Microassay of cyclic nucleotides in vessel wall. IV. Cyclic GMP phosphodiesterase activity

Following our microassay for cyclic AMP phosphodiesterase (1978, Microvascular Res. 15:229), a new microassay for cyclic GMP phosphodiesterase (c-GMPPDE) activity was devised, combining the quantitative histochemical method of O.H. Lowry and J.V. Passonneau (1971, A Flexible System of Enzymatic Analysis, Academic Press, New York) with the thin-layer chromatography method of W.A. Scott and B. Solomon (1973, Biochem. Biophys. Res. Comm., 53, 1024). Using this method, c-GMPPDE activity can be accurately measured in a 250 microgram dry weight sample of tissue from the aortic wall. The optimal amount of sample and incubation time were studied, and two Km values were obtained. Low Km is 4.00 x 10(-6) and high Km is 1.25 x 10(-5). The activity of this enzyme was measured in the intima and media of the aorta of three rabbits, three cows and three pigs. The cyclic GMPPDE activities in tissue from cows, pigs and rabbits were 26.61 +/- 2.19, 20.40 +/- 1.35, 43.08 +/- 4.11 pmole/mg dry weight/min in the intima; 52.56 +/- 2.73, 16.07 +/- 3.30 and 66.51 +/- 4.60 pmole/mg dry weight/min in the media. With regard to the relationship between levels of cAMP and cGMP, the activities of cGMPPDE were 10-20 times higher than those of cAMPPDE. These assay systems should provide accurate tools for researching biological, physiological and pathological states of arterial tissues, particularly in the case of atherosclerosis.