n(6)-cyclopentyladenosine and Hypotension

Mortality and occurrence of cholinergic symptoms upon sarin intoxication (144 micro g/kg s.c., approximately 2 x LD50) in rats is completely prevented by treatment with the adenosine A1 receptor agonist N6-cyclopentyladenosine (CPA, 2 mg/kg i.m.). Previously, we have shown that CPA treatment altered the distribution of sarin into the brain, presumably through its cardiovascular side effects. Therefore, the objective of the present study was to evaluate the contribution of the cardiodepressant effects of CPA to its therapeutic efficacy against sarin intoxication. Intramuscular treatment of rats with 0.5 and 2.0 mg/kg CPA 1 min after sarin poisoning attenuated most cholinergic symptoms and prevented mortality, which seemed to be directly associated with an immediate strong and long-lasting bradycardia and hypotension caused by CPA. Treatment with lower doses of CPA (0.1 and 0.05 mg/kg i.m.) caused similar levels of bradycardia and hypotension, albeit a few minutes later than at the higher doses of CPA. Upon sarin intoxication, this was correlated with increased incidence of cholinergic symptoms and decreased survival rates. Pretreatment with the peripheral adenosine A1 receptor antagonist 8- p-sulphophenyltheophylline (8-PST, 20 mg/kg i.p.) counteracted the cardiodepressant effects of 0.05 mg/kg CPA almost completely, thereby nearly abolishing its therapeutic efficacy against sarin poisoning. In conclusion, the present results strongly indicate that bradycardia and hypotension induced by the peripheral adenosine A1 receptor play a prominent role in the therapeutic efficacy of CPA in cases of sarin poisoning.

Topics: Adenosine; Animals; Bradycardia; Chemical Warfare Agents; Dose-Response Relationship, Drug; Drug Antagonism; Drug Therapy, Combination; Heart Diseases; Hypotension; Injections, Intramuscular; Male; Poisoning; Purinergic P1 Receptor Agonists; Rats; Sarin; Theophylline

The synthesis and pharmacological profile of a series of neuroprotective adenosine agonists are described. Novel A(1) agonists with potent central nervous system effects and diminished influence on the cardiovascular system are reported and compared to selected reference adenosine agonists. The novel compounds featured are derived structurally from two key lead structures: 2-chloro-N-(1-phenoxy-2-propyl)adenosine (NNC 21-0041, 9) and 2-chloro-N-(1-piperidinyl)adenosine (NNC 90-1515, 4). The agonists are characterized in terms of their in vitro profiles, both binding and functional, and in vivo activity in relevant animal models. Neuroprotective properties assessed after postischemic dosing in a Mongolian gerbil severe temporary forebrain ischemia paradigm, using hippocampal CA1 damage endpoints, and the efficacy of these agonists in an A(1) functional assay show similarities to some reference adenosine agonists. However, the new compounds we describe exhibit diminished cardiovascular effects in both anesthetized and awake rats when compared to reference A(1) agonists such as (R)-phenylisopropyladenosine (R-PIA, 5), N-cyclopentyladenosine (CPA, 2), 4, N-[(1S,trans)-2-hydroxycyclopentyl]adenosine (GR 79236, 26), N-cyclohexyl-2'-O-methyladenosine (SDZ WAG 994, 27), and N-[(2-methylphenyl)methyl]adenosine (Metrifudil, 28). In mouse permanent middle cerebral artery occlusion focal ischemia, 2-chloro-N-[(R)-[(2-benzothiazolyl)thio]-2-propyl]adenosine (NNC 21-0136, 12) exhibited significant neuroprotection at the remarkably low total intraperitoneal dose of 0.1 mg/kg, a dose at which no cardiovascular effects are observed in conscious rats. The novel agonists described inhibit 6, 7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate-induced seizures, and in mouse locomotor activity higher doses are required to reach ED(50) values than for reference A(1) agonists. We conclude that two of the novel adenosine derivatives revealed herein, 12 and 5'-deoxy-5'-chloro-N-[4-(phenylthio)-1-piperidinyl]adenosine (NNC 21-0147, 13), representatives of a new series of P(1) ligands, reinforce the fact that novel selective adenosine A(1) agonists have potential in the treatment of cerebral ischemia in humans.

Topics: Adenosine; Animals; Blood Pressure; Brain; Brain Ischemia; Cardiovascular System; Cell Line; Gerbillinae; Guinea Pigs; Hypotension; Mice; Mice, Inbred Strains; Neuroprotective Agents; Protein Binding; Purinergic P1 Receptor Agonists; Rats; Rats, Inbred Strains