25 or 50 mg/kg, p.o.) was attenuated by pretreatment with ritanserin (0.5-5 mg/kg, s.c., a 5-HT(2A/2C/2B) receptor antagonist), but not with MDL 72222 (1 and 5 mg/kg, s.c.) and metoclopramide (10 mg/kg, s.c.) (5-HT3 receptor antagonists) or tropisetron (1 and 10 mg/kg, s.c., a 5-HT(3/4) receptor antagonist). Furthermore, pretreatment with ketanserin (0.05-5 mg/kg, s.c.), haloperidol (1-5 mg/kg, s.c.) and spiperone (0.5-5 mg/kg, s.c.) (5-HT2A receptor antagonists), as well as a bolus of dl-p-chlorophenylalanine methyl ester (PCPA, 1000 mg/kg, p.o., 1, 6 or 24 h before administration of the sample) (an inhibitor of 5-HT synthesizing enzyme tryptophan hydroxylase) and reserpine (5 mg/kg, p.o.) (a 5-HT depletor), but not 6-hydroxydopamine (80 mg/kg, i.p., a dopamine depletor) or repeated PCPA (300 mg/kg x2, p.o., 72 and 48 h before administration of the sample), also attenuated the effects of escin Ib. It is postulated that escin Ib accelerates GIT, at least in part, by stimulating the synthesis of 5-HT to act through 5-HT2, possibly 5-HT2A receptors, which in turn causes the release of NO and PGs.     

Role of benzodiazepine-GABAA receptor complex in attenuation of U-50,488H-induced analgesia and inhibition of tolerance to its analgesia by ginseng total saponin in mice

In the present study, the role of benzodiazepine-GABAA receptor complex in the attenuation of U-50,488H (U50), a selective kappa opioid agonist-induced analgesia and inhibition of tolerance to its analgesia by ginseng total saponin (GTS) was investigated using the mice tail-flick test. The intraperitoneal (i.p.) treatment of GTS (100 and 200 mg/kg) and diazepam (0.1-1 mg/kg) dose-dependently attenuated the U50 (40 mg/kg, i.p.)-induced analgesia. GTS (0.001-10 microg/ml) did not alter binding of [3H]naloxone to mice whole brain membrane. The attenuation effect of GTS (100 mg/ kg) and diazepam (0.5 mg/kg) on U50-induced analgesia was blocked by flumazenil (0.1 mg/kg, i.p.), a benzodiazepine receptor antagonist, and picrotoxin (1 mg/kg, i.p.), a GABAA-gated chloride channel blocker. However, bicuculline (1 mg/kg, i.p.), a GABAA receptor antagonist blocked the attenuation effect of diazepam (0.5 mg/kg) but not GTS (100 mg/kg) on U50-induced analgesia. Chronic treatment (day 4-day 6) of GTS (50-200 mg/kg) and diazepam (0.1-1 mg/kg) dose-dependently inhibited the tolerance to U50-induced analgesia. Flumazenil (0.1 mg/kg) and picrotoxin (1 mg/kg) on chronic treatment blocked the inhibitory effect of GTS (100 mg/kg) and diazepam (0.5 mg/kg) on tolerance to U50-induced analgesia. On the other hand, chronic treatment of bicuculline (1 mg/kg) blocked the inhibitory effect of diazepam (0.5 mg/kg) but not GTS (100 mg/kg) on tolerance to U50-induced analgesia. In conclusion, the findings suggest that GTS attenuates U50-induced analgesia and inhibits tolerance to its analgesia and this action involves benzodiazepine receptors and GABAA-gated chloride channels.     

Micronucleus test with 6-mercaptopurine monohydrate administered intraperitoneally and orally

The effect of route of administration on the induction of micronucleated polychromatic erythrocytes (MNPCEs) was examined. 6-Mercaptopurine monohydrate (6-MP) was administered intraperitoneally (i.p.) or orally (p.o.) to 2 strains of mice, MS/Ae and CD-1. From the results of an acute toxicity test and a pilot micronucleus test, the doses selected for the final micronucleus test were 12.5-100 mg/kg for the i.p. route and 25-200 mg/kg for the p.o. route. The sampling time was 48 h. Frequencies of MNPCEs increased dose-dependently by the i.p. route but peaked at 50 or 100 mg/kg for the p.o. route. 6-MP induced MNPCEs more efficiently after p.o. administration than after i.p. treatment in both strains.     

