Production of hyperalgesic prostaglandins by sympathetic postganglionic neurons

Prostaglandin E2 and prostacyclin (prostaglandin I2) produce hyperalgesia in animals and humans. Because there is evidence that prostaglandins contribute to pain maintained by sympathetic nervous system activity, we evaluated whether sympathetic postganglionic neurons synthesize these hyperalgesic prostaglandins, and whether production of prostaglandins by these neurons can contribute to sensitization of primary afferent nociceptors. Intradermal injection of arachidonic acid but not linoleic acid, in the rat hindpaw, produces a decrease in mechanical nociceptive threshold. This hyperalgesic effect is prevented by indomethacin, an inhibitor of prostaglandin synthesis or by prior surgical removal of the lumbar sympathetic chain. To test the hypothesis that sympathetic postganglionic neurons are the source of prostaglandins, we measured production of prostaglandin E2 and 6-keto-prostaglandin F1 alpha (the stable metabolite of prostacyclin) by homogenates of adult rat sympathetic postganglionic neurons from superior cervical ganglia. These homogenates produced significant amounts of prostaglandin E2 and 6-keto-prostaglandin F1 alpha, and most of this production is eliminated by neonatal administration of 6-hydroxydopamine which selectively destroys sympathetic postganglionic neurons. These results demonstrate that sympathetic postganglionic neurons produce prostaglandins, and supports further the hypothesis that the release of prostaglandins from sympathetic postganglionic neurons contributes to the hyperalgesia associated with sympathetically maintained pain.

Altered autonomic function in patients with arthritis or with chronic myofascial pain

Dynamic autonomic function tests (pupillary light reflex, Valsalva maneuver, and mental arithmetic) were used to evaluate autonomic function (pupil size, heart rate, and skin conductance) in patients with inflammatory arthritis or with chronic myofascial pain. Physiological responses in both groups of patients suggest concurrent increases in tonic pupillary autonomic activity (sympathetic and parasympathetic), with a relative sympathetic dominance, and a decrease in tonic parasympathetic cardiovascular activity. Furthermore, in the arthritis group, the data suggest decreased cardiovascular parasympathetic reaction and enhanced sudomotor reaction.

Contribution of guanine nucleotide regulatory proteins to prostaglandin hyperalgesia in the rat

The contribution of the stimulatory guanine nucleotide regulatory protein (Gs) to prostaglandin E2 (PGE2)-induced hyperalgesia was investigated in the hairy skin of the rat hindpaw using the Randall-Selitto paw-withdrawal test. Although without effect alone, guanosine-5'-[gamma-thio]triphosphate (GTP gamma S) and cholera toxin--which activate Gs--both increased, while guanosine-5'-[beta-thio] diphosphate (GDP beta S)--which prevents the activation of Gs--decreased the hyperalgesia induced by PGE2. These data support the hypothesis that the action of PGE2 on primary afferent nociceptors leading to decreases in paw-withdrawal threshold is Gs-mediated.

Prostaglandin effects after elimination of indirect hyperalgesic mechanisms in the skin of the rat

In this study we eliminated known indirect hyperalgesic mechanisms by blocking the cyclooxygenase pathway of arachidonic acid metabolism with indomethacin, depleting sympathetic postganglionic neurons with 6-hydroxydopamine and depleting polymorphonuclear leukocytes with hydroxyurea. These treatments did not significantly affect the dose-dependence relationship for prostaglandin E2 (PGE2)- and prostaglandin I2 (PGI2)-induced changes in the mechanical nociceptive threshold in the rat. These data are compatible with the hypothesis that PGE2 and PGI2 act directly on peripheral terminals of nociceptive afferents to produce hyperalgesia.

