Reevaluation of the Role of Cyclic Adenosine 3',5'-Monophosphate and Protein Kinase in the Stimulation of Steroidogenesis by Luteinizing Hormone in Bovine Corpus Luteum Slices1

Abstract

Incubation of bovine corpus luteum slices at 37 C with luteinizing hormone showed that 10.0 microng LH/ml caused a maximum rise in tissue cyclic AMP content within 15 min. Slices incubated with 1.0 or 0.1 microng LH/ml showed a much more gradual accumulation of this nucleotide. In the absence of added LH, a marked decline in the amount of cyclic AMP was observed during the first 60 min. The possible role of cyclic AMP in the action of LH was reexamined by studying the dose-response effect of LH on the stimulation of progesterone synthesis, cyclic AMP-dependent protein kinase activation, and cyclic AMP accumulation. After a 2-h incubatin, the results showed that the dose required to elicit a minimal significant stimulation of steroidogenesis was 0.01 microng/ml LH. At this and higher concentrations of LH, a concomitant stimulation of protein kinase activity and progesterone synthesis was also consistently observed. However, significant accumulation of cyclic AMP became consistently detectable only at 0.1 microng/ml LH. This report is the first to show a positive correlation between the activation of cyclic AMP-dependent protein kinase and the stimulation of steroidogenesis in the corpus luteum at the same minimal effective level of LH. These results indicate that cyclic AMP and the cyclic AMP-dependent protein kinase probably play important intermediary roles in the stimulation of steroidogenesis by LH in the bovine corpus luteum.