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 and control tissues to KCl. Maximum responses (E(m)) to noradrenaline and serotonin were reduced in hyperthyroid rabbit aortic rings compared to those euthyroid rings. The sensitivity (i.e., EC(50)) of hyperthyroid aortic rings to noradrenaline and serotonin compared to euthyroid controls was unchanged. The K(b) value of prazosin against 10(-6) M noradrenaline-induced contractions in eu- and hyperthyroid states was 1.97 ± 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 contractions 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 vascular reactivity is altered in experimental hyperthyroidism and this alteration, if any, do not occur at the receptor level.