Mesenteric hemodynamics in early experimental renal hypertension in dogs.

Abstract

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.

Abnormal ion and water composition of veins and normotensive arteries in coarctation hypertension in rats.

“…17 We have previously reported that femoral 18 and mesenteric 19 venous compliances are decreased in perinephritic hypertensive dogs. We suggested that abnormal venous wall ionic and water composition may underlie this decreased venous compliance.…”

“…We suggested that abnormal venous wall ionic and water composition may underlie this decreased venous compliance. 19 It is also possible that abnormalities in ionic composition of veins may be related to the enhanced responses of veins to norepinephrine and nerve stimulation observed in coarctation hypertension. 20 Furthermore, if abnormalities in ionic and water composition in hypertension reflect underlying defects in ion metabolism, as suggested by Tobian, 1 our present data would suggest that such underlying defects may be present not only in arterial but also in venous tissue.…”

Venous responses to salt loading in hypertensive subjects.

“…However, this possibility is unlikely since the segments of forearm veins from which the venous pressure-volume relationship was examined should have been nearly collapsed by the external water pressure of 20 mm Hg. It has been shown that the baseline venous volume and transmural venous pressure under these conditions are constant and reproducible in a given subject.1', 7 In this study, we examined whether the external water pressure of 20 mm Hg was in fact sufficient to reduce the volume of blood in the forearm to the mini-…”

Report of the Hypertension Task Force of the National Heart, Lung, and Blood Institute. Current research and recommendations from the Subgroup on Local Hemodynamics.

“…In anesthetized dogs with acute or chronic stages of one-kidney, one wrapped Page hypertension, gut blood flow is reported elevated. 45 ' ' 17 These studies, in man and animals, again provide evidence that splanchnic hemodynamics differ in species, forms, and stages of renal hypertension.…”