Kétamine à faibles doses : antihyperalgésique, non analgésique

Recent data in animal experiments as in clinical trials have clearly reported that pain modulation is related to an equilibrium between antinociceptive and pronociceptive systems. Therefore, the apparent pain level could not only be a consequence of a nociceptive input increase but could also result from a pain sensitization process. Glutamate, via NMDA receptors, plays a major role in the development of such a neuronal plasticity in the central nervous system, leading to a pain hypersensitivity that could facilitate chronic pain development. By an action on NMDA receptors opioids also induce, in a dose dependent manner, an enhancement of this postoperative hypersensitivity. "Antihyperalgesic" doses of ketamine, an NMDA receptor antagonist, were able to decrease this central sensitization not only in painful animal but also in human volunteers exposed to different pain models, or in the postoperative period. Many studies have reported that ketamine effects are elicited when this drug is administered the following manner: peroperative bolus (0.1 to 0.5 mg/kg), followed by a constant infusion rate (1 to 2 microg/kg per min) during the peroperative period and for 48 to 72 hours after anaesthesia. Those ketamine doses improved postoperative pain management by reducing hyperalgesia due to both surgical trauma and high peroperative opioid doses. This antihyperalgesic action of ketamine also limited the postoperative morphine tolerance leading to a decrease in analgesic consumption and an increase in the analgesia quality.

[Complexity and physiology of the analgesic effects of opioids]

Nowadays, it is considered that clinical pain is not only a reflexion of the nociceptive stimulus intensity, but is to a large extent the expression of neural plasticity including both peripheral and central sensitization. N-Methyl-D-aspartate receptors (NMDA-Rs) play a critical role in the central pain sensitization process leading to exaggerated pain and chronic pain. Although opioids are unsurpassed analgesics, we observed that opioids induced delayed and sustained NMDA-related hyperalgesia after an initial analgesia suggesting a pain sensibilisation process. It is shown that NMDA receptor antagonists and specific diets able to negatively modulate NR2B subunit containing NMDA receptors prevented abnormal pain hypersensitivity, partially reversed chronic pain and restored the opioid effectiveness on opioid-resistant pain models.

Interaction between neuropeptide FF and opioids in the ventral tegmental area in the behavioral response to novelty

Considerable evidence has focused on the interaction between endogenous opioid peptides and the dopaminergic mesocorticolimbic system in behavioral responses to stress. Recently, it has been proposed that the CNS synthesizes and secretes neuropeptides that act as part of a homeostatic system to attenuate the effects of morphine or endogenous opioid peptides. Among these antiopioids, neuropeptide FF (NPFF) is particularly interesting since both NPFF immunoreactive-like terminals and NPFF binding sites are located in the vicinity of the dopaminergic cell bodies within the ventral tegmental area (VTA) suggesting an interaction at this level. The purpose of the present study was to evaluate the respective implication of opioid and antiopioid peptides at the level of the VTA in the locomotor response to novelty in rats. The results indicate that s.c. naloxone pretreatment, an opiate receptor antagonist, reduced locomotor activity in rats placed in a novel environment without having any effect in a familiar environment. This effect takes place in the VTA since intra-VTA administration of naloxone methobromide diminished similarly and dose-dependently the motor response to novelty. This effect is mainly dependent on opioid peptides released at VTA level since local injections of thiorphan, an inhibitor of enkephalin degradation, strongly increased locomotor response to novelty and this effect is completely prevented by the co-administration of naloxone methobromide. When injected in the VTA, NPFF is acting as an antiopioid compound, i.e. it reduces the locomotor activity triggered by exposure to novelty to the level recorded in a familiar environment. Moreover, NPFF decreased dose-dependently the potentiation of novelty-induced locomotor response produced by VTA injection of thiorphan. Taken together, these results suggest that NPFF neurons may participate at the level of the VTA to a homeostatic regulating process counteracting opioid effects induced by a mild stress such as novelty.

The neuropeptide FF analogue, 1DMe, acts as a functional opioid autoreceptor antagonist in the rat spinal cord

We assessed the possible influence of a neuropeptide FF analogue, 1DMe ([D-Tyr(1),(NMe)Phe(3)]neuropeptide FF), on the inhibitory action of endogenous and exogenous partial differential-opioid receptor agonists on K(+)-evoked [Met(5)]-enkephalin release from superfused rat spinal cord slices. 1DMe (0.1-10 microM) dose-dependently enhanced the increase in superfusate [Met(5)]-enkephalin content due to the peptidase inhibitors thiorphan (1 microM) and bestatin (20 microM), and prevented the reduction in [Met(5)]-enkephalin release due to stimulation of partial differential receptors by 1 microM deltorphin I. Because it had the same effects as partial differential-opioid receptor antagonists, 1DMe might act through the functional blockade of presynaptically located partial differential-opioid autoreceptors.

Lessons from an unpleasant surprise: a biochemical strategy for the diagnosis of pheochromocytoma

OBJECTIVE

To audit the performances of the analytes used in the diagnosis of pheochromocytoma and to present a graphical guideline to help the diagnosis.

DESIGN

A 5 year retrospective study.

SETTINGS

Laboratory and departments of a university hospital.

PARTICIPANTS

In-patients, suspected of bearing a pheochromocytoma, were investigated for urinary metanephrines and catecholamines (photometric method) and vanillylmandelic acid, fractionated catecholamines and metanephrines [high pressure liquid chromatography (HPLC) coupled to electrochemical detection (ED)] urinary excretion.

MAIN OUTCOME

Patients with a pheochromocytoma (24 out of 2003 patients) were diagnosed by the combination of normetanephrine and metanephrine determination.

RESULTS

All analytes but dopamine were significantly elevated in patients with a pheochromocytoma. The area under the receiver operating characteristics (ROC) curves were the highest for total metanephrines, normetanephrine and metanephrine determinations. Because of analytical interferences in the metanephrines determination, the normetanephrine and metanephrine performed better. It is noteworthy that all pheochromocytomas had either normetanephrine or metanephrine levels above their respective optimal threshold (sensitivity 100%). The best optimal threshold performance was reached by the mean of three daily samples. Total or fractionated catecholamines or vanillylmandelic acid were less accurate tools.

CONCLUSION

Amongst urinary tests, the combined use of HPLC/ED determination of normetanephrine and metanephrine seems the most effective screening strategy for the diagnosis of pheochromocytoma. The older total metanephrine photometric assay is grieved by analytical interferences.

