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Biomedical subjects

H W Kosterlitz

Publications and source records attributed to H W Kosterlitz.

At least 73 records · Page 4Linked to original sources
PubMed1980

Characterization of opioid receptors in nervous tissue.

The concept that endogenous opioid peptides interact with at least two different receptor sites developed from several experimental approaches. First, when the peptides were assayed by their effects on two pharmacological and two binding models, the rank order of activity differed in these four systems. Secondly, naloxone had a smaller antagonist effect on delta-receptors in the mouse vas deferens than on its mu-receptors. Thirdly, the enkephalins and morphine each occupied less than half of the total number of sites available in brain homogenates. Fourthly, cold ligands of the delta-type protected the binding of tritiated delta-agonists better than that of mu-agonists, and vice versa. Finally, tritiated ethylketazocine binds the kappa-receptor sites in homogenates of guinea-pig brain. It is readily displaced by etorphine, which binds uniformly to mu-, delta- and kappa-receptors, but only by very high concentration of mu- or delta-agonists. An interesting phenomenon is the potentiation of activity when a enkephalin analogue is conjugated to tobacco mosaic virus by the group of R. Schwyzer.

Animals↗
PubMed1980

Effects of electrical stimulation on the enkephalins in guinea-pig small intestine.

When myenteric plexus-longitudinal muscle preparations of the guinea-pig small intestine are stimulated electrically in the presence of cycloheximide there is a decrease in the content of enkephalins which is taken to be due to their release. With supramaximal stimuli, the release per pulse is similar at 1 and 10 Hz but it is lower with submaximal than with maximal stimuli. Met-enkephalin is more readily released than Leu-enkephalin.

Animals↗
PubMed1980

Opioid peptides and their receptors.

The three agonists, methionine-enkephalin, leucine-enkephalin and beta-endorphin have different pharmacological patterns. It may be of particular importance that they vary in their relative affinities to the enkephalin and naltrexone binding sites in the brain; the former are probably related to delta-receptors prevalent in the mouse vas deferens and the later to mu-receptors prevalent in the guinea-pig. It is possible that mu-receptors are more important for the mediation of analgesic effects than delta-receptors. An understanding of the pharmacokinetics of the opioid peptides will be of basic importance for the design of enkephalin analogues suitable for use as analgesics in man.

Animals↗
PubMed1980

Comparison of the binding characteristics of tritiated opiates and opioid peptides.

1 Binding assays on homogenates of guinea-pig brain showed that the maximal number of binding sites was different tritiated ligands interacting with the opiate receptors. 2 At 25 degrees C the binding capacity of morphine or dihydromorphine was only about 3 pmol/g fresh brain whereas etorphine and D-Ala2-L-Leu5- and D-Ala2-L-Met5-enkephalin amide had capacities of 13 to 15 pmol/g brain. D-Ala2-D-Leu5-enkephalin had an intermediate capacity of about 6 pmol/g brain. 3 The binding capacities of the natural methionine- and leucine-enkephalins measured at 0 degrees C were 5 to 6 pmol/g brain. At this temperature, the binding capacity of dihydromorphine, D-Ala2-D-Leu5-enkephalin and of the two enkephalin amides was only slightly lower than at 25 degrees C. 4 In assays in which unlabelled ligand competed with the same labelled ligand, the inhibition constants (KI) were equal to or not more than twice as large as the equilibrium dissociation constant (KD) determined in saturation assays. In contrast, the KI of unlabelled dihydromorphine against [3H]-D-Ala2-D-Leu5-enkephalin or of unlabelled D-Ala2-D-Leu5-enkephalin against [3H]-dihydromorphine was about 20 times higher than the respective KD values. 5 When for a given compound the ratio of the KI value against [3H]-D-Ala2-D-Leu5-enkephalin to the KI value against [3H]-dihydromorphine (discrimination ratio) is calculated, a high value indicates selectivity in favour of the mu-receptor and a low value selectivity in favour of the delta-receptor. The most selective mu-agonist known so far is normorphine with a discrimination ratio of 70 and the most selective delta-agonist is D-Ala2-D-Leu5-enkephalin with a ratio of 0.11. The selectivity of the known antagonists is in favour of the mu-receptor, since their discrimination ratios are larger than 1, varying between 10 for naloxone and 4 for Mr 2266.

Animals↗
PubMed1980

Effects of changes in the structure of enkephalins and of narcotic analgesic drugs on their interactions with mu- and delta-receptors.

1 The activity pattern of analogues of the enkephalins was determined in four parallel assays, the inhibition of the electrically evoked contraction of the guinea-pig ileum and mouse vas deferens at 36 degrees C and the inhibition of [(3)H]-naltrexone and [(3)H]-leucine-enkephalin binding at 0 to 4 degrees C in homogenates of guinea-pig brain.2 The activity pattern was best characterized by the ratio of the potency in the guinea-pig ileum to that in the mouse vas deferens (G.p.i./M.v.d.) and the ratio of the potency in inhibiting [(3)H]-naltrexone binding to that in inhibiting [(3)H]-leucine-enkephalin binding (Nal/Leu).3 The enkephalins had low G.p.i./M.v.d. (0.02 to 0.09) and low Nal/Leu (0.05 to 0.18) ratios whereas the corresponding values for morphine were 7.0 and 7.5.4 Analogues obtained by substituting D-Ala for Gly(2) and D-Met or D-Leu for L-Met(5) or L-Leu(5) showed only minor changes in G.p.i./M.v.d. (0.01 to 0.11) and in Nal/Leu (0.06 to 0.13) ratios.5 Analogues in which resistance to enzymatic degradation was brought about by amidation of the C-terminal carboxylic group or methylation of the amino group of tyrosine or both modifications, had G.p.i./M.v.d. ratios of 1.2 to 5.5 and Nal/Leu ratios of 0.5 to 21. High values (2.1 and 3.4) were found for the potent antinociceptive analogue of Sandoz, Tyr-D-Ala-Gly-NCH(3)Phe-Met(O)-ol.6 In the mouse vas deferens, some of the analogues with high G.p.i./M.v.d. and Nal/Leu ratios were tested for antagonism by naloxone and found to require less than the high concentration needed for the natural enkephalins. C57/BL mice, which have a lowered sensitivity to morphine but a normal response to peptides with low G.p.i./M.v.d. and Nal/Leu ratios, had a lowered sensitivity to analogues with high ratios.7 In the alkaloid-like series of narcotic analgesic drugs, ketobemidone, levorphanol, methadone, etorphine and the antagonist Mr 2266 had lower Nal/Leu ratios (1.0 to 2.8) than morphine, normorphine, naloxone and naltrexone (8 to 12).8 It would appear that compounds with low G.p.i./M.v.d. and Nal/Leu ratios interact mainly with delta-receptors in the brain and peripheral nervous system while compounds with high ratios interact mainly with mu-receptors. For antinociceptive action mu-receptors may be more important than delta-receptors.