Expression of c-fos protein in interneurons and projection neurons of the rat spinal cord in response to noxious somatic, articular, and visceral stimulation

This study used immunocytochemistry to examine the pattern of noxious-stimulus evoked expression of the proto-oncogene c-fos in the spinal cord of the rat. Both noxious somatic and joint stimulation in awake rats evoked the expression of c-fos protein in similar areas of the lumbar spinal cord. C-fos-immunoreactive neurons were found in laminae I and outer II, in the lateral part of the neck of the dorsal horn, and in laminae VII, VIII, and X. All of the labelled neurons were located ipsilateral to the injured hindpaw, except for lamina VIII where bilateral labelling was recorded. The c-fos-immunoreactive neurons in lamina I extended from the L3 segment to the rostral sacral cord; staining in outer lamina II was only found at the L4 segment. The more deeply located cells, of the dorsal and medioventral horns, had the most extensive rostrocaudal spread; they were found from L1 through the rostral sacral segments. The pattern of c-fos-immunoreactivity produced by visceral stimulation, in anesthetized rats, differed in several ways from that produced by somatic stimulation. First, there was considerable bilateral, symmetrical labelling of cells. Second, there was a much more extensive rostrocaudal spread of the labelling, from cervical through sacral cord. Third, the greatest rostrocaudal spread was found for neurons in the superficial dorsal horn; labelled cells in the neck of the dorsal horn and in lamina X were restricted to segments at the thoracolumbar junction, which is also where the superficial dorsal horn cells were most concentrated. Fourth, there were very few labelled neurons in the outer part of the substantia gelatinosa. To determine whether any neurons that express the c-fos protein in response to noxious stimulation project to supraspinal sites, we combined the immunocytochemical localization of c-fos with the localization of a retrogradely transported protein-gold complex that was injected into the thalamic and brainstem targets of the major ascending spinal pathways. In rats that received the somatic noxious stimulus, 90% of all of the c-fos projection neurons were recorded in four major areas of the cord: lamina I (37%), the lateral part of the neck of the dorsal horn (24%), laminae VIII (9%), and X (29%). The remainder were scattered throughout the spinal gray. With the exception of lamina VIII, which contained c-fos projection neurons contralateral to the inflamed paw, all of the c-fos projection neurons were located ipsilateral to the injured paw.(ABSTRACT TRUNCATED AT 400 WORDS)

Neural control of vascular permeability: interactions between primary afferents, mast cells, and sympathetic efferents

1. This study addressed the contribution of primary afferents, mast cells, and sympathetic efferents to the control of vascular permeability in synovial joints. Extravasation of Evans blue dye into the synovial space was measured by perfusion of the knee joint in the adult rat. Plasma extravasation (PE) was evoked by pharmacologic activation of either unmyelinated primary afferents, mast cells, or sympathetic postganglionic nerve (SPGN) terminals with acute injection of either capsaicin, compound 48/80, or 6-hydroxydopamine (6-OHDA), respectively. In otherwise untreated control rats, acute infusion of capsaicin or compound 48/80 produced a brief increase in vascular permeability; infusion of 6-OHDA produced a larger and more prolonged increase. 2. To evaluate the contribution of an interaction of different cellular elements in the joint to PE, we repeated these experiments in rats pretreated with capsaicin, compound 48/80, or 6-OHDA; administered quercetin; or surgically sympathectomized by excision of the lumbar sympathetic chain. Eliminating unmyelinated afferent nerve terminals by neonatal treatment with capsaicin only reduced the increase in PE produced by acute infusion of capsaicin. Degranulating mast cells by pretreatment with compound 48/80, or preventing the degranulation of mast cells by treatment with quercetin, reduced the increase in PE evoked by infusion of either capsaicin or compound 48/80. Finally, sympathectomy, produced by excision of the lumbar sympathetic chain or by pretreatment with 6-OHDA, significantly reduced PE elicited by acute infusion of capsaicin, compound 48/80, or 6-OHDA. 3. Neither infusing substances normally localized to sympathetic efferents nor inducing changes in blood pressure could mimic the profound increase in PE evoked by activation of sympathetic postganglionic neurons with acute infusion of 6-OHDA. Thus norepinephrine produced a significant decrease in PE, adenosine triphosphate produced only a brief increase, neuropeptide Y had no effect, and manipulating blood pressure (either up or down) had no effect on either base-line or 6-OHDA-induced PE. 4. Indomethacin treatment significantly reduced the increase in PE produced by 6-OHDA. This effect of indomethacin was reversed by the addition of prostaglandin E2 (PGE2) to the 6-OHDA in the perfusion fluid. This finding implicates prostaglandins (i.e., cyclooxygenase products of arachidonic acid metabolism) in SPGN-dependent generation of PE.(ABSTRACT TRUNCATED AT 400 WORDS)

