Thermodynamic in vitro studies as a method to investigate the pharmacodynamic behavior of adenosine A1 receptor ligands.
OBJECTIVE
A thermodynamic analysis of the binding to rat cortex adenosine A1 receptor of N6-substituted (full agonists) and N6-substituted-deoxyribose (partial agonists) adenosine derivatives was performed. The intrinsic activity of the compounds was evaluated by measurements of the inhibition of forskolin stimulated 3', 5'-cyclic adenosine monophosphate (c-AMP) levels in isolated epididymal rat adipocytes.


METHODS
The thermodynamic parameters deltaG(o) (standard free energy), deltaH(o) (standard enthalpy), and deltaS(o) (standard entropy) of the binding equilibrium were determined by means of affinity measurements carried out at different temperatures (0, 10, 20, 25, 30 degrees C). Levels of c-AMP were evaluated performing competitive protein binding assays.


RESULTS
The binding of the ligands increases with temperature enhancement and, as a consequence, is totally entropy driven. Standard entropy values correlate significantly with intrinsic activity ones.


CONCLUSIONS
It is proposed the data obtained by these in vitro experiments can be used to investigate the in vivo pharmacodynamic of A, full and partial agonists.
Dalpiaz
A
A
Department of Pharmaceutical Sciences, Ferrara, Italy.
Scatturin
A
A
Pavan
B
B
Varani
K
K
IJzerman
A P
AP
Andrea Borea
P
P
D000241:Adenosine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D017667:Adipocytes / Q000187:drug effects / Q000378:metabolism; D000818:Animals; D001921:Brain / Q000378:metabolism; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D007700:Kinetics; D008024:Ligands; D008297:Male; D058906:Purinergic P1 Receptor Agonists; D058915:Purinergic P1 Receptor Antagonists; D051381:Rats; D017208:Rats, Wistar; D018047:Receptors, Purinergic P1 / Q000737:chemistry* / Q000378:metabolism; D013696:Temperature; D013816:Thermodynamics
D008024:Ligands; D058906:Purinergic P1 Receptor Agonists; D058915:Purinergic P1 Receptor Antagonists; D018047:Receptors, Purinergic P1; D005576:Colforsin; C027513:N(6)-cyclohexyladenosine; C048599:N(6)-cyclopentyladenosine; D000242:Cyclic AMP; D000241:Adenosine