adenosine-5--(n-ethylcarboxamide) and Pain

cis-4-(Piperazin-1-yl)-5,6,7a,8,9,10,11,11a-octahydrobenzofuro[2,3-h]quinazolin-2-amine, 4 (A-987306) is a new histamine H(4) antagonist. The compound is potent in H(4) receptor binding assays (rat H(4), K(i) = 3.4 nM, human H(4) K(i) = 5.8 nM) and demonstrated potent functional antagonism in vitro at human, rat, and mouse H(4) receptors in cell-based FLIPR assays. Compound 4 also demonstrated H(4) antagonism in vivo in mice, blocking H(4)-agonist induced scratch responses, and showed anti-inflammatory activity in mice in a peritonitis model. Most interesting was the high potency and efficacy of this compound in blocking pain responses, where it showed an ED(50) of 42 mumol/kg (ip) in a rat post-carrageenan thermal hyperalgesia model of inflammatory pain.

Topics: Animals; Anti-Inflammatory Agents, Non-Steroidal; Benzofurans; Carrageenan; Disease Models, Animal; Drug Design; Drug Evaluation, Preclinical; Humans; Hyperalgesia; Ligands; Mice; Molecular Structure; Pain; Peritonitis; Quinazolines; Rats; Receptors, G-Protein-Coupled; Receptors, Histamine; Receptors, Histamine H4; Stereoisomerism; Structure-Activity Relationship

Although it is well established that adenosine exerts antinociceptive effects at the spinal level in various species including human, the mechanisms responsible for such effects are still a matter of debate. We presently investigated whether adenosine-induced antinociception might possibly be related to an inhibitory influence of this neuromodulator on the spinal release of neuropeptides implicated in the transfer and/or control of nociceptive signals. For this purpose, the K(+)-evoked overflow of substance P-, calcitonin gene-related peptide (CGRP)- and cholecystokinin-like materials was measured from slices of the dorsal half of the rat lumbar enlargement superfused with an artificial cerebrospinal fluid supplemented with increasing concentrations of various adenosine receptor ligands. The data showed that stimulation of adenosine A(1) and (possibly) A(3) receptors, but not A(2A) receptors, exerted an inhibitory influence on the spinal release of CGRP-like material. In contrast, none of the adenosine A(1), A(2A) and A(3) receptor agonists tested within relevant ranges of concentrations significantly affected the release of substance P- and cholecystokinin-like materials. These results support the idea that adenosine-induced antinociception at the spinal level might possibly be caused, at least partly, by the stimulation of inhibitory adenosine A(1) receptors located presynaptically on primary afferent fibres containing CGRP but not substance P.

Topics: Adenosine; Adenosine-5'-(N-ethylcarboxamide); Animals; Calcitonin Gene-Related Peptide; Cholecystokinin; Dose-Response Relationship, Drug; In Vitro Techniques; Male; Neuropeptides; Pain; Phenethylamines; Potassium; Purinergic P1 Receptor Agonists; Purinergic P1 Receptor Antagonists; Rats; Rats, Sprague-Dawley; Receptors, Purinergic P1; Spinal Cord; Substance P; Xanthines

Adenosine analogs have been shown to produce antinociception after intrathecal administration. To determine the adenosine receptor subtype involved in spinal antinociception, the effects of selective agonists and an antagonist on the evoked potentials recorded from a neonatal rat spinal cord were studied. The measured potentials are a slow ventral root potential (slow VRP), which is the C-fiber-evoked excitatory response associated with nociceptive information; a monosynaptic reflex (MSR), which reflects a non-nociceptive transmission related to motor function; and a dorsal root potential (DRP), which reflects a gamma-aminobutyric acidA (GABA(A)) receptor-mediated presynaptic inhibition associated with analgesia.. The evoked potentials were recorded in response to electric stimulation of a lumbar dorsal root. Dose-response curves of agonists for these responses were obtained to determine their relative potency order. The antagonist dissociation constants (K(D) values) were estimated by Schild analysis.. Adenosine agonists dose dependently inhibited the slow VRP and the MSR. However, the slow VRP was five to eight times more sensitive to them than was the MSR. The rank order of agonist potency was N6-cyclohexyladenosine (CHA) = N6-(R)-phenylisopropyladenosine (R-PIA) > 5'-N-ethylcarboxamidoadenosine (NECA) >> CGS 21680 in both responses. 8-Cyclopentyltheophylline produced dose-dependent parallel shifts to the right of NECA dose-response curves for these responses. Schild analysis gave linear plots with slopes near unity. The K(D) values of CPT for the MSR and the slow VRP were estimated to be 5.5 nM and 4.3 nM, respectively. The DRP was also depressed by adenosine agonists with potency order of CHA > NECA >> CGS 21680. 8-Cyclopentyltheophylline antagonized the inhibitory effects of CHA on the DRP.. The results indicate that adenosine agonists inhibit spinal sensory transmission related to nociception by acting at the A1 receptors. The A1 receptor also seems to be involved in transmission related to the spinal motor system. Feedback inhibition mediated by GABA(A) receptors does not contribute to this antinociceptive action.