Differential effects of acetylsalicylic acid and acetaminophen on sleep abnormalities in a rat chronic pain model

We studied the effects of two non-steroidal anti-inflammatory analgesics (NSAIAs), acetylsalicylic acid (ASA) and acetaminophen, on sleep patterns in rats with adjuvant-induced arthritis. We found that in the normal rat both NSAIAs reduced non-rapid eye movement (NREM) sleep. In arthritic rats ASA and acetaminophen had opposite effects on sleep. ASA increased wakefulness and decreased all sleep stages and acetaminophen decreased wakefulness and increased NREM sleep and paradoxical sleep during the light hours (the hours of maximal sleep in the normal rat). When the effects of severity of arthritis were factored out, both drugs still had large and significant effects on sleep and wakefulness. Thus, two prostaglandin synthetase inhibitors showed differential effects on sleep and wakefulness in the normal rat and in rats experiencing chronic pain. Although ASA is important in the treatment of pain in rheumatic diseases, it may contribute to abnormal sleep patterns.

The contribution of training to sensitivity in the nociceptive paw-withdrawal test

An important limitation in behavioral tests of the hyperalgesic and analgesic effects of drugs is the low sensitivity of the measuring technique associated with inter- and intra-subject variability. Since familiarity with the experimental situation and novelty of the stimulus significantly influences an animal's behavior, we have tested the hypothesis that intensive training of rats, in the Randall-Selitto paw-withdrawal test, will increase the sensitivity of this test for detecting hyperalgesic effects of intradermal injections of the inflammatory mediator, bradykinin (BK). Mean baseline of the mechanical nociceptive threshold decreased between the first and second, and stabilized by the third day of training. Although there was no significant difference between the effects of BK or its vehicle (saline) on nociceptive threshold on day 1, on subsequent days BK produced a dose-dependent decrease in nociceptive threshold that could be distinguished from the effect of vehicle. These data demonstrate that training in the experimental paradigm can increase sensitivity for detecting hyperalgesic effects of inflammatory mediators in behavioral tests.

Beta-estradiol induced catecholamine-sensitive hyperalgesia: a contribution to pain in Raynaud's phenomenon

The physiological basis of the pain and hyperalgesia observed in patients with Raynaud's phenomenon (RP) is unknown. Since estrogen-induced effects on sympathetic postganglionic neurons (SPGNs) have been implicated in the vasomotor abnormalities in patients with RP, we have studied the effects of estradiol on nociceptive thresholds and noradrenaline sensitivity in a nociceptive flexion reflex in the rat. We report that estradiol induces a catecholamine sensitive hyperalgesia. This hyperalgesia is antagonized by yohimbine (an alpha 2-adrenergic antagonist) but not prazosin (an alpha 1-adrenergic antagonist) as well as by inhibitors of the cyclooxygenase pathway of arachidonic acid metabolism. These data are compatible with the hypothesis that the sensory abnormalities observed in patients with RP may depend on estradiol-induced changes in SPGN, resulting in a sympathetically-dependent production of cyclooxygenase products of arachidonic acid.