Progressive enhancement of delayed hyperalgesia induced by repeated heroin administration: a sensitization process

It is difficult to conceive that tolerance and sensitization processes, two apparently opposite phenomena, can concomitantly modify one given biological process, i.e., the processing of pain. We have shown recently that opiates produce not only analgesia but also long-lasting hyperalgesia in rats. This suggests that tolerance to the analgesic effect of an opiate, especially heroin, could be in part the result of an actual sensitization of pronociceptive systems. Here, we show that both magnitude and duration of heroin-induced delayed hyperalgesia increase with intermittent heroin administrations, leading to an apparent decrease in the analgesic effectiveness of a given heroin dose. Our observation that a small dose of heroin which is ineffective for triggering a delayed hyperalgesia in non-heroin-treated rats induced an enhancement in pain sensitivity for several days after a series of heroin administrations is in agreement with the sensitization hypothesis. The effectiveness of the opioid receptor antagonist naloxone to precipitate hyperalgesia in rats that had recovered their pre-drug nociceptive value after single or repeated heroin administrations indicates that heroin-deprived rats were in a new biological state associated with a high level balance between opioid-dependent analgesic systems and pronociceptive systems. Because the NMDA receptor antagonist dizocilpine maleate (MK-801) prevented both heroin-induced long-lasting enhancement in pain sensitivity and naloxone-precipitated hyperalgesia, these findings further suggest that tolerance, sensitization, and one withdrawal symptom, hyperalgesia, are issued from a neuroadaptive process in which NMDA systems play a critical role.

Long-lasting hyperalgesia induced by fentanyl in rats: preventive effect of ketamine

BACKGROUND

It has been reported that mu-opioid receptor activation leads to a sustained increase in glutamate synaptic effectiveness at the N-methyl-D-aspartate (NMDA) receptor level, a system associated with central hypersensitivity to pain. One hypothesis is that postoperative pain may result partly from the activation of NMDA pain facilitatory processes induced by opiate treatment per se. The authors tested here the effectiveness of the opiate analgesic fentanyl for eliciting a delayed enhancement in pain sensitivity.

METHODS

The consequences of four bolus injections (every 15 min) of fentanyl (20-100 microg/kg per injection, subcutaneously) on immediate (for several hours) and long-term (for several days) sensitivity to nociceptive stimuli in the rat (paw-pressure vocalization test) were evaluated. The effects of the combination of the NMDA-receptor antagonist ketamine (10 mg/kg, subcutaneously) with fentanyl also were assessed.

RESULTS

Fentanyl administration exhibited a biphasic time-dependent effect: first, an early response (for 2-5 h) associated with a marked increase in nociceptive threshold (analgesia), and second, a later response associated with sustained lowering of the nociceptive threshold (5 days for the longest effect) below the basal value (30% of decrease for the maximal effect) indicative of hyperalgesia. The higher the fentanyl dose used, the more pronounced was the fentanyl-induced hyperalgesia. Ketamine pretreatment, which had no analgesic effect on its own, enhanced the earlier response (analgesia) and prevented the development of long-lasting hyperalgesia.

CONCLUSIONS

Fentanyl activates NMDA pain facilitatory processes, which oppose analgesia and lead to long-lasting enhancement in pain sensitivity.

Evidence for opiate-activated NMDA processes masking opiate analgesia in rats

The acute interaction between opioid receptors and N-methyl-D-aspartate (NMDA) receptors on nociception was examined in rats using tail-flick and paw-pressure vocalisation tests. When injected at various times (1 to 6 h) after morphine (5 to 20 mg/kg, i.v.) or fentanyl (4x40 microgram/kg, i.v.), the opioid receptor antagonist naloxone (1 mg/kg, s.c.) not only abolished the opiate-induced increase in nociceptive threshold, but also reduced it below the basal value (hyperalgesia). The noncompetitive NMDA receptor antagonist MK-801 (0.15 or 0.30 mg/kg, s.c.) prevented the naloxone-precipitated hyperalgesia and enhanced the antinociceptive effects of morphine (7.5 mg/kg, i.v.) and fentanyl (4x40 microgram/kg, i.v.). These results indicate that the antinociceptive effects of morphine and fentanyl, two opiate analgesics widely used in humans in the management of pain, are blunted by concomitant NMDA-dependent opposing effects which are only revealed when the predominant antinociceptive effect is sharply blocked by naloxone. This study provides new rationale for beneficial adjunction of NMDA receptor antagonists with opiates for relieving pain by preventing pain facilitatory processes triggered by opiate treatment per se.

Opiate tolerance to daily heroin administration: an apparent phenomenon associated with enhanced pain sensitivity

From a classical viewpoint, tolerance to analgesic effects of opiates refers to the decreased effectiveness of a given opiate following its repeated use. Despite much research, it has not been conclusively demonstrated in vivo that functional changes observed at the opioid receptor level in the responsiveness to opiates account for development of tolerance. An alternative hypothesis is that opioid receptors remain operative following repeated opiate administration but that opioid receptor activation rapidly induces a prolonged increase in pain sensitivity which opposes the predominant opiate analgesic effect following repeated opiate administration. We recently showed that a single heroin administration induces an enhanced pain sensitivity for several days, a phenomenon which is prevented by the non-competitive N-methyl-D aspartate receptor antagonist MK-801. Herein we report that repeated once-daily heroin injections induced a gradual lowering of the nociceptive threshold which progressively masked a sustained heroin analgesic functional effect. MK-801 prevented such opiate-induced allodynia and thereby prevented development of an apparent decrease in the effectiveness of heroin. These results indicate that intermittent heroin administration induced a persistent increase in the basal pain sensitivity which, if not taken into account gives the impression of less analgesia, i.e. apparent tolerance.

Neuropeptide FF in the rat adrenal gland: presence, distribution and pharmacological effects

Neuropeptide FF (NPFF, FLFQPQRFamide) is an FMRFamide-like octapeptide exhibiting antiopiate activity. The presence of both NPFF-immunoreactivity (NPFF-IR) and NPFF-specific receptors has been described in the mammalian central nervous system (CNS). The peripheral effects of NPFF indicate that NPFF-IR material is present outside the CNS. Biochemical and immunohistochemical methods enabled us to determine the presence and distribution of NPFF-IR in the rat adrenal gland. The amount of NPFF-IR material in whole gland was estimated by radioimmunoassay to be 19.00 +/- 4.00 fmol/gland. High performance liquid chromatography analysis of adrenal extracts revealed a single molecular form which coeluted with authentic NPFF. Demedullation decreased adrenal NPFF-IR content, indicating that NPFF-IR was present in both cortex and medulla. Light microscopy revealed NPFF-IR in beaded fibers confined in the outer part of the cortex and in medullary cells. Double-labeling with antityrosine-hydroxylase and anti-NPFF antibodies showed NPFF-IR in cortical catecholaminergic postganglionic fibers restricted to the subcapsular and glomerulosa zonae. NPFF-IR was also located in medullary chromaffin cells and in rays and islets of chromaffin cells dispersed throughout the cortex. Insulin-induced hypoglycemia did not alter NPFF-IR content. Denervation lowered adrenal NPFF-IR content. These data indicate that this peptide is present in nerve fibers of extrinsic origin. In vitro approaches using adrenal slices have shown that NPFF inhibited aldosterone release in a dose-dependent manner. Taken together, these data suggest that NPFF may participate in the control of aldosterone production and adrenal blood supply.

