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Biomedical subjects

M Hamon

Publications and source records attributed to M Hamon.

At least 415 records · Page 23Linked to original sources
PubMed1986

Effects of kelatorphan and other peptidase inhibitors on the in vitro and in vivo release of methionine-enkephalin-like material from the rat spinal cord.

The effects of the novel mixed peptidase inhibitor, kelatorphan [N-(R)-3-(N-hydroxyaminocarbonyl-2-benzyl-1-oxopropyl)-L-alanine], were compared to those of a combination of the potent "enkephalinase" inhibitor thiorphan and the nonselective aminopeptidase inhibitor bestatin, on the catabolism of [3H]Met-enkephalin and on the release of endogenous Met-enkephalin by the rat spinal cord in vitro and in vivo. At 20 microM, kelatorphan almost prevented completely the degradation of exogenous [3H] Met-enkephalin by slices of the dorsal zone of the lumbar enlargement. Similarly, the addition of 20 microM kelatorphan to a [3H] Met-enkephalin-containing artificial cerebrospinal fluid superfusing the whole spinal cord of halothane-anesthetized rats efficiently protected the exogenous peptide from enzymatic degradation. In contrast, in the same in vitro and in vivo models, thiorphan (1 microM) or bestatin (20 microM) alone was inactive, and only their combination induced a significant protection of the exogenous peptide. In vitro and in vivo, kelatorphan (20 microM) increased markedly the spontaneous outflow of endogenous Met-enkephalin-like material as well as the peptide overflow due to K+-induced depolarization (in vitro and in vivo) or noxious stimulation (in vivo). Under similar conditions, thiorphan (1 microM) plus bestatin (20 microM) also enhanced the efflux of Met-enkephalin-like material, but generally to a lower extent than kelatorphan. Compared to thiorphan plus bestatin, kelatorphan exerts additional inhibitory effects on dipeptidylaminopeptidase activity and the present results could indicate that this enzyme also may be involved in the inactivation of extracellular Met-enkephalin at the spinal level in rats.

Animals↗
PubMed1986

Partial characterization of angiotensin II-like material extracted from the rat brain.

Angiotensin II (ANG II)-like material was detected in acid extracts of rat brain using radio-immunoassay (RIA) and a radioreceptor assay (RRA). This material, expressed as ANG II equivalents, corresponded to 131 +/- 20 fmol/g and 33 +/- 4 pmol/g as assessed by RIA and RRA respectively. Such quantitative differences indicated that the brain material did not behave as authentic ANG II in both assays, and further chromatographic investigations confirmed this inference. In particular, gel filtration through Sephadex G-25 and TSK Spherogel 3000 SW revealed that the apparent molecular weight of ANG II-like material was much higher (approximately 5000-7000) than that of authentic ANG II. Furthermore, in contrast to the marked hypertension due to ANG II, a decrease in blood pressure (BP) was observed in rats following the systemic administration of chromatographic eluates enriched with brain ANG II-like material.

Angiotensin II↗
PubMed1986

Mechanisms of transfer of steroid hormones and growth factors into milk.

In this paper we examine the ability of the mammary gland to remove from circulating blood three compounds which differ in their physico-chemical and structural properties. Mammary extraction of progesterone, oestrone sulphate and epidermal growth factor (EGF) is similar at peak lactation in goats, but the proportion of labelled infusate that is transferred into milk is greater for oestrone sulphate and EGF than progesterone which is rapidly metabolised by mammary tissue. The kinetics of transfer of progesterone, oestrone sulphate and EGF from blood into milk show that transcellular processes are involved, and on the basis of earlier hypotheses and new information reported here the results indicate the probable importance of simple and facilitated diffusion pathways for progesterone and oestrone sulphate, and secretory mechanisms for oestrone sulphate and EGF. Although evidence is lacking for a direct effect of hormones in milk on mammary function, their concentration in milk may reflect changes in local regulation of mammary secretion. Considerable practical value is attached to the immunodiagnostic use of milk hormone concentrations to determine ovarian and placental endocrine activity during pregnancy in domestic ruminants.

Animals↗
PubMed1985

Local and remote effects of intra-caudate administration of GABA-related drugs on Met-enkephalin release in the basal ganglia.