Topics: Adenosine; Adenosine-5'-(N-ethylcarboxamide); Analgesics; Animals; Dose-Response Relationship, Drug; Female; Male; Pain; Rats; Rats, Wistar; Receptors, Purinergic P1; Reflex, Monosynaptic; Spinal Cord; Theophylline

The purpose of this study was to examine whether adenosine or serotonin is involved in mediation of the antinociception produced by norepinephrine at the spinal cord level. Aminophylline, an adenosine receptor antagonist and naloxone given intrathecally (i.t.) were used to test the antinociception produced by i.t. norepinephrine, serotonin, morphine or the adenosine receptor agonist 5'-N-ethylcarboxamidoadenosine (NECA) by using the tail-flick assay in rats. It was observed that (1) aminophylline blocked the antinociception produced by norepinephrine, but exhibited no effect on the antinociception produced by serotonin, (2) aminophylline blocked the antinociception produced by morphine similarly to naloxone, (3) aminophylline blocked the antinociception produced by NECA and (4) naloxone failed to block the antinociception produced by NECA and serotonin. The results suggest that adenosine is involved in mediation of the norepinephrine-produced antinociception at the spinal level and that norepinephrine and adenosine may act in a sequential manner in norepinephrine-induced antinociception.

Topics: Adenosine; Adenosine-5'-(N-ethylcarboxamide); Aminophylline; Animals; Female; Male; Morphine; Naloxone; Norepinephrine; Pain; Purinergic P1 Receptor Agonists; Rats; Rats, Wistar; Serotonin; Spinal Cord; Time Factors

Intrathecal administration of an adenosine receptor antagonist, theophylline, elicited nociceptive behavior such as licking, biting and scratching in mice. This behavioral response was dose-dependently reduced by simultaneous injection of an adenosine receptor agonist, 5'-N6-ethylcarboxamidoadenosine, or a selective N-methyl-D-aspartate (NMDA) receptor antagonist, D-2-amino-5-phosphonovalerate. This theophylline-induced behavior was not significantly reduced by the substance P (SP) analogue, the neurokinin receptor antagonist, [D-Arg1, D-Trp7.9, Leu11]SP (spantide). These results suggest the possibility that theophylline-induced nociceptive behavior may be mediated through interactions with both spinal adenosine- and NMDA receptors separately, or only through interaction(s) with adenosine receptors localized on the axon terminals of excitatory amino acid neurons. Present data have failed to reveal involvement of SP.

Topics: 2-Amino-5-phosphonovalerate; Adenosine; Adenosine-5'-(N-ethylcarboxamide); Animals; Behavior, Animal; Male; Mice; Pain; Receptors, N-Methyl-D-Aspartate; Receptors, Purinergic; Spinal Cord; Substance P; Theophylline

Intrathecal (i.t.) coadministration of calcium (Ca2+), 50 micrograms potentiates the spinal antinociceptive action of morphine and noradrenaline (NA) but not cyclohexyladenosine, 5'-N-ethylcarboxamido adenosine or 5-hydroxytryptamine in the rat tail flick test. This dose of Ca2+ has no intrinsic effect in this test. Higher doses of Ca2+ (200-400 micrograms) produce antinociception in the tail flick and hot plate tests, which is completely blocked by pretreatment with the adenosine receptor antagonists theophylline, 50 micrograms and 8-phenyltheophylline, 3 micrograms. 8-Phenyltheophylline also eliminates potentiation of the antinociceptive action of NA by 50 micrograms Ca2+. The intrinsic antinociceptive effect of Ca2+ is blocked by i.t. pretreatment with the neurotoxins capsaicin, 50 micrograms and 6-hydroxydopamine, 50 micrograms but not 5,7-dihydroxytryptamine, 50 micrograms. Antinociception also is blocked by pretreatment with phentolamine but not by methysergide. These results suggest that the antinociceptive action of high doses of Ca2+ is due to release of adenosine (or a nucleotide which is metabolized to adenosine) from the spinal cord. At lower doses, the release of adenosine is insufficient to cause antinociception, but potentiates the action of NA. Adenosine appears to originate from capsaicin-sensitive small diameter primary afferent nerve terminals. A subsequent interaction of adenosine with spinal adrenergic receptors contributes to antinociception.