Paradoxical analgesia produced by low doses of the opiate-antagonist naloxone is mediated by interaction at a site with characteristics of the delta opioid receptor

This study addressed the opiate receptor subclass which underlies the paradoxical analgesic action of intrathecal administration of low doses of the stereospecific opiate receptor antagonist, naloxone. The analgesic effect of low dose naloxone was abolished in rats that had been pretreated 24 hr earlier with a large intrathecal dose of naloxone or 20 min previously with the delta receptor specific antagonist, ICI-174,864. A large intrathecal dose of naloxone administered 24 hr previously also abolished the analgesic effects of the delta-specific ligands [D-Pen2,5]-enkephalin and [D-Ser2]-Leu enkephalin-Thr but not those produced by mu-ligands Tyr-D-Ala-Gly-NMe-Phe-Gly-ol and beta-Casomorphin(1-4) amide or by the kappa-specific ligand, U50,488H. Furthermore, the analgesic action of low dose naloxone (on thermal and mechanical nociceptive threshold tests) persisted in rats made tolerant to mu-opioid receptor specific ligands. We conclude that the analgesic action of a low dose of naloxone is mediated via interaction with a stereospecific binding site with the characteristics of the delta-opioid receptor.

Total pancreatectomy for ductal cell carcinoma of the pancreas. An update

Forty-eight patients with ductal cell carcinoma of the pancreas underwent total pancreatectomy. During 1970-1976, there were four deaths (a mortality of 18%). During the last twenty-eight operations (1977-1986), there were no hospital deaths. Seventeen per cent of the patients suffered intraoperative complications involving the mesenteric vessels. Twenty-seven per cent suffered postoperative complications. Twenty-five per cent of the patients left the hospital within 2 weeks, 50% left within 4 weeks, and another 25% remained in the hospital for longer than 4 weeks. Thirty-five per cent of the patients have returned to their preoperative job or similar life activity. Another 35% were able to lead an active life but did not return to regular work, and 30% were to some degree incapacitated by their operative procedure and disease. Twenty-one per cent of the patients lived for 4 years, and 14% survived for 5 years.

Decreased slow-wave and paradoxical sleep in a rat chronic pain model

Diurnal sleep-wake patterns in the normal and the adjuvant arthritic rat were measured during the first 3 h of both light and dark periods. During the hours of maximal sleep in the normal rat, arthritic rats showed a significant increase in wakefulness (Wake), a shift to non-rapid-eye-movement (NREM) stages with lower amplitudes (LS and HS1), and a large reduction of NREM sleep with the highest-amplitude (HS2) and paradoxical sleep. Arthritic rats also showed marked sleep fragmentation manifested by more episodes of Wake, LS, and HS1 and shorter episodes of HS2 during both the light and the dark periods. Thus, arthritic rats cannot sustain long periods of sleep. In contrast to control rats, arthritic rats lacked a diurnal variation in Wake, total sleep, and electroencephalographic (EEG) delta activity. They also showed a decrease in overall EEG amplitude. In addition, there was a positive correlation between the severity of arthritis and the percentages of NREM sleep with low (LS) and moderate (HS1) amplitude. Thus, the decline in EEG amplitude could indicate a deficit of EEG generating mechanisms or some aspect of disease severity, such as pain.

An animal model to detect the neuropsychological toxicity of anticancer agents

The unexpected discovery that certain chemotherapeutic agents used in the treatment of childhood cancers have neurocognitive side effects has prompted a search for techniques that identify those medications that place children at risk. An animal model for the assessment of resultant neurocognitive toxicity is described which makes use of simple classical conditioning. We have shown that rats learn about environmental events more slowly following neonatal administration of methotrexate. The changes after methotrexate exposure are not related to stimulus characteristics or to perceptual abilities, but rather to damage to the neural systems involved in acquisition, retention, or recall. Similar problems with learning have been observed in children treated with methotrexate. An effective animal model such as the one described here may help detect and avoid antineoplastic agents that produce severe cognitive defects in childhood cancer patients.