Acute tolerance associated with a single opiate administration: involvement of N-methyl-D-aspartate-dependent pain facilitatory systems

Mechanisms underlying the development of acute tolerance to the analgesic effect of opiates were investigated. In the rat tail-flick test, administration of naloxone (1 mg/kg, s.c.) 40 min after heroin (1 mg/kg, s.c.) was shown to induce hyperalgesia, indicative of a short-onset, opiate-activated pain facilitatory systems masking the opiate analgesia. Pretreatment with the N-methyl-D-aspartate receptor antagonist dizocilpine maleate blocked, in a dose-dependent manner, the naloxone-induced hyperalgesia and potentiated the heroin-induced analgesia. Using a schedule of two successive injections of 1 mg/kg heroin, acute tolerance was indicated by a marked reduction (-52%) in analgesia induced by the second dose. After pretreatment with dizocilpine maleate, the acute tolerance was abolished and the analgesic effects of both injections of heroin were strongly potentiated. These observations indicate that acute tolerance appears after the first exposure to opiates and stems from opiate activation of N-methyl-D-aspartate-dependent pain facilitatory systems.

Long-lasting increased pain sensitivity in rat following exposure to heroin for the first time

Acute dependence, defined as a precipitation of somatic signs by an antagonist, may occur after a single administration of an opiate drug. Because hyperalgesia is a consistent sign of the withdrawal syndrome, we tested the effectiveness of heroin, an opiate used by addicts, to induce pain facilitation even after a first exposure to the drug. In opiate-naive rats, subcutaneous injection of heroin induced analgesia followed by allodynia, a decrease in pain threshold. This latter phenomenon was observed in the absence of noxious stimuli and lasted several days. An N-methyl-D-aspartate (NMDA) receptor antagonist, MK-801 prevented such long-lasting allodynia. These results suggest that allodynia is an early sign reflecting neural plasticity associated with the development of dependence.

Evidence for multiple opioid receptors in the human posterior pituitary

The distribution and quantification of opioid receptor types in post-mortem human pituitary cryostat sections was determined by quantitative in vitro receptor autoradiography. Highly specific radioligands were used for each opioid receptor type i.e. [125l]-FK-33-824 for mu-opioid sites, [125l][D.Ala2]-Deltorphin-l for delta-opioid sites and 3H-U69,593 for kappa-opioid sites. None of the five specimens tested exhibited any labeling in the anterior lobe of the pituitary for the three radioligands. As for the posterior pituitary, all 5 specimens contained both mu and kappa-opioid binding sites whereas none of them showed delta-binding sites. The presence of both mu- and kappa-opioid binding sites in the human posterior pituitary contrasts with previous findings in the rat where only kappa-sites have been found. The present study could contribute to understanding of the functional action of opioids in the human pituitary.

Simultaneous activation of spinal antiopioid system (neuropeptide FF) and pain facilitatory circuitry by stimulation of opioid receptors in rats

Neuropeptide FF (NPFF) is a mammalian FMRFamide-like octapeptide with antiopioid properties that inhibits morphine-induced analgesia but also produces hyperalgesia. In the present study, a series of three experiments was carried out to investigate the interactions between opioid receptor stimulation and antiopioid systems. First, by using in vitro superfusion system with rat spinal cord slices, we showed that morphine stimulated NPFF release in a dose-dependent manner. The stimulating effect which was observed with morphine concentrations as low as 100 fM reached a maximum at 0.1 nM, then decreased and was ineffective at 10 microM. The morphine-induced release of NPFF was abolished by naloxone (1 microM) but unaltered by tetrodotoxin. Second, by an in vivo approach, we showed that a single heroin administration (2.5 mg/kg, s.c.) elicited in 30 min a drastic drop (38%) in spinal NPFF content. In a third experiment, we evaluated the capacity of naloxone in revealing an antiopioid component associated with opioid receptor stimulation. The administration of naloxone (1 mg/kg, s.c..) 25 min following that of heroin (2.5 mg/kg, s.c.) not only abolished the heroin-induced increase of tail-flick latency, but also lowered it under the basal value by 30%. These results indicate that opioid receptor stimulation activates both pain inhibitory and pain facilitatory systems in which NPFF may play a significant role and that opiate-induced analgesia is always partly masked.

Distribution of neuropeptide FF (FLFQPQRFamide) receptors in the adult rat spinal cord: effects of dorsal rhizotomy and neonatal capsaicin

By using quantitative autoradiography and highly selective iodinated ligands, we quantified modifications in neuropeptide FF binding sites in the superficial layers (laminae I and II) of the cervical (C6-C8 segments) and lumbar (L3-L5 segments) enlargements in two models: (i) rats neonatally treated with capsaicin; (ii) rat submitted 15 days before to unilateral dorsal rhizotomies. We comparatively analysed the distribution of mu-opioid binding sites in the same animals. We have shown that the [125I]YLFQPQRFamide (neuropeptide FF sites) labelling is not significantly modified following selective damage of fine afferent fibres by neonatal capsaicin treatment. In the cervical and lumbar enlargements, capsaicin-treated/control binding ratios for [125I]YLFQPQRFamide were 0.90 and 0.86, respectively. While unilateral dorsal rhizotomy induced a drastic decrease in [125I]FK-33-824 labelling in the side ipsilateral to the lesion as compared to the intact side of (yielding ratios of 0.29 and 0.31 for cervical and lumbar levels, respectively), [125I]YLFQPQRFamide labelling was not significantly modified, yielding ratios of 0.98 and 0.91 for cervical and lumbar levels, respectively. These data suggest that, in contrast with a majority of mu-opioid receptors, neuropeptide FF receptors are not located on fine primary afferent fibers carrying nociceptive information from the fore- or hindlimb in the rat. This preferential postsynaptic localization, together with the reported "morphine modulating" action of this peptide, support the proposal of a role for neuropeptide FF in intraspinal modulation of nociceptive input.

[Neurobiology of dependence]

Investigations concerning dependence to drug of abuse are of pluridisciplinary nature. It is clear that to understand this complex phenomenon will not be the privilege of one particular level of psychobiological organizations. Whatever the theories, it must be stated that correlational relations exist between behavior, mental states, and brain-neuronal states whatever the transduction principles in cause. An important neglected problem to be investigated concerns the vulnerability presented by some organisms and not by other, either for the search of a drug-stimulus or to repeat the first encounter with the pharmacological agent, potentially a drug of abuse. Such vulnerability corresponds to a neurobiological state considered far from the equilibrium, i.e. homeostasis. Whether the drug, as many other agents, environmental, nutritional, sexual, tends to reduce the imbalance within the neuronal systems is a matter of debate.

Release of neuropeptide FF, an anti-opioid peptide, in rat spinal cord slices is voltage- and Ca(2+)-sensitive: possible involvement of P-type Ca2+ channels

Neuropeptide FF (NPFF), an FMRFamide-like peptide with antiopioid properties, inhibits morphine-induced analgesia but also produces hyperalgesia. In the present study, the mechanisms of NPFF release were investigated in an in vitro superfusion system with rat spinal cord slices. The opening of voltage-sensitive Na+ channels with veratridine (20 microM) induced calcium-dependent NPFF release, which was abolished by tetrodotoxin (1 microM), suggesting that NPFF release depends on nerve impulse activity. We also showed that NPFF release was a function of the extent of depolarization and was calcium dependent. The 30 mM K(+)-induced release was blocked by Co2+ or Ni2+ (2.5 mM) but was unaffected by Ca2+ channel blockers of the L type--Cd2+ (100 microM), nifedipine or nimodipine (10 microM), diltiazem (20 microM), or verapamil (50 microM)--or the N type--omega-conotoxin GVIA (1 microM). In contrast, omega-agatoxin IVA (1 microM) led to a 65% reduction in NPFF release, suggesting that P-type Ca2+ channels play a prominent role. The 35% remaining release resulted from activation of an unknown subtype. The NPFF-like material in superfusates recognized spinal NPFF receptors, suggesting that NPFF release in the spinal cord has a physiological role.

