Abstract: Hypoxic-ischemic encephalopathy is a severe complication of perinatal asphyxia and causes lifelong deficits in infants and children. Multiple mechanisms acting in serial or parallel fashion are likely to be involved in this procedure. The neuronal injury is strongly related to iron-catalysed oxygen radical production and subsequent peroxidative damage to lipids and protein. Excessive release of excitatory amino acids (EAA) glutamate and aspartate, with consequent overstimulation of glutamate receptors, is also thought to be an important mechanism in this brain injury. Deferoxamine (DFO), a chelator of non-protein-bound iron, has been shown to inhibit lipid peroxidation and hydroxyl radical production via the Fenton reaction and to decrease hypoxic-ischemic and reperfusion associated brain injury. However, the exact mechanism of neuroprotection of DFO and its possible effect on the neurotransmitters' release is currently being investigated. In the present study, a well-established model of perinatal asphyxia was used to investigate the effect of DFO on hypoxic-ischemic-induced damage to different hippocampal brain structures. DFO was administrated subcutaneously immediately after the asphyctic insult. Histological examination of the hippocampus was conducted and the tissue levels of glutamate and aspartate in the same area were determined. A remarkable reduction of hypoxia-ischemia-evoked neurons in the CA1 hippocampal region and a decrease in the asphyxia-induced hippocampal tissue levels of glutamate and aspartate was noted after DFO treatment. These findings suggest a complex action of DFO, which could be neuroprotective when administrated in the immature brain immediately after hypoxia-ischemia.
Abstract: Hypoxic-ischaemic (HI) encephalopathy is a severe complication of perinatal asphyxia and remains a frequent cause of a variety of brain disorders with long-term effects on the patients' life. The associated brain damage is strongly related to the toxic action of excitatory amino acids, especially glutamate and aspartate. Lamotrigine is an anti-epileptic drug that blocks the voltage-gated sodium channels of the presynaptic neuron and inhibits the release of glutamate. In the present study a well-established model of perinatal asphyxia in 7-d-old rats was used to investigate the effect of lamotrigine on HI-induced damage to different hippocampal brain structures, since disruption of this brain area is thought to play a key role in schizophrenia and epilepsy. Therefore, a combination of ischaemia, induced by unilateral occlusion of the left common carotid artery, followed by exposure to a 1-h period of hypoxia, was carried out in neonatal 7-d-old rats. Immediately after the insult, lamotrigine was given i.p. The histological outcome in the hippocampus was conducted and the tissue levels of glutamate, aspartate, GABA, and glutamine in the same area were determined. A remarkable reduction of HI-evoked damaged neurons in most of the investigated hippocampal regions was noted after lamotrigine administration. Furthermore, lamotrigine decreased the asphyxia-induced hippocampal tissue levels of glutamate and aspartate. Immediately after perinatal asphyxia GABA levels were enhanced, while levels of glutamine were decreased. Lamotrigine administration did not affect either GABA or glutamine levels. These results suggest a neuroprotective effect of lamotrigine in this particular animal model of neonatal HI encephalopathy.
Abstract: Anabolic androgenic steroids (AASs) affect areas of the central nervous system, which are involved in emotional and cognitive responses such as sexuality, anxiety, and memory. In the present study we imitated the abuse of AASs by administering high doses of the AAS nandrolone decanoate (ND) to rats. Thereafter rats were exposed to an elevated plus-maze and an olfactory social memory test to evaluate their anxiety-like and cognitive behaviour. To reveal whether these emotional and cognitive changes evoked by ND were caused via direct activation of androgenic receptors (ARs) in the brain, the AR antagonist flutamide (FL) was administered intracerebroventricularly (i.c.v.). Male rats were randomly divided in four groups, one group received 15 mg/kg ND subcutaneously, once daily for 6 wk (ND group). In the second group, in addition to ND, a daily dose of 5 microg FL was injected i.c.v. also for 6 wk (ND+FL group). The third group of rats received only FL and in the control group the vehicle was injected. The ND group clearly spent more time investigating the open arms in the maze test and recognizing the juvenile during the olfactory social memory test in comparison to the control group. In the ND+FL group rats showed similar emotional behaviour and cognitive ability to that of the control group. Injection of FL alone did not affect either anxiety or memory. These results indicate that repeated, high-dose administration of ND decreases anxiety and impairs memory in rats via direct activation of central ARs.