The possible influence of GABAergic systems on the activity of enkephalinergic neurones within the basal ganglia was examined by measuring the release of Met-enkephalin in the caudate nuclei and pallida of halothane-anesthesized cats treated by intra-caudate applications of GABA-related drugs. Depending on the concentration used, GABA exerted local stimulatory (at 10 microM of the amino acid) or inhibitory (at 0.5 mM) action on Met-enkephalin release in the cat caudate nucleus. Only the inhibition was reproduced by the GABA agonists muscimol (1 microM) and (-)-balcofen(10 microM) and by diazepam 10 microM). Conversely, the intra-caudate application of the GABA antagonist bicuculline enhanced markedly the local release of the pentapeptide. Complementary studies using slices of the rat striatum (caudate nucleus + putamen) revealed that a low concentration of GABA (10 microM) tended to increase the K+-evoked efflux of Met-enkephalin, whereas a high concentration of the amino acid exerted a strong inhibitory effect on the peptide release. Such in vivo and in vitro findings suggest that the GABA-induced inhibition of Met-enkephalin release took place via the stimulation of specific GABA A and GABA B receptors within the caudate nucleus, whereas the GABA-induced increase of the peptide release might involve some intracellular regulatory processes in striatal neurones containing both GABA and enkephalins. In addition to altering the local release of Met-enkephalin, intra-caudate applications of GABA-related drugs affected the peptide release in the ipsilateral globus pallidus and contralateral basal ganglia. The observed changes suggest that GABA A, but not GABA B, receptors participated in some tonic inhibitory influence of striatal GABAergic neurones on the striato-pallidal enkephalinergic system. Furthermore, the present results confirmed previous studies (Bourgoin et al.) showing that GABAergic neurones can contribute to some bilateral modulation of enkephalinergic neurones within the basal ganglia.

Animals↗
PubMed1985

In vitro and in vivo effects of kelatorphan on enkephalin metabolism in rodent brain.

Biologically relevant assays were used to compare the potency of kelatorphan (N-[3(R)-[(hydroxyamino)carbonyl]-2-benzyl-1-oxopropyl]-L-alanine) as inhibitor of the peptidase-induced metabolism of enkephalins to that of bestatin, a non-specific inhibitor of aminopeptidase and thiorphan, a highly potent blocker of the neutral endopeptidase (EC 3.4.24.11) designated as enkephalinase. Kelatorphan almost completely inhibited the formation of the three metabolites [3H]Tyr, [3H]Tyr-Gly and [3H]Tyr-Gly-Gly produced by incubation of [3H][Tyr1,Met5]enkephalin with rat striatal slices. Co-administered with [Met5]enkephalin in mouse brain, kelatorphan was able to prevent by 80% the degradation of the exogenous peptide. Moreover, a mixture of thiorphan (1 microM) and bestatin (20 microM) or kelatorphan alone (20 microM) induced a 2.2 to 2.5-fold increase in endogenous [Met5]enkephalin overflow after evoked depolarization of superfused rat striatal slices. In this assay, kelatorphan was the only compound to increase by 63% the basal level of released [Met5]enkephalin. Kelatorphan was about 100 times less potent than bestatin to inhibit the total rat striatal aminopeptidases, but as efficient (IC50 = 4 X 10(-7) M) as bestatin to inhibit a minor aminopeptidase activity resembling aminopeptidase M. Therefore the reported enhanced analgesic potency of kelatorphan with regard to the association of bestatin and thiorphan is very likely related to its ability to almost completely inhibit enkephalin-degrading enzymes (including the Tyr-Gly releasing peptidase) and to its better selectivity for the biologically relevant aminopeptidase M. Kelatorphan would be a valuable probe, preferable to the association of bestatin and thiorphan, to investigate the physiological functions regulated by a phasic enkephalinergic activity.

Aminopeptidases↗
PubMed1985

Spontaneous and evoked release of methionine-enkephalin-like material from the rat spinal cord in vivo.

In vivo perfusion of the subarachnoid space with an artificial cerebrospinal fluid (CSF) in paralyzed halothane-anesthetized rats allowed the collection of methionine-enkephalin (Met-Enk)-like material (MELM) released from the spinal cord. Bio-Gel P2 chromatography and high-performance liquid chromatography showed that 65% of this material corresponded to authentic Met-Enk. Under resting conditions, about 1 pg of MELM per minute was regularly released for at least 3 h; for Met-Enk, this value corresponded to a fractional rate constant of 0.002% (i.e. tissue content of the pentapeptide which was released per minute from the whole spinal cord). Perfusion with K+-enriched (40-60 mM) CSF resulted in a marked enhancement (+ 150-200%) of spinal MELM release. Similarly, calibrated pinches of the muzzle and i.p. administration of acetic acid, two strong noxious stimuli in awake animals, induced a significant increase (+ 75-150%) in spinal MELM release. In contrast, pinches applied to the tail did not enhance but instead slightly reduced (-35%) MELM release from the rat spinal cord. These data suggest that mechanisms other than segmental controls could be involved in the activation of spinal enkephalinergic neurons by some nociceptive stimuli.

