Spontaneously hypertensive rat resistance artery structure related to myogenic and mechanical properties

This investigation related arterial structure to myogenic (pressure-dependent) contractile responses in resistance arteries from spontaneously hypertensive rats (SHRs) and Wistar-Kyoto (WKY) normotensive control rats under pressurized conditions in vitro. Femoral and mesenteric resistance arteries from either strain were cannulated and pressurized in an arteriograph for the determination of pressure-diameter relationships under passive and active conditions in the range 5-200 mmHg transmural pressure. Arterial geometrical measurements were made under relaxed conditions at 100 mmHg. Media thickness/lumen diameter (M/L) ratios were significantly increased in SHR femoral (5.00 +/- 0.44% compared with 3.63 +/- 0.34%; P < 0.05) and mesenteric (4.40 +/- 0.29% compared with 2.62 +/- 0.23%; P < 0.001) arteries compared with those from WKY rats. Maximum myogenic contractions, assessed as minimum normalized diameters, were not significantly different in SHR and WKY rat femoral (0.41 +/- 0.03 and 0.40 +/- 0.02 respectively) or mesenteric (0.56 +/- 0.02 and 0.63 +/- 0.03 respectively) arteries. Arterial mechanical analyses demonstrated that incremental elastic modulus is reduced in SHR mesenteric arteries, but is not significantly different in SHR femoral arteries, compared with those from WKY rats. Additionally, wall stress at estimated in vivo pressures under passive and active conditions are similar in SHR and WKY rat arteries. These data demonstrate that increased M/L ratios in resistance arteries from SHRs are not associated with increased maximum pressure-dependent contractile responses. Increased M/L ratios in resistance arteries from SHRs are not accounted for by increased vessel wall stiffness, but the hypertension-associated arterial geometrical abnormalities act to normalize wall stress in the face of increased arterial pressure.