Rainer Amann

Anti-inflammatory effects of aspirin and sodium salicylate.

Aspirin (acetylsalicylic acid) is one of the most widely used drugs worldwide. It acetylates cyclooxygenases thereby irreversibly blocking the conversion of arachidonic acid to prostanoids. Biotransformation of aspirin yields salicylate, a compound that possesses similar anti-inflammatory potency as aspirin but lacks aspirins inhibitory effect on the activity of isolated cyclooxygenase. This article is aimed at providing an overview about the often conflicting results concerning the mechanisms of action of aspirin and sodium salicylate. At present, there is no common agreement about the extent to which salicylate contributes to aspirins anti-inflammatory properties, as well as there is still no final conclusion reached about the mechanisms of action of sodium salicylate. Several possible sites of action of salicylate have been suggested: It has been shown that in intact cells-but not in purified enzyme preparations-, sodium salicylate inhibits prostanoid biosynthesis. This effect seems to be prevented in the presence of high concentrations of arachidonic acid, which has been shown to interfere with inhibition by salicylate of cyclooxygenase-2-mediated prostanoid formation in vitro. Other possible sites of action that are not directly related to cyclooxygenase inhibition have been suggested based on observations made in vitro using high concentrations of aspirin and sodium salicylate. These effects target intracellular signaling mechanisms such as kinases, including the mitogen activated protein-kinases (MAPK) cascade. With the exception of reported salicylate-induced activation of p38 MAPK, observed effects are usually inhibitory. This may be one reason for the observation that, downstream to kinases, inhibitory effects of salicylates have been observed on several nuclear transcription factors, such as nuclear transcription factor kappa B (NF-kB) or activator protein 1 (AP-1). Several reports have also shown interference by salicylates with the expression of cyclooxygenase-2, which, depending on experimental models, can be observed as inhibitory but also stimulatory effects. Antioxidant properties of salicylates, adenosine release induced by sodium salicylate and aspirin-triggered lipoxin formation are additional mechanisms that may contribute to anti-inflammatory properties of aspirin and/or sodium salicylate. An additional focus of this review is the discussion of interactions between aspirin, sodium salicylate and other non-steroidal anti-inflammatory drugs (NSAIDs), which are of particular relevance in the gastro-intestinal and cardiovascular systems.

Release of calcitonin gene-related peptide induced by capsaicin in the vascularly perfused rat stomach

It has been suggested that capsaicin-induced gastric mucosal protection results from the local release of vasodilator peptides such as calcitonin gene-related peptide (CGRP) from afferent nerve endings within the stomach, since CGRP is able to reduce gastric lesion formation. This concept is supported by the present finding that capsaicin (10(-5) M), administered to the vascularly perfused stomach of the rat, produces a more than 30-fold rise of the CGRP content of the venous effluent. High-pressure liquid chromatography revealed only one peak of immunoreactivity coeluting with synthetic CGRP.

Intraplantar injection of nerve growth factor into the rat hind paw: local edema and effects on thermal nociceptive threshold

&NA; Nerve growth factor (NGF) is known to produce hyperalgesia as well as to stimulate synthesis of neuropeptides in dorsal root ganglia (DRG). In the present study, we wanted to determine the effects of local NGF administration and assess to which extent mast cell‐dependent factors are mediating NGF responses. Rats received 1 daily unilateral intraplantar injection for 3 days. Local edema (days 1–3), changes in thermal nociceptive threshold (days 1–4), and the content of calcitonin gene‐related peptide (CGRP) and substance P (SP) in the sciatic nerve (day 4), were determined. NGF injection caused edema which was absent in rats pretreated with compound Symbol as well as in rats treated neonatally with capsaicin (‘capsaicin denervation’). NGF‐induced edema was not reduced by the neurokinin‐1 receptor antagonist SR140333, but attenuated by the CGRP receptor antagonist CGRP[8–37]. Symbol. No caption available On each day, NGF injection caused a decrease in thermal nociceptive threshold which lasted for less than 3 h. Capsaicin denervation, but not treatment with indomethacin, abolished NGF‐induced thermal hyperalgesia. Treatment with compound Symbol attenuated hyperalgesia produced by the first, but not by subsequent, NGF injections. Symbol. No caption available On day 4, 24 h after the last of 3 NGF injections, thermal nociceptive threshold was not different from control values, but at that time, CGRP and SP were elevated in the sciatic nerve. We suggest therefore that NGF‐induced local edema was caused by mast cell‐derived vasoactive compounds which act together with afferent neuron‐derived CGRP to increase vascular permeability. NGF‐induced thermal hyperalgesia most likely was caused by an increased sensitivity of peripheral endings of capsaicin sensitive afferents. This effect of NGF was not mediated by products of the cyclooxygenase pathway, and was also observed in mast cell‐depleted rats.