Neuropeptide FLFQRFamide receptors within the ventral mesenchephalon and dopaminergic terminal areas: localization and functional antiopioid involvement

The neuropeptide FLFQPQRF amide is a FMRFamide-like peptide with some anti-opiate properties. Neuropeptide FLFQPQRFamide receptors are present in the mammalian central nervous system and have been clearly identified as different from opiate receptors. Autoradiography has revealed neuropeptide FLFQPQRFamide receptor localization within the ventral mesencephalon, where opiate receptors are also located. In order to delineate anatomical localization of neuropeptide FLFQPQRFamide receptors, we used selective chemical lesions of dopaminergic cells and intrinsic perikarya of the ventral mesencephalon, coupled with in vitro autoradiographic techniques. We show that: (i) unilateral lesions of dopaminergic perikarya produced by 6-hydroxydopamine did not affect either ipsi or contralateral neuropeptide FLFQPQRFamide receptor density within the mesencephalon; (ii) unilateral lesions of intrinsic perikarya by ibotenic acid injected into the ventral tegmental area produced a significant reduction of neuropeptide FLFQPQRFamide receptors (40%) in this region; (iii) in the substantia nigra pars compacta, ibotenic acid unilateral lesions did not affect the density of neuropeptide FLFQPQRF-amide receptors; (iv) unilateral 6-hydroxydopamine or ibotenic acid lesions failed to affect neuropeptide FLFQPQRFamide binding in the dopaminergic projection areas. These results suggest that, like opiate receptors, the neuropeptide FLFQPQRFamide binding sites are not localized on dopaminergic neurons but are distributed on both soma of non dopaminergic cells in the ventral tegmental area and on fibers afferent to the ventral tegmental area and substantia nigra pars compacta. To evaluate the possibility that the stimulation of neuropeptide FLFQPQRFamide receptors may affect the opioid modulation of mesocorticolimbic dopaminergic neuron activity, we tested the effects of neuropeptide FLFQPQRFamide ventral tegmental area infusion (0.25-10 micrograms) on the behavioral activation induced by intra-ventral tegmental area morphine infusion. We observed that in the ventral tegmental area, the stimulation of neuropeptide FLFQPQRFamide receptors inhibits morphine-induced locomotor hyperactivity. These results suggest that in the ventral tegmental area, neuropeptide FLFQPQRFamide may participate, via an indirect mechanism, to the control of the mesocorticolimbic dopaminergic system activity by counteracting the effect of opioids.

Characterization of binding sites for neuropeptide FF on T lymphocytes of the Jurkat cell line

Neuropeptide FF (NPFF) is a neuropeptide with antiopiate properties able to antagonize the action of both endogenous and exogenous opiates. Because we have recently shown that NPFF modulates the proliferation of human T lymphocytes, we have searched for binding sites for this peptide on T lymphocytes. Our study shows that T lymphocytes of the Jurkat cell line express binding sites for [125I]YLFQPQRFamide, an iodinated analogue of NPFF. This binding is time and dose dependent, reversible, saturable, and may be resolved in two distinct components of high and low affinity. The opiate receptor agonists mu, delta, and kappa, as well the antagonist naloxone, were unable to affect binding. Beside the effects of opiates on immune cells, our results suggest that an antiopiate peptide, such as NPFF, could play a role in the modulation of the immune system.

Changes in CNS neuropeptide FF-like material, pain sensitivity, and opiate dependence following chronic morphine treatment

Tolerance and dependence to opiates may be an adaptive process that limits excessive effects of morphine on the CNS. Because no consistent opiate receptor reduction in chronically treated rats seems to underlie the hyposensitivity to morphine, an alternative hypothesis has postulated a role of "antiopioid" peptides. It is possible to speculate that the administration of morphine stimulates antiopioid systems such as neuropeptide FF (NPFF), as part of an homeostatic mechanism contributing to the development of tolerance. To test this hypothesis, pain sensitivity, opiate dependence, and CNS NPFF-IR levels were estimated at different times after implantation of morphine pellets (2 x 75 mg; NIDA). Three hours after morphine pellet treatment the analgesic effect was maximum and it decreased rapidly during the following 12 h. Naloxone-precipitated withdrawal syndrome was detected as soon as 3 h after morphine pellet implantation and was maximal after 24 h. NPFF-IR levels were measured in the spinal cord, brain stem, and hypothalamus. A significant decrease of NPFF-IR was observed 1 h after morphine pellet implantation (-25% to -45% depending on the structures) followed by a drastic increase of NPFF-IR levels (+60 to +140%) between 3 and 6 h. NPFF-IR levels rapidly returned to baseline after 24-36 h. It is suggested that the activity of these NPFF-IR neurones may increase gradually as a consequence of the continuous stimulation of opiate receptors and be part of an adaptive process that is able to counteract morphine effects and to induce dependence and tolerance to the analgesic effects of opiates.

Modulation of neuropeptide FF release from rat spinal cord slices by glutamate. Involvement of NMDA receptors

This study examined the effects of glutamate receptor agonists on the release of neuropeptide FF-like immunoreactivity from rat spinal dorsal half slices. Glutamate (10 microM) only induced release in Mg(2+)-free medium enriched with glycine (1 microM) and with slight depolarization (15 mM K+). This effect was abolished by the NMDA receptor antagonist, 2-amino-5-phosphonovalerate (100 microM), suggesting major participation of NMDA receptors. The quisqualate and metabotropic receptor agonists, alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) and trans-1-hydroxy-5-methylisoxazole-4-propionate (t-ACPD) respectively, had no effect at 10 microM. In contrast, NMDA dose dependently stimulated neuropeptide FF release, even in the presence of the Na+ channel blocker, tetrodotoxin (1 microM), suggesting that NMDA receptors involved in the release of neuropeptide FF are mainly located on nerve terminals. The NMDA receptor antagonists, 2-amino-5-phosphonovalerate or (+)-5-methyl-10-11-dihydro-5H-dibenzo [a,d]cyclohepten-5,10-imine (MK-801) (100 microM), blocked the 10 microM NMDA effect. Furthermore, neuropeptide FF-like material inhibited binding of [125I]Y8Fa, a radioiodinated analog of neuropeptide FF, to spinal membranes, suggesting physiological relevance of NMDA-induced release. Taken together, these results suggest a relationship between neuropeptide FF and NMDA receptors in the spinal cord.