Abstract: BACKGROUND: Lesions of cutaneous lupus erythematosus (CLE) are refractory to a wide range of topical or systemic therapies. The pathogenesis of CLE is multifactorial and polygenic, and many of its details remain unclear. However, immunologic evidence suggests the possible therapeutic use of tacrolimus and pimecrolimus. CLE is one of the most common dermatological autoimmune disorders worldwide, which includes systemic lupus erythematosus (SLE) with malar rash, subacute cutaneous lupus erythematosus (SCLE) and discoid lupus erythematosus (DLE). OBJECTIVE: Our aim was to determine the efficacy of topical pimecrolimus and tacrolimus in the treatment of cutaneous lupus erythematosus. METHODS: The literature was systematically reviewed. Medline, Embase, and the Cochrane Database were searched for systemic reviews, randomised controlled trials and nonrandomised clinical trials using the search terms "pimecrolimus", "Elidel", "SDZ ASM 981", "tacrolimus", "Protopic", "FK506" and "cutaneous lupus erythematosus". Studies were assessed independently by two authors. RESULTS: Five studies were eligible for inclusion in this review. Only one of them was a randomised controlled trial (RCT). There was no significant difference between tacrolimus and clobetasol; however, evidence indicates the highest tolerability of tacrolimus compared with corticosteroids. This review indicates the efficacy of tacrolimus and pimecrolimus in, at least initial, cutaneous lesions of SLE. However, in SCLE and DLE lesions, the efficacy appears to be lower, perhaps due to the chronicity of those lesions. CONCLUSION: The lack of RCTs is characteristic. Future studies should focus on efficacy, short- and long-term effects and cost-effectiveness. However, tacrolimus and pimecrolimus show efficacy, and such effort is worthwhile.
Abstract: BACKGROUND: Spinal-cord injury (SCI) is a leading cause of neuropathic pain (NP). Current pharmaceutical treatments for NP in SCI patients are not effective. Two promising options are gabapentin (GP) and pregabalin (PB). Their predominant mechanism of action is believed to be the inhibition of calcium currents, leading in turn to reduced neurotransmitter release and attenuation of postsynaptic excitability. This could explain much of their efficacy in the treatment of both seizure disorders and pain syndromes. However, evidence for their efficacy in attenuating NP of SCI is still controversial. OBJECTIVE: To efficiently integrate valid information and provide a basis for rational decision making, through determining PB and GP efficacy in treating NP in SCI. METHODS: Literature was systematically reviewed. Medline, Embase, CINAHL and Cochrane Database were searched using search terms 'gabapentin', 'pregabalin', 'neurontin', 'lyrica', 'neuropathic pain' and 'spinal-cord injury'. Studies were assessed independently by two authors. RESULTS: Five studies were eligible for inclusion. Two of them studied PB and three GP. Both GP and PB appear to be efficacious for NP in SCI. A clear comparison between the two drugs could not be performed. The literature data suggest that PB is more efficacious than GP in many important variables for NP in SCI, although PB use is followed by more side effects than GP. PB reduced Visual Analogue Score (VAS) in both studies (P < 0.001 and P = 0.016). On the other hand, for GP a maximum dosage of 3,600 mg/day reduced VAS score (P = 0.000), whereas a maximum dosage of 1,200 mg/day failed to do so. CONCLUSION: There is a lack of studies comparing GP and PB in treating NP in SCI. This systematic review indicates the possible efficacy of PB and GP in NP of SCI. Recommendations for future research to inform clinical practice should include cost-effectiveness studies and dose-response analysis in order to determine the schema employed and the duration of treatment.
Abstract: Sciatic nerve injury in neonatal rats results in significant reduction in the number of surviving motoneurons and impairs muscle development. We examined the possible neuroprotective effects of daily in vivo administration of 1,4,7,8,9,10-hexahydro-9-methyl-6-nitropyrido[3,4-f]quinoxaline-2,3-dione (PNQX), an AMPA/kainate receptor antagonist, on sciatic nerve injured rats, during the period of plasticity of the rat nervous system. Furthermore, we investigated the effect of PNQX on muscle properties impaired by nerve crush. At the second postnatal day, the sciatic nerve of the rat left hind limb was crushed. Twenty-four rats were subsequently treated with PNQX and an equal number of rats, as control group, were treated with saline. PNQX was injected subcutaneously once daily (14 mg kg(-1) body weight). Treatment continued until the rats were 14 days old. Measurements were then carried out to assess the contractile properties of the extensor digitorum longus (EDL), a fast-contracting muscle, and of the soleus muscle, a slow-contracting muscle, in four "age groups" of rats, each consisting of six PNQX-treated and six control animals: (a) postnatal day (P) 14, (b) postnatal day (P) 21, (c) postnatal day (P) 28 and (d) adult rats. The following parameters were recorded: number of motor units, muscle weight, maximal tetanic tension (TET 100), time to peak (TTP), half relaxation time (HRT), and fatigue index (FI). Improvement in motor unit survival after nerve injury was observed in all age groups administering PNQX. Also axotomy-induced impairment of muscle properties such as muscle weight, tension development, contraction and relaxation velocity was counteracted by injection of PNQX. The fatigue index was altered by axotomy and mostly normalized by treatment with this compound. AMPA/kainate receptor antagonists, with low toxicity, may serve in the future, as possible neuroprotective agents after acute neural injury or even as therapeutic agents in neurodegenerative diseases.