Similarities and differences in the action of resiniferatoxin and capsaicin on central and peripheral endings of primary sensory neurons.

We have compared the ability of capsaicin and resiniferatoxin, a natural diterpene present in the latex of plants of the Euphorbia family to excite and desensitize capsaicin-sensitive primary afferents in a variety of models. Both capsaicin and resiniferatoxin inhibited the twitch contractions of the rat isolated vas deferens and prevented, in a concentration-related manner, the effect of a subsequent challenge with 1 microM capsaicin (desensitization). Resiniferatoxin was 1000-10,000 times more potent than capsaicin in both cases. The time course of action of resiniferatoxin was much slower than that of capsaicin, suggesting a slower penetration rate in the tissue. The action of resiniferatoxin was blocked by Ruthenium Red, a proposed antagonist at the cation channel coupled to the capsaicin receptor. Both capsaicin and resiniferatoxin produced a contraction of the rat isolated urinary bladder. Resiniferatoxin was about as potent as capsaicin in this assay although it was 500-1000 times more potent than capsaicin in desensitizing the primary afferents to a subsequent challenge with capsaicin itself. Resiniferatoxin did not affect motility in the isolated vasa deferentia or urinary bladder from capsaicin-pretreated rats. After topical application onto the rat urinary bladder both resiniferatoxin (10 nM) and capsaicin (10 microM) increased bladder capacity as assessed in a volume-evoked micturition reflex model in rats without affecting micturition contraction. Intrarterial injection of resiniferatoxin or capsaicin in the ear of anesthetized rabbits evoked a systemic depressor reflex due to activation of paravascular nociceptors, resiniferatoxin being about three times more potent than capsaicin.(ABSTRACT TRUNCATED AT 250 WORDS)

Galanin and vasopressin coexist in the rat hypothalamo-neurohypophyseal system.

Using indirect immunofluorescence methods and antisera raised against galanin (GAL) and vasopressin (VP), we have demonstrated both peptides coexisting in the very same cell bodies in the supraoptic and magnocellular paraventricular nuclei and the magnocellular accessory cells of the lateral hypothalamic area. Furthermore, dehydration and salt loading, which is known to cause release and depletion of VP and oxytocin from the neurohypophysis, also caused a marked reduction of GAL-like immunoreactivity in the posterior lobe of the pituitary but had no effect on hypothalamic GAL immunoreactivity. Systemically administered GAL caused a brief small increase in blood pressure with no effect on heart rate. A thousandfold molar concentration of GAL, compared of VP, was required to induce comparable effects on blood pressure. GAL itself had no modulatory effect on VP-induced pressor response. Systemically administered GAL resulted in mild diuresis whereas VP caused complete and sustained inhibition of diuresis. GAL had no effect on VP-induced anti-diuresis effects. The significance of the coexistence and corelease of GAL and VP remains to be elucidated.

