Premium
The influence of thyroid states upon responses of the rat aorta to catecholamines
Author(s) -
Gunasekera Ranjan D.,
Kuriyama Hirosi
Publication year - 1990
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1990.tb12965.x
Subject(s) - endocrinology , medicine , euthyroid , phenylephrine , prazosin , chemistry , thyroid , isoprenaline , contraction (grammar) , yohimbine , stimulation , receptor , antagonist , blood pressure
1 Mechanical responses to various stimulants and the distribution of adrenoceptor subtypes were investigated in smooth muscle cells of the rat aorta in eu‐ (control), hyper‐ and hypo‐thyroid states. 2 Concentration‐response relationships for K showed that the KCl EC 50 value was slightly higher (28.4 m m K) in hypothyroid than in euthyroid and hyperthyroid states (22.5 m m and 22.8 m m K, respectively). The order of maximum amplitudes of KCl contraction was control > hypothyroid > hyperthyroid. 3 The EC 50 values for the noradrenaline (NA)‐induced contraction for eu‐, hypo‐ and hyper‐thyroid states were 7.4, 12.5 and 5.5 n m , respectively. The density of α 1 ‐adrenoceptors was increased to 1.4 times the control in the hypothyroid state and reduced to 0.26 times the control in the hyperthyroid state. 4 The EC 50 values for the phenylephrine‐induced contraction in eu‐, hypo‐ and hyper‐thyroid states were 43.4, 247 and 41.5 n m , respectively, and those for clonidine 104, 1360 and 56.5 n m , respectively. The IC 50 values for prazosin against 0.1 μ m NA‐induced contractions in eu‐, hypo‐ and hyper‐thyroid states were 5.8, 3.5 and 0.7 n m , respectively, and those for yohimbine 8.9, 5.4 and 4.1 μ m , respectively. 5 The IC 50 values for isoprenaline against phenylephrine‐induced contractions were 63 n m and 2.4 μ m in hyper‐ and eu‐thyroid states, respectively, and the corresponding IC 25 values for eu‐ and hypo‐thyroid states were 72 and 423 n m , respectively. The density of β‐adrenoceptors was increased to 3.91 times the control in the hyperthyroid and reduced to 0.68 times the control in the hypothyroid states. The amount of adenosine 3′: 5′‐cyclic monophosphate (cyclic AMP) synthesized by isoprenaline increased in parallel with the density of β‐adrenoceptors in the three thyroid states. 6 NA consistently increased the amount of inositol 1,4,5‐trisphosphate (IP 3 ) within 30 s in the three thyroid states. In the hypothyroid state, the amount of IP 3 was slightly increased and in the hyperthyroid condition, it occurred to a lesser extent than in the euthyroid state. 7 The results indicate that in hypothyroidism, the density of α 1 ‐adrenoceptors is increased and that of β‐adrenoceptors reduced in vascular beds. The latter but not the former is accompanied by corresponding mechanical responses. In hyperthyroidism, the density of α 1 ‐adrenoceptors is decreased and β‐adrenoceptors increased with parallel changes in mechanical responses.