AGE-DEPENDENT REDUCTIONS IN A(1) ADENOSINE RECEPTOR EXPRESSION IN RATTESTES

The rat testis expresses high levels of A(1) adenosine receptors (A(1) AR) that couple to the inhibition of adenylyl cyclase activity. Howev er, the physiological role of these receptors in the testis is not cle ar. Previous studies have documented a number of changes in the testis associated with the aging process. The goal of this study was to asse ss whether alteration in the expression and function of the testicular A(1) AR occurs in aging, using the Fischer 344 rats as an aging model . Quantitation of A(1) AR expression by radioligand binding of [H-3]1, 3-dipropyl-8-cyclopentylxanthine, an antagonist radioligand, indicates reductions in receptor number by 35 +/- 13.3 and 53 +/- 18.2% in 18- and 25-mo-old rats, respectively, compared with 3-mo-old rats. Similar reductions in A(1) AR expression were determined using Western blotti ng and receptor autoradiography. Quantitation of the G(i) proteins usi ng selective antibodies indicate age-dependent reductions in the level s of alpha(i-1,2-), alpha(i-3)- and beta-subunits. Furthermore, the mo dulatory influences of guanosine 5'-O-(3-thiotriphosphate) on the bind ing of agonist and antagonist radioligands to the A(1) AR were substan tially reduced. Northern blotting analysis of rat testicular poly(A)() RNA indicates both a 3.4-kb transcript and a 5.6-kb transcript that hybridized to the canine A(1) AR cDNA probe. The levels of the 5.6-kb transcript were decreased by 24 +/- 18 and 52 +/- 3% in the 18- and 25 -mo-old rats, respectively, compared with the 3-mo-old rats. These res ults indicate age-dependent deficits in the A(1) AR signal transductio n pathway in the testes and predict concomitant reductions in the acti on of adenosine.