Mediation of primary afferent peripheral hyperalgesia by the cAMP second messenger system

Cyclooxygenase (prostaglandin E2 and prostaglandin I2) and lipoxygenase [8(R), 15(S)-dihydroxyicosa-(5E-9,11,13Z)-tetraenoic acid] products of arachidonic acid metabolism are thought to produce peripheral hyperalgesia by a direct action on the primary afferent nociceptor. In this study we investigated the possibility that these eicosanoids generate hyperalgesia through a common second messenger in the rat. We report that 8-bromo cAMP, a membrane permeable analogue of cAMP, produces a dose-dependent hyperalgesia that is not affected by treatments that interrupt indirect routes of hyperalgesia production including sympathectomy with 6-hydroxydopamine, depletion of polymorphonuclear leukocytes (a source of hyperalgesic eicosanoids) with hydroxyurea, or blockade of the cyclooxygenase pathway of arachidonic acid metabolism with indomethacin. The phosphodiesterase inhibitor isobutyl-methylxanthine markedly prolongs the hyperalgesic effect of 8-bromo cAMP as well as those of the directly acting hyperalgesic agents prostaglandin E2, prostaglandin I2 and 8(R),15(S)-dihydroxyicosa-(5E-9,11,13Z)-tetraenoic acid. We conclude that the effect of all known hyperalgesic eicosanoids is mediated by the cAMP second messenger system and suggest, therefore, that cAMP mediates peripheral hyperalgesia in primary afferent nociceptors.

Involvement of the mu-opiate receptor in peripheral analgesia

The intradermal injection of mu (morphine, Tyr-D-Ala-Gly-NMe-Phe-Gly-ol and morphiceptin), kappa (trans-3,4-dichloro-N-methyl-N[2-(1-pyrrolidinyl) cyclohexyl]benzeneactemide) and delta ([D-Pen2.5]-enkephalin and [D-Ser2]-[Leu]enkephalin-Thr) selective opioid-agonists, by themselves, did not significantly affect the mechanical nociceptive threshold in the hindpaw of the rat. Intradermal injection of mu, but not delta or kappa opioid-agonists, however, produced dose-dependent inhibition of prostaglandin E2-induced hyperalgesia. The analgesic effect of the mu-agonist morphine was dose-dependently antagonized by naloxone and prevented by co-injection of pertussis toxin. Morphine did not, however, alter the hyperalgesia induced by 8-bromo cyclic adenosine monophosphate. We conclude that the analgesic action of opioids on the peripheral terminals of primary afferents is via a binding site with characteristics of the mu-opioid receptor and that this action is mediated by inhibition of the cyclic adenosine monophosphate second messenger system.

Potentiation of pentazocine analgesia by low-dose naloxone

The analgesia produced by combinations of low-dose naloxone with pentazocine or morphine was studied in 105 patients with moderately severe postoperative pain after standardized surgery for removal of impacted third molars. Pain intensity was quantified using a visual-analogue scale. To eliminate the release of endogenous opioids produced by the placebo component of open drug administration, all injections were made by a preprogrammed infusion pump. The analgesia produced by pentazocine, an agonist-antagonist opiate-analgesic acting predominantly at the kappa opiate receptor, was potentiated by low-dose naloxone, whereas the analgesia produced by morphine, a mu-agonist, was attenuated by low-dose naloxone. To evaluate whether similar potentiation would be present in an animal model, and specifically, in the absence of diazepam, which patients receive, we performed an analogous experiment in rats in which nociceptive threshold was determined using the Randall-Selitto paw-withdrawal test. The results were completely analogous to the clinical results: pentazocine analgesia was potentiated by low-dose naloxone, whereas morphine analgesia was attenuated by low-dose naloxone. These data demonstrate a novel interaction between opiates, and suggest a rationale for opiate combinations to produce potent analgesia with fewer autonomic side effects and less abuse potential than presently available analgesics.

