Decreased cardiac concentration of cGMP kinase in hypertensive animals. An index for cardiac vascularization?

Cyclic GMP (cGMP) kinase is intimately involved in the regulation of vascular smooth muscle tone. Its tissue concentration was determined in normotensive and hypertensive rats by use of monospecific anti-cGMP kinase antibodies. Hearts of spontaneously hypertensive rats and renovascular (Goldblatt II) hypertensive rats contained half the concentration of cGMP kinase than those of the respective normotensive animals. The increase in blood pressure and the resulting left ventricular hypertrophy were correlated inversely with the left ventricular cGMP kinase concentration. This decrease was specific for the left ventricle and was not observed in other tissues. In addition, the cardiac concentration of cGMP kinase was unchanged in hyperthyroid animals that had comparable left ventricular hypertrophy and mild hypertension. This suggested that in severe renovascular hypertension the decrease in cardiac cGMP kinase concentration is caused by a relative lack of cardiac vessel growth during the development of hypertrophy. In agreement with this conclusion, immunohistochemistry of cardiac cross sections showed that cGMP kinase was exclusively located in cardiac vessels. In support of this localization, the maximal arterial blood flow of heart, liver, skeletal muscle, and kidney correlated excellently with the cGMP kinase content of the respective organ. These results suggest that the cGMP kinase concentration of nonsmooth muscle tissues depends on the amount of organ-specific vascular smooth muscle and may be used as an index for the vascularization of these organs.