Structure-activity study of neuropeptide FF: contribution of N-terminal regions to affinity and activity

Twenty neuropeptide FF (NPFF) analogs having various lengths were synthesized by solid-phase peptide synthesis to gain more information on the role of N-terminal residues for the NPFF receptor affinity. The affinities were evaluated in the rat spinal cord membrane preparations, and the biological activities were measured on morphine analgesia in the mouse tail-flick test. Shortening of the NPFF sequence from the N-terminal produced only a moderate decrease in affinity until NPFF (4-8) was reached. In the same way, NPFF(3-8) significantly decreased morphine analgesia, while NPFF(4-8) had no significant effect at a dose of 22 nmol. The introduction in the N-terminal part of NPFF of a D-enantiomer at positions 2 and 1 or the presence of an N-methyl group on position 3 did not modify affinity and activity. Substitution of proline5 by the D-isomer decreased the affinity of NPFF analogs whatever their length, and [Tyr1,D-Pro5]NPFF(1-8) was 2.5-fold less potent than [Tyr1]NPFF(1-8) in reversing morphine-induced analgesia. In contrast, the presence of a glycine residue in position 5 did not influence the affinity toward NPFF receptors. Data provide evidence that the N-terminal segment of neuropeptide FF is responsible for high-affinity binding.

Characterization of a potent agonist for NPFF receptors: binding study on rat spinal cord membranes

Specific receptors for the octapeptide FLFQPQRFamide (NPFF), a mammalian FMRFamide-like neuropeptide with anti-opiate properties have been identified in rat central nervous system. However, exploration of the biological role of this peptide requires a peptidase-resistant agonist. In this study, the stability and binding characteristics of [125I]DYLMeFQPQRFamide, a radioiodinated analogue of NPFF, on rat spinal cord tissue were determined and compared with those of [125I]YLFQPQRFamide, the reference ligand which previously permitted to characterize NPFF binding sites. In a binding assay, [125I]DYLMeFQPQRFamide remained intact in the presence of membranes without peptidase inhibitors, whereas [125I]YLFQPQRFamide was completely hydrolysed. The specific binding was time-dependent, dose-dependent, saturable and reversible. [125I]DYLMeFQPQRFamide shared the same binding characteristics as [125I]YLFQPQRFamide (Kd = 0.07 nM; Bmax = 14.7 fmol/mg protein). Binding was not affected by various spinal cord opioids or peptides. Autoradiographic studies indicated that binding sites were mainly located in the most external layers of dorsal horn where high densities of NPFF binding sites have previously been described. [125I]YLFQPQRFamide and [125I]DYLMeFQPQRFamide binding sites were both GTP-regulated. These findings indicate that DYLMeFQPQRFamide should be of value in studies on NPFF-mediated actions in vivo.

Autoradiographic localization of receptors for neuropeptide FF, FLFQPQRFamide, in human spinal sensory system

The regional distribution of FLFQPQRFamide binding sites on fresh unfixed cryostate sections from post mortem specimens of human spinal cord and lower medulla oblongata was studied by quantitative autoradiographic methods using [125I]YLFQPQRFamide as ligand. Samples were taken from five cases who had died with no history of neurological disease at ages ranging from 5 months to 66 years. The biochemical and pharmacological characteristics of [125I]YLFQPQRFamide binding to mounted tissue sections were comparable to those reported for the rat in a previous study. [125I]YLFQPQRFamide appeared to interact reversibly with high affinity binding sites (Kd = 0.06 nM), distinct from opiate receptors. Sites labelled with [125I]YLFQPQRFamide were distributed unevenly within the human spinal cord and lower medulla oblongata, with the highest density in the superficial layers of the dorsal horn and the spinal trigeminal nucleus. Although moderate labelling was observed in the ventral part of spinal grey matter, dense labelling appeared in the gracile and cuneate nuclei. No binding sites were detected in white matter. These results show that, as in the rat, FLFQPQRFamide receptors in the human spinal cord and lower medulla oblongata, are mainly concentrated within spinal areas implicated in the analgesic action of opiates. The possible role of these receptors in modulating spinal nociceptive information is discussed with respect to the pharmacological effects of substances acting on FLFQPQRFamide receptors in animals.

Biphasic effect on nociception and antiopiate activity of the neuropeptide FF (FLFQPQRFamide) in the rat

The purpose of the present study was to systematically investigate the effects of the mammalian neuropeptide Phe-Leu-Phe-Gln-Pro-Gln-Arg-Phe-NH2 (NPFF) on nociception, using the tail-flick test. We report that ICV administration of NPFF induces a rapid and short-lasting hyperesthesic effect during day or night, for doses ranging from 10 ng to 10 micrograms. During the night, this hyperesthesic effect is followed by a long-lasting analgesic effect, the magnitude of which is related to the magnitude of the hyperesthesic effect. In addition to this intrinsic effect of NPFF, we report that NPFF reverses morphine-induced analgesia and that the magnitude of the response elicited by NPFF increases as a function of morphine-induced analgesia.

NPFF, a FMRF-NH2-like peptide, blocks opiate effects on ileum contractions

We studied the ability of NPFF, a FMRFamide-like peptide with certain antiopiate properties, to affect the inhibitory effect of morphine on the electrically induced contraction of guinea pig ileum. Neuropeptide FF had no effect when administered alone but reduced morphine inhibition in a noncompetitive manner. Neuropeptide FF also altered the inhibitory effect of opioid peptides as released by an intense electrical stimulation at 10 Hz. These results suggest that NPFF receptors exist in guinea pig ileum in association with opiate receptors, and that endogenous NPFF may play a role in the diarrhea observed in the morphine withdrawal syndrome.

Characterization of a morphine-modulating peptide, FLFQPQRFamide, in the rat hypophysis: biochemical and immunocytochemical studies

The octapeptide FLFQPQRFamide (F8Fa) is a FMRFamide-like peptide with a certain number of antiopiate properties. Previous studies have shown that both F8Fa specific receptors and F8Fa-like material are present in the rat central nervous system. In this study, RIA revealed that the rat neurohypophysis also contains F8Fa immunoreactive (IR) material (230 +/- 49 pg/neural lobe). HPLC profiles revealed several forms of F8Fa IR. Neurohypophysis extracts can also inhibit the binding of F8Fa to rat spinal cord preparations, which suggests that this F8Fa-like material has a biological activity. Immunocytochemical observations, at the light and electron microscopic levels, confirmed the presence throughout the neural lobe of F8Fa IR, in axonal fibers and terminals similar to those containing the more classical neurohypophysial hormones. Immunogold staining showed that F8Fa IR was restricted to neurosecretory granules in certain axonal and terminal profiles. Double staining of the same ultrathin sections, using our anti-F8Fa antiserum and vasopressin or its neurophysin specific antibodies, revealed that F8Fa IR was colocalized with vasopressin. F8Fa IR was not visible in ocytocinergic fibers or terminals. A striking depletion of F8Fa IR (80%) was observed in rats which were given 2% saline to drink for 6 days. Similarly, an ip injection of an hypertonic saline solution was shortly followed by a 20% drop of F8Fa IR. In vitro F8Fa IR release from isolated neurohypophysis was evoked under a 56 mM KCl depolarization. These results suggest that F8Fa IR may act as a paracrine/endocrine mediator released from the rat neurohypophysis.

