The influence of thyroid states upon responses of the rat aorta to catecholamines

Abstract

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 KCI EC50 value was slightly higher (28.4 mm K) in hypothyroid than in euthyroid and hyperthyroid states (22.5 mm and 22.8 mm K, respectively). The order of maximum amplitudes of KCI contraction was control > hypothyroid > hyperthyroid. 3 The EC50 values for the noradrenaline (NA)-induced contraction for eu-, hypo-and hyper-thyroid states were 7.4, 12.5 and 5.5 nm, respectively. The density of a,-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 EC50 values for the phenylephrine-induced contraction in eu-, hypo-and hyper-thyroid states were 43.4, 247 and 41.5 nm, respectively, and those for clonidine 104, 1360 and 56.5 nm, respectively. The IC50 values for prazosin against 0.1 Mm NA-induced contractions in eu-, hypo-and hyper-thyroid states were 5.8, 3.5 and 0.7 nm, respectively, and those for yohimbine 8.9, 5.4 and 4.1 gM, respectively. 5 The IC50 values for isoprenaline against phenylephrine-induced contractions were 63 nm and 2.4Mm in hyper-and eu-thyroid states, respectively, and the corresponding IC25 values for eu-and hypo-thyroid states were 72 and 423 nm, respectively. The density of,-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 fB-adrenoceptors in the three thyroid states. 6 NA consistently increased the amount of inositol 1,4,5-trisphosphate (1P3) within 30s in the three thyroid states. In the hypothyroid state, the amount of IP3 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 a,-adrenoceptors is increased and that of ,B-adrenoceptors reduced in vascular beds. The latter but not the former is accompanied by corresponding mechanical responses. In hyperthyroidism, the density of a1-adrenoceptors is decreased and f-adrenoceptors increased with parallel changes in mechanical responses.

Vascular Reactivity to Vasoconstrictors in Aorta and Renal Vasculature of Hyperthyroid and Hypothyroid Rats

“…In addition, this alteration in the responsiveness to vasoconstrictors may play a role in the reduced blood pressure of hypothyroid rats, as well as in the preventive effects of hypothy roidism on experimental hypertension. The results in aortic strips agree with those re ported previously [9,14,16], with the same preparation. However, when the data ob tained in the renal vasculature are compared with the results obtained in other vascular beds, our results confirm the reduced sensitiv ity observed by Brown and Pollock [11] in hindlimb preparations but contrast with the increased responsiveness reported by Koehn et al [7], and with the normal response re ported in the mesenteric vasculature [12,15].…”

“…The data we obtained in aortic strips from hyperthyroid rats agree with those reported by Rahmani et al [14] in aortic strips but con trast with the increased [9] and decreased [13,16] reactivity reported by other authors. In creased reactivity to vasoconstrictors in iso lated perfused kidneys from hyperthyroid rats reported here contrasts with the normal re sponse previously reported in dog hindlimb vasculature [5,6], as well as in the isolated rat mesenteric [12] and hindlimb [7] vascular beds.…”

Endothelium-Dependent and Endothelium-lndependent Vasodilation in Hyperthyroid and Hypothyroid Rats

“…Differences in the prepara tion used may be the main cause of discrepan cies, as suggested by our data. In hypothyroid rats, a decreased responsiveness to isoprenaline has also been reported in the mesenteric vascular bed [16] and in the aorta [17], ac cording to the reduced (3-adrenergic receptor concentration observed in the vasculature of these rats [17], The reduced responsiveness to vasodilators in the renal vasculature reported here suggests that this alteration may play a role in the increased total peripheral vascular resistance previously reported in these ani mals [1. 2], It is also interesting to note that the bolus administration of nitroprusside produced a dual response in the preconstricted renal vas culature from hypothyroid rats: vasoconstric tion at low doses and vasodilation at high doses.…”

The Influence of Hyperthyroidism on Vasoconstrictor and Vasodilator Responses in Isolated Coronary and Renal Resistance Arteries

“…7], The influence of hyper thyroidism on p-adrenoceptor-mediated va sodilation appeared to be dependent on the tissue investigated. Both an increased sensi tivity [5,[8][9][10] and unaltered responses [4] towards p-adrenoceptor agonists have been reported for different vascular smooth muscle preparations taken from hyperthyroid ani mals.…”

“…It has been demonstrated that some of these symp toms are accompanied by pharmacological al terations. For example, in some but not all tis sues of experimental animals, an upregulation of (i-adrenoceptor density and enhanced ago nist responsiveness have been found [2][3][4][5], The majority of these studies were performed in the heart and large conduit vessels.…”