Cyclic 3',5'-adenosine monophosphate phosphodiesterase (cAMP PDE) and cyclic 3',5'-guanosine monophosphate phosphodiesterase (cGMP PDE) in microvessels isolated from bovine cortex.

It was established that microvessels of a bovine cortex exhibit significant cyclic 3',5'-adenosine monophosphate phosphodiesterase (cAMP PDE) and cyclic 3',5'-guanosine monophosphate phosphodiesterase (cGMP PDE) activities. These activities are dependent on the presence of Mg2+. Absence of Ca2+ was virtually without effect. When both Mg2+ and Ca2+ were absent, PDE activities increased compared with activities observed in the absence of Mg2+. Xanthines (caffeine, theobromine, and theophylline) were better inhibitors of cAMP PDE than of cGMP PDE. Imidazole, in very high concentration (1 X 10(-2) M) only, exhibited PDE stimulatory activity at high concentrations of both substrates. Otherwise, it exhibited PDE-inhibitory properties.