Stimulation by nerve growth factor of neuropeptide synthesis in the adult rat in vivo: bilateral response to unilateral intraplantar injections

Unilateral intraplantar injections (1/day for 3 days) of 4 mu g nerve growth factor (NGF) into the rat hindpaw increased the expression of prepro-tachykinin (PPT)- and prepro-calcitonin gene-related peptide (ppCGRP)-mRNA in bilateral L5 dorsal root ganglia (DRGs). This was accompanied by an increase of CGRP-like immunoreactivity in the ipsi- and contralateral sciatic nerve but by no detectable change of CGRP-IR in other afferents. NGF injections into the skin of one ear or into the plantar side of one forepaw increased CGRP-IR in the respective afferents (trigeminal ganglion, or nerves arising from the brachial plexus, respectively), but had no effect on sciatic CGRP-IR. This suggests that the NGF-induced symmetrical increase of CGRP synthesis in L5 DRGs was not caused by systemic action of NGF, which, therefore, may be a useful tool to further investigate mechanisms which are responsible for contralateral effects of unilateral inflammation.

Absorption and metabolism of capsaicinoids following intragastric administration in rats.

SummaryThis study was performed to examine the metabolism and absorption of intragastrically administered capsaicinoids in the anaesthetized rat.[3H]-dihydrocapsaicin ([3H]-DHC) and unlabelled capsaicin were readily absorbed from the gastrointestinal tract but were almost completely metabolized before reaching the general circulation. A certain degree of biotransformation already took place in the intestinal lumen. Unchanged compounds (identified by chromatography) were present in portal vein blood. There seems to be a saturable absorption and degradation process in the gastrointestinal tract and a very effective metabolism in the liver.Less than 5% of the total amount of extracted radioactivity consisted of unchanged [3H]-DHC in trunk blood and brain 15 min after gastrointestinal application. On the other hand, approximately 50% unchanged [3H]-DHC was detected in these tissues 3 min after i.v. or 90 min after s.c. application of the capsaicinoids. Dihydrocapsaicin (DHC) or [3H]-DHC were metabolized when incubated in vitro with liver tissue but not with brain tissue. The metabolic product(s) did not show capsaicin-like biological activity.It can be concluded that rapid hepatic metabolization limits systemic pharmacological effects of enterally absorbed capsaicin.

HUMAN AND RAT PRIMARY C-FIBRE AFFERENTS STORE AND RELEASE SECRETONEURIN, A NOVEL NEUROPEPTIDE

Secretoneurin is a recently discovered neuropeptide derived from secretogranin II (SgII). Since this peptide could be detected in the dorsal horn of the spinal cord we studied whether it is localized in and released from primary afferent neurons. Secretoneurin was investigated with immunocytochemistry and radioimmunoassay in spinal cord, dorsal root ganglia and peripheral organs. SgII mRNA was determined in dorsal root ganglia. Normal rats and rats pre‐treated neonatally with capsaicin to destroy selectively polymodal nociceptive (C‐) fibres were used. Slices of dorsal spinal cord were perfused in vitro for release experiments. Immunocytochemistry showed a distinct distribution of secretoneurin‐immunoreactivity (IR) in the spinal cord and lower brainstem. A particularly high density of fibres was found in lamina I and outer lamina II of the caudal trigeminal nucleus and of the spinal cord. This distribution was qualitatively identical in rat and human post‐mortem tissue. Numerous small diameter and some large dorsal root ganglia neurons were found to contain SgII mRNA. Capsaicin treatment led to a marked depletion of secretoneurin‐IR in the substantia gelatinosa, but not in other immunopositive areas of the spinal cord and to a substantial loss of small (<25 μm) SgII‐mRNA‐containing dorsal root ganglia neurons. Radioimmunoassay revealed a significant decrease of secretoneurin‐IR in the dorsal spinal cord, the trachea, heart and urinary bladder of capsaicin‐treated rats. Perfusion of spinal cord slices with capsaicin as well as with 60 mM potassium led to a release of secretoneurin‐IR. In conclusion, secretoneurin is a neuropeptide which is stored in and released from capsaicin‐sensitive, primary afferent (C‐fibre) neurons. It may, therefore, be a novel peptidergic modulator of pain transmission or of C‐fibre mediated non‐nociceptive information.