Analogues of F8Famide resistant to degradation, with high affinity and in vivo effects

Four analogues of Phe-Leu-Phe-Gln-Pro-Gln-Arg-Phe-NH2, a mammalian FMRFamide-like peptide with antiopiate properties, were synthesized with N-terminus modifications and were shown to have high affinity for F8Famide binding sites. The degradation rate of these analogues in mouse brain slices was 3 times lower than that of the natural peptide. One analogue, (2DME)Y8Fa (D.Tyr-D.Leu-[N-Me]Phe-Gln-Pro-Gln-Arg-Phe-NH2), produced a clear hyperalgic effect and inhibited morphine analgesia in the mouse tail-flick test at lower doses than did the parent compound. (3D)Y8Fa (D.Tyr-D.Leu-D.Phe-Gln-Pro-Gln-Arg-Phe-NH2) and (2D)Y8Fa (D.Tyr-D.Leu-Phe-Gln-Pro-Gln-Arg-Phe-NH2) in contrast did not decrease morphine analgesia but were analgesic alone. The analgesic effects of 22 nmol (2D)Y8Fa and (3D)Y8Fa were decreased by (1DME)Y8Fa (D.Tyr-Leu-[N-Me]Phe-Gln-Pro-Gln-Arg-Phe-NH2) or (2DME)Y8Fa and were reversed by naloxone. These results indicate opioid modulating properties of F8Famide. These analogues may prove to be useful tools for studying the modulation of pain by F8Famide.

Autoradiographic distribution of receptors to FLFQPQRFamide, a morphine-modulating peptide, in rat central nervous system

The neuropeptide FLFQPQRFamide is a structure related to FMRFamide which is able to inhibit the effects of both endogenous and exogenous opiates. This morphine-modulating activity is mediated via the stimulation of specific FLFQPQRFamide receptors, different from opiate receptors. In vitro quantitative receptor autoradiography was performed on frozen sections of rat central nervous system to characterize binding properties and visualize FLFQPQRFamide receptors using the specific ligand [125I]YLFQPQRFamide, a radio-iodinated analogue of FLFQPQRFamide. [125I]YLFQPQRFamide appeared to interact reversibly with a single class of binding sites (KD = 0.2 nM). The specific binding represented 80% of the total binding at 0.05 nM, the FLFQPQRFamide concentration used in this mapping study. Sites labelled with [125I]YLFQPQRFamide were distributed heterogeneously within the brain and spinal cord. A high density of FLFQPQRFamide binding sites was detected in the most external layers of the dorsal horn of spinal cord and various nuclei of pons and medulla including trigeminal, dorsal tegmental and reticular nuclei. Nucleus of solitary tract, parabrachial, ambiguous and facial nuclei are also intensively labelled. Some structures of mesencephalon and diencephalon exhibited a high density of FLFQPQRFamide binding sites: central gray, raphe nuclei and thalamic nuclei such as parafascicular, laterodorsal, central median, paratenial and paraventricular nuclei. Suprachiasmatic and mammillary nuclei, lateral, posterior and anterior areas of hypothalamus and medial preoptic area exhibited high labelling. FLFQPQRFamide binding sites were also seen in some structures of the dopaminergic meso-cortico-limbic system including ventral tegmental area, cingulate cortex, lateral septum and the head of the caudate-putamen. Dense labelling appeared in the presubiculum of hippocampus. The dissimilar mapping of FLFQPQRFamide and opiate brain receptors confirms our previous pharmacological findings in FLFQPQRFamide binding studies on rat spinal cord membranes, showing that FLFQPQRFamide receptors are different from opiate receptors. There was a good correspondence between localization of binding sites and that of the putative endogenous peptide. Both occur in brain areas previously associated with analgesic action of opiates. However, the mapping of FLFQPQRFamide receptors in the central nervous system suggests that the FLFQPQRFamide system could be implicated in other physiological functions.

Modulation of human lymphocyte proliferation by FLFQPQRFamide, a FMRFamide-like peptide with anti-opiate properties

The octapeptide Phe-Leu-Phe-Gln-Pro-Gln-Arg-Phe-NH2 (F8Fa), originally detected in mammalian brain by antisera raised against the invertebrate peptide Phe-Met-Arg-Phe-NH2 (FMRFamide) is a neuropeptide able to antagonize the actions of both endogenous and exogenous opiates. Since it is well accepted that lymphocytes are targets for opiates, we have tested the effect of F8Fa on T cell proliferation from normal human peripheral blood lymphocytes. Our study shows that F8Fa exerts a concentration-dependent diphasic modulation of human T lymphocyte proliferation. Thus, despite a great variability between individuals, 10(-13) M F8Fa was found to enhance the proliferation of T cells induced by phytohemagglutinin or anti-CD2 monoclonal antibodies, while 10(-7) M F8Fa inhibited T cell proliferation, without affecting cell viability. When F8Fa was tested on monocyte-depleted cell preparations, only the inhibitory effect was observed. These results indicate that F8Fa may stimulate T cells via monocytes, but may also directly inhibit T lymphocyte proliferation. Given the presence of F8Fa-like peptide in human plasma, we suggest that F8Fa may act as a neurohormone in the control of the immune system.

[Spontaneous splenic rupture disclosing a pheochromocytoma]

Clinical manifestation of a phaeochromocytoma may range from no symptoms to an acute abdominal emergency. These abdominal emergencies are related to haemorrhagic necrosis of the tumour, or massive bleeding in the retroperitoneal space. The authors report a case of splenic rupture revealing a phaeochromocytoma. The mechanism of splenic rupture is discussed as is the conservative treatment of phaeochromocytoma during splenic surgery. The authors observed no correlation between plasma catecholamine concentration and blood pressure.

[Plasma catecholamines in brain death]

The purpose of this study was to find out whether a severe fall in plasma catecholamines levels can be observed in brain dead patients, that might contribute to haemodynamic disturbances in these patients. Plasma catecholamines (epinephrine and norepinephrine) were measured by HPLC combined with electrochemical detection in 18 consecutive brain dead patients referred to the multiorgan donors unit at the Bordeaux University Hospital. Two samples were obtained: the first one at the time of donor referral (11.2 +/- 9 h after the clinical onset of brain death), and the second one just before organ procurement (19.8 +/- 1 h after the clinical onset of brain death). The results showed that plasma catecholamines levels were similar in both samples, with mean values within the normal range. There was no correlation between the plasma levels of each of the catecholamines and the mean arterial pressures at the time of sampling. Very high plasma catecholamines levels have been found by other authors after brain injuries. After the onset of brain death, they return to basal rest values and do not continue to fall as is the case in animal experiments. The haemodynamic disturbances observed in brain dead patients therefore cannot be due only to sympathoadrenal failure.