Topics: 5,7-Dihydroxytryptamine; Adenosine; Adenosine-5'-(N-ethylcarboxamide); Animals; Calcium; Drug Synergism; Hot Temperature; Hydroxydopamines; Male; Methysergide; Norepinephrine; Oxidopamine; Pain; Phentolamine; Rats; Rats, Inbred Strains; Receptors, Purinergic; Serotonin; Spinal Cord; Theophylline

It is well-established that intrathecal injection of noradrenergic agonists produces dose-dependent antinociception in rats. Recently, the antinociceptive actions of norepinephrine in the central nervous system have been shown to be modulated by adenosine and adenosine analogs. This study examined whether there is an interaction between norepinephrine and adenosine analogs in the regulation of nociceptive transmission in the rat spinal cord using the tail flick and hot plate tests. The results indicate that dose-dependent antinociception was produced by intrathecal injection of norepinephrine (4.8-195 nmol), the A1/A2 adenosine agonist 5'-N-ethylcarboxamide adenosine (NECA; 0.97-4.9 nmol), and the A1 adenosine agonist R-phenylisopropyladenosine (R-PIA; 0.78-26 nmol). Furthermore, subeffective doses of NECA and norepinephrine interacted synergistically to produce potent antinociception. In contrast, no synergistic interaction was observed between norepinephrine and doses of R-PIA as high as 26 nmol. The antinociception produced by coadministration of norepinephrine and NECA appears to be mediated by adenosine receptors, since it was attenuated by pretreatment with theophylline, a non-selective adenosine antagonist. The synergistic interaction between NECA and norepinephrine did not appear to result from alterations in cardiovascular tone because blood pressure values were not significantly altered by drug administration. These results suggest that purinergic and noradrenergic systems interact synergistically to modify nociceptive transmission in the spinal cord. The purinergic component of this interaction may be mediated, in part, by adenosine A2 receptors.

Topics: Adenosine; Adenosine-5'-(N-ethylcarboxamide); Analgesics; Animals; Blood Pressure; Dose-Response Relationship, Drug; Drug Interactions; Male; Norepinephrine; Pain; Rats; Rats, Inbred Strains; Receptors, Purinergic; Spinal Cord

Recently, it has been shown that intrathecal injection of norepinephrine and the mixed A1/A2 adenosine agonist 5'-N-ethylcarboxamide adenosine (NECA) interact in a supra-additive manner to produce antinociception. The present studies were designed to determine whether alpha 1 or alpha 2 noradrenergic receptors are involved in producing the antinociception induced by NECA and norepinephrine. The results indicated that intrathecal injection of NECA (0.97-4.9 nmol), the alpha 2 noradrenergic agonist clonidine (3.8-375 nmol), or the alpha 1 agonist phenylephrine (4.9-73.4 nmol) produced dose-dependent antinociception in rats. Furthermore, intrathecal injection of subeffective doses of NECA and clonidine interacted supra-additively to produce potent antinociception. In contrast, no supra-additive interaction was observed between NECA and phenylephrine. The supra-additive interaction of NECA and clonidine did not appear to result from alterations in cardiovascular tone because changes in blood pressure and nociceptive thresholds were not correlated in time. These results suggest that the noradrenergic component of the supra-additive interaction between adenosine A2 receptor agonists and noradrenergic agonists is mediated by alpha 2 noradrenergic receptors.