Abstract: Male Sprague-Dawley rats underwent sinoaortic denervation (SAD) or sham operation. We examined changes in the release rates of GABA, glutamate and arginine in the locus coeruleus (LC) elicited by experimental blood pressure increases (i.v. noradrenaline infusion for 3 min, 4 microg kg(-1)min(-1)) or decreases (i.v. sodium nitroprusside infusion for 3 min, 150 microg kg(-1)min(-1)). The release of the neurotransmitters was monitored by the push-pull superfusion technique. Mean blood pressure did not differ between sham-operated and SAD rats but blood pressure lability was greatly enhanced in SAD rats and accompanied by increased basal release of glutamate in the LC. GABA release was not affected. A rise in blood pressure induced by noradrenaline enhanced GABA release in the LC of sham-operated rats. This effect was abolished by SAD. Glutamate release did not respond to hypertension either in SAD or in sham-operated rats. Nitroprusside led to a fall in blood pressure which was more pronounced and lasted longer in SAD than in sham-operated rats. In SAD rats, glutamate release was enhanced by nitroprusside. The depressor response had no effect on glutamate release in sham-operated rats. GABA release did not respond to this stimulus in either SAD or sham-operated rats. SAD and blood pressure changes did not influence the release rate of arginine. In conclusion, experimental hypertension increases GABAergic activity in the LC by stimulating peripheral baroreceptors. In SAD rats, augmented blood pressure lability seems to be at least partly due to elevated glutamate outflow within the LC.
Abstract: The objective of this study was to determine the effects of oral phentolamine, administered before sleep, on nocturnal penile erectile activity of men with mild to moderate erectile dysfunction (ED). We studied five patients with mild to moderate ED (mean age 34.8 +/- 8.13 and mean duration of ED 31.8 +/- 23.5 months), in a double-blind, placebo-controlled, crossover study. All patients received oral phentolamine (Vasomax) at a dose of 40 mg and placebo for three consecutive nights respectively and were submitted to nocturnal penile tumescence and rigidity monitoring (NPTR) with the Rigiscan device. NPTR parameters of the two 3-night recordings were evaluated and compared. Administration of oral phentolamine before sleep was associated with a statistically significant increase in the number of erectile events with rigidity > or = 60% lasting > or = 10 min (P = 0.02), as well as the rigidity activity units (RAU) value per hour sleep, both at the base (P = 0.023) and the tip of the penis (P = 0.019). The number of events as measured by Rigiscan software (20% change in circumference), as well as tumescence activity units (TAU)/h values did not show any statistical difference. No adverse effects were recorded. It is concluded that oral phentolamine administered before sleep enhanced NPTR parameters associated with the quality of the erectile events. Such results provide a pathway for the development of a prevention strategy for ED. Future studies will elucidate whether vasoactive agents taken on a regular basis before sleep, can prevent ED in men at risk, protecting also minimally and moderately impotent patients to become moderately and severely impotent respectively.