Animals↗
PubMed1985

Irreversible blockade of central 5-HT binding sites by 8-methoxy-2'-chloro-PAT.

We have synthesized 8-methoxy-2-(N-2'-chloropropyl, N-propyl) aminotetralin (8-methoxy-2'-chloro-PAT), an alkylating agent derived from the potent 5-HT agonist, 8-hydroxy-2-(N,N-dipropyl)-aminotetralin (PAT). As expected for an irreversible ligand, the blockade of 3H-PAT or 3H-5-HT binding to post-synaptic 5-HT1 (A and B) sites in rat hippocampal membranes pretreated with 8-methoxy-2'-chloro-PAT could not be prevented by extensive washing of membranes. Prior occupancy of 5-HT1 sites by 5-HT or PAT prevented any subsequent irreversible blockade by the alkylating agent. Similar irreversible blockade by 8-methoxy-2'-chloro-PAT was found on 3H-PAT binding to striatal membranes suggesting that presynaptic 5-HT binding sites (see Gozlan et al., Nature, Lond. 305, 140, 1983) were sensitive also to the alkylating agent. In contrast, the modifying agent N-ethylmaleimide (NEM) reduced markedly 3H-PAT binding to postsynaptic hippocampal 5-HT1 sites, but did not alter 3H-PAT binding to striatal presynaptic 5-HT sites. Although 8-methoxy-2'-chloro-PAT bound irreversibly to different classes of 5-HT binding sites (5-HT1A, 5-HT1B, presynaptic sites), it can be considered a selective alkylating agent, since it exerted no action on 3H-spiperone binding to 5-HT2 sites, 3H-muscimol binding to GABA sites, or 3H-flunitrazepam binding to benzodiazepine sites.

2-Naphthylamine↗
PubMed1985

Characteristics of tyrosine hydroxylase activation by K+-induced depolarization and/or forskolin in rat striatal slices.

The mechanisms of tyrosine hydroxylase (TH) activation by depolarization or exposure of dopaminergic terminals to cyclic AMP have been compared using rat striatal slices. Tissues were incubated with veratridine or 60 mM K+ (depolarizing conditions), on the one hand, and forskolin or dibutyryl cyclic AMP, on the other. K+-(or veratridine-)induced depolarization triggered an activation of TH (+75%) that persisted in soluble extracts of incubated tissues. This effect disappeared when drugs (EGTA, N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide, Gallopamil) preventing Ca2+- and calmodulin-dependent processes were included in the incubating medium. In contrast, prior in vivo reserpine treatment or in vitro addition of benztropine did not affect the depolarization-induced activation of TH. In vitro studies of soluble TH extracted from depolarized tissues indicated that activation was associated with a marked increase in the enzyme Vmax but with no change in its apparent affinity for the pteridin cofactor 6-methyl-5,6,7,8-tetrahydropterin (6-MPH4) or tyrosine. Furthermore, the activated enzyme from depolarized tissues exhibited the same optimal pH (5.8) as native TH extracted from control striatal slices. In contrast, TH activation resulting from tissue incubation in the presence of forskolin or dibutyryl cyclic AMP was associated with a selective increase in the apparent affinity for 6-MPH4 and a shift in the optimal pH from 5.8 to 7.0-7.2. Clear distinction between the two activating processes was further confirmed by the facts that heparin- and cyclic AMP-dependent phosphorylation stimulated TH activity from K+-exposed (and control) tissues but not that from striatal slices incubated with forskolin (or dibutyryl cyclic AMP). In contrast, the latter enzyme but not that from depolarized tissues could be activated by Ca2+-dependent phosphorylation. These data strongly support the concept that Ca2+- but not cyclic AMP-dependent phosphorylation is responsible for TH activation in depolarized dopaminergic terminals.

Animals↗
PubMed1985

[3H]8-hydroxy-2-(di-n-propylamino)tetralin binding to pre- and postsynaptic 5-hydroxytryptamine sites in various regions of the rat brain.

