Parathyroid Hormone Activation of Adenylate Cyclase in Liver

Abstract

Summary

The effect of parathyroid hormone (PTH) on the membrane bound enzyme adenylate cyclase in rat and cat liver tissue homogenates was studied. Bovine PTH increased the accumulation of cyclic AMP (cAMP) over a range of 6 × 10⁻⁸ − 1 × 10⁻⁶ M . The synthetic N-terminal peptide (1–34 amino acids) of the hormone increased the accumulation of cAMP over a range of 6 × 10⁻⁹ − 6 × 10⁻⁷ M. Compared to well studied stimulators of liver adenylate cyclase, glucagon and epinephrine, PTH produced a greater stimulation than epinephrine but less than glucagon. Calcitonin, thyrotropin, and gastrin did not stimulate the liver adenylate cyclase. Maximal concentrations of the 1–34 peptide and epinephrine were additive but maximal concentrations of the 1–34 peptide and glucagon were only partially additive.

The concentration of PTH showing maximal stimulation of liver adenylate cyclase is equivalent to that reported for bone and kidney, the two well studied end organs for the hormone. Although the data suggest that the liver is an end organ for PTH, there is no known physiologic role for this hormone in the liver except for a possible requirement for PTH in liver regeneration.