n-((1s-trans)-2-hydroxycyclopentyl)adenosine and 1-3-dipropyl-8-cyclopentylxanthine

There is a considerable literature to suggest that adenosine A1 receptor agonists may have anti-nociceptive effects, and we sought to explore the role of adenosine A1 receptors in a model of trigeminovascular nociceptive transmission. Cats were anaesthetized (alpha-chloralose 60 mg/kg, intraperitoneally), and prepared for physiological monitoring. The superior sagittal sinus (SSS) was stimulated electrically, and linked units were recorded in the trigeminocervical complex. Post-stimulus histograms were constructed to analyse the responses and the effect of drug administration. Blood was sampled from the external jugular vein to determine levels of calcitonin gene-related peptide (CGRP) release before and after drug administration. Intravenous administration of the highly selective adenosine A1 receptor agonist, GR79236 (3-100 microg/kg) had a dose-dependent inhibitory effect on SSS-evoked trigeminal activity. The maximal effect (80 +/- 6% reduction in probability of firing) was seen at 100 microg/kg. The neuronal inhibitory effect of GR79236 could be inhibited by the selective adenosine A1 receptor antagonist DPCPX (300 microg/kg; P < 0.05). SSS stimulation increased cranial CGRP levels from 33 +/- 2 pmol/l (n = 6) to 64 +/- 3 pmol/l, an effect substantially reduced by pre-treatment with GR79236 (30 microg/kg; P < 0.01). The selective low efficacy adenosine A1 receptor agonist, GR190178 (30-1000 microg/kg i.v.), also inhibited SSS-evoked neuronal activity in a dose-dependent fashion. In this model of trigeminovascular nociception, adenosine A1 receptor activation leads to neuronal inhibition without concomitant vasoconstriction, suggesting a novel avenue for the treatment of migraine and cluster headache.

Topics: Adenosine; Animals; Blood Pressure; Cats; Dose-Response Relationship, Drug; Heart Rate; Neural Inhibition; Pain Measurement; Purinergic P1 Receptor Agonists; Purinergic P1 Receptor Antagonists; Receptors, Purinergic P1; Synaptic Transmission; Trigeminal Nuclei; Xanthines

The purpose of this study was to use intravital microscopy to determine the effect of a selective adenosine A1 receptor agonist, GR79236 (1, 3 and 10 microg/kg i.v.), on neurogenic dural blood vessel dilation in anaesthetized rats. Vasodilation was evoked either by electrical stimulation of perivascular trigeminal nerves or by intravenous CGRP. GR79236 (1-10 microg/kg i.v.) caused a dose-dependent inhibition of neurogenic vasodilation, but had no significant effect on dural vasodilation caused by CGRP. GR79236 (1-3 microg/kg i.v.) had no effect on basal dural vessel diameter, but caused transient dose-dependant bradycardia and hypotension. Bradycardia was more prolonged following 10 microg/kg i.v. GR79236. Pre-treatment with the adenosine A1 receptor antagonist DPCPX (1 mg/kg i.v.) prevented the inhibitory effect of GR79236 (10 microg/kg i.v.) on neurogenic vasodilation as well as GR79236-induced bradycardia and hypotension. These data suggest that the inhibition of neurogenic vasodilation by GR79236 is mediated via the activation of prejunctional adenosine A1 receptors. Provided the systemic cardiovascular effects could be limited, such a mechanism may offer a novel approach to migraine therapy.

