THE EFFECT OF CALCITRIOL ON ATRIAL NATRIURETIC FACTOR RELEASE FROM ISOLATED ATRIUM

Abstract Previous studies in our laboratory have shown that patients with idiopathic hypercalciuria (IH) have low basal atrial natriuretic factor (ANF) levels in the plasma. These depressed ANF levels are associated with a high plasma calcitriol levels. In this study, we have evaluated the effect of acute calcitriol administration on ANF release in the isolated atrium. There was a gradual reduction of ANF release as the dosage of calcitriol increased from 1 ng to 10 ng. Beyond 10 ng, additional suppression of ANF release by calcitriol was not observed. These results indicate that acute calcitriol administration causes a significant decrease in ANF release. To further determine whether this reduction in ANF release is due to changes in plasma calcium, additional studies were conducted to examine the effect of acute changes in perfusate calcium on ANF release by isolated atria. Acute elevation of perfusate calcium caused an increase in ANF release, whereas a reduction significantly decreased the secretory rate. These observations suggest that calcitriol affects ANF release by a mechanism not dependent on changes in plasma calcium.