Reduced expression and desensitization of adenosine A 1 receptor/adenylyl cyclase pathway after chronic (−)N 6-phenylisopropyladenosine intake during pregnancy

Abstract

Little is known about the G protein–coupled receptor desensitization process during pregnancy. Wistar pregnant rats were treated with (−)N 6-phenylisopropyladenosine (R-PIA), an adenosine A 1 receptor (A 1R) agonist, in their drinking water during pregnancy, and the effect on A 1R/adenylyl cyclase system was studied in both maternal and fetal brain. In maternal brain, binding assays revealed a significant decrease in total receptor numbers in plasma membranes (27%, P<0.05), with no significant changes in receptor affinity. The effect of R-PIA on plasma membranes from fetal brains was more marked, with approximately 42% ( P<0.05) of the total receptors detected in control fetuses. Real time reverse transcriptase polymerase chain reaction (RT-PCR) analyses showed that chronic R-PIA treatment during the whole gestational period only decreased significantly mRNA level coding A 1R in maternal brain ( P<0.05). αGi 1,2 and αGi 3 subunits were not affected in mothers or fetuses as revealed by immunoblotting. mRNA levels coding these subunits were also unaffected in mothers and fetuses. On the other hand, forskolin- and forskolin-plus guanosine-5′-O-(3-thiotriphosphate) (GTPγS)–stimulated adenylyl cyclase activity was decreased in maternal ( P<.01) and fetal brain ( P<.001). Furthermore, adenylyl cyclase inhibition elicited by N 6-cyclohexyladenosine (CHA), a selective A 1R agonist, was significantly decreased in both maternal ( P<0.05) and fetal brain ( P<.01), suggesting a desensitization of the A 1R/adenylyl cyclase pathway. Therefore, these results suggest that R-PIA intake during pregnancy causes desensitization of the A 1R-mediated inhibitory transduction pathway in both maternal and fetal brain, probably due to the decreased density of A 1R at the cell surface.