Topics: Adenosine; Adenosine-5'-(N-ethylcarboxamide); Analgesia; Animals; Blood Pressure; Clonidine; Dose-Response Relationship, Drug; Drug Interactions; Hot Temperature; Injections, Spinal; Male; Norepinephrine; Pain; Phenylephrine; Rats; Rats, Inbred Strains; Spinal Cord; Vasodilator Agents

The effects on nociception, motor and autonomic function produced by the intrathecal administration of three adenosine analogs: N6-(L-2-phenylisopropyl)-adenosine, N6-cyclohexyladenosine and 5'-(N-ethylcarboxamido)-adenosine were examined in rats. Over the range of 0.3 to 1.0 nmol these agents produced a dose-dependent antinociception in the hot plate and tail-flick tests. In addition, 5'-(N-ethylcarboxamido)-adenosine and N6-(L-2-phenylisopropyl)-adenosine both suppressed the chemically evoked writhing response as well as the touch-evoked hyperesthesia normally observed in rats receiving low doses of intrathecal strychnine. These adenosine analogs examined at doses higher than 1.5 nmol produced a dose-dependent motor impairment as measured behaviorally and by electromyography, and an increase in the volume distention required to evoke micturition. Statistically significant effects on heart rate or blood pressure were not observed at any of the doses tested. The effects of the adenosine analogs on nociceptive and motor endpoints were partially antagonized by pretreatment with intrathecal caffeine (2 mumol). These results suggest a probable association of spinal adenosine receptors with a number of spinal sensory and motor systems other than those involved with nociceptive processing.

Topics: Adenosine; Adenosine-5'-(N-ethylcarboxamide); Animals; Autonomic Nervous System; Blood Pressure; Caffeine; Male; Movement; Pain; Phenylisopropyladenosine; Rats; Rats, Inbred Strains; Receptors, Purinergic; Spinal Cord; Urinary Bladder

Analogues of adenosine were injected intrathecally into rats implanted with chronic indwelling cannulae in order to determine a rank order of potency and hence characterize adenosine receptors involved in spinal antinociception. In the tail flick test L-N6-phenylisopropyl adenosine (L-PIA), cyclohexyladenosine (CHA) and 5'-N-ethylcarboxamide adenosine (NECA) produced dose-related antinociception which attained a plateau level. NECA and CHA also produced an additional distinct second phase of antinociception. D-N6-Phenylisopropyl adenosine (D-PIA) and 2-chloroadenosine (CADO) had very little antinociceptive activity in this test. The rank order of potency in producing the plateau effect was L-PIA greater than CHA greater than NECA greater than D-PIA = CADO, while that for the second phase of antinociception was NECA greater than-CHA. Pretreatment with both theophylline and 8-phenyltheophylline (8-PT) antagonized antinociception produced by CHA, with 8-PT being at least an order of magnitude more potent than theophylline. Both antagonists produced a significant hyperalgesia in the tail flick test. L-PIA and CHA also produced methylxanthine-sensitive antinociception in the hot plate test. These results suggest that activation of A1-receptors in the spinal cord can produce antinociception. Activation of A2-receptors may produce an additional effect, but the relative activity of CHA in this component of activity is unusual.

Topics: 2-Chloroadenosine; Adenosine; Adenosine-5'-(N-ethylcarboxamide); Animals; Dose-Response Relationship, Drug; Male; Pain; Phenylisopropyladenosine; Rats; Rats, Inbred Strains; Receptors, Cell Surface; Receptors, Purinergic; Spinal Cord; Theophylline

When injected intrathecally in mice in a volume of 5 microliter, adenosine had no effect on tail-flick or hot-plate reaction latencies at dosages up to 1 mM concentration. There were no other behavioral effects observed either. Injecting 1 mM of the adenosine receptor agonist, 5'-N-ethylcarboxamide adenosine (NECA) caused both motor paralysis of the hind-legs with a duration of approximately 4 h and simultaneous antinociception. A slight weakness of the hindlegs, but a profound antinociceptive effect, was observed after the 100 microM dose only. After 10 microM, there was no effect on motor behavior but still a prolongation of the tail-flick and hot-plate reaction latencies. Pretreatment with the adenosine receptor antagonist theophylline attenuated the antinociceptive effect of NECA. Activation of spinal adenosine receptors thus appears to selectively elicit analgesia.

Topics: Adenosine; Adenosine-5'-(N-ethylcarboxamide); Analgesics; Animals; Injections, Spinal; Male; Mice; Pain; Reaction Time; Receptors, Cell Surface; Receptors, Purinergic; Spinal Cord