Mesenteric hemodynamics in early experimental renal hypertension in dogs

To investigate mesenteric hemodynamics in early perinephritic hypertension, we measured blood flows and intravascular pressures in innvervated, collateral-free, naturally perfused loops of ileum in 50 male mongrel dogs anesthetized with sodium pentobarbital. In addition, we studied venous pressure-volume relationships in temporarily occluded segments of mesenteric veins in vivo and in excised segments of mesenteric veins in vitro. In 10 dogs (group H-1), one kidney was wrapped in silk 11 days before study; in 15 other dogs (group H-2), one kidney was wrapped 4 weeks before study and the other was removed 2 weeks before study. Twenty-five additional dogs were prepared as normotensive controls: in 10 one kidney was sham-wrapped (group C-1), and in 15 one kidney was sham-wrapped and the other was removed (group C-2). A significant rise in mean arterial blood pressure occurred in groups H-1 and H-2. Compared to controls, (1) ileal blood flow in the hypertensive dogs (H-1 plus H-2) was increased by 17% (P smaller than 0.05), (2) calculated ileal vascular resistances (total and segmental) were unchanged (P smaller than 0.05), and (3) in vivo and in vitro mesenteric vein pressure-volume curves of H-2 (but not of H-1) hypertensive dogs were shifted in the direction of the pressure axis (P smaller than 0.05). These data suggest that in the early stages of perinephritic hypertension in dogs (1) ileal blood flow is increased. (2) ileal vascular resistance is not elevated, and (3) mesenteric venous compliance is reduced. Analysis of the venous pressure-volume curves suggests that the decreased venous compliance is attributable to factors other than smooth muscle contraction.