ACTIVATION OF GUANOSINE 3',5'-CYCLIC-MONOPHOSPHATE (CGMP)-DEPENDENT PROTEIN-KINASE IN RABBIT AORTA BY NITROGLYCERIN AND SODIUM-NITROPRUSSIDE

It is generally accepted that cGMP mediates the vascular relaxant effe cts of nitrovasodilators such as sodium nitroprusside (SNP) and nitrog lycerin (NTG). It has been suggested that the relaxant effects of cGMP are mediated via activation of a specific, cGMP-dependent protein kin ase (PKG). The objective of this study was to determine whether PKG ca n be activated by SNP and by NTG in intact strips of rabbit aorta and, if so, whether a good correlation exists between activation of PKG an d relaxation of the arteries by the nitrovasodilators. PKG activity wa s measured by means of a recently described assay using a peptide subs trate, BPDEtide, that exhibits good sensitivity and specificity for PK G compared with other protein kinases. Verification of the specificity of the assay for PKG was obtained using MonoQ chromatography to resol ve soluble extracts of the rabbit aorta and subsequent immunoblotting to identify the kinase by means of a PKG-specific antibody. The role o f PKG in vascular relaxation was investigated by simultaneously monito ring the effects of SNP and NTG on cGMP levels, PKG activity ratios an d tension in isolated strips of rabbit aorta exposed to varying concen trations of the nitrovasodilators for varying times. The results indic ate that PKG can be activated in a concentration- and time-dependent m anner by both SNP and NTG in intact vascular preparations and that rea sonably good correlations exist between PKG activation and relaxation in these experiments. Although a causal relationship between the two p arameters has not been definitely established, these results are consi stent with the proposed role for PKG as a mediator of the vascular rel axant effects of cGMP-elevating agents such as SNP and NTG.