Adrenoreceptor-mediated responses in the isolated portal vein of the hypothyroid rat.

1 The effect of hypothyroidism, induced by methimazole, upon the response of the isolated portal vein of the rat to adrenoceptor agonists and antagonists, to angiotensin II and to papaverine has been investigated. 2 The positions and maxima of log doses-response curves, to the vasoconstrictor agonists, noradrenaline and angiotensin II, and to the vasodilator agonists isoprenaline and papaverine, were unaffected by methimazole treatment. 3 The alpha-adrenoreceptor antagonist phentolamine competitively inhibited the effects of noradrenaline to a similar extent in preparations from control and hypothyroid animals. The competitive antagonism of isoprenaline by the beta-adrenoreceptor antagonist propranolol was similarly unaffected by hypothyroidism. 4 These results taken together indicate that hypothyroidism is without significant effect upon either the properties of postjunctional alpha- and beta-adrenoreceptors in the rat portal vein, or upon the reactivity of this blood vessel to the vasoactive agonists studied.