In the present study we have examined the effects of FSH, forskolin, and (Bu)2cAMP on messenger RNA (mRNA) levels for all known subunits of cAMP-dependent protein kinase in rat Sertoli cells, using newly developed complementary DNA (cDNA) probes. mRNAs for the three regulatory subunits [RI alpha, RII51, (RII beta), and RII54 (RII alpha)] and the catalytic subunit C alpha were shown to be present in cultured rat Sertoli cells, whereas mRNAs for the subunits designated RI beta and C beta were below the level of detection. A high-levelled, concentration-dependent increase in a 3.2 kilobase mRNA for RII51 was observed when cultured immature Sertoli cells were incubated with increasing concentrations of (Bu)2cAMP (10(-6) to 5 X 10(-3) M) for 16 h. Densitometric scanning indicated a maximal stimulation by (Bu)2cAMP of 30- to 40-fold. Incubation with forskolin (100 microM) and FSH (200 ng/ml) gave rise to a smaller but significant increase in mRNA for RII51. When cultured Sertoli cells were incubated in the presence of 10(-4) M (Bu)2cAMP for varying time periods, there was a biphasic regulation of mRNA for RII51. (Bu)2cAMP caused an initial increase in mRNA for RII51 with maximal levels obtained after 10-16 h, after which a time-dependent decrease was observed. For the other three subunits present in Sertoli cells (RI alpha, RII54, and C alpha) a smaller but significant stimulation by (Bu)2cAMP and forskolin (2-4 fold) was seen. The functional implications of these changes in mRNA levels for the different subunits of cAMP-dependent protein kinase have not yet been revealed. However, our data clearly demonstrate differential regulation of the various subunits of cAMP-dependent protein kinase in Sertoli cells. Furthermore, these results document the presence of distinct adaptational changes taking place at the level of cAMP-dependent protein kinase in response to long term elevation of cAMP.