Spindle-cell adenomyoepithelioma of the breast. A microscopic, ultrastructural, and immunocytochemical study

Two patients developed nodular, well-circumscribed tumors of the breast, discovered by mammography. They were fibroadenoma-like by gross examination and biphasic by light microscopy, containing both tubular glands and spindled myoid cells. Immunocytochemical studies revealed cytokeratin and S-100 immunoreactivity in both the spindled myoid cells and in the tubuloglandular cells (S-100 was focal in the latter). In addition, the spindled myoid cells were immunoreactive for vimentin but negative for desmin. Ultrastructural studies showed the tubular glands to be composed of luminal epithelial cells focally surrounded by myoepithelial cells, but the stroma contained spindled myoepithelial cells admixed with occasional fibroblasts. The diagnostic term, "adenomyoepithelioma," is appropriate for biphasic tumors having both glandular and myoepitheliomatous differentiation. Although additional experience is necessary to be conclusive regarding the biologic behavior of these unusual lesions, the authors believe the adenomyoepitheliomas described here are benign. They were well circumscribed without invasion of adjacent breast, contained neither mitotic figures nor cytologic atypia, and have not recurred or metastasized (6 and 10 months after removal).

Characterization of the arachidonic acid metabolites mediating bradykinin and noradrenaline hyperalgesia

It has been suggested that bradykinin (BK) and norepinephrine (NE) induce hyperalgesia, indirectly, by stimulating the production of prostaglandin products of the cyclo-oxygenase pathway of arachidonic acid metabolism. However, the specific PGs that mediate the hyperalgesic effects of BK and NE are unknown. Two endogenous PGs, prostaglandin E2 (PGE2) and prostacyclin (PGI2) are known to produced hyperalgesia. Since the hyperalgesic effects of PGE2 and PGI2 can be distinguished by the duration of the hyperalgesia they induce, we have compared the duration of BK and NE hyperalgesia with those of PGE2 and PGI2. To further address the type of PG mediating BK and NE hyperalgesia, we have evaluated the ability of SC19220, a PG-receptor antagonist, to distinguish the hyperalgesia induced by PGE2 and PGI2. BK induces hyperalgesia with duration similar to that of PGE2. NE induces hyperalgesia with duration similar to that of PGI2. SC19220, at low doses, antagonizes PGE2 and BK hyperalgesia but not PGI2 and NE hyperalgesia. These data are compatible with the suggestion that the prostaglandin products mediating BK and NE hyperalgesia differ, BK hyperalgesia being mediated by PGE2 and NE hyperalgesia by PGI2.

Differing correlations between pain measures in syndromes with or without explicable organic pathology

We investigated the use of pain measures in chronic pain syndromes with and without explicable organic cause by correlating scores obtained from the Visual Analog Scale and from subscales of the McGill Pain Questionnaire in patients with either inflammatory arthritis or primary fibrositis. We confirmed the finding that patients with fibrositis, despite having significantly less demonstrable pathology, report more pain on a significant number of measures. In patients with arthritis, we observed large positive correlations between scores on different pain measures, supporting the hypothesis that these scores validly measure pain secondary to tissue injury. In the fibrositis group, however, significantly lower correlations, and one even strongly negative, were found between scores on different measures. We suggest that commonly used pain measures which have been shown to be valid to study patients with demonstrable pathology may be less valid for measurement of pain in patients with syndrome such as fibrositis, whose pain may be different or more complex than that of patients with explicable organic basis.

Leukotriene B4 decreases the mechanical and thermal thresholds of C-fiber nociceptors in the hairy skin of the rat

1. We have recently shown that leukotriene B4 (LTB4), a product of the 5-lipoxygenase pathway of arachidonic acid metabolism, sensitizes nociceptors to mechanical stimuli. The present study examined whether LTB4 also induces a heat sensitization of cutaneous C-fiber nociceptors. The C-fiber nociceptors studied had von Frey hair thresholds greater than 5 g and were characterized according to their responses to noxious heat and chemical stimuli, including glacial acetic acid, bradykinin, and capsaicin. Thirty-four of the C-fibers that were activated by intense thermal stimulation were also activated by topical application of glacial acetic acid. They were classified as C-polymodal nociceptors (2, 28). Those that were activated by intense mechanical and thermal stimulation, but were unresponsive to acid, were classified as C-mechanoheat nociceptors (27). 2. Ninety-four percent of C-polymodal nociceptors and 60% of C-mechanoheat nociceptors were sensitized by LTB4. All C-fiber nociceptors that showed a decrease of their heat threshold also had a decrease of their mechanical threshold. LTB4 (75 ng) lowered the average heat threshold from 45 degrees C to 35 degrees C and produced an average decrease in the mechanical threshold of 86%. 3. The magnitude of the LTB4-evoked decrease in thermal threshold was similar to that produced by 75 ng of prostaglandin E2 (PGE2). These data demonstrate that LTB4 sensitizes C-mechanoheat nociceptors to both mechanical and thermal stimuli. 4. We conclude that LTB4 may contribute to the component of hyperalgesia that is resistant to nonsteroidal anti-inflammatory agents.

