Reduced expression and desensitization of adenosine A1 receptor/adenylyl cyclase pathway after chronic (−)N6-phenylisopropyladenosine intake during pregnancy

Little is known about the G protein–coupled receptor desensitization process during pregnancy. Wistar pregnant rats were treated with (−)N6-phenylisopropyladenosine (R-PIA), an adenosine A1 receptor (A1R) agonist, in their drinking water during pregnancy, and the effect on A1R/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 A1R in maternal brain (P<0.05). αGi1,2 and αGi3 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 N6-cyclohexyladenosine (CHA), a selective A1R agonist, was significantly decreased in both maternal (P<0.05) and fetal brain (P<.01), suggesting a desensitization of the A1R/adenylyl cyclase pathway. Therefore, these results suggest that R-PIA intake during pregnancy causes desensitization of the A1R-mediated inhibitory transduction pathway in both maternal and fetal brain, probably due to the decreased density of A1R at the cell surface.