In this study, the serum level of renin was decreased in hypothyroid rats; this change most probably is due to the reduction of the metabolic rate and dysfunction of juxtaglomerular cells, which is the site of renin release;44, 45 in addition, the hypothyroidism state decreases the sensitivity of β‐adrenergic receptors, which is another stimulation mechanism for renin release.33 After oral administration of eplerenone for 14 days, the serum renin concentration increased significantly. The gene discussed is REN; the disease is hypothyroidism.