Sleep fragmentation in the arthritic rat

We examined the diurnal sleep-wake patterns in the adjuvant arthritic rat. In contrast to control rats, arthritic rats lacked a normal diurnal variation in sleep and wakefulness. Thus, arthritic rats exhibited no differences in the mean number or duration of bouts of sleep and episodes of wakefulness between light and dark hours. Arthritic rats also had a marked increase in the fragmentation of their sleep manifested by an increased number of sleep bouts and episodes of wakefulness and a decrease in the duration of episodes of deep sleep recorded both during the time of maximal sleep (08.00-11.00 h) and of maximal wakefulness (20.00-23.00 h). The possibility that the experience of chronic pain causes these marked changes in sleep patterns in the arthritic rat is discussed.

Beta 2-adrenergic mechanisms in experimental arthritis

We have studied (i) the contribution of specific adrenergic receptors to the proinflammatory effects of the sympathetic nervous system in experimental arthritis and (ii) the phases of the disease during which the sympathetic nervous system influences joint injury. Severity of joint injury was measured radiographically 28 days after induction of adjuvant arthritis in control rats and in rats treated with a variety of sympatholytic agents at various times during the course of the disease. Rats treated with a nonspecific catecholamine depletor (reserpine) or a beta-adrenergic receptor antagonist (propranolol) had a delayed onset and significantly less severe joint injury than saline-treated controls when treatment began prior to injection of the adjuvant and continued to day 28 after the injection. When administered over the same treatment period, neither nonselective (phenoxybenzamine) nor selective [prazosin (alpha 1) and yohimbine (alpha 2)] alpha-adrenergic receptor antagonists affected the onset or severity of joint injury. Metoprolol, a beta 1 antagonist, was also without effect. In contrast, two beta 2 antagonists (butoxamine and ICI 118,551) significantly retarded disease onset and reduced the severity of joint injury. When reserpine or butoxamine treatment was initiated after the onset of clinically apparent arthritis, it was still possible to favorably influence the course of the disease. These data indicate an important contribution of the beta 2-adrenergic receptor to joint injury in experimental arthritis.

Synergism between the analgesic actions of morphine and pentazocine

In a double-blind, placebo-controlled study the analgesic efficacy of the combination of morphine, a mu-opiate receptor agonist and pentazocine, a kappa-opiate receptor partial-agonist was evaluated. Groups of 20 patients received either vehicle, morphine (2, 4, 8 or 16 mg), pentazocine (15, 30 or 60 mg) or a combination of morphine and pentazocine (2 mg or 4 mg and 15 mg or 30 mg, respectively). The combination of morphine and pentazocine produced a level of analgesia significantly greater than can be accounted for by simple addition of the analgesic effects of each opiate analgesic alone. We propose that the observed synergism between morphine and pentazocine is due to interaction between mu- and kappa-opioidergic components of endogenous opioid-mediated analgesia systems.

The effect of gold, an antirheumatic therapy, on substance P levels in rat peripheral nerve

Intramuscular injections of gold sodium thiomalate in the rat produce a significant depletion of the proinflammatory neuropeptide substance P (SP) from the sciatic nerve. The greatest reduction in SP content occurred during the first two months of treatment. The level of SP in the nerve, however, remained low, throughout an eight month administration of gold. These results, coupled with previous findings that gold produces a selective decrease in the number of unmyelinated axons in peripheral nerve, are consistent with the hypothesis that the anti-inflammatory action of gold involves a neurotoxic effect on peptidergic afferents.