Abstract: To reveal the functional importance of amino acid neurotransmission in the amygdala (AMY) of conscious spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats, the in vivo release of glutamate (GLU) and GABA in this brain structure was studied using the push-pull superfusion technique. Basal GLU and GABA release rates in the AMY were comparable in SHR and WKY rats, although arterial blood pressure (BP) in SHR (152+/-6 mmHg) was higher than in WKY rats (102+/-4 mmHg). Neuronal depolarization by superfusion with veratridine enhanced the release of GLU and GABA to a similar extent in both rat strains. On the other hand, exposure to noise stress (95 dB) for 3 min led to a tetrodotoxin-sensitive increase in GLU release in the AMY of SHR, but not WKY rats. The concurrent pressor response to noise was enhanced in SHR as compared to WKY rats. A rise in BP induced by intravenous infusion of phenylephrine for 9 min had no effect on amino acid release in the AMY of both strains. The data suggest an exaggerated stress response of glutamatergic neurons in the AMY of SHR as compared with WKY rats, which might be of significance for the strain differences in the cardiovascular and behavioural responses to stress. The results also show that, in both rat strains, glutamatergic and GABAergic neurons in the AMY are not modulated by baroreceptor activation. Moreover, hypertension in adult SHR does not seem to be linked to a disturbed synaptic regulation of glutamatergic or GABAergic transmission in the AMY.
Abstract: We investigated the importance of endogenous amino acids in the locus coeruleus in inescapable electric shock and conditioned fear. In naive rats and in rats exposed to noise (N), light (L) and electric shock (S) or to N + L only, the locus coeruleus was superfused with artificial cerebrospinal fluid through a push-pull cannula and the release of GABA, taurine, glutamate, aspartate, serine and glutamine was determined in the superfusate by HPLC after derivatization with o-phthaldialdehyde. Locomotor activity, arterial blood pressure and heart rate were telemetrically monitored. The placement of naive rats or conditioned rats from their home cage to a chamber provided with a grid-floor for shock virtually did not change the release rates of the amino acids in the locus coeruleus. Motility was enhanced in naive and conditioned rats to a similar extent. Blood pressure and heart rate were enhanced in conditioned rats only. Exposure to N + L + S for 5 min greatly enhanced the release rates of all determined amino acids in the locus coeruleus. In conditioned rats the increase in release of most amino acids lasted longer than in naive rats. Electric shock also enhanced motility, blood pressure and heart rate. In conditioned rats, motility and cardiovascular changes were more pronounced and/or lasted longer than in naive rats. Exposure of conditioned rats to the conditioned stimuli N + L for 5 min led to an increased release of taurine and aspartate. The enhanced release of taurine lasted 30 min. Exposure to N + L did not affect the release rates of amino acids in naive rats. N + L did not influence motility but arterial blood pressure and heart rate were elevated in conditioned rats. The findings show that inescapable electric shock enhances the release of several amino acids in the locus coeruleus, while conditioned fear selectively increases the outflow of taurine and aspartate. Moreover, conditioned fear prolongs the response of excitatory and inhibitory amino acids to electric shock. The results suggest that an excitatory amino acid (aspartate) and an inhibitory amino acid (taurine) of the locus coeruleus are implicated in conditioned fear.
Abstract: Intravenous bolus injection of KCN (40 microg) elicited brief but pronounced tachypnea, bradycardia and pressor response, and led to a 37% increase in 5-hydroxytryptamine (serotonin) (5-HT) release in the locus coeruleus (LC) of freely moving rats. Slow infusion of KCN (15 microg/min) for 10 min induced only a slight pressor response, but increased the respiration rate (+39 breaths/min), as well as 5-HT release in the LC (+60%) throughout the infusion. In rats with transected chemoreceptor afferents, neither injection or infusion of KCN changed 5-HT release, suggesting that in intact animals, the effect on extracellular 5-HT was due to activation of peripheral chemoreceptors. In summary, we report that peripheral chemoreceptor activation enhances 5-HT release in the LC, indicating that 5-HT might be involved in the modulation of LC activity by ascending chemosensory information.
Abstract: The contractile effect of benzylpenicillin on isolated rings of human gallbladder was studied using preparations taken from surgical specimens after gallbladderectomy. The gallbladder was cut into two pieces and one ring was cut from each piece; one ring was mounted in a 100 ml organ bath containing Krebs solution and the isotonic changes of the preparation were recorded for each experiment. Benzylpenicillin (1 x 10(4) to 1 x 10(8) IU/l) was shown to exert a dose-dependent contractile effect on isolated human gallbladder rings which was blocked by atropine (1 x 10(-8) M). The benzylpenicillin-induced contractile effect was analogous to contraction observed with acetylcholine (1 x 10(-7) to 1 x 10(-2) M). The effect of benzylpenicillin on isolated human gallbladder may reflect a possible decrease in gallbladder emptying time in vivo, suggesting a beneficial effect of benzylpenicillin in antimicrobial treatment of gallbladder infections.
