Daily variations in cGMP, guanylate cyclase and phosphodiesterase in the golden hamster retina.

Daily variations in cGMP, guanylate cyclase and phosphodiesterase activity in golden hamster retina were studied. Cyclic GMP content exhibited significant variations throughout the 24-hr cycle with maximal values during the dark phase. In order to establish the relative participation of nucleotide synthesis and breakdown during a 24-hr cycle, guanylate cyclase and phosphodiesterase activity were measured in hamsters killed at eight intervals. Guanylate cyclase activity increased at night, peaking at 22.00 hr. Phosphodiesterase activity did not change significantly throughout the light-dark cycle. Light exposure during the night inhibited the nocturnal increase in cGMP content and guanylate cyclase activity, while phosphodiesterase remained unchanged. From these results, it might be presumed that in response to continuous (in a range of hr) light or dark stimuli, the retina would process the photic signal in a different way from that in the short term (in a range of msec).