Portal hypertension and liver lesions in chronically alcohol drinking rats prevented and reversed by stable gastric pentadecapeptide BPC 157 (PL-10, PLD-116), and propranolol, but not ranitidine.

Liver lesions and portal hypertension in rats, following chronic alcohol administration, are a particular target for therapy. Portal hypertension (mm Hg) assessed directly into the portal vein, and liver lesions induced by 7.28 g/kg b.w. of alcohol given in drinking water for 3 months, were counteracted by a stable gastric pentadecapeptide BPC 157, GEPPPGKPADDAGLV, M.W. 1419, known to have a beneficial effect in a variety of models of gastrointestinal or liver lesions (10 microg or 10 ng/kg b.w. i.p. or i.g.) and propranolol (10 mg/kg b.w. i.g.), but not ranitidine (10 mg/kg b.w. i.g.) or saline (5 ml/kg b.w. i.p./i.g.; control). The medication (once daily) was throughout either the whole 3 months period (1) or the last month only (2) (last application 24 h before sacrifice). In the background of 7.28 g/kg/daily alcohol regimen similar lesions values were assessed in control rats following alcohol consumption, after 2 or 3 months of drinking. Both prophylactic and therapeutic effects were shown. After a period of 2 or 3 months, in all control saline [intragastrically (i.g.) or intraperitoneally (i.p.)] treated rats, the applied alcohol regimen consistently induced a significant rise of portal blood pressure values over values noted in healthy rats. In rats that received gastric pentadecapeptide BPC 157 or propranolol the otherwise raised portal pressure was reduced to the values noted in healthy rats. Besides, a raised surface area (microm(2)) and increased circumference (microm) of hepatocyte or hepatocyte nucleus [HE staining, measured using PC-compatible program ISSA (VAMS, Zagreb, Croatia)] and an advanced steatosis [scored (0-4), Oil Red staining] (on 100 randomly assigned hepatocytes per each liver), an increased liver weight, all together parallel a raised portal pressure in controls. Some of them were completely eliminated (not different from healthy rats, i.e. portal pressure, the circumference and area of hepatocytes, liver weight), while others were markedly attenuated (values less than in drinking controls, still higher than in healthy rats, i.e. circumference and area of hepatocytes nucleus). On the other hand, ranitidine application attenuated only steatosis development. In summary, despite continuous chronic alcohol drinking, pentadecapeptide BPC 157, and propranolol may prevent portal hypertension as well as reverse already established portal hypertension along with related liver disturbances.     

Cardiovascular responses to intrathecal administration of endomorphins in anesthetized rats

Endomorphins (EMs), the endogenous, potent and selective mu-opioid receptor agonists, have been shown to decrease systemic arterial pressure (SAP) in rats after intravenous (i.v.) administration. In the present study, cardiovascular responses to intrathecal (i.t.) injection of EMs were investigated in urethane-anesthetized rats. It is noteworthy that EMs elicited decreases in SAP and heart rate (HR) in a dose-dependent manner; 10-300nmol/kg were injected intrathecally. Furthermore, these vasodepressor and bradycardic effects were significantly antagonized by naloxone (0.5mg/kg, i.t.). Interestingly, i.t. (5mg/kg) or i.v. (50mg/kg) administrations of N(omega)-nitro-l-arginine methylester (l-NAME) attenuated the vasodepressor and bradycardic effects. Moreover, pretreatment of the rats with muscarinic receptor antagonist atropine (2mg/kg, i.v.) and alpha-adrenoceptor antagonist phentolamine (1mg/kg, i.v.) significantly reduced the vasodepressor effects of EMs. Nevertheless, pretreatment with beta-adrenoceptor antagonist propranolol (2mg/kg, i.v.) could only block the bradycardia effects induced by EMs, but had no significant effects on the hypotension. In summary, all the results suggested that i.t. administration of EMs decreased SAP and HR which were possibly mediated by the activation of opioid receptors in the rat spinal cord. In addition, nitric oxide (NO) release in both the spinal cord and in peripheral tissues might regulate the cardiovascular activities of EMs, and the muscarinic receptor and adrenoceptor played an important role in the regulation of the cardiovascular responses to i.t. administration of EMs.