Abstract: The involvement of excitatory amino acids (EAA) in the pathogenesis of hypoxic-ischemic states is well-documented. Information on the role of overexcitation by EAA in perinatalasphyxia (PA), however, is limited and data from adult models cannot be directly extrapolated to immature systems. Moreover, most adult models of ischemia are representing stroke rather than PA. We decided to study long term effects in a non-invasive rat model of PA resembling the clinical situation three months following the asphyctic insult. Morphometry on Nissl - stained sections was used to determine neuronal death in frontal cortex, striatum, hippocampus CA1, hypothalamus and cerebellum L1, and the amino acids glutamate, glutamine, aspartate, GABA, taurine, arginine as well as histamine, serotonin and 5-hydroxy-indoleacetic acid were determined in several brain regions and areas. Morphometry revealed that neuronal loss was present in the hippocampal area CA1 in all groups with PA and that morphological alterations were significantly higher in the cerebellar granular layer. The prominent light microscopical finding in all areas of asphyctic rats studied was decreased Nissl-staining, suggesting decreased cellular RNA levels. Glutamate, aspartate and glutamine were significantly elevated in the hypothalamus of asphyctic rats probably indicating overstimulation by EAA. Excitotoxicity in this area would be compatible with findings of emotional / behavioral deficits observed in a parallel study in our model of PA. Our observations point to and may help to explain behavioral and emotional deficits in Man with a history of perinatal asphyxia.
Abstract: The establishment of a dose-response relationship and its quantification is the usual procedure for analysing drug action on an isolated organ. However, the time course of the effect seems to be an inherent characteristic of the agonist which produces it. In our study, we have analyzed the time-response curves of four cholinergic agonists (acetylcholine, methacholine, carbachol and bethanechol) which produce tonic contractions of the isolated rat gastric fundus. The order of affinity of agonists to muscarinic receptors on the rat fundus were carbachol > bethanechol > methacholine > acetylcholine (K(A) values: 46 +/- 12, 84 +/- 21, 380 +/- 110 and 730 +/- 120 nM, respectively). The effective concentrations which produced 60% of the maximal response (EC60) were used for establishing the time-response curves. The time-response curves were also recorded after partial alkylation of muscarinic receptors with phenoxybenzamine, after exposure of the isolated rat fundus to physostigmine and after addition of supramaximal concentrations of the agonists. The experimental time-response curve for acetylcholine was on the extreme left, followed by curves for methacholine, bethanechol and carbachol, respectively. Phenoxybenzamine and supramaximal doses of the agonists did not change the order of response development in time, but supramaximal doses shifted all curves to the left and phenoxybenzamine shifted all time-response curves to the right. Only physostigmine shifted the time-response curve for methacholine to the right. The results of our study suggest that the response rate of the isolated rat gastric fundus to cholinergic agonists depends on the intrinsic activity of these agents, but not on their affinity for muscarinic receptors.
Abstract: We investigated in conscious, freely moving rats whether the release of GABA, taurine and arginine in the hypothalamus is influenced by impulses originating from peripheral baroreceptors. The posterior hypothalamic nucleus was superfused with artificial cerebrospinal fluid through a push-push cannula and the release of amino acids was determined in the hypothalamic superfusate of control rats, as well as of rats after bilateral aortic denervation (AD). AD led to hypertension and increased the lability of arterial pressure. In sham-operated rats, intravenous infusion of phenylephrine increased blood pressure and the hypothalamic release of GABA and taurine. AD almost abolished the phenylephrine-induced release of the inhibitory amino acids. Similarly, the pressor response to hypervolaemia, elicited by blood injection, enhanced the release rates of GABA and taurine only in sham-operated rats. Baroreceptor unloading evoked either by intravenous infusion of nitroprusside, or by haemorrhage, decreased the release rates of GABA and taurine in sham-operated rats but not in AD rats. Electrical stimulation of the afferent aortic depressor nerve enhanced extracellular GABA and taurine in the posterior hypothalamic nucleus. The release rate of arginine was not influenced by alterations in baroreceptor activity either in sham-operated or in AD rats. The findings support the idea that, in the hypothalamus, GABA and taurine are involved in central blood pressure regulation. The release of these two amino acids seems to be driven tonically by baroreceptor impulses. Moreover, the findings indicate that the baroreceptors of the aortic arch play a crucial role in the mediation of changes in hypothalamic GABA and taurine outflow so as to counteract blood pressure fluctuations.
