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Biomedical subjects

E L Way

Publications and source records attributed to E L Way.

At least 55 records · Page 3Linked to original sources
PubMed1982

Potency of three opiate antagonists to reverse the inhibitory activity of dynorphin, enkephalins and opioid-like alkaloids on the guinea pig ileum.

To test the hypothesis that dynorphin is a K-opiate agonist acting on the myenteric plexus, the potency of two benzomorphan antagonists (Win 44, 441 and Mr 2266) to block the inhibitory action of dynorphin, enkephalins and opioid alkaloids was determined on the longitudinal muscle preparation of the guinea pig ileum. The effectiveness of these antagonists was compared to that of naloxone. Antagonistic potency was established by calculating the apparent antagonist dissociation constant, Ke, as derived from Schild plots. Win 44, 441 and Mr 2266 were about 7-8 times more potent than naloxone against dynorphin, dynorphin-(1-13) or ethylketocyclazocine. Although the Ke obtained with Win 44, 441 or Mr 2266 against dynorphin or ethylketocyclazocine were significantly lower than those of naloxone, the values obtained for these antagonists did not differ significantly in the case of each of these agonists. With respect to the antagonism of the enkephalins or normorphine, Win 44, 441 was the most potent antagonist. Its Ke value for the enkephalins was 2.5-3 times lower than those for dynorphin or ethylketocyclazocine and in comparison to naloxone, Win 44, 441 was about 5 times more potent. Although Mr 2266 was a potent antagonist of dynorphin, ethylketocyclazocine, the enkephalins or normorphine, it showed no selectivity of action. The fact that the 3 opiate antagonists evidenced similar Ke values for dynorphin and ethylketocyclazocine, but different ones for the enkephalins or normorphine supports the conclusion that dynorphin activates preferentially K- but not mu-opiate receptors in the myenteric plexus.

Animals↗
PubMed1982

Possible modulatory role of dynorphin on the excitation by neurotensin on the guinea pig myenteric plexus.

Dynorphin 1-13 antagonized in a concentration-dependent fashion the contractile effect of neurotensin on the isolated preparation of the guinea pig ileum myenteric plexus. The inhibitory action of dynorphin was reduced in the presence of naloxone indicating the opioid nature of this interaction. Atropine also reduced the excitatory component of the neurotensin-induced contractile response; the joint application of atropine plus dynorphin did not cause additional inhibition of the contractile effect of neurotensin.

Animals↗
PubMed1982

A high affinity Ca2+-ATPase in enriched nerve-ending plasma membranes.

A preparation of enriched synaptosomal plasma membrane (SPM) from mouse brain was found to contain a Mg2+-independent high affinity Ca2+-activated ATPase. The preparation readily accumulated Ca2+ at micromolar concentration from the medium in the presence or absence of Mg2+ and released previously accumulated calcium upon the addition of ATP. It is concluded that SPM Ca2+-ATPase may have a functional role in removal of cytosol Ca2+.

Animals↗
PubMed1982

Calcium-activated ATPases in presynaptic nerve endings.

We studied the properties of calcium-activated ATPases present in preparations of isolated presynaptic nerve ending (synaptosome) and its subfractions from mouse brain. ATPase activity in the preparation was stimulated by Ca2+ and by Mg2+, but not by Na+ and K+, when each was added alone. The substrate specificities were found to be similar. The ATPases hydrolyzed only the high-energy phosphate bond and similar activity was exhibited for all nucleoside triphosphates tested (ATP, CTP, GTP, UTP). Moreover, the enzymes were insensitive to mitochondrial markers and to ouabain, but were inhibited by La3+. La3+ produced uncompetitive inhibition of Ca2+-ATPase in intact synaptosomes. Inhibition by La3+ was greatly increased after lysis of the synaptosomes, suggesting that the active sites of the enzymes may be on the cytosolic face of the membranes. The Ca2+-ATPase activity in synaptosomes was increased by increasing concentrations of external K+, suggesting that Ca2+ influx may be involved The Ca2+-ATPase in synaptosomal plasma membranes and synaptic vesicles had higher specific activities than those of intact synaptosomes and were activated, both in the presence and the absence of Mg2+, by Ca2+ concentrations approximating the intracellular level (10(-7) M). It is concluded that the nonmitochondrial synaptosomal Ca2+-ATPase may play an important role in the regulation of intracellular Ca2+.

Adenosine Triphosphate↗
PubMed1982

Modification of endorphin/enkephalin analgesia and stress-induced analgesia by divalent cations, a cation chelator and an ionophore.

The possibility that divalent cations may antagonize opiate peptide analgesia and stress-induced analgesia was examined. Intracerebroventricular injection of low doses of Ca2+, Mn2+ and Mg2+ antagonized beta-endorphin and methionine-enkephalin analgesia. Ba2+ and Cd2+ were without effect. The ionophore, A23187, significantly antagonized beta-endorphin analgesia and the effect was increased when a low dose of Ca2+ was injected at the same time as the ionophore. Ethylene glycol tetraacetic acid (but not ethylenediamine tetraacetic acid) significantly potentiated endorphin analgesia. Stress-induced analgesia, as determined by increased tail-flick latencies following intraperitoneal injection of acetic acid, was effectively antagonized by naloxone, Ca2+ and Mn2+. The frequency of writhing following acetic acid injection was increased by both naloxone and divalent metal ions, again suggesting antagonism of endogenous opiates. These results confirm previous findings indicating that divalent metal ions (and especially Ca2+) may be involved in the actions of opiates.

