Activation of Skeletal Adenyl Cyclase by Parathyroid Hormonein Vitro1

The effect of parathyroid hormone on adenyl cyclase from fetal rat calvaria was tested. Adenyl cyclase was assayed in particulate fractions from this tissue by measuring conversion of ATP-α-32P to 3′,5′-AM32P. Parathyroid hormone caused rapid stimulation of enzyme activity; the degree of stimulation was related to the log of hormone concentration. Adenyl cyclase in calvaria was not sensitive to a variety of hormones known to stimulate this enzyme in other tissues. The enzyme was sensitive to parathyroid hormone in skeletal and renal cortical tissue but not in heart, brain, spleen, thyroid, adrenal, or fat cells. Parathyroid hormone and sodium fluoride also stimulated theenzyme in calcified bone from adult rats. Neither parathyroid hormone nor thyrocalcitonin affected the activity of cyclic nucleotide phosphodiesterase in skeletal tissue, nor did thyrocalci tonin affect adenyl cyclase. These observations provide the basis for the concept that a single type of interaction between hormone and enzyme bound to the cell membrane can account for the mechanism of action of parathyroid hormone on its 2 principal receptor tissues. The primary action of the hormone in both skeletal and renal tissue appears to be activation of adenyl cyclase, with consequent increase in intracellular concentration of cyclic 3′,5′-AMP. (Endocrinology84:761, 1969)