RENAL FUNCTION AND PLASMA RENIN ACTIVITY AS POTENTIAL FACTORS CAUSING HYPERKALEMIA IN PATIENTS WITH THYROID CARCINOMA UNDERGOING THYROID HORMONE WITHDRAWAL FOR RADIOACTIVE IODINE THERAPY.

Objective: Hypothyroidism is not commonly considered a cause of hyperkalemia. We previously reported that hyperkalemia was observed mainly in elderly patients treated with renin-angiotensin-aldosterone system (RAS) inhibitors when levothyroxine treatment was withdrawn for the thyroidectomized patients with thyroid carcinoma to undergo radioactive iodine treatment. Here, we investigated whether acute hypothyroidism causes hyperkalemia in patients who were not treated with RAS inhibitors. We also investigated factors influencing potassium metabolism in hypothyroid patients. Methods: We conducted a single-center, prospective cohort study of 46 Japanese patients with thyroid carcinoma undergoing levothyroxine withdrawal prior to radioiodine therapy. All patients were normokalemic before levothyroxine withdrawal. Blood samples were analyzed 3 times: before, and at 3 and 4 weeks after levothyroxine withdrawal. We investigated factors that may be associated with the elevation of serum potassium levels from a euthyroid state to a hypothyroid state. Results: None of the patients developed symptomatic hyperkalemia. The mean serum potassium level was significantly higher at 4 weeks after levothyroxine withdrawal compared to baseline. The serum sodium levels, the estimated glomerular filtration rate (eGFR), and the plasma renin activity (PRA) decreased significantly as hypothyroidism advanced. In contrast, the plasma levels of adrenocorticotropic hormone, cortisol, aldosterone, and antidiuretic hormone were not changed, while serum thyroid hormone decreased. At 4 weeks after their levothyroxine withdrawal, the patients' serum potassium values were significantly correlated with the eGFR and the PRA. Conclusion: Acute hypothyroidism can cause a significant increase in the serum potassium level, which may be associated with a decreased eGFR and decreased circulating RAS. Abbreviations: ACTH = adrenocorticotropic hormone; ADH = antidiuretic hormone; ATPase = adenosine triphosphatase; eGFR = estimated glomerular filtration rate; HbA1c = glycated hemoglobin; K+ = potassium; Na+ = sodium; PRA = plasma renin activity; RAS = renin-angiotensin-aldosterone system; T4 = thyroxine; TSH = thyroid-stimulating hormone.

Sex differences in insulin and glucagon responses for glucose homeostasis in young healthy Japanese adults.

It has been reported that glucose responses during the oral glucose tolerance test differ between healthy women and men. However, it remains unknown what factors contribute to these differences between the sexes. The present study analyzed the insulin and glucagon responses during the oral glucose tolerance test in 25 female and 38 male healthy young adults aged 22-30 years. The plasma glucose levels at 120 min were significantly higher in women than men. Insulin secretion was significantly greater at 30, 90 and 120 min from baseline in women than men. Glucagon suppression was greater at 30 and 120 min from baseline in men than women when determined by a sandwich enzyme-linked immunosorbent assay glucagon kit. These results suggest that the differences in glucose responses during the oral glucose tolerance test are mediated by the difference between the sexes in bi-hormonal responses in healthy individuals.