Topics: Adenosine; Anesthesia, General; Animals; Blood Pressure; Bradycardia; Calcitonin Gene-Related Peptide; Drug Evaluation, Preclinical; Dura Mater; Electric Stimulation; Heart Rate; Hypotension; Male; Purinergic P1 Receptor Agonists; Purinergic P1 Receptor Antagonists; Rats; Rats, Sprague-Dawley; Receptors, Purinergic P1; Trigeminal Nerve; Vasodilation; Xanthines

Sarcolemmal Na(+)/H(+) exchanger (NHE) activity is increased by stimulation of G(q) protein-coupled receptors (G(q)PCRs), but the roles of other GPCRs are largely unknown. We determined the effects of N-[(1S,trans)-2-hydroxycyclopentyl]adenosine (GR79236), a selective agonist of the G(i)PCR adenosine A(1) receptor, on sarcolemmal NHE activity in adult rat ventricular myocytes (n=8-10 per group). NHE activity was indexed by the H(+) efflux rate after intracellular acidification, measured by microepifluorescence. GR79236 alone (0.01-10 microM) had no effect on NHE activity. However, co-administration of GR79236 inhibited, in a concentration-dependent manner, the stimulation of NHE activity by the alpha(1)-adrenoceptor agonist phenylephrine (10 microM). The inhibitory effect of GR79236 (10 microM) was abolished by (1) the selective A(1) antagonist 1,3-dipropyl-8-cyclopentylxanthine (0.1 microM), confirming an A(1) receptor-mediated action, and (2) pre-treatment with pertussis toxin (5 microgram ml(-1) for 60 min), indicating a G(i) protein-mediated mechanism. Our data suggest the existence of inhibitory crosstalk between the G(i)PCR adenosine A(1) receptor and the G(q)PCR alpha(1)-adrenoceptor in the regulation of sarcolemmal NHE activity.

Topics: Adenosine; Adrenergic alpha-1 Receptor Antagonists; Animals; Male; Myocardium; Pertussis Toxin; Phenylephrine; Rats; Rats, Wistar; Receptors, Purinergic P1; Sarcolemma; Sodium-Hydrogen Exchangers; Thrombin; Virulence Factors, Bordetella; Xanthines

The cardioprotective effects of the selective adenosine A1-receptor agonist, GR79236 (N-[(1S, trans)-2-hydroxycyclopentyl]adenosine), were examined in a porcine model of myocardial ischaemia-reperfusion injury. When pigs were subjected to a 50-min coronary artery occlusion followed by 3-h reperfusion, GR79236 (10 nmol/kg, i.v.) significantly reduced infarct size whether given 10 min before the onset of ischaemia or reperfusion. This effect was independent of the bradycardia induced by GR79236, as it was also observed in animals in which heart rate was maintained by electrical pacing. However, GR79236 administered 10 min after reperfusion did not reduce infarct size. GR79236 had no effect on the incidence or outcome of ventricular dysrhythmias in this pig model of infarction. Similarly, ischaemic preconditioning (IPC, 2 x 10-min ischaemia and 10-min reperfusion) significantly reduced infarct size. The selective adenosine A1-receptor antagonist, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX; 3.3 micromol/kg, i.v.), abolished the haemodynamic and cardioprotective effects of GR79236 and the cardioprotective effects of IPC in anaesthetised pigs. In conclusion, GR79236 exerted a marked cardioprotective effect in a porcine model of myocardial ischaemia-reperfusion injury, provided that it was administered before reperfusion. This suggests that GR79236 may have clinical utility in the treatment of various aspects of ischaemic heart disease.

Topics: Adenosine; Anesthesia; Animals; Blood Pressure; Coronary Disease; Female; Heart Rate; Male; Molecular Structure; Myocardial Infarction; Purinergic P1 Receptor Agonists; Reperfusion Injury; Swine; Time Factors; Ventricular Dysfunction; Xanthines

