EFFECTS OF ADENOSINE ON CAMP PRODUCTION DURING EARLY DEVELOPMENT IN THE OPTIC TECTUM OF CHICKS

Accumulation of cyclic adenosine monophosphate (cAMP) elicited by aden osine was studied in slices and membrane preparations of optic tectum from chicks aged 1-13 days post-hatch. Accumulation of cAMP promoted b y adenosine declined with age, the highest value being observed in thr ee-day-old chicks and the lowest in 11-day-old chicks. However, when t he slices were incubated with adenosine and the phosphodiesterase inhi bitor-Ro 20-1724 the differences between the two ages were abolished, suggesting a higher phosphodiesterase activity in 11-day-old chicks. I n membrane preparations, although basal adenylate cyclase activity was lower in three-day-old chicks, the guanylyl-imidodiphosphate (Gpp(NH) p) concentration curves for stimulation of adenylate cyclase activity indicated a higher sensitivity of G protein to Gpp(NH)p at this age. T his hypothesis was reinforced by the observation that the binding of [ H-3]Gpp(NH)p to the membrane preparation was greater in three-day-old animals. In spite of these differences, the percentage of adenylate cy clase activity stimulation by 2-chloroadenosine (2CADO)+Gpp(NH)p was t he same at both ages. These findings suggest that the decreased respon se evoked by adenosine during development is probably due to increased phosphodiesterase activity and a lower sensitivity of adenylate cycla se activity to Gpp(NH)p.