THE INFLUENCE OF EXPERIMENTAL HYPERTHYROIDISM ON RESPONSIVENESS IN RABBIT AORTIC SMOOTH-MUSCLE

This study investigated the responsiveness of hyperthyroid and control (euthyroid) rabbit aortic rings to vasoconstrictor agents. There was no significant difference between the responsiveness of hyperthyroid a nd control tissues to KCl. Maximum responses (E(m)) to noradrenaline a nd serotonin were reduced in hyperthyroid rabbit aortic rings compared to those euthyroid rings. The sensitivity (i.e., EC(50)) of hyperthyr oid aortic rings to noradrenaline and serotonin compared to euthyroid controls was unchanged. The K-b value of prazosin against 10(-6) M nor adrenaline-induced contractions in eu- and hyperthyroid states was 1.9 7 +/- 0.59 . 10(-9) M and 1.92 +/- 0.79 . 10(-9) M, respectively. The K-b value of methisergide against 10(-6) M serotonin-induced contracti ons in eu- and hyperthyroid states was 1.46 +/- 0.80 . 10(-9) M and 1. 10 +/- 0.16 . 10(-9) M, respectively. These data indicate that vascula r reactivity is altered in experimental hyperthyroidism and this alter ation, if any, do not occur at the receptor level. (C) 1997 Elsevier S cience B.V.