STUDIES ON THE EFFECT OF PARATHYROID-HORMONE-(1-84) ON GLUCOSE OUTPUTIN THE LIVER - COMPARISON OF EFFECTS IN ISOLATED HEPATOCYTES AND IN PERFUSED LIVER

This study was conducted to determine the action of parathyroid hormon e (1-84) (PTH(1-84)) on glucose output both in perfused liver and in i solated hepatocytes. In isolated rat hepatocytes, PTH(1-84) stimulated glucose output in a concentration-dependent manner. The action was de tected at 10(-11) M and, at 10(-9) M, PTH produced its maximal effect. The magnitude of the maximal effect of PTH(1-84) was about 65% of tha t of phenylephrine. In contrast, PTH(1-84) had no effect on glucose ou tput in perfused rat liver. Concentration of PTH(1-84) in effluent of perfused liver was less than that in the inflow. However, when the eff luent obtained from liver perfused with 10 nM PTH(1-84) was added to i solated hepatocytes, a considerable amount of glucose was released, wh ich was reversed by PTH(7-34), a competitive inhibitor of PTH receptor . These results indicate that PTH(1-84) increases glucose output in is olated hepatocytes but not in intact liver. It is suggested that the a ction of PTH(1-84) is blocked in intact liver by a yet unknown mechani sm.