The specific binding of [3H]8-hydroxy-2-(di-n-propylamino)tetralin ([ 3H]8-OH-DPAT) to 5-hydroxytryptamine (5-HT)-related sites was investigated in several regions of the rat brain. Marked differences were observed in the characteristics of binding to membranes from hippocampus, striatum, and cerebral cortex. Hippocampal sites exhibited the highest affinity (KD approximately 2 nM) followed by the cerebral cortex (KD approximately 6 nM) and the striatum (KD approximately 10 nM). Ascorbic acid inhibited specific [3H]8-OH-DPAT binding in all three regions but millimolar concentrations of Ca2+, Mg2+, and Mn2+ enhanced specific binding to hippocampal membranes, whereas only Mn2+ increased it in the cerebral cortex and all three cations inhibited specific binding to striatal membranes. Guanine nucleotides (0.1 mM GDP, GTP) inhibited binding to hippocampal and cortical membranes only. As intracerebral 5,7-dihydroxytryptamine markedly decreased [3H]8-OH-DPAT binding sites in the striatum, but not in the hippocampus, the striatal sites appear to be on serotoninergic afferent fibers. In contrast, in the hippocampus the sites appear to be on postsynaptic 5-HT target cells, as local injection of kainic acid decreased their density. Both types of sites appear to be present in the cerebral cortex. The postsynaptic hippocampal [3H]8-OH-DPAT binding sites are probably identical to the 5-HT1A subsites, but the relationship between the presynaptic binding sites and the presynaptic autoreceptors controlling 5-HT release deserves further investigation.

5,7-Dihydroxytryptamine↗
PubMed1985

Prostaglandin F-2 alpha is transferred from the uterus to the ovary in the sheep by lymphatic and blood vascular pathways.

[3H]Prostaglandin F-2 alpha (PGF-2 alpha) was infused into a uterine lymphatic vessel or a uterine vein for up to 1 h, or injected into the uterine lumen of anaesthetized non-pregnant sheep 7-15 days after oestrus. After an intraluminal injection, labelled PGF-2 alpha was recovered in uterine lymph and peak radioactivity was reached 50 min after injection. [3H]PGF-2 alpha infused at a constant rate into a uterine lymphatic vessel resulted in a maximum concentration of radioactivity in plasma which was 5.6- and 1.7-fold higher in the adjacent utero-ovarian and ovarian vein, respectively, than in carotid arterial plasma. Estimation of the amount of infusate transferred from a lymphatic into ovarian venous blood gave a value (0.4%) similar to that for transfer from a uterine vein (0.3%). Evidence for local transfer was substantiated by the presence of significantly higher concentrations of 3H-labelled compounds in the ovary and corpus luteum adjacent to the site of intra-lymphatic infusion compared with those in the opposite organs. The concentrations in the adjacent ovary and corpus luteum were significantly greater when an intra-lymphatic rather than intra-uterine vein infusion was adopted. The results show that [3H]PGF-2 alpha is transferred locally from uterine lymphatic vessels into the adjacent ovary, corpus luteum and ovarian vein.

Animals↗
PubMed1985

[The spinal enkephalinergic and serotoninergic systems in the control of transmission of nociceptive messages].

Numerous anatomical, pharmacological and electrophysiological data described in the literature indicate that spinal enkephalinergic and serotoninergic systems are probably involved in the control of nociceptive inputs from the periphery to the cerebral cortex. However, reported evidence was generally indirect and did not provide a real demonstration of the physiological participation of these neurones in pain control. This led us to select appropriate experimental approaches for studying directly the activity of spinal enkephalinergic and serotoninergic systems in animals (rat, cat) submitted to noxious stimuli. Owing to two catheters introduced into the subarachnoidal space of anesthetized rats, it was possible to perfuse the whole spinal cord with an artificial cerebro-spinal fluid and thus collect the neuroactive compounds released by spinal neurones (at least those in superficial layers) under various experimental conditions. Using this technique, we observed that some (but not all) nociceptive stimuli such as intense pinching of the muzzle, intraperitoneal injection of acetic acid or noxious heat applied to the muzzle or the tail induced a significant increase in met-enkephalin release from the spinal cord (see fig. 2). Similar effects were observed following the blockade of enkephalin catabolism by thiorphan and bestatin (see fig. 1) indicating that they were not due to some alteration of peptidase activities but really involved the activation of spinal enkephalinergic systems. Since cervical cord transection suppressed the stimulatory action of noxious stimuli on spinal met-enkephalin release, it could be proposed that the mechanisms involved were not limited to the cord but depended on supraspinal structures. Bulbo-mesencephalic serotoninergic neurones projecting to the spinal cord might well correspond to such structures (or at least to some of them) since nociceptive stimuli (such as noxious heat applied to the tail) also evoked a marked increase of serotonin (5-HT) release at the spinal level (fig. 3). Such observations together with indirect evidence reported in the literature suggested therefore that the activation of spinal enkephalinergic systems triggered by noxious stimuli might result from excitatory influence due to descending serotoninergic projections. However, in vitro studies using slices of the dorsal zone of the rat lumbar cord did not reveal any stimulatory effect of 5-HT on the spontaneous or K+-evoked release of met-enkephalin (fig. 4).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