Down-regulation of rat brain adenosine A1 receptors at the end of pregnancy.
The status of the adenosine A1 receptor/adenylyl cyclase (A1R/AC) transduction pathway in rat brain was analysed at the end of pregnancy using different approaches. Pregnancy at term caused a significant decrease in the Bmax value obtained by saturation binding assays using [3H]DPCPX as radioligand, suggesting a down-regulation of adenosine A1 receptor. Moreover, A1 receptor immunodetection in pregnant rat membranes and the level of mRNA coding A1 receptor were significantly decreased. This loss of A1 receptor was associated with a significant increase in receptor affinity, since the KD value from the [3H]DPCPX saturation curve and Ki for N6-cyclohexyladenosine (CHA) were decreased in pregnant rats. Surprisingly, CHA-mediated inhibition of adenylyl cyclase was increased, reflecting enhanced receptor responsiveness. On the other hand, immunoblotting of different alphaGi-protein isoforms revealed a significant increase in alphaGi3 level in membranes from pregnant rats. Pre-incubation of membranes with anti-alphaGi3 antibody blocked the guanosine triphosphate (GTP) or CHA inhibitory effect on adenylyl cyclase in both pregnant and non-pregnant rats, pointing to alphaGi3 as the main isoform involved in the A1 receptor response. These results suggest that, at the end of pregnancy, there is a down-regulation of adenosine A1 receptors counterbalanced with a strengthened functionality, probably due to an increase in both alphaGi3 protein and receptor affinity.
León
David
D
Area de Bioquímica, Facultad de Químicas, Centro Regional de Investigaciones Biomédicas, Universidad de Castilla-La Mancha, Ciudad Real, Spain.
Albasanz
José Luis
JL
Fernández
Mercedes
M
Ruíz
Maria Angeles
MA
Martín
Mairena
M
D000241:Adenosine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000262:Adenylyl Cyclases / Q000378:metabolism; D000446:Aldehyde-Lyases / Q000494:pharmacology; D000818:Animals; D000959:Antihypertensive Agents / Q000494:pharmacology; D001665:Binding Sites; D015152:Blotting, Northern; D001921:Brain / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D005576:Colforsin / Q000494:pharmacology; D003720:Densitometry / Q000379:methods; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D004347:Drug Interactions; D005260:Female; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D015151:Immunoblotting / Q000379:methods; D010627:Phenethylamines / Q000494:pharmacology; D011247:Pregnancy; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D017208:Rats, Wistar; D043682:Receptor, Adenosine A1 / Q000187:drug effects / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D014316:Tritium / Q000493:pharmacokinetics; D014970:Xanthines / Q000493:pharmacokinetics
D000959:Antihypertensive Agents; D010627:Phenethylamines; D012333:RNA, Messenger; D043682:Receptor, Adenosine A1; D014970:Xanthines; D014316:Tritium; C061282:2-(4-(2-carboxyethyl)phenethylamino)-5'-N-ethylcarboxamidoadenosine; D005576:Colforsin; D016244:Guanosine 5'-O-(3-Thiotriphosphate); C051360:1,3-dipropyl-8-cyclopentylxanthine; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; C470744:4-carboxy-4-hydroxy-2-oxoadipate aldolase; D000446:Aldehyde-Lyases; D000262:Adenylyl Cyclases; D000241:Adenosine