Radioligand binding studies agonists

Creese, L, Sibley, D.R., Leff, S.E. (1984). Agonist interactions with dopamine receptors focus on radioligand-binding studies. Fed. Proc. 43 2779-84. 

In a search for more potent and selective Ai adenosine receptor agonists, and taking in mind that at Ai receptor the most active analogues were substituted adenosines, a series of N -cycloalkyl-1-deazaadenosine derivatives were synthesized and evaluated in radioligand binding studies and adenylate cyclase assays [13]. N -Cyclopentyl-2-chloro-1-deazaadenosine (1-deazaCCPA) showed the highest affinity at Ai receptor with more than two fold higher Ai selectivity than N -cyclopentyladenosine (CPA). 

Radioligand binding studies are a rapid means to determine the affinities of reference and novel ligands for a receptor. It is less realised, however, that this technique can equally be applied as a protocol for the discrimination between agonists and antagonists. Therefore some attention in this chapter will be paid to this methodology and its biochemical background. 

Subsequently, we synthesized the 7-ribosides of theophylline, 1,3-dipropylxanthine and 1,3-dibutylxanthine [46]. The Kj values at 25 °C of the three xanthines, the corresponding xanthine-7-ribosides and the reference full agonist R-PIA were obtained in radioligand binding studies with the tritiated agonist N -cyclohexyladenosine (CHA) on rat brain membranes. The results are summarized in Table 1. 

Therefore, while behavioral and radioligand-binding studies suggest interactions between can-nabinoid agonist and 5-HT2 receptors (Kimura et al., 1998 Cheer et al., 1999 Darmani, 2001 Devlin and Christopoulos, 2002), the phenotype of the neuronal components participating in these interactions are as yet unknown. 

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