Acetates↗
PubMed1982

Studies on the structural prerequisites for the activation of the beta-endorphin receptor on the rat vas deferens.

The inhibitory activity of a variety of opioid peptides was tested on the electrically stimulated rat vas deferens. Human beta-endorphin (beta h-EP) was the most potent of the opoioid-like peptides; it produced half-maximal inhibition of the neuromuscular twitching at a concentration of about 100 nM. The potency of beta h-EP was greater than that of camel, porcine, ovine or leucine5 beta h-EP, alpha-N-acetyl beta-ovine-EP was inactive. In contrast to beta-endorphin (beta-EP), methionine and leucine-enkephalin, dynorphin-(1-13), morphine and other narcotic analgesics were devoid of opioid-like activity. Fragments of beta-EP with amino acid deletions at the carboxy end of the molecule were considerably less potent than the parent compound. The fragment beta h-EP 1-21 was 70 times less potent than beta h-EP, whereas the segments beta h-EP 1-19 and beta h-EP 1-16 were both completely inactive. Deletions at the amino terminal of beta-EP yielded inactive compounds. The potency of beta h-EP was reduced in a dose-related fashion by applications of nanomolar concentrations of naloxone or N-allylnormetazocine and by micromolar concentrations of levorphanol or morphine. In decided contrast, opioid peptides such as methionine enkephalin, dynorphin-(1-13), beta-casomorphan derivatives or short chain beta h-EP segments such as beta-EP 1-16, beta-EP 1-19, beta-EP 6-31, beta-EP (1-5)-(16-31), methionine enkephalin plus beta-EP 6-31 or the N-acetyl beta-bovine-EP did not antagonize the inhibitory action of beta h-EP. The present results demonstrate that the rat vas deferens contains opioid receptors with considerable selectivity for beta-EP. It is concluded from this structure activity relationship study that the activation of the beta-EP receptor involves at least two sites of recognition on the beta-EP structure.

Animals↗
PubMed1981

Effects of amino acids, especially taurine and gamma-aminobutyric acid (GABA), on analgesia and calcium depletion induced by morphine in mice.

The analgesic effect of morphine was antagonized in mice by intracerebroventricular pretreatment with taurine, gamma-aminobutyric acid (GABA) or glycine and was potentiated by ethylene glycol tetra-acetic acid (EGTA) but not altered by L-glutamate or L-aspartate. The potentiation of morphine analgesia by EGTA was reversed by a concentration of taurine that did not alter the tail-flick response. The selective depletion of 45Ca2+ from synaptic vesicles observed with morphine administration was significantly inhibited by taurine injection (1.2 mumol/brain, i.vt.) but was not altered by the same dose of GABA. Inhibition of ATP-dependent 45Ca2+ uptake in synaptosomes by morphine was also completely reversed by taurine (10(-2)M which by itself did not alter 45Ca2+ uptake. These results suggest that antagonism of morphine analgesia by taurine may be caused by blockade of the morphine-induced inhibition of both ATP-dependent synaptosomal 45Ca2+ uptake and changes in synaptic vesicular 45Ca2+ localization, while the antagonism by GABA was not associated with synaptosomal Ca2+.

Amino Acids↗
PubMed1981

Contractile effect of morphine and related opioid alkaloids, beta-endorphin and methionine enkephalin on the isolated colon from Long Evans rats.

1 Morphine and related synthetic surrogates as well as beta-endorphin and methionine enkephalin caused a contractile response of the longitudinal musculature of the terminal colon of Long Evans rats.2 The muscular contraction caused by the narcotic analgesics exhibited stereospecificity, with levorphanol being about 50 times more potent than dextrorphan and (-)-methadone 4 times more potent than (+)-methadone. In addition, the rank order in potency of a homologous series of N-alkyl substituted norketobemidones demonstrated that the activity of these compounds in eliciting contractile responses corresponded to that for analgesic efficacy in the rat and also correlated to the ability of these derivatives to inhibit the muscular twitch evoked by electrical stimulation of the guinea-pig ileum.3 Naloxone blocked the contractile response of the opiates following competitive kinetics; the naloxone pA(2) values for morphine, etorphine, levorphanol and methadone were very close, in spite of the marked differences in potency of these agents.4 The contractile effect of morphine on the rat colon was abolished by incubation of the tissues with tetrodotoxin 2.0 x 10(-7) M or by decreasing the external Ca(2+) level 100 fold. Increasing the external Ca(2+) concentration caused an apparent non-competitive antagonism of the response to morphine.5 Pretreatment of the tissues with hexamethonium 8.3 x 10(-5) M caused a modest antagonism of the morphine effect while atropine 5.8 x 10(-7) M did not significantly modify the morphine contractile effect. In contrast, methysergide 10(-5) M caused a 10 fold increase in the morphine EC(50).6 Colons from rats rendered tolerant-dependent on morphine were markedly less sensitive to the contractile effects of morphine than those from placebo-treated controls. Tolerance to morphine was also accompanied by an increased sensitivity to the contractile effects of 5-hydroxytryptamine (5-HT).7 A marked increase in the spontaneous muscular activity of segments of the terminal colon of rats chronically treated with morphine was found to occur upon removal of the residual morphine in the tissues by repetitive washings. The spontaneous activity was arrested by applications of morphine, suggesting that physical dependence can be demonstrated in vitro in this particular preparation.8 It is concluded that the opiate-induced contractile response is mediated via stereospecific, naloxone-sensitive, opiate receptors and that the muscular response involves the activation of a 5-HT neurone in the nerve terminals of the colon.

Animals↗