Analgesics, Opioid↗
PubMed1979

Opioid activities of fragments of beta-endorphin and of its leucine65-analogue. Comparison of the binding properties of methionine- and leucine-enkephalin.

For characterisation in vitro, four parallel assays were used: the guinea-pig ileum and mouse vas deferens as pharmacological models at 36 degrees C and the inhibition of binding of [3H]-naltrexone, [3H]-leucine-enkephalin and [3H]-methione-enkephalin at 0 degrees C. The Leu65-analogue of beta-andorphin and its fragments (61-65, 61-76 and 61-77) have a lower affinity to the [3H]-naltrexone binding site of mu-receptors than the corresponding Met65-peptides wereheas no such difference was found for the [3H]leucine-enkephalin binding sites or delta-receptors. When the binding of [3H]-methionine-enkephalin or [3H]-leucine-enkephalin was inhibited by cold ligands interacting with delta-, mu-, or kappa-receptors, no evidence was obtained for more than one type of delta-binding site.

Animals↗
PubMed1979

Specific protection of the binding sites of D-Ala2-D-Leu5-enkephalin (delta-receptors) and dihydromorphine (mu-receptors).

Phenoxybenzamine causes a long-lasting inactivation of the opiate receptors of the mu- and delta-type in homogenates of guinea-pig brain. The effect is selectively prevented when, before exposure to phenoxybenzamine, the homogenate is pre-incubated with ligands of high affinity for either of the two binding sites, i.e. dihydromorphine for the mu-receptor and Tyr-D-Ala-Gly-Phe-D-Leu for the delta-receptor. In contrast, Tyr-D-Ala-Gly-Phe-L-Leu amide, which has high affinities for both binding sites, protects both receptor sites.

Animals↗
PubMed1979

Synthesis of enkephalins by guinea-pig striatum in vitro.

A method for obtaining incorporation of labelled amino acids into enkephalins of guinea-pig striatum in vitro and isolating the labelled enkephalins is described. The incorporation of [3H]tyrosine increases with time after a delay of 2 h. Cycloheximide added during this time, but not at later stages, inhibits incorporation. The results indicate that the enkephalins are produced locally, probably by ribosomal synthesis. The lag period may be due to the time required for the synthesis of precursors and their conversion to the enkephalins.

Animals↗
PubMed1979

Comparison of binding of [3H]-methionine-enkephalin, [3H]-naltrexone and [3H]-dihydromorphine in the mouse vas deferens and the myenteric plexus and brain of the ginea pig.

[3H]-Methionine-enkephalin, [3H]-naltrexone and [3H]-dihydromorphine are specifically bound in homogenates of not only the brain and myenteric plexus of the guinea pig but also the vas deferens of the mouse. Brain has a ratio of methionine-enkephalin to dihydromorphine binding in favour of methionine-enkephalin binding and the myenteric plexus a ratio in favour of dihydromorphine binding, with the mouse vas deferens being intermediate.

Animals↗
PubMed1979

The inhibitory effects of presynaptic alpha-adrenoceptor agonists on contractions of guinea-pig ileum and mouse vas deferens in the morphine-dependent and withdrawn states produced in vitro.

1 Isolated ilea from guinea-pigs implanted with morphine pellets were stimulated coaxially, either with or without morphine present in the bath fluid, and the longitudinal contractions recorded. 2 In the absence of morphine the inhibitory effects of the presynaptic alpha-adrenoceptor agonists, clonidine and oxymetazoline were much reduced and the dose-response curve was flat. This state of 'withdrawal' was readily reversed by morphine and levorphanol but not its inactive (+)-isomer, dextrophan. 3 The kappa-agonists, ketazocine and ethylketazocine, also restored the effects of clonidine as did the opioid peptides Tyr-D-Ala-Gly-Phe-D-Leu, acting preferentially on delta-receptors, and Tyr-D-Ala-Gly-MePhe-Met(O)-ol, acting mainly on micro-receptors. 4 The inhibitory effects of adrenaline and adenosine 3',5'-diphosphate were reduced at low but not at high concentrations. 5 In contrast, the inhibitory effect of clonidine on the electrically evoked contractions of vasa deferentia from mice implanted with morphine pellets was not abolished by the lack of morphine in the bath fluid or by addition of naloxone. 6 A possible explanation is suggested for the loss of the inhibitory effects of presynaptic alpha-adrenoceptor agonists in the withdrawn state of the dependent ileum.

Adenosine Diphosphate↗