Hemodynamic and Biochemical Characteristics of the Aorta in the WKY, SHR, WKHT, and WKHA Rat Strains

: This study was designed to characterize the hemodynamic and biochemical properties of the abdominal aorta in four genetically related inbred rat strains that express genetic hypertension and hyperactive behavior in varying combinations. These include (1) the spontaneously hypertensive rat (SHR), which is hypertensive, hyperactive, and hyperreactive to stress; (2) Wistar-Kyoto (WKY) rats, which express none of these traits; (3) WKHT rats, which are hypertensive but not hyperactive; and (4) WKHA rats, which are hyperactive and hyperreactive to stress, but normotensive. Together, these four strains allowed us to examine the structural and functional changes in the aorta in the hypertensive SHR, the most widely used animal model of genetic hypertension, while controlling for the variables of hyperactivity and hyperreactivity that are also expressed in the SHR. Four groups of animals of both sexes were studied: (1) WKY, n = 101, (2) WKHA, n = 33, (3) WKHT, n = 91, and (4) SHR, n = 28. Blood pressure (BP) was determined by tail plethysmography as well as direct intraarterial monitoring under anesthesia. Fixed specimens were prepared for histologic analysis and the wall thickness determined morphometrically. Quantification of soluble tissue protein, elastin, and collagen in the aortic tissue was determined by measuring leucine (leu), hydroxyproline (HP/leu), and desmosine (DES/leu). The hypertensive strains (SHR and WKHT) had significantly higher tail BP than the normotensive strains (WKY and WKHA)-WKY: 128.7 +/- 22.3; WKHA: 126.7 +/- 14.6; WKHT: 162.8 +/- 21.2; SHR: 164.2 +/- 36.1 (p < 0.0001). Additionally, intraaortic diastolic BP and mean BP were higher in SHR rats than in WKHT. Morphometric studies showed the media thickness in the SHR rats was significantly greater than in the WKY and WKHA rats and no different than in the WKHT rats. Significantly less of the aortic wall protein was present as elastin in the hypertensive rats (SHR and WKHT), as well as the hyperactive rats (WKHA), compared to rats that had neither trait (WKY). These studies provide new information regarding aortic structure and function in genetic hypertension using inbred strains to control for the hyperactivity/hyperreactivity traits that coexist with hypertension in the SHR. They reveal that hypertensive aortas have altered matrix proteins that cannot be explained simply on the basis of blood pressure alone.