ISOPRENALINE INDUCES ENDOTHELIUM-INDEPENDENT RELAXATION AND ACCUMULATION OF CYCLIC-NUCLEOTIDES IN THE RAT AORTA

The role of endothelium in isoprenaline-induced relaxation was investi gated in aortic rings brought to different levels of pre-contraction. Relaxation elicited by isoprenaline decreased with increasing pre-cont raction. However, relaxation was identical in rings with and without e ndothelium brought to the same initial tension by adjusting the noradr enaline concentration. Furthermore, isoprenaline increased cAMP and cG MP contents to the same levels whether endothelium was present or not. These results do not support an obligatory role for the endothelium i n isoprenaline-induced relaxation in rat aorta. They indicate that rel axation induced by isoprenaline can be enhanced by the endothelium as a consequence of its effect on the precontraction lever of the aorta.