Selective Activation of Rabbit Ovarian Protein Kinase Isozymes in Rabbit Ovarian Follicles and Corpora Lutea

The magnitude of activation of the type I and type II forms of cAMP-dependent protein kinase was investigated in estrous follicles and corpora lutea (CL) obtained from ovaries of control rabbits and rabbits injected acutely with human chorionic gonadotropin (hCG). To this end, a chromatographic technique which permitted quantitative evaluation of the in vivo activational state of the two forms of cAmP-dependent protein kinase was developed and verified. Results revealed that in follicles obtained from ovaries of untreated estrous rabbits, 15% of the soluble cAMP-dependent protein kinase, all of which exists as the type II isozyme, is activated. Intravenous administration of a single bolus of hCG promoted a concentration-dependent activation (in 10 min) of this protein kinase isozyme. In CL obtained from ovaries of control, 4-day pseudopregnant rabbits, 32% of the total soluble cAMP-dependent protein kinase exists as the type I form and 68% exists as the type II form. Both types of protein kinase are approximately 10% dissociated in CL from ovaries of untreated rabbits. Upon intravenous administration of hCG, only the type I form of cAMP-dependent protein kinase is further activated (in 10 min). Dissociation of this protein kinase is dependent upon the time and concentration of hCG. Preferential activation of the type I form of cAMP-dependent protein kinase in CL is also demonstrable in in vitro studies using exogenous cAMP. These data suggest that the physiological intracellular mediator of acute cAMP-regulated, hCG-triggered functions in rabbit ovarian follicles is the type II isozyme of cAMP-dependent protein kinase while in CL of 4-day pseudopregnant rabbits, it is the type I enzyme form.