Peripheral effects of opioid drugs on capsaicin-sensitive neurones of the guinea-pig bronchus and rabbit ear

SummaryThe effect of a potent opioid agonist, [d-Met2, Pro5]-enkephalinamide was investigated on two responses involving capsaicin-sensitive afferent neurones, namely, atropine-resistant contractions of the guinea-pig bronchus evoked by electrical field stimulation and the nociceptor stimulation to intraarterial injections of acetylcholine or capsaicin into the vascularly isolated rabbit ear. The hypotheses to be tested were whether (a) opioid receptor activation may inhibit mediator release from primary afferent neurones and (b) the opioid could exert an analgesic effect at a peripheral site of action. Non-cholinergic contractions of the guinea-pig isolated main bronchi due to electrical stimulation were concentration-dependently inhibited by [d-Met2, Pro5]-enkephalinamide (10 nM–1 μM). This effect was abolished by naloxone (1 μM). Naloxone alone induced no change in the stimulation-evoked contractions of the bronchus, indicating that no endogenous opioid control was present. Substance P and neurokinin A induced bronchial contractions that were not influenced by [d-Met2, Pro5]-enkephalinamide. This indicates that [d-Met2, Pro5]-enkephalinamide inhibits electrically-evoked bronchial contractions by reduced mediator release from capsaicin-sensitive sensory nerve endings, since these contractions are most probably brought about by tachykinins, released from afferent neurones. Capsaicin-induced bronchial contractions were in contrast to electrical stimulation not influenced by [d-Met2, Pro5]-enkephalinamide which suggests a different site of action. The activation of sensory neurones in the rabbit ear by i. a. injection of acetylcholine and capsaicin was not reduced under infusion of [d-Met2, Pro5]-enkephalinamide (1 and 10 μM) or lofentanil (1 and 10 μM). The enhancement of the effect of acetylcholine by infusion of prostaglandin E2 (0.15 μM) also remained unchanged under infusion of 10 μM [d-Met2, Pro5]-enkephalinamide. A peripheral analgesic action of the two opioid agonists studied is therefore not indicated.

Participation of capsaicin-sensitive afferent neurons in gastric motor inhibition caused by laparotomy and intraperitoneal acid

Stimulation of somatic or visceral nociceptors causes changes in gastrointestinal motor activity and blood pressure. The present study examined the possible participation of capsaicin-sensitive afferent and noradrenergic efferent neurons in the blood pressure and gastric motor responses to laparotomy and intraperitoneal injection of capsaicin or hydrochloric acid in the rat. Gastric motor activity was measured by recording the intragastric pressure of phenobarbital-anaesthetized rats via an oesophageal catheter. Laparotomy as well as intraperitoneal injection of capsaicin (33 and 330 microM) or hydrochloric acid (30 mM) caused a transient reduction of gastric motor activity stimulated by intravenous infusion of bombesin (200 pmol/min) and a brief fall of blood pressure (depressor effect). The depressor effect of laparotomy was followed by prolonged hypertension. Defunctionalization of capsaicin-sensitive afferent neurons by systemic pretreatment of rats with capsaicin (0.4 mmol/kg) prevented the depressor effect and gastric motor inhibition elicited by laparotomy, intraperitoneal capsaicin (33 microM) or intraperitoneal hydrochloric acid (30 mM). However, the effects of 330 microM capsaicin on blood pressure and gastric motility were only partially reduced by capsaicin pretreatment. Blockade of noradrenergic sympathetic neurons by pretreating rats with guanethidine (0.225 mmol/kg) prevented the gastric motor inhibition and depressor effects of laparotomy and intraperitoneal injection of hydrochloric acid (30 mM). The inhibition of gastric motility caused by capsaicin (33 and 330 microM) was only partially reduced by guanethidine pretreatment. The secondary hypertension following the depressor effect of intraperitoneal capsaicin or hydrochloric acid was enhanced in guanethidine-pretreated rats whereas the prolonged hypertension induced by laparotomy was left unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)