Characterization and localization of a putative morphine-modulating peptide, FLFQPQRFamide, in the rat spinal cord: biochemical and immunocytochemical studies

The bovine octapeptide Phe-Leu-Phe-Gln-Pro-Gln-Arg-Phe-NH2 (FLFQPQRFamide), originally detected by antisera raised against the invertebrate peptide, Phe-Met-Arg-Phe-NH2, is a neuropeptide which antagonizes the actions of endogenous and exogenous opiates. Using a sensitive radioreceptor assay, we show that rat spinal cord extracts were able to inhibit binding of FLFQPQRFamide, suggesting that a biologically active FLFQPQRFamide-like material exists in the rat spinal cord. We also raised antibodies against the peptide and used them, together with radioimmunological and immunohistochemical methods, to characterize this material further and analyse its cellular and subcellular localization in this area of the central nervous system. Radioimmunoassay showed that extracts from cervical and thoracolumbar levels contained measurable amounts of FLFQPQRFamide-immunoreactive material (about 3 ng/g tissue), present essentially in the dorsal horn. Analytical reverse-phase chromatography revealed that this material existed in several molecular forms. One of these fractions (about 20% of the total immunoreactivity) had the elution characteristics of synthetic FLFQPQRFamide. Light microscopic immunohistochemistry showed FLFQPQRFamide immunoreactivity at all spinal levels, localized mainly in a dense plexus of fibers in the superficial layers of the dorsal horn. Immunoreactive profiles were also seen in the lateral funiculi and around the central canal at all levels and in the intermediolateral columns; some rare immunoreactive fibers were also noted in the ventral horn at cervical and thoracic levels. FLFQPQRFamide-positive cell bodies were never detected in any of our sections. Electron microscopy of ultrathin sections of the dorsal horn and central gray treated with our antisera and a post-embedding immunogold procedure revealed that the immunoreactivity, at least within these areas, was restricted to dense-cored vesicles (90-120 nm in diameter) in axonal and terminal profiles. As seen by radioimmunoassay and immunohistochemistry, unilateral rhizotomy of all dorsal roots between segments C4 and T2 did not change the levels of FLFQPQRFamide immunoreactivity in the ipsilateral C6-C8 segments. Taken together with our recent data showing the existence of specific FLFQPQRFamide receptors at the spinal cord level, our present observations suggest that the dorsal horn of the rat spinal cord may be a site where vertebrate Phe-Met-Arg-Phe-like peptides, and in particular, FLFQPQRFamide, may exert opiate modulating activities.

Differential interactions of cholecystokinin and FLFQPQRF-NH2 with mu and delta opioid antinociception in the rat spinal cord

An in vivo preparation of the rat spinal cord was used to investigate the electrophysiological actions of two non-opioid peptides, cholecystokinin (CCK8) and FLFQPQRF-NH2 (FMRFamide-like peptide) applied intrathecally. These compounds were examined alone and as a pretreatment before DAGO, a mu opioid agonist, and DSTBULET, a delta opioid agonist, both which selectively reduce C-fibre evoked dorsal horn neurone activity elicited by transcutaneous electrical stimulation. Given alone, CCK8 (1 microgram) elicited a modest enhancement of C-fibre induced activity which returned to control levels after 20 min, while FLFQPQRF-NH2 (10 micrograms) had no significant effect on C-fibre evoked firing. As a pretreatment, however, both peptides selectively prevented the inhibition of C-fibre evoked activity normally resulting from intrathecal DAGO, while having no effect on that resulting from DSTBULET. Further, CCK8 enhanced the facilitation of C-fibre evoked firing normally observed with low doses of DAGO. These data indicate that the anti-opioid roles suggested for CCK8 and FLFQPQRF-NH2 may be specific for neural elements utilizing the mu opioid receptor.

Electrophysiological effects of FLFQPQRF amide, an endogenous brain morphine modulating peptide, on cultured mouse spinal-cord neurons

Intracellular recordings were made from dissociated fetal mouse spinal cord neurones in primary culture. Micropressure application of FLFQPQRFamide (10(-5) M in the delivery pipette), an endogenous mammalian brain morphine modulating peptide, onto the surface of spinal cord neurones induced, in a dose dependent manner, a transitory hyperpolarization followed by a long lasting depolarization of the membrane potential (n = 37). In contrast, no response was observed when the peptide was applied on dorsal root ganglia neurones (n = 30). The depolarizing phase of this response was underlied by an increase of the input resistance. Extrapolated reversal potential for the depolarizing phase was close to -80 mV while it was close to -40 mV for the hyperpolarizing phase. Increasing extracellular K+ concentration raised the reversal potential value of depolarizing phases to more positive values. The amplitude of the depolarizing phase was reduced by application of tetraethylammonium (50 mM) while it was enhanced by application of 4-aminopyridine (3 mM). CaCl2 application (3 mM) reversibly blocked the hyperpolarization and decreased the subsequent depolarization. In presence of Ba2+ the extrapollated reversal potential of the hyperpolarizing phase was dramatically shifted to a more positive value. Finally FLFQPQRFamide induced response can be partially mimicked by FMRFamide application. Our observations indicate that FLFQPQRFamide can have multiple effects on membrane conductance of mammalian spinal cord neurones by acting on a single class of receptor. These effects of FLFQPQRFamide were found to be mainly excitatory.

Characterization of rat spinal cord receptors to FLFQPQRFamide, a mammalian morphine modulating peptide: a binding study

An in vitro binding assay, using 125I-YLFQPQRFamide, a newly synthetized iodinated analog of FLFQPQRFamide, in which Phe1 (F) has been substituted by a Tyr (Y), was developed to demonstrate and characterize putative binding sites of this brain morphine modulating peptide. This radioligand bound in a time-dependent manner to rat spinal cord membrane preparation. This binding was dose-dependent, saturable and reversible. Both kinetic data and saturation measured at equilibrium lead to the existence of a homogenous population of high affinity binding sites with a Kd value of 0.09-0.1 nM and a maximal capacity Bmax of 14.5 +/- 2 fmol/mg protein. Results of competition experiments show that both FLFQPQRFamide and its analog YLFQPQRFamide had a similar capacity to inhibit the 125I-YLFQPQRFamide binding, suggesting that this radioiodinated analog is a good tool to study binding characteristics of FLFQPQRFamide receptors. The related octadecapeptide AGEGLSSPFWSLAAPQRFamide, another mammalian morphine modulating peptide competes for radioligand binding with similar potency. Our results also show that mu, delta and kappa opiate receptor agonists as well as the antagonist naloxone were not able to affect binding either in presence or in absence of 120 mM NaCl. Together, these data demonstrate that FLFQPQRFamide does not function as an endogenous opiate receptor antagonist and that is capacity to reduce opiate-induced analgesia is supported by specific binding sites.

