Optimum Conditions for the Assay of Cardiac RNA: Comparative Content and Effect of Hypertension

Abstract

An investigation was made into techniques for the routine measurement of cardiac ribonucleic acid (RNA). Conditions were defined for the determination of rat ventricular RNA, based on uv absorption spectrophotometry. Optimum RNA hydrolysis occurred at 0.3 mol/liter alkali at 37 degrees C for 1 h. Suitable correction factors for non-RNA material were also described and these gave similar results to RNA assayed by colorimetric methods. It was concluded that many of the methods previously reported may cause artifactual observations (in some cases apparent negative amounts of RNA). The technique was applied to the assay of RNA in various regions of the heart (i.e., left and right atrial and the left and right ventricular regions) and compared with noncardiac tissues (i.e., skeletal muscle, liver, bone, intestine, and kidney). The left ventricular RNA concentrations were comparable to the right ventricle and the interventricular septum, but approximately half that of atria. There were very little differences between left and right atrial regions. Differences between atrial and ventricular regions were reduced when data were expressed relative to DNA. The cardiac RNA content was shown to be comparable to skeletal muscle and bone. However, cardiac RNA concentrations were lower than those of kidney, liver, lung, and small intestine. Data were also expressed relative to DNA and showed that cardiac RNA/DNA ratios were higher than those of skeletal muscle and lower than those of bone, kidney, liver, lung, and small intestine. The assay procedure for cardiac RNA was applied to investigations in the hypertrophied left ventricle induced by aortic constriction. After 10 days the RNA concentration (mg/g wet wt) and RNA content (mg/region) increased by 7 and 43%, respectively.