Venous smooth muscle in hypertension. Enhanced contractility of portal veins from spontaneously hypertensive rats.

Abstract

In isolated bath studies smooth muscle from the rat portal vein was evaluated for its reactivity and contractility, and the whole vessel wall was evaluated for its extensibility. Smooth muscle from the spontaneously hypertensive rat (SHR) had the following characteristics when compared with that from normotensive controls: (1) Spontaneous phasic contractions were more frequent and developed more tension; (2) threshold concentrations for responses to prostaglandins A-2 and B-2 were lower, but those for responses to epinephrine, norepinephrine, KCl, BaCl-2, and SrCl-2 were similar; (3) high concentrations of calcium had a less depressant action on the responses to the prostaglandins but not on the responses to the other agonists; (4) maximal contractile tensions to all agonists were greater; and (5) passive extensibility was less. These differences, because they are in the venous system, cannot be secondary to the increase in wall stress of arterial hypertension. The decreased passive extensibility in this vein in SHR creates a stiffer framework on which the active contractile process is able to develop greater tension. If this increase in active tension is generalized to all veins, it could be responsible for a decrease in venous capacity which increases the rate of venous return and, hence, increases cardiac output.

Evidence for a Visceral Smooth Muscle Abnormality in Okamoto Spontaneous Hypertension

“…In all cases, all the observed alterations may result from adaptive changes to an increase in blood pressure, produced by a primary increase in cardiac output (Finkielman, Worcel & Agrest, 1965) induced by various humoral factors (Guyton, Coleman & Granger, 1972). This possibility may have been excluded by Greenberg & Bohr (1975) Vane (1957). The strips were equilibrated for 2h in a solution containing (mM): Na+ 137.5, K+ 5.9, Ca2+ 2.5, Mg2+ 1.2, Tris 15.5, H2PO4 1.2, Cl-134.1, glucose 1 1.5 aerated with 100% 02 at 370C.…”

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

“…There is now evidence that venous compliance may be decreased in several forms of hypertension. The passive extensibility in vitro of strips of portal veins excised from 5-month-old SHR was observed to be less than that in normotensive control rats; 178 at 60% strain, the elastic modulus of strips from SHR was increased by approximately fivefold. This finding has subsequently been confirmed.…”

“…171 ' 17S Venous wall collagen content may be normal 172 or decreased. 17 * Rats with twokidney, one clip hypertension apparently do not develop muscle hypertrophy in portal vein, 178 but onekidney, one clip rats may. 17 " The composition of walls of veins from patients with hypertension has not yet been reported.…”

“…1 "-1M - 188 With regard to mechanisms, the decreased extensibility of portal veins from SHR 178 persisted after pretreatment with a calcium-binding agent (EDTA) to inactivate any smooth muscle contraction. In venous segments removed from perinephritic hypertensive dogs and studied in vitro, decreased venous compliance was observed even after pretreatment with cyanide to relax the venous smooth muscle."…”

Ratos Espontaneamente Hipertensos E Neuropatias Periféricas

“…Por exemplo, alteração da geometria vascular 18,23 , alterações da membrana celular da musculatura lisa vascular 24 , ou diminuição da densidade arteriolar da musculatura esquelética 25 . Foi demonstrado, ainda, um aumento da resistência venosa 26 , possivelmente relacionada ao aumento da atividade simpática 22,27 e/ou hipertrofia venular 26 . Estudos mais recentes 28 mostraram que nos SHR as alterações das propriedades funcionais precedem o desenvolvimento da hipertensão arterial, e que a redução da distensibilidade e complacência vascular nos animais jovens resulta de uma hipertrofia da camada média ao invés de alterações intrínsecas das propriedades elásticas dos vasos.…”