Characteristics and specific localization of receptors for atrial natriuretic peptides at non-neuronal cells in cultured mouse spinal cord cells

Characteristics of atrial natriuretic peptide receptors were determined in cultured mouse spinal cord cells. Saturation and competition experiments demonstrated the presence of a single class of atrial natriuretic peptide binding sites with high affinity (KD = 0.054 nM) and a density of 1.92 fmoles/10(6) cells. A similar affinity (KD = 0.070 nM) was observed in rat spinal cord membrane preparations. These atrial natriuretic peptide binding sites were functional receptors since the treatment of cells with atrial natriuretic peptide increased cyclic guanosine monophosphate levels within these cells in a classical time-dependent manner. When atrial natriuretic peptide was applied onto the cell body of intracellularly recorded spinal cord neurons, this peptide did not evoke a change of the input resistance or of the resting membrane potential value. Light-microscopic autoradiography studies showed that no atrial natriuretic peptide binding could be detected on typical birefringent neurons but it could be located on astroglial and epithelial cells as identified by immunocytochemical markers. These results show that functional atrial natriuretic peptide receptors with high affinity exist in cultured mouse spinal cord cells and are not located on neurons. The presence of atrial natriuretic peptide receptors on astrocytes suggests that this neuropeptide might be a good candidate for neuron-glial communication. As the atrial natriuretic peptide binding sites previously shown in epithelia responsible for maintaining fluid and electrolyte gradients, the atrial natriuretic peptide receptors on epithelial cells in these spinal cord cultures may be involved in vivo in the control of water balance in the central nervous system.

Aldosterone secretion and adrenal angiotensin II receptors in the Brattleboro rat

The basal secretion of aldosterone, measured in adrenal venous blood, was three- to fourfold lower in Brattleboro than in Long-Evans rats used as controls. Infusion of a low dose of angiotensin II (1 ng/min per 100 g body/wt) to Long-Evans rats caused a fourfold increase in aldosterone release but neither the low dose nor a tenfold higher dose changed the rate of release in Brattleboro rats. Only a very high dose (300 ng/min per 100 g body wt) succeeded in increasing the secretion of aldosterone in Brattleboro rats but throughout the time-course of the infusion, secretion remained about fivefold lower than in Long-Evans rats and the incremental response was reduced by 74.9%. Adrenal zona glomerulosa angiotensin II receptor sites had similar affinity and maximum binding capacity in the two groups of rats. It is suggested that the reduced corticosteroidogenic capacity of the adrenal cortex of Brattleboro rats results from an impairment of the post-receptor mechanisms involved in the biosynthesis of aldosterone.

Location of angiotensin II binding sites on neuronal and glial cells of cultured mouse spinal cord: an autoradiographic study

Cultures of mouse spinal cord were used to visualize binding sites for [125I]angiotensin II (AII) by autoradiography. Visualization by light microscopy shows that neurones, but also glial cells possess angiotensin II binding sites which are located both on soma and processes. These findings open a new field of investigation for the understanding of the physiological significance of AII in the CNS.

Solubilization and characterization of covalently labeled angiotensin II receptors in cultured mouse spinal cord cells

To investigate the physicochemical characteristics of angiotensin II receptors in nervous tissue, [125I]-labeled AII was covalently linked to its binding sites in cultured mouse spinal cord cells, using the chemical crosslinking agent disuccinimidyl suberate. The liganded complexes were analyzed by SDS/polyacrylamide gel electrophoresis. Autoradiograms revealed a single band which corresponding to a component with a calculated Mr value of 68,000 +/- 5,000. The same radioactive band was observed under reducing or non-reducing conditions, although in the presence of beta-mercaptoethanol the band was less intense. This suggests that the AII binding unit may contain essential disulfide bonds close to the AII binding site. After solubilization with 1% Triton X-100, extracts were analyzed by HPLC gel filtration. Three radioactive species were identified with apparent molecular weights of 65,000; 115,000 and 185,000. Results obtained in the presence or absence of 10 nM unlabeled AII showed that these three units were common to both the high and the low affinity binding sites. The results also demonstrate that AII receptors in nervous tissue have similar physicochemical properties to those from other tissues, and that the 68,000 subunit probably contains the AII binding site.

Angiotensin II inactivation process in cultured mouse spinal cord cells

The pattern of hydrolysis of [3H]angiotensin II ( [3H]AII; 20 nM) by intact cells was studied on cultured mouse spinal cord cells. Degradation products were identified by HPLC analysis after incubation for 2 h at 37 degrees C. In the absence of peptidase inhibitors, 70% of [3H]AII was degraded, and the main labeled metabolite was [3H]tyrosine (40% of total radioactivity). Minor quantities of [3H]AII1-5 and [3H]AII4-8 were formed. Results obtained in the presence of various inhibitors indicate that several enzymes were involved in the AII-hydrolyzing process. Dipeptidyl aminopeptidase III (EC 3.4.14.4) could play a critical role, as suggested by the formation of [3H]Val3-Tyr4 and [3H]-Tyr4-Ile5 in the presence of bestatin (2 X 10(-5) M). This hypothesis was confirmed by the potency of dipeptidyl amino-peptidase III inhibitors to inhibit both [3H]AII hydrolysis and formation of these 3H-labeled dipeptides. An arylamidase-like activity could also be participating in [3H]AII hydrolysis, because higher concentrations of bestatin (10(-4) M) in association with dipeptidyl aminopeptidase III inhibitors totally inhibited [3H]tyrosine formation, increased protection of [3H]AII and [3H]AII1-7 formed, and provoked a slight accumulation of [3H]AII2-8. These results suggest that the formation of [3H]AII2-8 is due to the action of a bestatin-insensitive acidic aminopeptidase and that the Pro7-Phe8 cleavage is also a step of AII hydrolysis, resulting from the action of an unidentified peptidase different from prolyl endopeptidase.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Simultaneous determination of radio-immunoassayable methionine-enkephalin and radioreceptor-active opiate peptides in CSF of chronic pain suffering and non suffering patients

Radio-immunoassayable methionine-enkephalin (ME) and radioreceptor-active opiate peptide levels (OP) were determined in CSF from patients, both with and without chronic pain, under investigation for vertebral disk disease. This study showed: that there was no direct correlation between ME and OP levels in CSF; OP levels were negatively correlated with the ME/OP ratio; migraine patients had higher levels of ME; ME concentrations were reduced in patients receiving anti-inflammatory drugs (nonsteroidal): patients with chronic pain (non migraine, no anti-inflammatory drug therapy) had lower ME levels than patients without pain. The data are discussed in relation to animal models of chronic pain.

Characterization of two angiotensin II binding sites in cultured mouse spinal cord neurones

Characteristics of angiotensin II (AII) binding have been determined in cultured mouse spinal cord neurones using [125I]AII and [3H]AII. The Scatchard plot of equilibrium binding was curvilinear and could be described by postulating the existence of two different classes of independent binding sites (Kd1 = 0.43 nM, Bmax1 = 12.5 fmol/1.5 X 10(6) cells; Kd2 = 25.6 nM, Bmax2 = 220 fmol/1.5 X 10(6) cells). These values are in close agreement with the Kd values obtained from kinetic studies. The high affinity binding sites appeared to be similar to the single class of sites described in other studies. The relative inhibition potency of AII-related peptides was studied. Sar1,-Leu8-AII was the most potent in inhibiting specific AII binding. The characteristics of the two AII binding sites suggest that they correspond to two receptors as described in a previous electrophysiological approach using this model in our laboratory. Taken together, these data confirm that this model of neurones in primary culture is a unique and very attractive model of receptor studies. The classical criteria necessary for positive identification of a ligand-receptor have been satisfied: saturability, reversibility, specificity and most importantly correlation of the binding parameters and biological effects of AII.