Cardiovascular dysfunction in hypercholesterolemia associated with enhanced formation of AT1-receptor and of eicosanoids.

Abstract

In hypercholesterolemia with or without atherosclerosis cardiovascular dysfunction and altered signalling of angiotensin (Ang II), nitric oxide (NO), or prostanoids are intimately related to enhanced oxidant stress and concomitant changes in gene expression. We analyzed cardiac angiotensin receptor (AT1) expression and metabolism of Ang II, eicosanoids, and NO in hypercholesterolemic animals. Guinea pigs were fed a 1% cholesterol diet for 8 weeks (Chol). Hemodynamics were analyzed in Langendorff hearts. Spectrophotometric determination of plasma lipids and radioimmunological detection of eicosanoids/cyclic guanosine monophosphate (cGMP). Activities of NO synthase III (NOS-III) or angiotensin converting enzyme (ACE) were determined by enzymatic assays. AT1 receptor density was assessed by radioligand binding assay. NOS-III mRNAs were quantitated by reverse transcription polymerase chain reaction. Hypercholesterolemia was associated with fatty degeneration of the liver and profound myocardial and coronary (e.g., endothelial) dysfunction. In Chol Langendorff hearts we observed significant increases in coronary flow (26.0 +/- 1.0 vs. 17.5 +/- 0.5 mL/min/g tissue) but diminished coronary responses to bradykinin (Bk, 250 ng bolus) or adenosine (Ado, 250 micrograms bolus) (delta CPPBk/Ado: 5 +/- 0.5 vs. 7.2 +/- 1/0.9 +/- 0.1 vs. 1.9 +/- 0.3 cm2 (area under the curve)). AT1 receptor expression was significantly increased in Chol hearts (72 +/- 6.8 vs. 45 +/- 5.6 fmol/mg protein), whereas marked suppression of cardiac activities of ACE (1.96 +/- 0.34 vs. 4.90 +/- 0.20 nmol/min/mg tissue) and of the entire cardiac nitric oxide-cGMP axis (e.g., NOS-III activity: 1.9 +/- 0.4 vs. 3.1 +/- 0.1 pmol/min/mg tissue; NOS-III mRNA: 0.82 +/- 0.16 vs. 1.20 +/- 0.12 arbitrary units; cGMP release: 0.41 +/- 0.02 vs. 0.54 +/- 0.04 pmol/min/g tissue) were shown in Chol. Finally, cardiac release of eicosanoids prostacyclin (PGI2) and thromboxane (TxA2) were significantly enhanced (0.48 +/- 0.05 vs. 0.38 +/- 0.05 and 0.60 +/- 0.10 vs. 0.24 +/- 0.10 ng/min/g tissue, respectively). Enhanced cardiac PGI2 release and suppression of cGMP synthesis in Chol were even more pronounced on stimulation with Bk (38.2 +/- 3.0 vs. 28.2 +/- 2.0 ng/min/g tissue and 1.9 +/- 0.3 vs. 3.0 +/- 0.3 pmol/min/g tissue, respectively). Altered angiotensin-mediated signal transduction probably related to augmented eicosanoid formation does not compensate for the limited endogenous NO production and for cardiovascular dysfunction in hypercholesterolemic guinea pigs. In this context, changes in redox-sensitive regulation of gene expression (AT1 receptor, NOS-III--caused by enhanced oxidant stress--could play a pivotal role.