1 The cardioprotective effect of N-[(1S, trans)-2-hydroxycyclopentyl]adenosine (GR79236), an adenosine A1 receptor agonist, was compared with that produced by ischaemic preconditioning in an anaesthetized rabbit model of myocardial ischaemia and reperfusion. In addition, we examined the effect of different body core temperatures on GR79236- or ischaemic preconditioning-induced cardioprotection when administered prior to ischaemia, and on cardioprotection induced by GR79236 administered 10 min prior to the onset of reperfusion. 2 When rabbits were subjected to 30 min occlusion of the left coronary artery, followed by 2 h reperfusion, GR79236 (3 x 10(-8) mol kg-1 i.v. (10.5 microg kg-1 i.v.)) or ischaemic preconditioning (5 min ischaemia followed by 5 min reperfusion), administered or applied 10 min prior to the occlusion, significantly limited the development of infarction. The cardioprotective effect of ischaemic preconditioning was significantly greater than that seen after administration of GR79236. Pre-treatment with the selective adenosine A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX, 3.3 x 10(-6) mol kg-1 (1 mg kg-1 i.v.)), prevented the cardioprotective effect of GR79236, but not that of ischaemic preconditioning. 3 Maintaining body core temperature at 38.5 degrees C rather than at 37.0 degrees C did not influence infarct size in control groups of rabbits, but reduced the cardioprotective effect of GR79236 when administered 10 min prior to occlusion or 10 min prior to the onset of reperfusion. The cardioprotective effect of ischaemic preconditioning was not temperature-dependent. 4 In conclusion, myocardial protection conferred by GR79236 in anaesthetized rabbits is mediated via adenosine A1 receptors. Myocardial protection can be conferred when GR79236 is administered before the onset of ischaemia or reperfusion, and is reduced when body core temperature is maintained at 38.5 degrees C rather than at 37.0 degrees C. In contrast, myocardial protection conferred by ischaemic preconditioning is not reduced by adenosine A1 receptor blockade, or by maintaining body core temperature at 38.5 degrees C rather than at 37.0 degrees C. These findings point to distinct differences in the mechanisms of induction of myocardial protection by adenosine A1 receptor agonist and ischaemic preconditioning. They also highlight the need for careful control of body core temperature when investigating the phenomenon of cardioprotection.

Topics: Adenosine; Anesthesia; Animals; Blood Pressure; Body Temperature; Heart Rate; Ischemic Preconditioning, Myocardial; Male; Myocardial Infarction; Myocardial Ischemia; Myocardial Reperfusion Injury; Purinergic P1 Receptor Agonists; Rabbits; Xanthines

We tested the hypothesis that adenosine excites nociceptive primary afferents innervating the knee joint. Neuronal recordings were made from fine nerve filaments innervating the knee joint in rats anaesthetized with pentobarbitone. Drugs were injected close-arterially (i.a.) or into the articular space (i.art.). We studied normal and chronically inflamed arthritic joints, the latter 14-21 days after a single intra-articular injection of Freund's Complete Adjuvant, performed under halothane anaesthesia. Adenosine injected i.a. caused delayed (approximately 10 s) excitation of the majority of polymodal C-fibre afferents, and had similar effects when injected directly into the joint. Adenosine triphosphate (ATP) had biphasic effects on discharge, a fast (<1 s) excitation was followed by a delayed increase similar to that seen with adenosine. The adenosine A1 receptor agonists N6-cyclopentyladenosine (CPA) and N-[(1S,trans)-2-hydroxypentyl] adenosine (GR79236) also excited the C-fibre afferents. The A1 antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) antagonized the responses evoked by adenosine, CPA, and the delayed increase seen after ATP, indicating that excitation of the nociceptive afferents was mediated via adenosine A1 receptors. Adenosine and ATP evoked delayed excitatory effects of similar magnitude, regardless of whether or not the knee joint was chronically inflamed. The increased basal discharge observed in arthritic joints was unaffected by DPCPX, which implies that the increase in spontaneous activity associated with arthritis is unlikely to involve tonically released adenosine. The results support the hypothesis that adenosine excites primary afferent nociceptive nerve terminals in the rat knee joint, an effect mediated by adenosine A1 receptors. ATP, adenosine, and A1 receptors may play a role in generating the peripheral nociceptive (pain) signal.

Topics: Action Potentials; Adenosine; Adenosine Triphosphate; Analgesics; Animals; Arthritis, Experimental; Hypolipidemic Agents; Knee Joint; Male; Neurons, Afferent; Nociceptors; Purinergic P1 Receptor Agonists; Purinergic P1 Receptor Antagonists; Rats; Rats, Wistar; Receptors, Purinergic P1; Xanthines