Effects of adenosine analogs on glucagon-stimulated adenosine 3',5'-monophosphate formation in Sertoli cell cultures from immature rats.

In the present study, we have examined the effects of two adenosine analogs, (-)N6-(R)phenyl-isopropyl-adenosine (PIA) and 2-chloro-adenosine, on glucagon- and FSH-stimulated cAMP production in Sertoli cell cultures isolated from immature (19-day-old) rats. Both FSH and glucagon caused a 5- to 10-fold stimulation of cAMP levels in the spent media from Sertoli cell cultures during an 18-h incubation. Addition of 1 microM PIA significantly inhibited both FSH- and glucagon-stimulated cAMP levels. In the presence of a maximal concentration of glucagon (2.5 micrograms/ml), PIA caused a concentration-dependent inhibition of cAMP formation, and the concentration of PIA causing half-maximal inhibition of cAMP formation (IC50) ranged from 0.5-1 nM. When Sertoli cells were incubated with increasing concentrations of glucagon (1.28 ng/ml to 4.00 micrograms/ml) in the absence and presence of either PIA (1.0 microM) or 2-chloro-adenosine (10.0 microM), the responses to glucagon, measured as cAMP formation, were almost completely abolished. 1-Methyl-3-isobutylxanthine (MIX), a well known inhibitor of cAMP phosphodiesterase activity, is also an inhibitor of adenosine binding to receptors on the cell membrane. When Sertoli cells stimulated with glucagon (2.5 micrograms/ml) were incubated in the absence and presence of MIX (0.1 mM) and increasing concentrations of PIA (0.025-10,000 nM), the presence of MIX reduced the inhibitory activity of PIA by almost 2 orders of magnitude (IC50 without MIX, 0.5 nM; IC50 with MIX, 20 nM). Thus, the present study shows that adenosine analogs inhibit agonist-stimulated cAMP formation in cultured Sertoli cells, and that MIX reduces this effect. This indicates that cultured Sertoli cells from immature rats contain A1-receptors for adenosine mediating inhibitory effects on adenylate cyclase.