INFLUENCE OF TEMPERATURE BASIC TENSION AND PROPANOLOL ON EFFECT OF NORADRENALINE IN ISOLATED VASCULAR STRIP OF RAT AORTA

In isolated helical strips of the rat aorta, dose-response curves of noradrenaline were tested in concentrations ranging between 3×10-10 and 5×10-6g NA/ml. The following results were obtained: 1. There was a positive logarithmical correlation with increasing doses of noradrenaline between 10-8 and 10-6 g NA/ml. Further increases of noradrenaline resulted in a significant decrease of the isometric tension of the vascular smooth muscle, this being also concentration-dependend (Fig. 2). 2. At 37° C and 6000-7000 mg/mm2 tension/cross section (or 2000 mg basic tension of the strip), the peak of the dose-response curve was found at 1×10-6 g NA/ml; this corresponding to the local concentration at the nerve endings by electrical stimulation. 3. The passive thermoelastic properties of the tissue changed the basic tension about 15,4 mg/o C (Fig. 1). 4. Reducing the bath temperature to 30° C, as well as enhancing the tension from 500 to 2000 mg, the maximum of the dose-response curve was displaced to lower concentrations. The negative correlation between noradrenaline-concentrations and tension developed became more pronounced (Fig. 2 and 3). 5. Propanolol shifted the peak of the dose-response curve to higher noradrenaline-concentrations (Fig. 4). 6. If noradrenaline was added in a single dose instead of cumulatively, the doseresponse curve was passed until the corresponding concentration was reached. At higher noradrenaline-concentrations the tension could be changed biphasically (escape phenomenon"). This effect disappeared following propanolol (Fig. 5). © 1969 Springer-Verlag."