The Renin-Angiotensin System in Thyroidectomized Rats*

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Abstract
The influence of thyroidectomy on the reninangiotensin system was studied in the rat. From 1–6 weeks after thyroidectomy, PRA and plasma renin substrate (PRS) decreased, but the plasma renin concentration remained unchanged, and the renal renin content increased. T3 injection corrected the changes in the plasma renin-angiotensin system of thyroidectomized rats within 20–40 h. After ethinylestradiol treatment, the PRS in thyroidectomized rats rose in the same proportion as that in normal rats, but remained below the normal level. After binephrectomy, on the other hand, the PRS was high, and PRS levels in normal and thyroidectomized animals were similar. Isoproterenol increased PRA and plasma renin concentration in control animals but had no effect on thyroidectomized rats. From the above results it may be concluded that angiotensinogen production is dependent on thyroid hormones and that renin release depends on β-adrenergic receptor sensitivity to catecholamines, which is reduced by thyroidectomy.