Abstract: We have investigated the effects of beta-lactam antibiotics on isolated preparations of rat fundus, ileum, and the body of feline stomach. Isotonic changes of isolated preparations were recorded. Benzylpenicillin (EC50 = 1.31 +/- 0.13 x 10(-5) M), ampicillin (EC50 = 2.16 +/- 0.15 x 10(-5) M), cefotaxime (EC50 = 1.33 +/- 0.15 x 10(-5) M), ceftriaxone (EC50 = 4.39 +/- 0.13 x 10(-5) M) and ceftazidime (EC50 = 1.42 +/- 0.01 x 10(-3) M) produced concentration-dependent tonic contractions of rat fundus. Rat ileum and feline stomach did not respond on these substances. Lidocaine (2.3 x 10(-5) M) and physostigmine (1.0 x 10(-8) M) significantly potentiated contractions produced by benzylpenicillin. On the other hand, methysergide (1.4 x 10(-7) M) and atropine (9.6 x 10(-9) M) significantly blocked tonic contractions produced by benzylpenicillin. Effects of beta-lactam antibiotics on smooth muscle isolated preparations were tissue and species dependent, indicating selectivity of their action.
Abstract: The routine procedure for analysing the drug action on isolated organs is the establishment of the dose-response relationship and its quantification. In the first part of the experiment, we established the dose-response relationship for acetylcholine, carbachol, betanechol and 5-hydroxytriptamine on isolated preparations of rat fundus. In the second part, we analyzed the development in time of the rat fundus response to a single concentration of each of the four agonists. The single concentrations used were slightly higher than the EC50 of the agonists eliciting an optimal response. Responses to betanechol and carbachol developed with essentially the same rate, while responses to acetylcholine and 5-hydroxytriptamine developed more rapidly and more slowly, respectively. Since the rate of response development is highly dependent on the type of the receptor the agonist activated, analysis of response development in time could be an useful adjunctive tool in the pharmacodynamic studies.
Abstract: This study concerns the investigation of felodipine's influence on some parameters of vasomotion physiology. Felodipine is a new generation 1,4 dihydropyridine (1,4 DHP) Ca(2+)-entrance blocker with marked vascular selectivity. It was found that felodipine 1-10 microM presents a Ca2+ entrance-blocking activity when the bovine aortic smooth muscle is normal or stimulated by K+ 65.4 mM or the alpha-adrenoceptor agonist phenylephrine 1 microM. The same action is observed after nifedipine, a first-generation 1,4 DHP derivative with less angioselectivity in clinical practice. It was also found that felodipine 1-10 microM antagonizes the contraction of the bovine aortic ring that is induced by phenylephrine 10 microM or KCl 65.4 mM. On the contrary, felodipine 1-10 microM increases the contraction of the rat aortic ring that is induced by the same substances. It is known that some 1,4 DHP derivatives that are Ca2+ activators can also behave as Ca2+ blockers and that their final action is dependent upon membrane potential. Now it is also proved that the kind of animal species may also influence the action of the 1,4 DHP derivatives. It was finally found that felodipine increases the catecholamine stores of the sympathetic nerve terminal at the mouse heart (H) and liver (L). Obtained values were as following: control 15.00 +/- 7.7 (H) and 17.72 +/- 3.5 (L). Felodipine 54.50 +/- 4.9 (H) and 41.54 +/- 10.4 (L). Since catecholamine stores depend on secretion (Ca(2+)-dependent) and reabsorption (mostly Na(+)-dependent) rates, the increase after felodipine may be attributed to a decreased secretion due to a Ca2+ entry inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)
Abstract: The influence of methionine-5-enkephalin (M-5-E), an endogenous opioid receptor agonist, on calcium uptake by bovine aortic media was investigated in vitro. 45Ca was used and radioactivity was counted in a beta scintillation counter. M-5-E increases Ca2+ uptake by the preparation. This action is inhibited by naloxone and that is proof that an opioid receptor is stimulated. A comparative study showed that phenylephrine, an alpha-adrenoceptor agonist, exhibits the same action as M-5-E, whereas morphine's action is negligible. Phenylephrine contracts the deendotheliazed ring of the bovine aorta, whereas M-5-E fails to do so. It is concluded that an opioid receptor was identified at the bovine aortic smooth muscle. This receptor is stimulated by M-5-E resulting in an increase of the extracellular Ca2+ entrance. Although no relationship was observed between the receptor and the contraction mechanism, a possible role of M-5-E in the maintenance of the vascular tone cannot be excluded.
