Ontogeny of adenosine 3',5'-monophosphate metabolism in guinea pig cerebral cortex. II. Development of responses to L-glutamate in the presence of adenosine or histamine

Effects of adenosine on cAMP production during early development in the optic tectum of chicks

Accumulation of cyclic adenosine monophosphate (cAMP) elicited by adenosine was studied in slices and membrane preparations of optic tectum from chicks aged 1-13 days post-hatch. Accumulation of cAMP promoted by adenosine declined with age, the highest value being observed in three-day-old chicks and the lowest in 11-day-old chicks. However, when the slices were incubated with adenosine and the phosphodiesterase inhibitor-Ro 20-1724 the differences between the two ages were abolished, suggesting a higher phosphodiesterase activity in 11-day-old chicks. In 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. This hypothesis was reinforced by the observation that the binding of [3H]Gpp(NH)p to the membrane preparation was greater in three-day-old animals. In spite of these differences, the percentage of adenylate cyclase activity stimulation by 2-chloroadenosine (2CADO)+Gpp(NH)p was the same at both ages. These findings suggest that the decreased response evoked by adenosine during development is probably due to increased phosphodiesterase activity and a lower sensitivity of adenylate cyclase activity to Gpp(NH)p.

Accumulation of adenosine 3',5'-monophosphate in slices of rat cerebral cortex induced by alpha-adrenergic agonists. I. Responses to methoxamine and norepinephrine in adult and neonatal tissue

The effects of adrenergic agonists and adenosine on the accumulation of adenosine 3',5'-monophosphate (cyclic AMP) were examined in cerebral cortical slices from adult and neonatal rats. Methoxamine (10 to 100 microM) produced up to a two-fold increase in tissue from adult animals only in the presence of optimal concentrations of adenosine (40 to 100 microM), but had no effect in neonatal tissue. Such responses were inhibited more readily by prazosin than by yohimbine, but the reverse was true for responses to norepinephrine; when tested without the addition of adenosine, however, responses to norepinephrine were somewhat more sensitive to prazosin. Under the latter conditions, norepinephrine induced about twice as much increase in cyclic AMP as did isoproterenol in adult tissue. While always prevented by alpha-adrenergic antagonists, the greater efficacy of norepinephrine was eliminated by methylxanthines only in some instances, but never in tissue from animals known to be less than 60 days of age. At 11 to 15 days of age, responses to norepinephrine were more than fourfold those to isoproterenol, even in the presence of methylxanthines, and were completely suppressed by propranolol. Responses to isoproterenol were enhanced when tested in the presence of adenosine, especially in neonatal tissue. The results suggest that both endogenous adenosine and age-related phenomena may account for some of the discrepancies among earlier studies. Moreover, they indicate that several populations of alpha-adrenergic receptors may be involved in responses to adrenergic agonists in rat cerebral cortical tissue.

Accumulation of adenosine 3',5'-monophosphate in slices of rat cerebral cortex induced by alpha-adrenergic agonists. II. Studies on mechanisms underlying the interaction with adenosine

Incubation of slices of rat cerebral cortex with the calcium ionophore A23187 produced small increases in the accumulation of adenosine 3',5'-monophosphate (cyclic AMP). While low concentrations of Ca2+ ions (e.g., 200 microM) were sometimes necessary, the presence of adenosine (e.g., 50 microM) was essential; no effect of ionophore was observed when isoproterenol or isobutylmethylxanthine was substituted for adenosine. These results are consistent with the previously advanced hypothesis that stimulation of alpha-adrenergic receptors in this issue may cause calcium mobilization and thereby produce a calmodulin-mediated stimulation of adenylate cyclase. However, there is no apparent explanation for the requirement for adenosine. In addition, the possibility that additional mechanisms may be operating was suggested by experiments in which the incorporation of 3H-adenine into cyclic AMP was examined under steady-state conditions. While brief exposure to 3H-adenine after maximal adenosine- or isoproterenol-induced accumulations had been achieved led to small increases in the specific activity of cyclic AMP, the combination of norepinephrine and adenosine (plus propranolol) produced substantial decreases in the specific activity of cyclic AMP. Since the rate of incorporation of radioactivity did not keep pace with the expansion of the cyclic AMP pool, it is possible that norepinephrine also caused some reduction in the rate of cyclic AMP degradation under these conditions. Other interpretations of these results are discussed.