New evidence for an acute role of protein kinase in hCG action.

The present experiments were designed to study whether exogenous hCG could elicit acute changes in the ovarian concentration of soluble cAMP-dependent protein kinases temporally related to binding of hCG and intracellular accumulation of cAMP. Cyclic AMP dependent protein kinase activity decreased five-fold within 5 to 30 min after intravenous administration of highly purified hCG to pseudopregnant rats. Moreover cAMP dependent protein kinase activity was totally suppressed with 0.5 IU hCG, whereas tissue concentration of cAMP continued to increase throughout the dose range (0.05-5.0 IU) of hCG used in the present studies. A marked fall in cAMP-dependent protein kinase activity had occurred before there was a significant change in intracellular accumulation of cAMP, possibly reflecting intracellular compartmentalization of cAMP. Inhibitors of protein did not affect the hCG-induced changes in tissue concentrations of cAMP and soluble cAMP dependent protein kinase activity but did suppress the recovery of cAMP dependent protein kinase activity to pretreatment levels. Cyclic AMP dependent protein kinases appear to play a significant role in mediating hormonal action in vivo. In addition the present studies suggest that, protein kinases may protect the cell from excessive hormonal stimulation.