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Structurally based increase of flow resistance in spontaneously hypertensive rats.

The resistance to flow in the maximally dilated systemic vascular bed (except the coronaries) was compared in spontaneously hypertensive rats (SHR) and normotensive controls. – The aortic root was cannulated for perfusion with an oxygenated plasma substitute, both the aortic inflow and the venous effluent via the right heart being recorded continuously. Temperature and viscosity of the perfusate were kept constant and it was checked with supramaximal doses of vasodilator drugs that complete vascular relaxation was at hand. Pressure-flow curves were plotted and flow resistances at equal pressure heads and transmural pressures were compared. — Flow resistance in the maximally dilated systemic vessels was increased in the spontaneously hypertensive rats to an extent that largely equalled their raised blood pressure during “resting” conditions, the difference to the control animals being highly significant. – The results suggest the presence of a morphological adaptation of the resistance vessels of the entire systemic circuit which raises the structurally set “baseline” for functional vascular adjustments, and which therefore may largely account for the increased flow resistance during rest. These findings are in agreement with earlier studies concerning the regional flow resistance in hypertensive man (Folkow 1956, Sivertsson and Olander 1968).