Increased arteriolar wall-to-lumen ratio in a normotensive vascular bed in coarctation hypertension

In rats with coarctation hypertension, resting resistance and resistance at maximal vasodilation are elevated in the hindquarters, although blood pressure in this vascular bed remains normal. To assess the nature of these non-pressure-related vascular abnormalities, we observed third- to fifth-order arterioles in the cremaster microcirculation using standard techniques and chloralose-urethan anesthesia in rats with coarctation or sham coarctation of the abdominal aorta. Four weeks after clipping, carotid pressure was significantly elevated in coarcted compared with sham-coarcted rats, but femoral pressure was not. The wall-to-lumen ratio and wall thickness in cremaster arterioles was elevated by 12-33% in coarcted compared with sham-coarcted rats in the resting state. After maximal arteriolar relaxation with topical nitroprusside, differences in wall-to-lumen ratio persisted. We also studied the microcirculation of one-kidney normotensive control and one-kidney, one-clip Goldblatt hypertensive rats. Femoral pressure in Goldblatt hypertensive rats was elevated, but changes in the microcirculation were similar to those observed in coarcted rats. These non-pressure-related changes in vascular structure in hypertension may result from systemic neural or humoral influences and/or growth factors local to vascular wall tissues.