REDUCED GENE-EXPRESSION OF VASCULAR ENDOTHELIAL NO SYNTHASE AND CYCLOOXYGENASE-1 IN HEART-FAILURE

Endothelium-dependent responses are depressed in coronary and peripher al blood vessels after the onset of pacing-induced heart failure in do gs and heart failure of various etiologies in humans. The present stud y was designed to examine whether these responses were due to decrease s in the expression of endothelial cell NO synthase (ecNOS) and cycloo xygenase-1 (COX-1). After 1 month of left ventricular pacing, 8 mongre l dogs were monitored for heart failure as defined by clinical signs a nd left ventricular end diastolic pressures >25 mm Hg. Total RNA and p rotein were isolated from endothelial cells scraped from the thoracic aorta and analyzed by Northern and Western blotting, respectively. Blo ts probed with P-32-labeled cDNAs for ecNOS and COX-1 were quantified densitometrically, and results were normalized against GAPDH or von Wi llebrand factor (vWF). In arbitrary units, the ratios of ecNOS to GAPD H were 2.66+/-0.77 (mean+/-SEM, n=17) and 1.12+/-0.37 (n=6), and the r atios of COX-1 to GAPDH were 1.52+/-0.52 and 0.56+/-0.15 before and af ter heart failure, respectively. These represent 56% to 64% (P<.05) re ductions in ecNOS and COX-1 gene expression. There was no change in th e ratios of either COX-1 or ecNOS to VWF. There was also a marked redu ction in ecNOS protein after heart failure, estimated at 70%. A marked reduction in nitrite production, a measure of enzyme activity, from t horacic aortas in response to stimulation by either acetylcholine or b radykinin also occurred. To determine whether ecNOS and COX-1 could be independently regulated, an orally active NO-releasing agent, CAS 936 , was given to 7 normal dogs for 7 days, and aortic ecNOS and COX-1 mR NAs were analyzed. The ratio of ecNOS to GAPDH was depressed by 52% (P <.05) in aortas from these dogs, whereas the ratio of COX-1 to GAPDH w as unchanged. Similar results were found when data were normalized to vWF. These results suggest that at least two endothelial vasodilator g ene products are reduced in heart failure, as opposed to a selective d efect in NO synthase gene expression.