Vascular effects upon experimental increase in the interstitial osmolarity

Experimental increase in the interstitial osmolarity in the limb of a cat is caused by intraarterial infusion of hypertonic solutions. The limb was autoperfused with blood at a constant flow using a roller pump. Hypertonic Tyrode solutions with increased content of NaCl, glucose, l-ascorbic acid, with normal or increased KCl content, were infused together with the blood. The perfusion and arterial pressures were measured and the constrictory response upon local intraarterial injection of 0.2 mug 1-noradrenaline was determined. The intraarterial hypertonic infusion evoked a vasodilatatory response which was maintained irrespective of the reduced or preserved vascular contractility. The magnitude of the vasodilatation was determined by the hypertonicity of the solution and by the KCl content. Hyperosmolaric reduction of the vascular contractility was lacking in the case of solutions with increased KCl content or addition of l-ascorbic acid. The vasodilatation observed also when the contractility was not reduced is discussed in view of the participation of a passive vasodilatation caused by the dehydration of the vascular wall. The effect of the changes in the transmembrane Na+ and Ka+ concentrations on the reduction of the vascular contractility is also discussed.