Regulation by Follicle-Stimulating Hormone and Dibutyryl Adenosine 3′,5′-Monophosphate of a Phosphodiesterase Isoenzyme of the Sertoli Cell*

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Abstract
The regulatory role of FSH on phosphodiesterase was studied in immature Sertoli cells in culture. Cells were prepared from 15-day-old immature rats, cultured for 3 days in defined medium, and then stimulated for 24 h with gonadotropin or with other factors known to regulate Sertoli cell cAMP. All agents that increased cAMP intracellular levels also had an effect on the total phosphodiesterase activity of cell homogenates, FSH and dibutyryl cAMP being the most potent stimulators. Further, stimulation was more evident when phosphodiesterase was measured at cAMP concentrations below micromolar. With 1 μM cGMP as substrate, no modification of the activity could be detected. Reversal of phosphodiesterase activation was observed at 24 or 40 h when dibutyryl cAMP was removed from the incubation medium. Separation of the isoenzymes present in the soluble fraction of Sertoli cell made it possible to demonstrate a selective stimulation of one isoenzyme. FSH and dibutyryl cAMP increased 10- and 50-fold, respectively, the activity of a high affinity cAMP phosphodiesterase, while the Ca2+-dependent cGMP hydrolyzing enzymes were not apparently affected. The enzyme regulated by FSH and dibutyryl cAMP had an apparent Km for cAMP of 2 μM, was Ca2+ and calmodulin insensitive, and migrated on sucrose density gradients with a sedimentation coefficient of 5.5S. These results indicate that FSH, after stimulation of intracellular cAMP, induces an increase in a high affinity phosphodiesterase and, therefore, an increased cAMP turnover in the Sertoli cell. This, in turn, might be a relevant phenomenon in the control of the responsiveness of this cell to gonadotropin.