Phosphodiesterase activities in the eye of old and young rats in normoxic, hypoxic and hyperoxic atmospheres

Phosphodiesterase activity was tested on homogenized eyes of young and old rats kept in hypoxic and hyperoxic conditions, with the aim of correlating any difference in PDE activity with aging and variations in atmospheric oxygen contents. The activities of the two enzymes, cAMP phosphodiesterase (cAMP-PDE) and cGMP phosphodiesterase (cGMP-PDE), were tested. Phosphodiesterases seem to be particularly susceptible to variations in oxygen tension, suggesting an important role of cyclic nucleotides in cellular adaptive processes. Particularly, cAMP-PDE activity increases lightly both in hypoxic and hyperoxic conditions in young and old rats. For cGMP-PDE activity of young rats, a similar behaviour to cAMP-PDE activity is observed with a similar increase in hypoxic and hyperoxic conditions respect to the control rats. Instead old rats seem to be quite insensible to hypoxia, while they show a fair increase in cGMP-PDE activity in the case of hyperoxia. The second messengers cAMP and cGMP play important roles in mediating the biological effects of a wide variety of first messengers. The intracellular levels of cyclic nucleotides depend upon rates of synthesis and degradation, actuated, respectively, by cyclases and phosphodiesterases (PDEs). Therefore, PDEs seem to play an important role in a wide variety of physiological processes.