Effects of Epinephrine and of Alteration in Glandular Blood Flow Upon Thyroid Function: Studies Using Thyroid Vein Cannulation in Dogs

Abstract

The effects of systemically infused epinephrine were studied by the thyroid vein cannulation technique in dogs whose thyroid iodine stores had been prelabeled with ¹³¹I. Epinephrine resulted in great reduction of thyroid blood flow and simultaneous comparable increase in thyroid veno-arterial plasma concentration difference (V-A) for PB¹³¹I; as a consequence, the thyroid secretion rate of hormonal iodine was relatively unchanged from control values, and in no case was secretion rate increased during infusion. The V-A for radioiodide derived from intraglandular deiodination also increased under these conditions, but,as in the case of hormonal iodine, release rate per min did not increase. Reduction of thyroid blood flow ininduced by controlled hemorrhage produced changes similar to epinephrine, i.e., increased V-A for both PB¹³¹I and mI-iodide generated in the gland, without great change in their release rate per min. Studies of glandular clearance of circulating iodide (¹²⁵I) under these conditions revealed that the decreased glandular perfusion, secondary to either epinephrine or removal of blood, caused a considerable decline in iodine clearance, despite a rise in glandular extraction ratio. The results suggest that the reported effects of epinephrine upon uptake and secretion of iodine by the thyroid may be mainly a reflection of the altered glandular blood flow. (Endocrinology84: 501, 1969)